JP6939045B2 - Electrical device - Google Patents

Description

The present invention relates to electrical devices. Specifically, the present invention relates to an electrical device having a high energy density and excellent cycle characteristics.

In recent years, as a drive power source for electronic devices and vehicle running, the development of an electric device having excellent cycle characteristics so that its performance does not deteriorate even if it is repeatedly charged and discharged has been promoted. In particular, lithium-ion secondary batteries are attracting attention as drive power sources for electric vehicles and the like because of their high energy density.

For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery containing Li, Ni, and Mn and using a lithium transition metal composite oxide having a layered structure as a positive electrode. Then, in Patent Document 1, the opposite charge capacity ratio between the positive electrode and the negative electrode when charging until ^{the potential of the positive electrode reaches 4.5 V (vs. Li / Li +) is 1.0 to 1.15.} By doing so, it is said that the thermal stability and safety of the non-aqueous electrolyte secondary battery can be improved.

Japanese Unexamined Patent Publication No. 2007-95433

However, the case where a solid solution lithium-containing transition metal oxide is used as the positive electrode active material and a silicon-containing alloy is used as the negative electrode active material has not been investigated. Further, according to the demand of the market, an electric device having a higher energy density and excellent cycle characteristics is desired.

The present invention has been made in view of the problems of the prior art. An object of the present invention is to provide an electric device having a high energy density and excellent cycle characteristics.

The electric device according to the aspect of the present invention includes a positive electrode containing a solid solution lithium-containing transition metal oxide and a negative electrode containing a silicon-containing alloy containing 20% by mass or more of silicon, and has a capacity of the negative electrode with respect to the capacity of the positive electrode. The ratio is within a predetermined range.

According to the present invention, it is possible to provide an electric device having a high energy density and excellent cycle characteristics.

It is sectional drawing which shows typically an example of the electric device which concerns on this embodiment. It is a graph which shows the charge / discharge curve of the half cell 1 which used the solid solution lithium-containing transition metal oxide as a positive electrode, and the half cell 2 which used a silicon-containing alloy as a negative electrode active material, and the potential difference between the half cell 1 and the half cell 2. It is a graph which shows the charge / discharge curve when the ratio of the capacity of a negative electrode to the capacity of a positive electrode is changed. It is a graph which shows the potential difference between the half cell 1 and the half cell 2 shown in FIG. It is a graph which shows the ratio of the capacity of a negative electrode to the capacity of a positive electrode, and the relationship between the expansion coefficient of the negative electrode active material layer, and the thickness of the negative electrode active material layer at the 0th cycle. It is a graph which shows the relationship between the ratio of the capacity of a negative electrode to the capacity of a positive electrode, and the utilization rate of a positive electrode. It is a graph which shows the relationship between the ratio of the capacity of a negative electrode to the capacity of a positive electrode, and energy density. It is a graph which shows the relationship between the ratio of the capacity of a negative electrode to the capacity of a positive electrode, and the discharge capacity retention rate.

Hereinafter, the electric device according to the present embodiment will be described in detail with reference to the drawings. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

[Electrical device]
In the electrical device of the present embodiment, the positive electrode active material contains a solid solution lithium-containing transition metal oxide, and the negative electrode active material contains a silicon-containing alloy containing 20% by mass or more of silicon. The ratio of the capacity of the negative electrode to the capacity of the positive electrode is more than 1.1 and less than 1.6. Therefore, it is possible to provide an electric device having a high energy density and excellent cycle characteristics.

In the present embodiment, the positive electrode active material contains a solid solution lithium-containing transition metal oxide having a predetermined composition formula. Such a solid solution lithium-containing transition metal oxide has higher capacity, energy density, crystal structure stability, and excellent cycle characteristics as compared with commonly used transition metal oxides and the like.

Further, in the present embodiment, the negative electrode active material contains a silicon-containing alloy containing 20% by mass or more of silicon. Silicon-containing alloys have a large capacity and excellent cycle characteristics as compared with carbon materials and the like.

However, in an electric device in which a solid solution lithium-containing transition metal oxide and a silicon-containing alloy are combined, the expected energy density and cycle characteristics may not be obtained. For example, when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is the same, that is, when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.0, the expected energy density and cycle characteristics cannot be obtained.

The reason is not clear, but since the ratio of the capacity of the negative electrode to the capacity of the positive electrode is small, lithium ions cannot be completely absorbed by the silicon-containing alloy after repeated charging and discharging, and are deposited as lithium metal on the surface of the silicon-containing alloy. That is considered to be one of the causes. In addition, since the voltage drop behavior of the solid solution lithium-containing transition metal oxide does not match the voltage drop behavior of the silicon-containing alloy, the capacity originally possessed by the solid solution lithium-containing transition metal oxide may not be fully utilized. It is considered to be one of the causes.

Therefore, in the present embodiment, the ratio of the capacity of the negative electrode to the capacity of the positive electrode is set to more than 1.1. Therefore, since the ratio of the capacity of the silicon-containing alloy is large even after repeated charging and discharging, lithium metal is less likely to precipitate, and the original characteristics of the solid solution lithium-containing transition metal oxide can be further utilized. Therefore, the cycle characteristics of the electric device can be improved.

On the other hand, if the ratio of the capacity of the negative electrode to the capacity of the positive electrode is too large, the number of silicon-containing alloys that are not involved in the charge / discharge reaction increases, and the energy density decreases. Further, although the silicon-containing alloy has a larger capacity than the carbon material, it has a property of easily expanding due to occlusion of lithium. Therefore, if the mass per unit area of the silicon-containing alloy is simply increased, it tends to expand beyond the yield stress of the binder during charging. Therefore, even if lithium ions are released from the silicon-containing alloy during discharging, the negative electrode active material. The layer tends to expand and become difficult to return to its original thickness. Therefore, if the capacity of the negative electrode is made too large with respect to the capacity of the positive electrode, the energy density of the electric device tends to be further lowered.

Therefore, in the present embodiment, the ratio of the capacity of the negative electrode to the capacity of the positive electrode is set to less than 1.6. Therefore, it is possible to suppress a decrease in energy density and cycle characteristics due to an increase in the silicon-containing alloy and expansion of the negative electrode active material layer.

As described above, in the electric device of the present embodiment, the ratio of the capacity of the negative electrode to the capacity of the positive electrode is within a predetermined range. Therefore, according to the electric device of the present embodiment, the precipitation of metallic lithium is suppressed, the utilization rate of the solid solution lithium-containing transition metal oxide is improved, and the negative electrode utilization rate is improved in consideration of the expansion of the silicon-containing alloy. be able to. Such a problem of improving energy density and cycle characteristics is a problem peculiar to the case where a solid solution lithium-containing transition metal oxide is used as a positive electrode active material and a silicon-containing alloy is used as a negative electrode active material.

It is more preferable that the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more and 1.5 or less. This is because the energy density and the cycle characteristics can be further improved by setting the capacity ratio in such a range. Further, it is more preferable that the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more and 1.4 or less. This is because the cycle characteristics can be further improved by setting the capacitance ratio in such a range.

The capacity of the positive electrode can be the capacity of an electric device manufactured by using a positive electrode active material containing a solid solution lithium-containing transition metal oxide as the positive electrode and using metallic lithium as the negative electrode. Further, the capacity of the negative electrode can be the capacity of an electric device manufactured by using metallic lithium as the positive electrode and using a negative electrode active material containing a silicon-containing alloy as the negative electrode. The capacity of the positive electrode and the capacity of the negative electrode are, for example, charged at a constant current of 0.1 C at room temperature (25 ° C.) until the maximum voltage reaches 4.6 V, and from 4.6 V until the minimum voltage reaches 2.0 V. It can be the discharge capacity when a constant current is discharged at 0.0C. The ratio of the capacity of the negative electrode to the capacity of the positive electrode is a value obtained by dividing the capacity of the negative electrode by the capacity of the positive electrode.

Hereinafter, the configuration of the electric device of the present embodiment will be described in detail with reference to the drawings.

In FIG. 1, a lithium ion secondary battery will be described as an example of the electric device 100 of the present embodiment. As shown in FIG. 1, the electric device 100 according to the present embodiment includes a positive electrode 10, a negative electrode 20, and a separator 30.

(Positive electrode 10)
The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 arranged on the surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be arranged on at least one surface of the positive electrode current collector 11.

(Positive Current Collector 11)
The positive electrode current collector 11 is connected to a positive electrode tab 60 or the like, which will be described later, and transfers electrons to the outside of the electric device 100. The material for forming the positive electrode current collector 11 is not particularly limited, and examples thereof include metals such as aluminum, nickel, iron, titanium, and alloys thereof. As the material for forming the positive electrode current collector 11, the above-mentioned simple substance of metal, the alloy of the above-mentioned metals, the plating material of the above-mentioned combination of metals, and the like can be used. Among them, the material forming the positive electrode current collector 11 preferably contains aluminum from the viewpoint of electron conductivity and battery operating potential. The thickness of the positive electrode current collector 11 is not particularly limited, but is usually about 1 to 100 μm.

(Positive electrode active material layer 12)
The positive electrode active material layer 12 contains 80% by mass to 98% by mass of the positive electrode active material. The film thickness of the positive electrode active material layer 12 is not particularly limited, but is preferably 20 μm to 80 μm, and more preferably 20 μm to 50 μm. In addition to the positive electrode active material, the positive electrode active material layer 12 can further contain a conductive auxiliary agent for the positive electrode and a binder for the positive electrode.

The positive electrode active material includes a chemical formula _{Li 1.5 [Ni a Co b Mn} c [Li] d] O z solid solution lithium-containing transition metal oxide represented by. In the above chemical formula, a, b, c and d satisfy the relationships of a + b + c + d = 1.5, 1.1 ≦ a + b + c ≦ 1.4 and 0.1 ≦ d ≦ 0.4. Further, in the above chemical formula, z is an oxygen number satisfying the valence. That is, in the above chemical formula, z is a number determined by the values of a, b, c and d, and is a numerical value uniquely determined by determining the number of elements other than oxygen. z takes a value such as 3, for example. The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

Such solid solution lithium-containing transition metal oxides include lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobalt oxide (LiCoO ₂ ), and a ternary composite oxide (Li [NiComn] O). _{It is} more balanced in terms of energy density, crystal structure stability, cycle characteristics, etc. than 2).

That is, as the positive electrode active material, lithium nickelate, lithium manganate, lithium cobalt oxide, ternary composite oxide and the like are known. However, each of these positive electrode active materials has the following features and drawbacks.

Although lithium nickelate has a relatively large capacity, oxygen tends to be easily desorbed in the crystal structure at a high temperature, which may induce ignition or explosion, and cannot be said to be highly safe. Further, lithium nickelate has a low average voltage of 3.5 V and a low discharge operating voltage, and tends to have low cycle characteristics.

Lithium manganate is resistant to overvoltage and has a low risk of ignition, so it is highly safe and has a high average voltage of 3.8 V and a high discharge operating voltage. In addition, the supply of lithium manganate is stable due to its abundant resources. However, lithium manganate has a relatively small capacity and a low energy density. Further, lithium manganate tends to have low cycle characteristics and storage stability because manganese itself has a property of being easily dissolved at a high temperature.

Lithium cobalt oxide has the second highest capacity after lithium nickel oxide, and has a high average voltage of 3.7 V and a high discharge operating voltage. Further, lithium cobalt oxide shows good reversibility in the voltage range of 2.5V to 4.3V, and has a relatively excellent balance between cycle characteristics and rate characteristics. However, if a large amount of lithium is released during charging, the crystal structure cannot be maintained, so that the entire theoretical capacity cannot be used, and the capacity that can actually be used is about half of that. In addition, cobalt is scarce in resources and highly scarce, which causes an increase in cost.

The ternary composite oxide is excellent in capacity and rate characteristics. However, since the characteristics of lithium nickel oxide are strongly reflected, there are drawbacks such as lower initial charge / discharge efficiency and cycle characteristics than lithium cobalt oxide.

However, in the present embodiment, the above-mentioned solid solution lithium-containing transition metal oxide is used as the positive electrode active material. Therefore, the capacity, energy density, and crystal structure stability are high, and the cycle characteristics are also excellent.

In the above chemical formula, a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0.1 ≦ d ≦ 0.4, a + b + c + d. It is preferable to satisfy the relationship of = 1.5 and 1.1 ≦ a + b + c ≦ 1.4. Further, in the above chemical formula, a, b, c and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <1.35, 0.15 <d ≦ 0.35, a + b + c + d. It is more preferable to satisfy the relationship of = 1.5, 1.15 ≦ a + b + c <1.35. Further, in the above chemical formula, a, b, c and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <1.3, 0.15 <d ≦ 0.35, a + b + c + d. It is more preferable to satisfy the relationship of = 1.5 and 1.2 ≦ a + b + c <1.3. When such a positive electrode active material containing a solid solution lithium-containing transition metal oxide is used, the capacity of the electric device 100 can be improved.

The average particle size of the positive electrode active material is not particularly limited, but from the viewpoint of increasing the output, it is preferably 1 μm to 30 μm, and more preferably 5 μm to 20 μm. The average particle size of the positive electrode active material may be the average value at the maximum particle size of several to several tens of particles actually measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). can.

The positive electrode active material is arranged on the surface of the solid solution lithium-containing transition metal oxide and the solid solution lithium-containing transition metal oxide, and is formed of an oxide of at least one metal selected from the group consisting of Al, Zr and Ti. It is preferable to include the coated coating layer. By arranging such a coating layer, the crystal structure of the solid solution lithium-containing transition metal oxide is stabilized, so that the elution of the transition metal and the release of oxygen are suppressed, and the cycle characteristics are improved.

The metal oxide forming the coating layer is not particularly limited, but is preferably at least one or more metal oxides selected from the group consisting of _{Al 2} O ₃ , ZrO ₂ and TiO _2. The coating layer may further contain at least one metal oxide selected from the group consisting of Nb, Sn, W, Mo and V.

The content of the oxide of the metal forming the coating layer is preferably 0.1% by mass to 3.0% by mass of the entire positive electrode active material. By setting the content of the coating layer in such a range, the crystal structure of the solid solution lithium-containing transition metal oxide is stabilized, so that the elution of the transition metal and the release of oxygen are suppressed, and the cycle characteristics are improved.

The average thickness of the coating layer is not particularly limited, but is preferably 2 to 20 nm from the viewpoint of improving the characteristics of the solid solution lithium-containing transition metal oxide as described above. The average thickness of the coating layer can be observed by, for example, SEM or TEM. The average thickness of the coating layer may be a value obtained by subtracting the average particle size of the solid solution lithium-containing transition metal oxide having no coating layer from the average particle size of the solid solution lithium-containing transition metal oxide containing the coating layer. can. The average particle size can be, for example, the particle size when the cumulative value of the particle size distribution on a volume basis measured by a laser diffraction method is 50%.

(Conductive aid for positive electrode)
The positive electrode conductive auxiliary agent can effectively form an electronic network inside the positive electrode active material layer 12 and increase the discharge capacity of the electric device 100. The content of the conductive auxiliary agent for the positive electrode contained in the positive electrode active material layer 12 is not particularly limited, but is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 6% by mass. By setting the content of the conductive auxiliary agent for the positive electrode within such a range, the conductivity of the positive electrode active material layer 12 can be improved.

(Binder for positive electrode)
The positive electrode binder can bond the positive electrode active materials to each other or the positive electrode active material and the positive electrode conductive auxiliary agent. Examples of the material for forming the binder for the positive electrode include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyether nitrile (PEN), and poly. Acrylonitrile (PAN), polyimide (PI), polyamide (PA), polyamideimide (PAI), carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF) ), Polytetrafluoroethylene (PTFE), thermoplastic resin such as polyvinyl chloride (PVF), thermocurable resin such as epoxy resin, styrene-butadiene rubber (SBR), isoprene rubber (IR), butadiene rubber (BR) Such as elastomer. These positive electrode binders may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of polyimide (PI), polyamide (PA), and polyamideimide (PAI) is preferable because of its excellent adhesiveness and heat resistance as a binder. The content of the positive electrode binder contained in the positive electrode active material layer 12 is not particularly limited, but is preferably 0.5% by mass to 15% by mass, more preferably 1% by mass to 10% by mass.

(Negative electrode 20)
The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 arranged on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be arranged on at least one surface of the negative electrode current collector 21.

(Negative electrode current collector 21)
The negative electrode current collector 21 is connected to a negative electrode tab 65 or the like, which will be described later, and transfers electrons to the outside of the electric device 100. The material for forming the negative electrode current collector 21 is not particularly limited, but for example, metals such as copper (Cu), titanium (Ti), nickel (Ni), and stainless steel (SUS) are preferable. Among these, copper (Cu) is preferably used as the material for forming the negative electrode current collector 21. The thickness of the negative electrode current collector 21 is not particularly limited, but is usually about 1 μm to 100 μm.

(Negative electrode active material layer 22)
The negative electrode active material layer 22 contains 40% by mass to 98% by mass of the negative electrode active material. The film thickness of the negative electrode active material layer 22 is not particularly limited, but is preferably 20 μm to 80 μm, more preferably 20 μm to 50 μm, further preferably 28 μm to 39 μm, and 29 μm to 36 μm before discharge. Is particularly preferable. By setting the film thickness of the negative electrode active material layer 22 in such a range, the energy density and cycle characteristics of the electric device 100 can be improved. The negative electrode active material layer 22 may further contain a negative electrode conductive auxiliary agent and a negative electrode binder in addition to the negative electrode active material.

(Negative electrode active material)
The negative electrode active material contains a silicon-containing alloy containing 20% by mass or more of silicon. Since the silicon-containing alloy is alloyed with lithium ions during charging, the discharge capacity per mass of the negative electrode active material can be increased as compared with a carbon-based negative electrode active material or the like. Therefore, the electric device 100 of the present embodiment can increase the discharge capacity of the electric device 100 by using a silicon-containing alloy. Further, by setting the silicon content of the silicon-containing alloy to 20% by mass or more, the phase transition of the amorphous-crystal can be suppressed. Therefore, the cycle characteristics of the electric device 100 can be improved.

In the present embodiment, the silicon-containing alloy contains elements of Si, Sn and M, where M is at least one element selected from the group consisting of transition elements, B, C, Mg, Al and Zn. preferable. The transition element refers to an element between the Group 3 element and the Group 11 element. By using such a silicon-containing alloy, the cycle characteristics of the electric device 100 can be enhanced.

M is at least one element selected from the group consisting of B, C, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo and Ta. More preferably. Further, M is more preferably at least one element selected from the group consisting of C, Al, Ti, V and Zn. Further, it is most preferable that it is at least one of Al and Ti. When the silicon-containing alloy contains such an element, the cycle characteristics can be further improved while maintaining the discharge capacity.

The silicon-containing alloy containing Si, Sn, and M elements may contain unavoidable impurities. Inevitable impurities mean those that are present in the raw material or are inevitably mixed in the manufacturing process. Although unavoidable impurities are originally unnecessary, they are permissible impurities because they are in trace amounts and do not affect the characteristics of the silicon-containing alloy. The content of unavoidable impurities is preferably less than 0.5% by mass, more preferably less than 0.1% by mass, and further preferably less than 0.01% by mass with respect to the entire silicon-containing alloy. preferable.

The general formula of the silicon-containing alloy is preferably Si—Sn—M, more preferably Si—Sn—Ti or Si—Sn—Ti—Al. Here, in the general formula Si-Sn-Ti, the Sn content is 7% by mass or more and 30% by mass or less, the Ti content is 0% by mass or more and 37% by mass or less, and the balance is Si and unavoidable impurities. preferable. Alternatively, in the general formula Si-Sn-Ti, it is preferable that the Sn content is 30% by mass or more and 51% by mass or less, the Ti content is 0% by mass or more and 35% by mass or less, and the balance is Si and unavoidable impurities. .. Further, in the general formula Si—Sn—Ti, it is more preferable that the Sn content is 7% by mass or more and 30% by mass or less, Ti is 7% by mass or more and 37% by mass or less, and the balance is Si and unavoidable impurities. Alternatively, it is more preferable that the Sn content is 30% by mass or more and 51% by mass or less, the Ti content is 7% by mass or more and 35% by mass or less, and the balance is Si and unavoidable impurities. Further, in the general formula Si-Sn-Ti, the Sn content is 7% by mass or more and 30% by mass or less, the Ti content is 18% by mass or more and 37% by mass or less, and the balance is Si and unavoidable impurities. preferable. Alternatively, in the general formula Si-Sn-Ti, the Sn content is 30% by mass or more and 51% by mass or less, the Ti content is 7% by mass or more and 20% by mass or less, and the balance is Si and unavoidable impurities. preferable. Further, in the general formula Si-Sn-Ti, the Sn content is 7% by mass or more and 21% by mass or less, the Ti content is 24% by mass or more and 37% by mass or less, and the balance is Si and unavoidable impurities. preferable. By setting the content of each element within the above range, it is possible to provide the electric device 100 having excellent cycle durability.

In the general formula Si-Sn-Ti-Al, the Sn content is 2% by mass or more and 10% by mass or less, the Ti content is 25% by mass or more and 35% by mass or less, and the Al content is 0.3% by mass. It is preferable that the amount is 3% by mass or less and the balance is Si and unavoidable impurities. By setting the content of each element within the above range, the cycle durability of the electric device 100 can be improved. The Sn content is more preferably 3% by mass or more. The Sn content is more preferably 9% by mass or less, and even more preferably 8.5% by mass or less. The Ti content is more preferably 28% by mass or more, further preferably 29% by mass or more. The Ti content is more preferably 34% by mass or less, further preferably 33% by mass or less, particularly preferably 32% by mass or less, and most preferably 31% by mass or less. The Al content is more preferably 0.35% by mass or more, further preferably 0.4% by mass or more. The Al content is more preferably 2.5% by mass or less, further preferably 2.0% by mass or less. The Si content is preferably 58% by mass or more, more preferably 58.5% by mass or more, and further preferably 59% by mass or more. The Si content is preferably 70% by mass or less, more preferably 68% by mass or less, further preferably 67% by mass or less, and particularly preferably 66% by mass or less.

The silicon-containing alloy preferably contains a parent phase containing amorphous or low-crystalline silicon as a main component and a silicide phase dispersed in the mother phase and containing a transition metal silicide. When the silicon-containing alloy contains such a matrix phase and a silicide phase, it is possible to provide an electric device 100 having excellent cycle characteristics and a large discharge capacity. The main component referred to here means that the parent phase contains 50% by mass or more of amorphous or low crystallinity silicon.

The mother phase containing silicon as a main component is a phase involved in occlusion and release of lithium ions when the electric device 100 is charged and discharged. Therefore, when the matrix phase containing silicon as a main component is a single phase composed of only silicon, it is preferable because it can occlude and release a large amount of lithium ions.

The matrix phase containing silicon as a main component is preferably amorphous rather than the silicide phase. By doing so, the discharge capacity of the electric device 100 can be further increased. It can be confirmed from the electron diffraction image obtained by the electron diffraction analysis that the matrix phase containing silicon as a main component is more amorphous than the VDD phase. The electron diffraction image of the single crystal phase is a net pattern (lattice-like spot) of a two-dimensional point arrangement, and the electron diffraction image of the polycrystalline phase is a device sheller ring (diffraction ring), and the electrons of the amorphous phase. The line diffraction image is a halo pattern.

By including silicide of _{a transition metal such as TiSi 2 in the} silicide phase, the affinity with the silicon-based matrix can be improved. Therefore, even when the silicon-containing alloy is volume-expanded by charging the electric device 100, it is possible to suppress the occurrence of cracks between the matrix phase and the silicide phase. Further, since the silicide phase tends to have higher electron conductivity and hardness than the parent phase, it also has a role of improving the electron conductivity of the silicon-containing alloy and suppressing the expansion of the silicon-containing alloy during charging and discharging. Have.

The silicide phase may _{have a plurality of phases having different silicon composition ratios, such as MSi 2} and MSi, or may have a plurality of phases containing silicides with different transition metal elements. The transition metal element contained in the silicide phase is preferably at least one element selected from the group consisting of Ti, Zr, Ni, Cu and Fe, more preferably at least one element of Ti and Zr, and further Ti. preferable. Since silicides with these transition metal elements have high electron conductivity and hardness, it is possible to improve the electron conductivity of the silicon-containing alloy and suppress the expansion of the silicon-containing alloy during charging and discharging. _{In particular, TiSi 2} , which is a silicide with Ti, is preferable because it has very high electron conductivity. When the silicide phase has a plurality of phases in which the composition ratio of silicon containing _{TiSi 2 is different and the transition metal element M is Ti, the ratio of TiSi 2 to} the entire silicide phase is preferably 50% by mass or more. More preferably, it is 80% by mass or more. Further, this ratio is more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

The size of the silicide phase is not particularly limited, but is preferably more than 0 nm and 50 nm or less. When the size of the silicide phase is within such a range, the discharge capacity of the electric device 100 becomes large, which is preferable.

When the silicon-containing alloy is X-ray diffracted using CuKα1 wire, the above in the range of 2θ = 37 ° to 45 ° with respect to the diffraction peak intensity of the Si (111) plane in the range of 2θ = 24 ° to 33 °. The ratio of diffraction peak intensities of silicide is preferably 0.41 or more. By setting the ratio of the diffraction peak intensities to 0.41 or more, the phase transition of the amorphous-crystal when Si and Li are alloyed is suppressed, and the expansion and contraction of the silicon-containing alloy is suppressed. Is preferable because it improves. The value of this diffraction peak intensity ratio is more preferably 0.89 or more, further preferably 2.55 or more, and particularly preferably 7.07 or more.

Here, the diffraction peak intensity of the Si (111) plane in the range of 2θ = 24 ° to 33 ° can be obtained as follows.

First, in the diffraction spectrum obtained by X-ray diffraction analysis, let a be the point where the perpendicular at 2θ = 24 ° and the diffraction spectrum intersect. Similarly, let b be the point where the perpendicular at 2θ = 33 ° and the X-line diffraction spectrum intersect. Here, let the line segment ab be the baseline, and let c be the point where the perpendicular line at the diffraction peak (2θ = about 28.5 °) of the (111) plane of Si intersects the baseline. Then, the length of the line segment cd connecting the apex d of the diffraction peak (2θ = about 28.5 °) of the Si (111) plane and the point c is defined as the diffraction peak intensity of the Si (111) plane. Can be done.

Similarly, the diffraction peak intensity of silicide in the range of 2θ = 37 ° to 45 ° can be determined as follows. In the following, a case where the transition metal silicide is TiSi ₂ will be described as an example.

First, in the diffraction spectrum obtained by X-ray diffraction analysis, let e be the point where the perpendicular at 2θ = 37 ° and the diffraction spectrum intersect. Similarly, let f be the point where the perpendicular at 2θ = 45 ° and the X-line diffraction spectrum intersect. Here, let the line segment ef be the baseline, and let g be the point where the perpendicular line at the diffraction peak of _{TiSi 2 (2θ = about 39 °) intersects the baseline.} Then, the length of a line segment gh connecting the vertex h and point g of the diffraction peak of TiSi ₂ (2 [Theta] = about 39 °), may be a diffraction peak intensity of TiSi _2.

The average particle size of the silicon-containing alloy is not particularly limited, but is preferably 0.1 μm to 20 μm, and more preferably 0.2 μm to 10 μm. The average particle size of the silicon-containing alloy represents the particle size when the cumulative value of the particle size distribution on a volume basis is 50%, and can be measured by, for example, a laser diffraction / scattering method.

The negative electrode active material may contain a negative electrode active material other than the above silicon-containing alloy. However, from the viewpoint of discharge capacity and cycle characteristics, the content of the silicon-containing alloy in the negative electrode active material is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 95% by mass or more, and 100% by mass. It is particularly preferable to have.

(Conductive auxiliary agent for negative electrode)
The negative electrode conductive auxiliary agent can effectively form an electronic network inside the negative electrode active material layer 22. Examples of the material for forming the conductive auxiliary agent for the negative electrode include carbon black such as acetylene black and carbon materials such as graphite and carbon fiber. These conductive auxiliary agents for negative electrodes may be used alone or in combination of two or more. The content of the conductive auxiliary agent for the negative electrode in the negative electrode active material layer 22 is not particularly limited, but is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 8% by mass. By setting the content of the conductive auxiliary agent for the negative electrode within such a range, the conductivity of the negative electrode active material layer 22 can be improved.

(Binder for negative electrode)
The negative electrode binder can bond the negative electrode active materials to each other or the negative electrode active material and the negative electrode conductive auxiliary agent. Examples of the material for forming the binder for the negative electrode include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyether nitrile (PEN), and poly. Acrylonitrile (PAN), polyimide (PI), polyamide (PA), polyamideimide (PAI), carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF) ), Polytetrafluoroethylene (PTFE), thermoplastic resin such as polyvinyl chloride (PVF), thermocurable resin such as epoxy resin, styrene-butadiene rubber (SBR), isoprene rubber (IR), butadiene rubber (BR) Such as elastomer. These negative electrode binders may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of polyimide (PI), polyamide (PA), and polyamideimide (PAI) is preferable because it has excellent adhesiveness and heat resistance as a binder for a negative electrode. The content of the negative electrode binder in the negative electrode active material layer 22 is not particularly limited, but is preferably 0.5% by mass to 15% by mass, more preferably 1% by mass to 10% by mass.

(Separator 30)
The separator 30 is arranged between the positive electrode 10 and the negative electrode 20. The separator 30 isolates the positive electrode 10 and the negative electrode 20 and mediates the movement of lithium ions. The film thickness of the separator 30 is preferably 1 μm to 100 μm, and more preferably 5 μm to 50 μm from the viewpoint of reducing internal resistance. The separator 30 can include a non-aqueous electrolyte. As the non-aqueous electrolyte, a gel-like or solid polymer electrolyte in which a lithium salt is dissolved in an ionic conductive polymer, and a liquid electrolyte in which a lithium salt is dissolved in an organic solvent can be used by being retained in a porous substrate layer.

Examples of the ionic conductive polymer used in the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), hexafluoropropylene, polyethylene glycol (PEG), polyacrylonitrile (PAN), and polymethyl. Examples thereof include methacrylate (PMMA) and polymers thereof.

Examples of the organic solvent used for the liquid electrolyte include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl. Examples thereof include carbonates such as carbonate (EMC) and methylpropyl carbonate (MPC).

The lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, compounds such as LiCF ₃ SO ₃ is Can be mentioned.

The material for forming the porous substrate layer is not particularly limited, but it is preferable to use a thermoplastic resin such as polyethylene, polypropylene, or an ethylene-propylene copolymer. The porosity of the porous substrate layer is not particularly limited, but is preferably 40% to 85%. When the porosity is 40% or more, sufficient ionic conductivity can be obtained. On the other hand, when the porosity is 85% or less, the strength of the porous substrate layer can be maintained satisfactorily.

In addition to the positive electrode 10, the negative electrode 20, and the separator 30, the electric device 100 of the present embodiment may further include a positive electrode tab 60, a negative electrode tab 65, an exterior body 70, and the like, as shown in FIG. good.

As shown in FIG. 1, a plurality of cell cell layers 40 including a positive electrode 10, a negative electrode 20, and a separator 30 are laminated and electrically arranged in parallel to be used as a power generation element 50. Further, the electric device 100 of the present embodiment is not limited to the form as shown in FIG. 1, for example, a positive electrode active material layer is arranged on one surface of the current collector, and a negative electrode is arranged on the other surface of the current collector. A bipolar battery including a bipolar electrode in which an active material layer is arranged may be used. Further, the present invention is not limited to the laminated electric device as in the embodiment of FIG. 1, and may be a wound electric device.

(Positive tab 60 and negative electrode tab 65)
The positive electrode tab 60 can electrically connect the positive electrode current collector 11 and an external device of the electric device 100. Further, the negative electrode tab 65 can electrically connect the negative electrode current collector 21 and an external device of the electric device 100. The material forming the positive electrode tab 60 and the negative electrode tab 65 is not particularly limited, and at least one metal selected from the group consisting of, for example, aluminum, copper, titanium, and nickel can be used. The materials forming the positive electrode tab 60 and the negative electrode tab 65 may be the same or different.

(Exterior body 70)
The exterior body 70 can accommodate the cell cell layer 40 or the power generation element 50. Examples of the exterior body 70 include those formed of a can or a film. The shape of the exterior body 70 is not particularly limited, and may be a cylindrical type, a square type, or a sheet type. Although not particularly limited, the exterior body 70 is preferably formed of a film from the viewpoint of miniaturization and weight reduction. Among them, from the viewpoint of high output and cooling performance, the film is preferably a laminated film, and the laminated film preferably contains aluminum. Further, the electric device 100 is preferably a flat laminated lithium ion secondary battery. Such a lithium ion secondary battery is most suitable for mounting on a vehicle because it can increase the discharge capacity and heat dissipation performance. An example of a laminated film containing aluminum is a PP / aluminum / nylon three-layer laminated film.

The electric device 100 of the present embodiment includes a positive electrode 10, a negative electrode 20, and a separator 30 arranged between the positive electrode 10 and the negative electrode 20. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 arranged on the surface of the positive electrode current collector 11. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 arranged on the surface of the negative electrode current collector 21. The positive electrode active material layer 12 contains a positive electrode active material of 80 wt% to 98 wt%, the solid solution of lithium positive electrode active material represented by the chemical formula _{Li 1.5 [Ni a Co b Mn} c [Li] d] O z Contains transition metal oxides. In the above chemical formula, a, b, c and d satisfy the relationships of a + b + c + d = 1.5, 1.1 ≦ a + b + c ≦ 1.4 and 0.1 ≦ d ≦ 0.4, and z represents the valence. Satisfactory oxygen count. The negative electrode active material layer 22 contains 40% by mass to 98% by mass of the negative electrode active material, and the negative electrode active material contains a silicon-containing alloy containing 20% by mass or more of silicon. The ratio of the capacity of the negative electrode 20 to the capacity of the positive electrode 10 is more than 1.1 and less than 1.6.

In the electric device 100 of the present embodiment, since the ratio of the capacity of the negative electrode 20 to the capacity of the positive electrode 10 is within a predetermined range, it is possible to reduce the precipitation of metallic lithium due to repeated charging and discharging, and improve the cycle characteristics. be able to. Further, since the ratio of the capacity of the negative electrode 20 to the capacity of the positive electrode 10 is within a predetermined range, the capacity originally possessed by the solid solution lithium-containing transition metal oxide can be effectively utilized. Further, since the ratio of the capacity of the negative electrode 20 to the capacity of the positive electrode 10 is within a predetermined range, it is possible to suppress an increase in the silicon-containing alloy and a decrease in energy density and cycle characteristics due to expansion of the negative electrode active material layer 22.

The application of the electric device 100 of the present embodiment is not particularly limited, but as described above, it has a high energy density and excellent cycle characteristics. Therefore, it can be suitably used for vehicles. Specifically, the electric device 100 of the present embodiment can be suitably used as a drive power source for a vehicle or the like.

[Manufacturing method of electrical devices]
The method for manufacturing the electric device according to the present embodiment is not particularly limited, but a method for manufacturing a lithium ion secondary battery will be described as an example. A method for manufacturing a lithium ion secondary battery includes, for example, an electrode manufacturing step and an assembling step.

(Electrode manufacturing process)
The electrode manufacturing process can be performed, for example, by preparing the active material slurry, applying the active material slurry on the current collector, drying, and pressing to form the active material layer. The active material slurry can contain a binder, a conductive additive and a solvent in addition to the above-mentioned active material. The electrodes include a positive electrode 10 and a negative electrode 20. A positive electrode active material is used when the positive electrode 10 is produced, and a negative electrode active material is used when the negative electrode 20 is produced.

The solvent of the active material slurry is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used.

The method of applying the active material slurry to the current collector is not particularly limited, and known methods such as a spray coating method, a roll coating method, a doctor blade method, a flow coating method, a dip coating method, a screen printing method, and an inkjet method are used. can do.

The method for drying the active material slurry is not particularly limited, and may be appropriately adjusted according to the characteristics of the active material slurry to be used. The press process is not particularly limited, and for example, a calendar roll, a flat plate press, or the like can be used.

(Assembly process)
The cell cell layer 40 can be produced by laminating the positive electrode 10 and the negative electrode 20 produced as described above with the separator 30 interposed therebetween. Further, if necessary, the power generation element 50 may be manufactured by stacking a plurality of cell cell layers 40. A lithium ion secondary battery can be manufactured by sealing the cell cell layer 40 or the power generation element 50 thus obtained in the exterior body 70.

In addition, in the method of manufacturing the electric device of this embodiment, in order to improve the cycle characteristics and the like, aging treatment, gas removal treatment, activation treatment and the like may be carried out.

The aging treatment is not particularly limited, but it is preferable to carry out the aging treatment as follows. First, charging is performed at 25 ° C. by a constant current charging method at 0.05 C for 4 hours (SOC of about 20%). Then, after charging to 4.45 V at 0.1 C at 25 ° C., charging is stopped and held in that state (SOC about 70%) for about 48 hours.

In the gas removal treatment, the gas in the exterior body 70 can be removed by opening a part of the exterior body 70 and compressing it. After removing the gas in the exterior body 70, a part of the opened exterior body 70 can be brought into close contact with the cell layer 40 or the power generation element 50 to be sealed. The gas removal treatment can be carried out at least one of after the aging treatment and after the activation treatment.

The activation treatment is not particularly limited, and for example, the following electrochemical pretreatment can be carried out. First, the battery is charged at 25 ° C. by a constant current charging method at 0.1 C until the voltage reaches 4.45 V, and then discharged to 2.0 V at 0.1 C twice. Similarly, at 25 ° C., after charging to 4.55 V at 0.1 C by the constant current charging method, one cycle of discharging to 2.0 V at 0.1 C is performed once, and 4.65 V at 0.1 C. After charging until it becomes, a cycle of discharging to 2.0 V at 0.1 C is performed once. Further, at 25 ° C., a constant current charging method may be used to charge the battery to 4.75 V at 0.1 C and then discharge to 2.0 V at 0.1 C once. In the above example, the charging method is the constant current charging method, but the constant current constant voltage charging method may be used. Further, in the above example, the termination condition is voltage, but the amount of charge or time may be used instead of voltage.

Hereinafter, the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present embodiment is not limited thereto.

[Example 1]
(Preparation of positive electrode)
28.61 g of manganese sulfate monohydrate (molecular weight 169.01 g / mol) and 17.74 g of nickel sulfate hexahydrate (molecular weight 262.85 g / mol) are added to 200 g of pure water, and the mixture is stirred, dissolved and mixed. The solution was adjusted.

Next, aqueous ammonia was added dropwise until the mixed solution reached pH 7. Then, while dropping ammonia water so that the pH of this mixed solution was maintained at 7, a 2 mol / L Na ₂ CO ₃ aqueous solution was dropped to precipitate the complex carbonate.

Then, the obtained precipitate was suction-filtered, washed thoroughly with water, and dried in a drying oven at 120 ° C. for 5 hours. Next, the obtained dried product was crushed in a mortar and then calcined at 500 ° C. for 5 hours. To the pre-baked powder, 10.67 g of lithium hydroxide monohydrate (molecular weight 41.96 g / mol) was added, and the mixture was kneaded in a mortar for about 30 minutes.

After the powder was 2 hours calcined at 500 ° C., containing solid solution lithium having the composition was fired at 900 ° C. 12 hours _{Li 1.5 [Ni 0.45 Mn 0.85 [} Li] 0.20] O z A transition metal oxide was obtained.

10.0 g of the solid solution lithium-containing transition metal oxide obtained as described above and 0.37 g of aluminum nitrate nineahydrate (molecular weight 375.13 g / mol) were added to 100 g of pure water, and the mixture was stirred and mixed. The mixed solution was prepared.

Next, while stirring the mixed solution, 5% aqueous ammonia was gradually added dropwise until the pH reached 7 to 8, aluminum hydroxide was precipitated on the particle surface of the solid solution lithium-containing transition metal oxide, and the mixed solution was further added to 5. Stirred for hours.

Then, the precipitate was suction-filtered, washed thoroughly with water, and dried in a drying oven at 100 ° C. for 1 hour. The dried powder was pulverized in a mortar and then fired at 450 ° C. for 5 hours to obtain a solid solution lithium-containing transition metal oxide containing a coating layer formed of _{Al 2} O _{3. The content of Al 2} O ₃ was 0.5% by mass with respect to the entire solid solution lithium-containing transition metal oxide including the coating layer. The average particle size of the solid solution lithium-containing transition metal oxide containing the coating layer was 8 μm.

Next, in order to prepare a slurry for a positive electrode, 4.0 parts by mass of a solvent (NMP) was further added to 1.5 parts by mass of a 20% by mass binder solution using NMP as a solvent. Then, these mixed solutions were stirred for 1 minute with a stirring defoaming machine (Shinky Co., Ltd. rotating and revolving mixer Awatori Rentaro AR-100) to prepare a binder diluted solution. Next, 0.3 parts by mass of the conductive additive, 9.4 parts by mass of the solid solution lithium-containing transition metal oxide having a coating layer, and 2.6 parts by mass of the solvent (NMP) were added to this binder diluted solution, and the mixture was removed by stirring. The mixture was stirred with a foaming machine for 3 minutes to prepare a slurry for a positive electrode having a solid content concentration of 55% by mass.

The positive electrode slurry thus obtained was placed on one surface of a current collector formed of 20 μm thick aluminum so that the thickness of the positive electrode active material layer after drying was 50 μm, and the doctor blade (tester) was used. It was applied with PI-1210 automatic coating device manufactured by Sangyo Co., Ltd.). Next, the current collector coated with this positive electrode slurry is placed on a hot plate and dried at 100 ° C. to 110 ° C. for 30 minutes so that the amount of NMP remaining in the positive electrode active material layer is 0.02% by mass or less. I let you. The product obtained by drying in this manner was compression-molded by a roller press and cut.

Next, the obtained cut piece was placed in a vacuum dryer ^{and depressurized to 1.33 × 10 4} Pa (100 mmHg) at room temperature (25 ° C.). Subsequently, the temperature was raised to 120 ° C. at a heating rate of 10 ° C./min while circulating nitrogen gas at 100 cm ^{3 / min.} Then, the temperature was kept at 120 ° C. under ^{reduced pressure to 1.33 × 10 4} Pa (100 mmHg) for 12 hours, and then the temperature was lowered to room temperature (25 ° C.). The dried product thus obtained was used as a positive electrode.

(Preparation of negative electrode)
First, using a planetary ball mill (P-6 manufactured by Frichchu, Germany), the metal powder was alloyed and pulverized by a mechanical alloy method. Specifically, the metal powder adjusted so that the mass ratio was Si: Sn: Ti = 80: 10: 10 and the zirconia crushed balls were put into a zirconia container. Then, the pedestal for fixing the zirconia container was rotated at 600 rpm for 24 hours to alloy the metal powder. Then, the pedestal was rotated at 400 rpm for 1 hour to pulverize the alloy. The average particle size of the obtained silicon-containing alloy was 0.3 μm.

The structure of the silicon-containing alloy thus obtained was analyzed by electron diffraction. As a result, diffraction spots and halo patterns showing the crystallinity of the silicide phase (TiSi ₂ ) were observed, and it was confirmed that the amorphous Si phase, which is the parent phase, had a structure in which the crystalline silicide phase was dispersed.

Moreover, the structure structure of the silicon-containing alloy thus obtained was analyzed by the X-ray diffraction measurement method. The equipment and conditions used for the X-ray diffraction measurement method are as follows.

Device name: X-ray diffractometer (SmartLab9kW) manufactured by Rigaku Co., Ltd.
Voltage: 45kV
Current: 200mA
X-ray wavelength: CuKα1

As a result of analysis by the X-ray diffraction measurement method, the diffraction peak intensity of the silicide in the range of 2θ = 37 ° to 45 ° with respect to the diffraction peak intensity of the Si (111) plane in the range of 2θ = 24 ° to 33 °. The ratio was 0.41. It was also confirmed by the analysis by the X-ray diffraction measurement method that all the Ti contained in the silicon-containing alloy _{was present in the silicide (TiSi 2) phase.}

80 parts by mass of the negative electrode active material thus obtained, 5 parts by mass of the conductive auxiliary agent, and 15 parts by mass of the binder were dispersed in 100 parts by mass of N-methylpyrrolidone, and a defoaming kneader (AR manufactured by Thinky Co., Ltd.) was used. The mixture was mixed in −100) to obtain a negative electrode slurry. Carbon black was used as the conductive auxiliary agent, and polyamic acid, which is a precursor of polyimide, was used as the binder.

The negative electrode slurry thus obtained is placed on one surface of a 10 μm-thick electrolytic copper current collector so that the thickness of the negative electrode active material layer after drying is 30.00 μm, so that the doctor blade (tester industry) It was applied with PI-1210 automatic coating device manufactured by Co., Ltd.). Next, the negative electrode current collector coated with this negative electrode slurry is placed on a hot plate, and the amount of NMP remaining in the negative electrode active material layer is 0.02% by mass or less at 100 ° C. to 110 ° C. for 30 minutes. It was dried. The product obtained by drying in this manner was compression-molded by a roller press and cut.

Next, the obtained cut piece was placed in a vacuum dryer ^{and depressurized to 1.33 × 10 4} Pa (100 mmHg) at room temperature (25 ° C.). Subsequently, the temperature was raised to 325 ° C. at a heating rate of 10 ° C./min while circulating nitrogen gas at 100 cm ^{3 / min.} Then, the temperature was kept at 325 ° C. under ^{reduced pressure to 1.33 × 10 4} Pa (100 mmHg) for 24 hours, and then the temperature was lowered to room temperature (25 ° C.). The dried product thus obtained was used as a negative electrode.

(Manufacturing of lithium-ion secondary battery)
First, two positive electrodes obtained as described above are cut out so that the area of the positive electrode active material layer is 2.5 cm in length × 2.0 cm in width, and two sheets are formed so that the positive electrode active material layer side is on the outside. The positive electrodes of the above were overlapped, and the outer peripheral portion on the positive electrode current collector side was spot welded. Then, an aluminum positive electrode tab was welded to the positive electrode current collector.

Next, two negative electrodes obtained as described above were cut out so that the area of the negative electrode active material layer was 2.7 cm in length × 2.2 cm in width. Then, a negative electrode tab made of electrolytic copper was welded to the negative electrode current collector.

Then, the negative electrodes were arranged on both sides of the positive electrode so that the active material layers of the positive electrode and the negative electrode face each other, and separators were arranged between the positive electrode and the negative electrode to prepare a power generation element. As the separator, porous polypropylene having a length of 3.0 cm, a width of 2.5 cm, a thickness of 25 μm, and a porosity of 55% was used. In the laminated power generation element thus obtained, the negative electrode / separator / positive electrode / separator / negative electrode layers are laminated in this order.

Then, aluminum laminate films (length 3.5 cm x width 3.5 cm) are arranged on both sides of the obtained power generation element, and the three sides of the aluminum laminate film are heat-sealed to use the power generation element as the outer body of the aluminum laminate film. Contained.

Then, from the unwrapped side not heat-sealed, the electrolytic solution was prepared as follows into the package body 0.8 cm ³ injected, was heat sealed unsealed edges. Since the power generation element of this embodiment has two cells, the amount of the electrolytic solution per cell is 0.4 cm ³ . Then, in order to allow the electrolytic solution to sufficiently permeate into the electrode pores, the lithium ion secondary battery was produced by continuously pressurizing at 25 ° C. for 24 hours so that the surface pressure was 0.5 MPa.

The electrolytic solution was adjusted as follows. _{First, 1.0 M of LiPF 6} (electrolyte) was dissolved in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC). Then, a solution _{prepared by dissolving 1.8% by mass of lithium difluorophosphate (LiPO 2} F ₂ ) and 1.5% by mass of methylenemethane disulfonic acid (MMDS) in the obtained solvent was used as an electrolytic solution.

For the positive electrode and the negative electrode obtained as described above, half cells having lithium metal as the counter electrode were prepared, and the capacities of the positive electrode and the negative electrode were measured. As a result, the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1. It was 2. The method for measuring the ratio of the capacity of the negative electrode to the capacity of the positive electrode will be described later.

[Example 2]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 32.50 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.3.

[Example 3]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 35.00 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.4.

[Example 4]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 37.50 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.5.

[Comparative Example 1]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 27.50 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.1.

[Comparative Example 2]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 40.00 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.6.

[Comparative Example 3]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 42.50 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.7.

[Comparative Example 4]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 45.00 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.8.

[Comparative Example 5]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 47.50 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.9.

[Comparative Example 6]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 50.00 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 2.0.

[Comparative Example 7]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was 25.00 μm and the ratio of the capacity of the negative electrode to the capacity of the positive electrode was 1.0.

[evaluation]
(Ratio of negative electrode capacity to positive electrode capacity)
The ratio of the capacity of the negative electrode to the capacity of the positive electrode was evaluated as follows. First, half cell 1 and half cell 2 were produced as follows. Next, the capacity of each half cell was measured as follows. Then, the capacity of the half cell 1 was defined as the capacity of the positive electrode, the capacity of the half cell 2 was defined as the capacity of the negative electrode, and the capacity of the negative electrode was divided by the capacity of the positive electrode to calculate the ratio of the capacity of the negative electrode to the capacity of the positive electrode.

(Making half cell 1)
A lithium ion secondary battery was produced by the same method as in Example 1 except that the negative electrode was replaced with metallic lithium.

(Making half cell 2)
A lithium ion secondary battery was produced by the same method as in Example 1 except that the positive electrode was changed to metallic lithium.

(capacity)
At room temperature (25 ° C.), constant current charging was performed at 0.1 C until the maximum voltage reached 4.6 V. Then, the discharge capacity at the time of constant current discharge at 1.0 C from 4.6 V to the minimum voltage of 2.0 V was defined as the capacity.

(Terminal potential)
The positive electrode terminal potential and the negative electrode terminal potential were obtained as follows. First, the half cell 1 and the half cell 2 produced as described above were constantly charged at room temperature (25 ° C.) at 0.1 C until the maximum voltage reached 4.6 V. Next, these half cells were discharged at a constant current of 1.0 C from 4.6 V until the minimum voltage became 2.0 V. Then, the potential of the half cell 1 when the potential difference of these half cells at the time of discharge became 2.5 V was defined as the positive electrode termination potential. Similarly, the potential of the half cell 2 when the potential difference of these half cells at the time of discharge becomes 2.5 V was defined as the negative electrode termination potential.

(Positive electrode utilization rate)
The positive electrode utilization rate was determined as follows. First, the half cell 1 produced as described above was constantly charged at room temperature (25 ° C.) at 0.1 C until the maximum voltage reached 4.6 V. Then, the half cell 1 was discharged at a constant current of 1.0 C from 4.6 V until the minimum voltage became 2.0 V. Then, the capacity immediately before discharge was set to 100%, and the percentage (%) of the capacity when discharged to the positive electrode terminal potential with respect to the capacity immediately before discharge was set as the positive electrode utilization rate.

(Negative electrode utilization rate)
The negative electrode utilization rate is a percentage when the capacity of the half cell 2 measured as described above is divided by the capacity of the half cell 1. That is, the negative electrode utilization rate is a percentage (%) when the capacity of the negative electrode is divided by the capacity of the positive electrode.

(Thickness of negative electrode active material layer)
The thickness of the negative electrode active material layer was calculated by subtracting the thickness of the negative electrode current collector from the thickness of the negative electrode obtained as described above. The thickness of the negative electrode and the thickness of the negative electrode current collector were measured with a thickness gauge. The thickness of the negative electrode active material layer in the 0th cycle is the thickness of the negative electrode active material layer before charging / discharging. The thickness of the negative electrode active material layer in the 100th cycle is 1 at room temperature (25 ° C.) after constant current charging at 0.1 C until the maximum voltage reaches 4.6 V and then until the minimum voltage reaches 2.0 V. It is the thickness of the negative electrode active material layer after 100 cycles of charge / discharge cycles of constant current discharge at 0.0C.

(Expansion rate of negative electrode active material layer)
The expansion rate of the negative electrode active material layer is a percentage (%) when the thickness of the negative electrode active material layer in the 100th cycle is divided by the thickness of the negative electrode active material layer in the 0th cycle.

(Energy density)
The energy density was calculated as follows. First, at room temperature (25 ° C.), constant current charging was performed at 0.1 C until the maximum voltage reached 4.6 V. Then, the discharge capacity at the time of constant current discharge at 1.0 C from 4.6 V to the minimum voltage of 2.0 V was defined as the capacity. The volume energy density (Wh / L) was calculated by multiplying the capacity measured as described above by the average voltage and dividing by the volume including the exterior of the electric device. Then, when the volume energy density of the electric device of Comparative Example 7 was set to 100%, the percentage of the volume energy density of each Example and Comparative Example was calculated as the energy density (%).

(Discharge capacity retention rate)
The discharge capacity retention rate was measured as follows. First, at room temperature (25 ° C.), a charge / discharge cycle is performed in which a constant current is charged at 0.1 C until the maximum voltage reaches 4.6 V, and then a constant current discharge is performed at 1.0 C until the minimum voltage reaches 2.0 V. , 100 cycles were performed. Then, in the first cycle and the 100th cycle, the discharge capacity when discharged from 4.6V to 2.0V is measured, and the percentage of the discharge capacity in the first cycle with respect to the discharge capacity in the 100th cycle is the discharge capacity retention rate (the discharge capacity retention rate). %).

Table 1 shows the evaluation results of the lithium ion secondary batteries of Examples and Comparative Examples produced as described above.

As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 4 have an energy density of 108% or more and maintain a discharge capacity because the ratio of the capacity of the negative electrode to the capacity of the positive electrode is within a predetermined range. The rate was 80% or more, the energy density was high, and the cycle characteristics were excellent.

On the other hand, in the lithium ion secondary batteries of Comparative Examples 1 to 7, the ratio of the capacity of the negative electrode to the capacity of the positive electrode was out of the predetermined range, so that the energy density and the energy density were compared with those of Examples 1 to 4. The cycle characteristics were not sufficient.

FIG. 2 shows the charge / discharge curves of the half cell 1 and the half cell 2 using the positive electrode and the negative electrode of Comparative Example 7 in which the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.0, and the potential difference between the half cell 1 and the half cell 2. It is a graph. As shown in FIG. 2, in Comparative Example 7, the potential difference between the positive electrode terminal potential and the negative electrode terminal potential becomes 2.5 V in a state where the positive electrode potential is high due to the decrease in the negative electrode potential peculiar to the silicon-containing alloy. From this, it can be seen that when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.0, there is a capacity that cannot be used in the solid solution lithium-containing transition metal oxide.

FIG. 3 is a graph showing a charge / discharge curve when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is changed. In the figure, the volume ratios of 1.0 to 1.5 correspond to the negative electrodes used in Comparative Examples 7 and Examples 1 to 4, respectively. As shown in FIG. 3, it can be seen that when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased, the potential of the negative electrode is less likely to decrease, so that the terminal potential of the positive electrode is lowered and the utilization rate of the positive electrode is improved.

FIG. 4 is a graph showing the potential difference between the half cell 1 and the half cell 2 shown in FIG. From the graph of FIG. 4, it can be seen that the capacity of the lithium ion secondary battery is improved as the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased.

On the other hand, as shown in Table 1 and FIG. 5, when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased, the amount of the negative electrode active material layer is increased, so that the thickness of the negative electrode active material layer at the 0th cycle is increased. It gets thicker. Then, when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased, the expansion coefficient of the negative electrode active material layer decreases. Therefore, it can be seen that as the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased, the ratio of the negative electrode active material not used in the charge / discharge reaction increases.

That is, as shown in Table 1 and FIG. 6, when the ratio of the capacity of the negative electrode to the capacity of the positive electrode is increased, the positive electrode utilization rate tends to increase, the precipitation of metallic lithium decreases, and the negative electrode utilization rate tends to decrease. ..

However, as shown in FIGS. 7 and 8, in the lithium ion secondary batteries of Examples 1 to 4, the ratio of the capacity of the negative electrode to the capacity of the positive electrode is within a predetermined range. Therefore, the lithium ion secondary batteries of Examples 1 to 4 have a higher energy density and excellent cycle characteristics than the lithium ion secondary batteries of Comparative Examples 1 to 7.

Although the present invention has been described above with reference to Examples and Comparative Examples, the present invention is not limited thereto, and various modifications can be made within the scope of the gist of the present invention.

10 Positive electrode 11 Positive electrode current collector 12 Positive electrode active material layer 20 Negative electrode 21 Negative electrode current collector 22 Negative electrode active material layer 30 Separator 100 Electrical device

Claims (4)

A positive electrode including a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector.
A negative electrode including a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector.
A separator arranged between the positive electrode and the negative electrode is provided.
The positive electrode active material layer contains 80% by mass to 98% by mass of the positive electrode active material.
Wherein comprises a positive electrode active material has the formula _{Li 1.5 [Ni a Co b Mn} c [Li] d] O z solid solution lithium-containing transition metal oxide represented by in Formula, a, b, c and d are , A + b + c + d = 1.5, 1.1 ≦ a + b + c ≦ 1.4, 0.1 ≦ d ≦ 0.4, and z is the number of oxygen satisfying the valence.
The negative electrode active material layer contains 40% by mass to 98% by mass of the negative electrode active material.
The negative electrode active material contains a silicon-containing alloy containing 20% by mass or more of silicon, and contains a silicon-containing alloy.
Wherein the ratio of the capacitance of the negative electrode with respect to the capacity of the positive electrode 1.1 Ri der and less than 1.6,
The capacity of the positive electrode and the capacity of the negative electrode are constantly charged at 0.1 C until the maximum voltage reaches 4.6 V at 25 ° C., and fixed at 1.0 C from 4.6 V until the minimum voltage reaches 2.0 V. discharge capacity der Ru electrical device at the time of the current discharge. The electric device according to claim 1, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more and 1.5 or less. The electric device according to claim 1 or 2, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more and 1.4 or less. The electric device according to any one of claims 1 to 3, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more and 1.3 or less.

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