JP7037873B2 - Positive electrode active material for lithium-ion batteries, positive electrode for lithium-ion batteries and lithium-ion batteries - Google Patents

Description

The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

A lithium-containing transition metal oxide is generally used as the positive electrode active material of a lithium ion battery. Specifically, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc. have improved characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction). , Rate characteristics) and these are being combined in order to improve safety. Lithium-ion batteries for large-scale applications such as in-vehicle use and road leveling are required to have characteristics different from those for conventional mobile phones and personal computers.

Surface modification is one of the techniques used for the positive electrode active material for lithium ion batteries. This is mainly based on the following three technologies (a), (b) and (c). First, there is (a) a technique for suppressing side reactions of decomposition of the electrolytic solution on the surface of the active material as much as possible. In the past, oxides of single elements such as Al ₂ O ₃ and Zr O ₂ were the main constituents of the modifying substance, but if the entire surface of the active substance is modified with this, Li ions cannot be inserted and removed. Therefore, at present, the main technique is to partially modify the surface or to modify the surface with a Li ion conductor or an active material.

Next, (b) there is a technique for preventing transition metals (particularly Mn) from elution from the active material due to hydrogen fluoride impurities in the electrolytic solution. In this case as well, since it is not possible to completely modify the surface of the active material as in (a) above, a technique for suppressing Mn elution by reacting hydrogen fluoride impurities in the electrolytic solution by blending with a Ni-based active material is currently performed. Is the main body. The reason why Mn is particularly targeted for elution suppression is that it easily reacts with the carbon of the negative electrode. When the positive electrode is a Mn-based active material and the negative electrode is a graphite-based active material, the battery is repeatedly charged and discharged. Depending on the design of, the discharge capacity will be 1/10 of the initial discharge capacity in 10 cycles.

Next, there is a technique of (c) coating an active material having low electron conductivity with a substance having high electron conductivity. This technology has been established as a technology for coating carbon materials on phosphate-based, silicate-based, and lithium-titanium-based active materials, and since it is easy to manufacture, it has been put to practical use in batteries for tools and the like. Has been done. Considering the above techniques (a), (b) and (c), the surface modification technique does not inhibit lithium ion conduction, suppresses electrolyte decomposition, and further improves battery characteristics. Can be said to be required.

Japanese Unexamined Patent Publication No. 2013-152866 WO2012 / 117852

As a recent trend, as seen in Patent Document 1, the positive electrode active material mounted on a lithium ion battery for high output applications such as cars is made by coating the active material with lithium tungstate or the like, and using it. By partially covering the battery instead of covering the entire surface, the insertion and removal of lithium ions can be made smoother, so that a large current can be taken out from the battery. Although this mechanism is not clear, it is speculated that lithium tungstate on the surface may play some catalytic role in Li insertion / desorption or SEI formation with the electrolytic solution.

However, this technique has a problem that the cycle characteristics at a high rate of 1C or more are deteriorated. That is, when a large amount of current flows, Joule heat is generated by the current flowing through the charge transfer resistance, and the temperature in the vicinity of the electrode rises. At this time, since the lattice constants of lithium tungstate and the like and the lithium nickel cobalt manganese composite oxide are different, the coatings are easily peeled off, and since lithium tungstate and the like expand due to the temperature rise, they are separated from each other. It is highly probable that they collided with each other and the coating was peeled off, reducing the high output of lithium tungstate and the like.

As a method for preventing this, as described in Patent Document 2, there is a method of maintaining the cycle characteristics at a high rate by adding an additive to the electrolytic solution, but the easiness of peeling of the coating does not change and it peels off. There was a case where the additive was consumed due to a side reaction between the lithium tungstate and the additive, and the effect of adding the additive was lost.

Therefore, it is an object of the present invention to provide a surface-modified positive electrode active material for a lithium ion battery having good cycle characteristics at a high rate.

As a result of various studies to solve such a problem, the present inventor has obtained ZrW ₂ O ₈ having a negative coefficient of thermal expansion in which the Ni composition is 0.5 or more in terms of molar ratio. By coating the surface of the positive electrode active material particles, which is a ternary Li composite oxide of Mn, the thermal stability and cycle characteristics obtained as the coating effect of ordinary expensive metals are improved, and the coating material can be coated. It was found that the cycle characteristics are improved even at a high rate due to the effect of making it difficult to peel off.

The present invention completed on the basis of the above findings has one aspect: composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.06, 0.5 ≦ b ≦ 0.9, 0.045 ≦ c ≦ 0.3, 0.045 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005 and M are at least one selected from the group consisting of Mg and Al.)
ZrW ₂ O ₈ is attached to the surface of the primary particles represented by, and the surface of the primary particles does not have a surface layer containing boron.
Zr / (Ni + Co + Mn + M) has a molar ratio of 0.001 to 0.005 , and W / (Ni + Co + Mn + M) has a molar ratio of 0.002 to 0.01.
In the diffraction pattern of XRD, the peak intensity Ia of the (003) plane present at 2θ = 18.5 ± 1 ° derived from the layered oxide Li _a Ni _{b Coc} Mn _{d Me} O ₂ and the cubic ZrW ₂ Ratio Ib / Ia of the peak intensity of the (210) surface existing at 2θ = 22.0 ± 1 ° and the peak intensity of the (211) surface existing at 2θ = 24.0 ± 1 ° derived from O ₈ to the total Ib. Is a positive electrode active material for a lithium ion battery of 0.0001 to 0.0009.

In another aspect, the present invention is a positive electrode for a lithium ion battery having the positive electrode active material for the lithium ion battery of the present invention.

In yet another aspect, the present invention is a lithium ion battery having a positive electrode for a lithium ion battery of the present invention.

According to the present invention, it is possible to provide a surface-modified positive electrode active material for a lithium ion battery having good cycle characteristics at a high rate.

(Composition of positive electrode active material for lithium-ion batteries)
The positive electrode active material for a lithium ion battery of the present invention has a composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.06, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.3, 0.1 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005 and M are at least one selected from the group consisting of Mg and Al.)
ZrW ₂ O ₈ is attached to the surface of the primary particles represented by, Zr / (Ni + Co + Mn + M) has a molar ratio of 0.001 to 0.005, and W / (Ni + Co + Mn + M) has a molar ratio of 0.002 to 0.002. It is controlled to 0.01.

The positive electrode active material for a lithium ion battery of the present invention has a lithium ratio of 1.0 to 1.06, but if it is less than 1.0, it is difficult to maintain a stable crystal structure, and if it exceeds 1.06, it is difficult to maintain a stable crystal structure. This is because the high capacity of the battery may not be secured. Further, since the composition of nickel is 0.5 to 0.9, the capacity, output, and safety of the lithium ion battery using the positive electrode active material for the lithium ion battery are improved in a well-balanced manner. The composition of nickel in the positive electrode active material for a lithium ion battery is preferably 0.7 to 0.9, more preferably 0.8 to 0.9.

The positive electrode active material for a lithium ion battery of the present invention contains ZrW ₂ O ₈ having a negative coefficient of thermal expansion and a Ni / Co / Mn ternary Li composite oxide having a Ni composition of 0.5 or more in molar ratio. The surface of the positive electrode active material particles is coated. Since ZrW ₂ O ₈ has a negative thermal expansion coefficient, it shrinks as the temperature rises. Therefore, when the temperature rises, the active material (primary particles) itself expands, but the ZrW ₂ O ₈ adhering to the surface of the active material particles shrinks, so that the ZrW ₂ O ₈ is transferred to the active material particles. The effect of increasing the adhesive strength can be obtained. Therefore, ZrW ₂ O ₈ is less likely to be peeled off from the surface of the active material particles, and the cycle characteristics at a high rate of 1C or more are improved.

Further, the positive electrode active material for a lithium ion battery of the present invention contains ZrW ₂ O ₈ having a negative coefficient of thermal expansion and a Ni / Co / Mn ternary Li composite having a Ni composition of 0.5 or more in terms of molar ratio. By coating the surface of the positive electrode active material particles which are oxides, the effect of improving the thermal stability (due to surface modification) and the cycle characteristics obtained as the coating effect of ordinary expensive metals can be obtained.

Further, in the positive electrode active material for a lithium ion battery of the present invention, Zr / (Ni + Co + Mn + M) has a molar ratio of 0.001 to 0.005 and W / (Ni + Co + Mn + M) has a molar ratio of 0.002 to 0. It is controlled by 01. When Zr / (Ni + Co + Mn + M) is less than 0.001 in molar ratio, or W / (Ni + Co + Mn + M) is less than 0.002 in molar ratio, the effect of improving thermal stability and cycle characteristics by surface modification can be obtained. do not have. Further, if Zr / (Ni + Co + Mn + M) exceeds 0.005 in molar ratio or W / (Ni + Co + Mn + M) exceeds 0.01 in molar ratio, there arises a problem that the capacity of the battery is lowered. It is preferable that Zr / (Ni + Co + Mn + M) is controlled to a molar ratio of 0.001 to 0.005, W / (Ni + Co + Mn + M) is controlled to a molar ratio of 0.002 to 0.01, and Zr / (Ni + Co + Mn + M) is controlled to a molar ratio of 0.002 to 0.01. It is more preferable that the molar ratio is controlled to 0.003 to 0.004 and W / (Ni + Co + Mn + M) is controlled to the molar ratio of 0.006 to 0.008.

Further, the positive electrode active material for a lithium ion battery of the present invention is present at 2θ = 18.5 ± 1 ° derived from the layered oxide _{Lia Nib Coc Mnd Me} O ₂ in the diffraction pattern of XRD (003). ) Surface peak intensity Ia and (210) surface peak intensity and 2θ = 24.0 ± 1 ° present at 2θ = 22.0 ± 1 ° derived from cubic ZrW ₂ O ₈ (211) ) The ratio Ib / Ia to the total peak intensity Ib of the surface is preferably 0.0001 to 0.001. If the ratio Ib / Ia is less than 0.0001, the effect of improving the thermal stability and cycle characteristics by surface modification may not be obtained. Further, if the ratio Ib / Ia exceeds 0.001, there may be a problem that the capacity of the battery is lowered. The ratio Ib / Ia is more preferably 0.0001 to 0.001, and even more preferably 0.0004 to 0.0008.

(Structure of positive electrode for lithium ion battery and lithium ion battery having it)
The positive electrode for a lithium ion battery according to the embodiment of the present invention is, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above configuration, a conductive auxiliary agent, and a binder from an aluminum foil or the like. It has a structure provided on one side or both sides of the current collector. Further, the lithium ion battery according to the embodiment of the present invention includes a positive electrode for a lithium ion battery having such a configuration.

(Manufacturing method of positive electrode active material for lithium-ion batteries)
Next, a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention will be described in detail.

As a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention, first, a ternary composite hydroxide of Ni / Co / Mn having a Ni composition of 0.5 or more in molar ratio or a ternary composite hydroxide of Ni / Co / Mn is used. A precursor of a quaternary composite hydroxide of Ni, Co, Mn and Mg or Al is prepared. Next, ZrW ₂ O ₈ and a Li source (Li carbonate, Li hydroxide, etc.) are dry-mixed with the composite hydroxide with a Henshell mixer or the like after adjusting the mixing ratio of each raw material, and then 720 ° C. A fired body (positive electrode active material) is obtained by firing at a temperature of about 950 ° C. for 12 to 24 hours.

Further, as a method for producing a positive electrode active material for a lithium ion battery according to another embodiment of the present invention, first, a ternary composite hydroxylation of Ni / Co / Mn having a Ni composition of 0.5 or more in molar ratio. Prepare a precursor of the substance (median diameter 3 to 20 μm). Next, the Ni / Co / Mn ternary composite oxide is mixed with ZrW ₂ O ₈ having a median diameter of 1 to 2 μm, a Li source (Li carbonate, Li hydroxide, etc.), and if necessary. The Mg source (Mg carbonate, Mg hydroxide, etc.) and Al source (Al carbonate, Al hydroxide, etc.) are mixed in a wet manner by adjusting the mixing ratio of each raw material, and then spray-dried with a micro mist dryer (MMD). The obtained dry powder is fired in the range of 700 ° C. to 950 ° C. for 12 to 24 hours to obtain a fired body (positive electrode active material).
Then, if necessary, the fired body is crushed using, for example, a palvelizer to obtain a powder of the positive electrode active material.

Hereinafter, examples for better understanding the present invention and its advantages are provided, but the present invention is not limited to these examples.

A ternary composite hydroxide of Ni / Co / Mn having a predetermined composition having a Ni composition of 0.5 or more in molar ratio, or a quaternary composite of Ni / Co / Mn and Mg or Al. A hydroxide precursor (median diameter 3 to 20 μm) was prepared. Next, in the composite hydroxide, ZrW ₂ O ₈ having a median diameter of 1 to 2 μm, a Li source (Li carbonate, Li hydroxide, etc.), and for some examples, an Mg source (carbonic acid). Mg, Mg hydroxide, etc.) and Al source (Al carbonate, Al hydroxide, etc.) are dry-mixed with a Henchel mixer after adjusting the mixing ratio of each raw material, and then at the firing temperature shown in Table 1 for 12 to 24 hours. By firing, a positive electrode active material in which ZrW ₂ O ₈ was attached to the surface of the primary particles, which was a fired body, was obtained.

(evaluation)
Each evaluation was carried out under the following conditions using the samples of each Example and Comparative Example thus prepared.
-Evaluation of positive electrode active material composition-
The metal content in each positive electrode active material was measured by an inductively coupled plasma emission spectrophotometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. In addition, the oxygen content was measured by the LECO method, and it was confirmed that both were "O ₂ " in the composition formula. Moreover, the molar ratio of Zr and W in the positive electrode active material, that is, Zr / (Ni + Co + Mn + M) and W / (Ni + Co + Mn + M) was evaluated by the measurement by the ICP-OES.

-Peak intensity ratio Ib / Ia-
According to the following measurement conditions, the peak intensity Ia of the (003) plane present at 2θ = 18.5 ± 1 ° derived from the layered oxide _{Lia Ni b Coc Mn d Me} O ₂ and the cubic crystal by XRD. Ratio of the peak intensity of the (210) plane present at 2θ = 22.0 ± 1 ° and the peak intensity of the (211) plane present at 2θ = 24.0 ± 1 ° from a certain ZrW ₂ O ₈ to the total Ib. Ib / Ia was evaluated.
-XRD diffractometer: SmartLab (manufactured by Rigaku Co., Ltd.)
-Radioactive source: CuK (λ = 1.5406Å)
-Apply the sample (positive electrode active material) to the glass sample holder (2 cm x 1.5 cm, depth 0.3 mm) -Detector: D / tex
-Measurement range: 2θ = 10 ° to 80 °
-Scan axis: 2θ / θ, scan speed: 1 minute min ^-1
-Step width: 0.01 degree
・ Slit width: IS (DS) 1/4 °, RS1 10mm, RS2 10mm

-Evaluation of battery characteristics-
The positive electrode active material, the conductive material, and the binder are weighed at a ratio of 90: 5: 5, and the positive electrode active material and the conductive material are mixed with the binder dissolved in an organic solvent (N-methylpyrrolidone) to form a slurry. It was coated on an Al foil, dried, and then pressed to obtain a positive electrode. Subsequently, a 2032 type coin cell for evaluation with Li as the counter electrode was prepared, and 1M-LiPF ₆ was dissolved in EC-DMC (1: 1) in an electrolytic solution, and the solution was obtained at a discharge rate of 0.1 C. Initial capacity (25 ° C, charge upper limit voltage: 4.3V, discharge lower limit voltage: 3.0V), high temperature cycle characteristics after 20 cycles at charge / discharge rate 1C, 45 ° C after 20 cycles at charge / discharge rate 3C The high temperature cycle characteristics were measured.
These results are shown in Tables 1 and 2.

Claims (3)

Composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.06, 0.5 ≦ b ≦ 0.9, 0.045 ≦ c ≦ 0.3, 0.045 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005 and M are at least one selected from the group consisting of Mg and Al.)
ZrW ₂ O ₈ is attached to the surface of the primary particles represented by, and the surface of the primary particles does not have a surface layer containing boron.
Zr / (Ni + Co + Mn + M) has a molar ratio of 0.001 to 0.005 , and W / (Ni + Co + Mn + M) has a molar ratio of 0.002 to 0.01.
In the diffraction pattern of XRD, the peak intensity Ia of the (003) plane present at 2θ = 18.5 ± 1 ° derived from the layered oxide Li _a Ni _{b Coc} Mn _{d Me} O ₂ and the cubic ZrW ₂ Ratio Ib / Ia of the peak intensity of the (210) surface existing at 2θ = 22.0 ± 1 ° and the peak intensity of the (211) surface existing at 2θ = 24.0 ± 1 ° derived from O ₈ to the total Ib. Is a positive electrode active material for lithium ion batteries, which is 0.0001 to 0.0009. The positive electrode for a lithium ion battery having the positive electrode active material for the lithium ion battery according to claim 1. The lithium ion battery having the positive electrode for the lithium ion battery according to claim 2.