JP3764320B2 - Lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery.
[0002]
[Prior art]
A lithium secondary battery using a non-aqueous electrolyte has a high battery voltage and a high energy density, and therefore has been actively developed and is already in practical use for information devices such as computers and mobile phones.
[0003]
However, high-input, high-output, large-capacity industrial batteries require a large amount of active material, so Co-based and Ni-based materials used in information equipment are put into practical use in terms of both cost and resources. It is considered impossible. For this reason, spinel type Mn-based materials are expected to solve these problems. However, spinel type Mn-based materials have problems such as poor cycle life at high temperatures, output characteristics, and input characteristics, which are the most important issues for industrial batteries.
[0004]
In order to apply lithium secondary batteries to power sources such as electric vehicles, parallel hybrid electric vehicles, power storage systems, elevators, power tools, etc., the cycle must be over 1000 cycles (capacity maintenance rate of 70% or more) at a high temperature of 50 ° C or higher. Although life and an output of 500 W / kg or more are required, such a long life and high power density cannot be achieved with conventional Mn-based materials.
[0005]
According to Japanese Patent Laid-Open No. 6-187993, an attempt is made to extend the life by increasing the Li / Mn ratio, which is the composition ratio of Li and Mn. However, capacity reduction of about several percent has occurred through 10 cycles of charge and discharge even at room temperature. The cycle life of a lithium secondary battery greatly depends on the ambient temperature, and particularly at a high temperature of 50 ° C. or higher, the life is significantly shorter than that at room temperature. Therefore, it is difficult to obtain a cycle life of 1000 cycles or more at a high temperature of 50 ° C. or higher only by increasing the Li / Mn ratio.
[0006]
In Japanese Patent Publication No. 8-24043, the Li / Mn ratio is similarly increased, and this is baked at 430 to 510 ° C., and this is attempted with a material having a lattice constant of 8.22 mm or less. However, there is no prospect of obtaining a cycle life of about 200 cycles at room temperature and 1000 cycles or more at 50 ° C. or higher. In JP-A-7-282798, Li (Mn), which is a material having a large Li / Mn ratio, is also used. _2-x Li _x ) O _Four (0.020 ≦ x ≦ 0.081) is used to extend the life, but even when x = 0.081 (Li / Mn = 0.58), 5% is obtained after about 100 cycles at room temperature. Thus, a cycle life of 1000 cycles or more cannot be obtained at a high temperature of 50 ° C. or higher.
[0007]
[Problems to be solved by the invention]
The reason for such a short lifetime is that the positive electrode active material repeats expansion and contraction due to repeated charging and discharging a plurality of times, and as a result, the crystal collapses and lithium cannot be reversibly occluded and released. This is because Mn ions are dissolved in the electrolytic solution at a high temperature, and the crystal of the positive electrode active material is more easily collapsed than at room temperature. In addition, the dissolved Mn ions are deposited on the negative electrode to inhibit the charge / discharge reaction of the negative electrode, thereby shortening the life of the negative electrode.
[0008]
Also, the reason why the output characteristics and input characteristics of lithium secondary batteries are low is that the diffusion rate related to the insertion / release of lithium ions is low because an organic solvent having a lower ionic conductivity than the aqueous solution system is used as the electrolyte. Because. In particular, the lithium ions that can no longer react on the negative electrode surface react with an organic solvent to form a film, and the resistance of the film further reduces the diffusion rate of lithium ions, resulting in poor output characteristics and input characteristics. . Moreover, since the organic solvent which is electrolyte solution remarkably falls in the ionic conductivity at low temperature, the output characteristic and input characteristic at the time of low temperature become worse.
[0009]
The first object of the present invention is to solve these problems and to receive or supply power promptly in response to fluctuations in the power supply or load due to long life by using a material having a long life at high temperatures. The object is to provide a lithium secondary battery.
[0010]
A second object of the present invention is to provide a lithium secondary battery having excellent characteristics as a power source for electric vehicles, parallel hybrid electric vehicles, power storage systems, elevators, electric tools and the like.
[0011]
[Means for Solving the Problems]
The lithium secondary battery of the present invention is characterized in that a material containing amorphous carbon is used as a negative electrode, and a positive electrode has a spinel crystal structure and is made of a composite oxide containing Li and Mn.
[0012]
As the positive electrode of the present invention, the composite oxide contains Li and Mn as essential elements, but may contain other transition metals other than Mn, IIa group or IIIb group elements. Examples of these include Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Be, Mg, Ca, Sr, Ba, Ra, B, Al, Ga, In, and Tl.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
First, the configuration of the positive electrode and the negative electrode will be described.
[0014]
As the positive electrode active material of the present invention, a composite oxide having a Li / Mn atomic ratio larger than 0.55 and smaller than 0.80 is used. When the Li / Mn atomic ratio is 0.55 or less, if the charge / discharge cycle is repeated at 50 ° C. or higher, Mn ions dissolve in the electrolytic solution, the crystal structure collapses, and the cycle life is shortened. Further, when the Li / Mn atomic ratio is 0.80 or more, the discharge capacity becomes small.
[0015]
A lattice constant in the spinel crystal of the composite oxide of the present invention is characterized by being smaller than 8.230Å and larger than 8.031０３. When the lattice constant is 8.230 mm or more, when the charge / discharge cycle is repeated at 50 ° C. or more, Mn ions dissolve in the electrolyte solution, the crystal structure collapses, and the cycle life is short. Moreover, when the lattice constant is 8.031 or less, the discharge capacity is small.
[0016]
Furthermore, the complex oxide of the present invention is characterized in that the half width of the 2θ angle of the (400) peak of the X-ray diffraction pattern is smaller than 0.20 °. In the measurement of X-ray diffraction, Cu-kα rays were used as a radiation source, and slits having a slit width of DS = SS = 0.5 and RS = 0.15 were used. When the full width at half maximum is 0.20 ° or more and the charge / discharge cycle is repeated at 50 ° C. or more, Mn ions dissolve in the electrolytic solution, the crystal structure collapses, and the cycle life is shortened.
[0017]
The specific surface area of the secondary particles of the composite oxide of the present invention is 1.5 m. ² / 10m smaller than / g ² It is characterized by being larger than / g. Specific surface area is 1.5m ² When the charge / discharge cycle is repeated at 50 ° C. or higher at M / g or higher, Mn ions dissolve in the electrolytic solution, the crystal structure collapses, and the cycle life is short. The specific surface area is 0.10m. ² / G or less, the power efficiency is low because the reaction field of the electrode active material itself is small in rapid charge / discharge.
[0018]
Furthermore, the average particle diameter of the primary particles of the composite oxide of the present invention is larger than 1 μm and smaller than 20 μm. When the average particle size is 1 μm or less, when the charge / discharge cycle is repeated at 50 ° C. or more, Mn ions dissolve in the electrolyte solution, the crystal structure collapses, and the cycle life is short. On the other hand, when the average particle size is 20 μm or more, the power active efficiency is low because the reaction field of the electrode active material itself is small in rapid charge and rapid discharge.
[0019]
Only when the positive electrode of the present invention is combined with a negative electrode containing amorphous carbon has a long lifetime at high temperatures, and the intended lithium secondary battery can be obtained. Furthermore, the negative electrode active material of the lithium secondary battery of the present invention contains amorphous carbon and has a negative electrode density of 0.95 g / cm. ^Three Larger than 1.5 g / cm ^Three It is characterized by being smaller than.
[0020]
When the charge / discharge cycle is repeated at 50 ° C. or higher, Mn ions are dissolved from the positive electrode active material in the electrolytic solution and are deposited at a portion where the Mn ion deposition start potential, that is, a potential of 2 V or less. A negative electrode, a separator, a current collector foil, a battery can, and the like are deposition sites. Negative electrode density is 0.95 g / cm ^Three In the following, since there are many voids in the negative electrode and the specific surface area as an electrode is large, a large amount of Mn ions are deposited on and inside the negative electrode. The deposited Mn greatly decreases the capacity of the negative electrode, and therefore the cycle life is short. Negative electrode density is 1.5 g / cm ^Three In the above, since there are few void parts of a negative electrode, electrolyte solution does not osmose | permeate inside an electrode and a negative electrode capacity | capacitance becomes low.
[0021]
Furthermore, the negative electrode active material of the lithium secondary battery of the present invention contains amorphous carbon and has a true density of 1.2 to 1.8 g / cm. ^Three It is characterized by being. When the charge / discharge cycle is repeated at 50 ° C. or higher, Mn ions are dissolved in the electrolyte from the positive electrode active material and become a Mn ion deposition start potential, that is, a potential of 2 V or less, such as a negative electrode, a separator, a current collector foil A battery can or the like becomes a deposition site.
[0022]
The true density of carbon is 1.2 g / cm ^Three If it is smaller, there are many voids inside the carbon and the specific surface area is also large, so that a large amount of Mn ions are deposited on and inside the carbon. The deposited Mn greatly reduces the capacity of the negative electrode, so that the cycle life is shortened. Moreover, the true density of carbon is 1.8 g / cm. ^Three If it is larger, the gap portion of the negative electrode is small, so that the electrolyte does not penetrate into the electrode, the negative electrode capacity is lowered, and it becomes difficult to obtain the intended lithium secondary battery.
[0023]
Furthermore, the negative electrode active material of the lithium secondary battery of the present invention includes amorphous carbon and has a crystal thickness Lc of 5 to 150 mm. The crystal thickness Lc of carbon is one of the indexes representing the crystallinity of carbon. When Lc is small, amorphization is strong, and when Lc is large, graphitization is strong.
[0024]
Lc is also an index representing the number of stacked layers in the direction perpendicular to the six-membered ring network surface. When Lc is small, the number of stacks is small, and further, the end of the six-membered ring, that is, the number of lithium insertion / release sites is small. When Lc is large, the number of stacks is large and the end of the six-membered ring, that is, lithium This means that there are many insertion / release sites.
[0025]
When the carbon crystal thickness Lc is smaller than 5 mm, the insertion / release reaction of lithium is not ensured, so that the insertion / release reaction does not proceed smoothly, and lithium ions are strongly trapped in the carbon. The characteristics are greatly reduced. In addition, when the carbon crystal thickness Lc is larger than 150 mm, the graphite-like property is stronger than the amorphous property, so that the six-membered ring network surfaces are stacked in parallel and the six-membered ring end portions are concentrated in one direction. End up. Therefore, directivity is generated at the lithium insertion / release site, and lithium insertion / release proceeds in only one direction, and output characteristics and input characteristics are greatly deteriorated.
[0026]
The lithium secondary battery of the present invention can obtain an input density of 300 to 1800 W / kg with a single battery. Further, it is possible to obtain a power density of 500 to 3500 W / kg with a single cell, and it is desirable to use within this range.
[0027]
Furthermore, the lithium secondary battery of the present invention can be an assembled battery, and an input density of 200 to 1300 W / kg is obtained. A power density of 360 to 2520 W / kg can be obtained with the assembled battery, and it is desirable to use within this range.
[0028]
The lithium secondary battery of the present invention has an input density of 300 to 1800 W / kg for a single cell and 200 to 1300 W / kg for an assembled battery at a use temperature of −10 ° C. to 50 ° C.
[0029]
Furthermore, the lithium secondary battery of the present invention can obtain an input density of 500 to 3500 W / kg for a single cell and 360 to 2020 W / kg for a battery pack at a use temperature of −10 ° C. to 50 ° C.
[0030]
As a method for producing the positive electrode active material of the present invention, manganese dioxide and lithium carbonate are mixed at a predetermined ratio, followed by preliminary firing at a temperature of 500 to 650 ° C. in air, and then 800 to 875 ° C. in the air. It is preferable to bake for 20 hours or more and cool at a rate slower than 2 ° C./min. The positive electrode active material thus produced has high crystallinity and remarkable grain growth, and exhibits good long-life cycle characteristics even at high temperatures.
[0031]
In particular, a cycle life of 1000 cycles or more can be obtained even at a high temperature of 50 ° C. or higher, and it has high input characteristics and output characteristics in a temperature range of −10 ° C. to 50 ° C. Therefore, the present invention can be applied to a power source that requires power assist.
[0032]
In order to extend the charge / discharge cycle life at a high temperature, it is important to increase the stability of the positive electrode active material crystal and suppress the collapse of the crystal structure accompanying the charge / discharge reaction.
[0033]
There are two factors in the collapse of the crystal structure associated with the charge / discharge reaction, one is mechanical breakdown caused by the expansion and contraction of the lattice during charge / discharge, and the other is tetravalent Mn generated during charge. This is a chemical decay caused by forming an organic complex with an organic solvent in the liquid and eluting it out of the crystal system.
[0034]
Since the positive electrode active material of the present invention uses a material having a large Li / Mn ratio, the proportion of Mn4 + ions having a small ionic radius is relatively increased compared to Mn3 + ions, and the Jahn-Teller instability of Mn3 + ions is increased. By suppressing, lattice distortion can be reduced, and both mechanical and chemical collapse can be suppressed.
[0035]
For example, when Li / Mn = 0.50, LiMn ₂ O _Four In view of the neutrality of the charge, the average valence of Mn ions is 3.5, that is, the same number of Mn3 + and Mn4 +. When Li / Mn = 0.58, Li _{1 + x} Mn _2-x O _Four When calculated from the above composition formula, the average valence of Mn ions becomes +3.63, and the proportion of tetravalent Mn4 + ions increases relatively.
[0036]
At this time, the lattice constant is smaller than that in the former case, so that the expansion / contraction amount during charging / discharging is reduced, so that mechanical collapse can be suppressed. Further, when the valence of Mn approaches tetravalence, lithium that cannot be released remains in the crystal system, so that it functions as a support for supporting the crystal structure and can suppress both mechanical and chemical collapse.
[0037]
Further, since the positive electrode active material of the present invention has high crystallinity and significant grain growth, the stability of the crystal is remarkable, and both mechanical and chemical collapse can be suppressed.
[0038]
However, even if the positive electrode active material of the present invention is used, elution of Mn to some extent is unavoidable depending on the temperature conditions of charge and discharge, even if chemical collapse does not occur. When Mn is eluted, the problem is where the eluted Mn is precipitated. If the eluted Mn is preferentially deposited on the negative electrode, the negative electrode capacity is reduced and the cycle life is shortened. In order to suppress this, by increasing the density of the negative electrode or the true density of carbon, the deposition site on the negative electrode can be reduced, and the capacity reduction can be suppressed.
[0039]
In order to obtain a long-life industrial battery, a negative electrode containing amorphous carbon is always used. When a negative electrode containing no amorphous carbon is used, the cycle life is short, and therefore, it is not preferable as an industrial battery that requires a cycle life of 1000 cycles or more even at a high temperature of 50 ° C. or higher.
[0040]
When a carbon negative electrode other than the conventional amorphous carbon is used, the organic solvent used as the electrolytic solution is easily decomposed at 50 ° C. or more, and carbon dioxide, hydrocarbon, lithium alkoxide, etc. are easily formed. . Since amorphous carbon is relatively less decomposed than other carbon materials, the life of the amorphous carbon can be extended.
[0041]
In addition, as a carbon material forming the battery, it is preferable to use a carbon material within the optimum range of the crystal thickness Lc in order to improve output characteristics and input characteristics. If Lc is too large or too small, the number of lithium insertion / release sites will decrease, or directionality will occur and the insertion / release speed will be reduced, affecting output characteristics and input characteristics.
[0042]
A lithium secondary battery having high input characteristics and output characteristics can be obtained only by combining the positive electrode and the negative electrode of the present invention. Furthermore, even when the battery of the present invention is an assembled battery, high input characteristics and output characteristics can be obtained.
[0043]
Due to the above, cycle life of 1000 cycles or more at high temperatures of 50 ° C or higher, such as electric vehicles, parallel hybrid electric vehicles, power storage systems, elevators, power tools, etc., and high input characteristics and output even in a temperature range of -10 ° C to 50 ° C A lithium secondary battery that can be applied as an industrial battery that requires characteristics can be obtained.
[0044]
[Example 1]
The positive electrode was mixed with 90% by weight of the positive electrode active material, 4% by weight of polyvinylidene fluoride as the binder, and 6% by weight of graphite as the conductive agent. It apply | coated to both surfaces of a 20 micrometer aluminum foil.
[0045]
The negative electrode is made of amorphous carbon powder. This is a mixture of 87% by weight, 6% by weight of acetylene black as a conductive agent, and 7% by weight of polyvinylidene fluoride as a binder. After mixing for 30 minutes, it was applied to both sides of a 10 μm thick copper foil.
[0046]
The positive and negative electrodes were rolled and formed with a press machine, the terminals were spot welded, and then vacuum dried at 150 ° C. for 5 hours.
[0047]
A positive electrode and a negative electrode were laminated via a microporous polypropylene separator, and this was wound in a spiral shape and inserted into a SUS battery can. The negative terminal was welded to the battery can and the positive terminal was welded to the battery lid. The electrolyte contains 1 mol LiPF ₆ Was dissolved in 1 liter of a mixed solution of ethylene carbonate and diethyl carbonate and poured into a battery can, and the battery lid was caulked to produce an 800 mAh capacity cylindrical battery. The battery was repeatedly charged at 800 mA at an ambient temperature of 4.2V and a constant current / constant voltage for 7 hours at 800 mA and then discharged at 800 mA to 2.8V.
[0048]
FIG. 1 shows the cycle life and discharge capacity with respect to the Li / Mn ratio of the positive electrode active material. Other conditions were set within the optimum range specified by the present invention. The Li / Mn ratio showed good characteristics in both cycle life and discharge capacity in a range larger than 0.55 and smaller than 0.8.
[0049]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0050]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0051]
Example 2
A battery was produced in the same manner as in Example 1. The positive electrode active material powder was measured by X-ray diffraction, and the lattice constant of the spinel cubic crystal was determined using the least square method. Other conditions were within the optimum range specified by the present invention. FIG. 2 shows the relationship between the cycle life and the discharge capacity with respect to the lattice constant of the positive electrode active material. From the figure, the cycle constant and the discharge capacity are good in the range where the lattice constant is larger than 8.031 and smaller than 8.230.
[0052]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0053]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0054]
[Example 3]
A battery was produced in the same manner as in Example 1. The half width of the (400) peak was determined by X-ray diffraction using a CuKα ray source as the positive electrode active material powder, with slit widths of DS = SS = 0.5 and RS = 0.15. Other conditions were within the optimum range specified by the present invention. FIG. 3 shows the relationship between the half width of the (400) peak of the positive electrode active material and the cycle life. From the figure, the cycle life was good in the range where the half width of the (400) peak was smaller than 0.2 (deg.).
[0055]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0056]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0057]
[Example 4]
A battery was produced in the same manner as in Example 1. Other conditions were within the optimum range specified by the present invention. The rapid discharge efficiency was the ratio of the discharge capacity to the charge capacity when discharged at 1600 mA to 2.8 V after charging at a constant current and constant voltage of 4.2 V for 7 hours at 800 mA at an ambient temperature of 20 ° C.
[0058]
FIG. 4 shows the relationship between the cycle life and the rapid discharge efficiency with respect to the specific surface area of the secondary particles of the positive electrode active material. From the figure, the specific surface area is 0.1m. ² Larger than 1.5g / 1.5m ² The cycle life and rapid discharge efficiency were good in a range smaller than / g.
[0059]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0060]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0061]
[Example 5]
A battery was produced in the same manner as in Examples 1 and 4. Other conditions were within the optimum range specified by the present invention.
[0062]
FIG. 5 shows the relationship between the cycle life and the rapid discharge efficiency with respect to the average primary particle diameter of the positive electrode active material. As shown in the figure, the average primary particle size was in a range larger than 1 μm and smaller than 20 μm, and the cycle life and rapid discharge efficiency were good.
[0063]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0064]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0065]
[Example 6]
A battery was produced in the same manner as in Example 1. Other conditions were within the optimum range specified by the present invention. Regarding the negative electrode discharge capacity, the capacity of the negative electrode single electrode was evaluated using Li metal as a counter electrode.
[0066]
FIG. 6 shows the relationship between the cycle life and the negative electrode discharge capacity with respect to the negative electrode density. From the figure, the negative electrode density is 0.95 g / cm. ^Three Larger than 1.5 g / cm ^Three In a smaller range, the cycle life and the negative electrode discharge capacity showed good characteristics.
[0067]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0068]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0069]
[Example 7]
The method for synthesizing the positive electrode material of the present invention will be described. Electrolytic manganese dioxide and lithium carbonate were blended as raw materials so that the Li / Mn ratio was 0.62. This was calcined at 615 ° C. for 15 hours, mixed again, and calcined at 825 ° C. for 30 hours. Here, the pre-baking step is an important step for improving the uniformity and crystallinity of the material and obtaining a good cycle life. The cooling rate was 1 ° C./min and cooling to room temperature.
[0070]
When the powder X-ray diffraction of the positive electrode material thus obtained was measured using a Cukα ray source, it was confirmed that the positive electrode material had a spinel crystal structure with no different phases. At this time, the lattice constant was 8.211 Å, and the half width of the (400) peak was 0.09 degrees. Furthermore, the average primary particle size is 3.1 μm, and the specific surface area of the secondary particles is 0.32 m. ² / G.
[0071]
Moreover, amorphous carbon is used for the negative electrode, and the density is 1.05 g / cm. ^Three It was. A battery was produced in the same manner as in Example 1, and the cycle characteristics when the ambient temperature was 60 ° C. were evaluated. FIG. 7 shows the relationship between the number of cycles and the discharge capacity.
[0072]
In this example battery A, a cycle life of 1000 cycles or more was obtained. Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0073]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0074]
[Comparative Example 1]
Electrolytic manganese dioxide and lithium carbonate were blended as raw materials so that the Li / Mn ratio was 0.62, and calcination was performed at 750 ° C. for 5 hours. Moreover, it cooled to room temperature by making the cooling rate into 5 degree-C / min. The active material obtained at this time had a lattice constant of 8.22 mm, which was found to be within the range of the lattice constant of the present invention. However, the half width of the (400) peak is 0.4 degrees, the average primary particle size is 0.6 μm, and the specific surface area of the secondary particles is 2.2 m. ² / G, deviating from the range specified by the present invention.
[0075]
The negative electrode density is 1.05 g / cm within the specific range of the present invention. ^Three As in Example 1, a battery was produced and the cycle characteristics were evaluated at an ambient temperature of 60 ° C. From FIG. 7, it was found that the battery B of this comparative example can only obtain a cycle life of about 100 cycles.
[0076]
Further, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 150 to 1300 W / kg, and the output density is 400 to 2800 W / kg. The range was inferior in input characteristics and output characteristics.
[0077]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of -10 ° C to 50 ° C, the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 90 to 780 W / kg. The output density is in the range of 240 to 1680 W / kg, and it was found that both the input characteristics and the output characteristics are inferior.
[0078]
[Comparative Example 2]
Electrolytic manganese dioxide and lithium carbonate were blended as raw materials so that the Li / Mn ratio was 0.65. This was calcined at 635 ° C. for 15 hours, mixed again, and calcined at 855 ° C. for 30 hours. The cooling rate is 1 ° C./min. At this time, the lattice constant of the active material is 8.190Å, the half width of the (400) peak is 0.08 degrees, the average primary particle size is 15 μm, and the specific surface area of the secondary particles is 0.12 m. ² / G, it was found that the positive electrode active material of the present invention was obtained.
[0079]
On the other hand, the density of the negative electrode is 0.92 g / cm. ^Three And lower than the scope of the present invention. A battery was produced in the same manner as in Example 1, and the cycle characteristics when the ambient temperature was 60 ° C. were evaluated. From FIG. 7, the battery C of this comparative example can obtain only a cycle life of about 50 cycles.
[0080]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 150 to 1300 W / kg, and the output density is 400 to 2800 W / kg. The range is inferior in input characteristics and output characteristics.
[0081]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of -10 ° C to 50 ° C, the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 90 to 780 W / kg. Yes, the output density is in the range of 240-1680 W / kg, and the input characteristics and output characteristics are inferior.
[0082]
[Comparative Example 3]
Electrolytic manganese dioxide and lithium carbonate were mixed as raw materials so that the Li / Mn ratio was 0.51, and calcination was performed at 900 ° C. for 5 hours. The cooling rate is 1 ° C./min. The lattice constant at this time was 8.237 mm, which was outside the range of the present invention, but the half width of the (400) peak was 0.08 degrees, the average primary particle size was 10 μm, and the specific surface area of the secondary particles was 0.15 m. ² / G and within the scope of the present invention.
[0083]
The negative electrode density is 1.05 g / cm. ^Three It was. A battery was produced in the same manner as in Example 1, and the cycle characteristics when the ambient temperature was 60 ° C. were evaluated. The comparative battery D of FIG. 7 has only a cycle life of about 150 cycles.
[0084]
Further, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 150 to 1300 W / kg, and the output density is 400 to 2800 W / kg. The range is inferior in input characteristics and output characteristics.
[0085]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of -10 ° C to 50 ° C, the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 90 to 780 W / kg. Yes, the output density is in the range of 240-1680 W / kg, and the input characteristics and output characteristics are inferior.
[0086]
[Comparative Example 4]
Electrolytic manganese dioxide and lithium carbonate were blended as raw materials so that the Li / Mn ratio was 0.62, and calcination was performed at 850 ° C. for 5 hours. The cooling rate is 1 ° C./min. At this time, the lattice constant was 8.22 、, and the half width of the (400) peak was 0.1 degree. Further, the average primary particle size is 2 μm and is within the scope of the present invention. However, the specific surface area of the secondary particles is 1.8m. ² Large as / g.
[0087]
Negative electrode density is 1.05 g / cm ^Three It is. A battery was produced in the same manner as in Example 1, and the cycle characteristics when the ambient temperature was 60 ° C. were evaluated. From FIG. 7, it was found that this comparative example battery E can obtain only a cycle life of about 500 cycles.
[0088]
Further, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 150 to 1300 W / kg, and the output density is 400 to 2800 W / kg. The range is inferior in input characteristics and output characteristics.
[0089]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of -10 ° C to 50 ° C, the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 90 to 780 W / kg. Yes, the output density is in the range of 240-1680 W / kg, and the input characteristics and output characteristics are inferior.
[0090]
[Example 8]
The lithium secondary battery using the composite oxide of the present invention for the positive electrode has the characteristics that the charge / discharge efficiency is almost 100% and the reversibility of insertion / release of Li is good in addition to the above-mentioned effects.
[0091]
FIG. 8 is a partial cross-sectional schematic diagram of the lithium secondary battery of the present invention. A negative electrode 2 and a positive electrode 3 were laminated via a microporous polypropylene separator 1, wound in a spiral shape, and inserted into a battery can 4 made of SUS.
[0092]
The negative electrode 2 is connected to the battery can 4 via the negative electrode lead wire 2a. The positive electrode 3 is connected to a metal member lid 4 via a positive electrode lead wire 3a. Between the lid 4 and the battery can 4, the inside of the battery can 4 is hermetically sealed via an insulating portion 5. An electrolyte solution was injected into the battery can 4. A positive terminal 6 is provided on the protrusion of the lid 4, and a negative terminal 7 is provided on the bottom of the battery can 4 on the opposite side of the protrusion.
[0093]
As shown in the schematic explanatory diagram of FIG. 9, the negative electrode 2 is provided with a carbon layer 2 </ b> C on a current collector 2 </ b> B. The positive electrode 3 is provided with a composite oxide layer 3C containing Li and Mn of the present invention on a current collector 3B. When a current is passed between both electrodes, Li ions can move from the composite oxide layer 3C to the carbon layer 2C without any obstacles.
[0094]
The reason for this will be described with reference to the schematic perspective view of FIG. 10 showing the crystal structure of the composite oxide layer. The composite oxide layer 3C is composed of a plurality of regular crystal lattices 3D. When Li ions are released from the crystal lattice 3D, since there are few obstacles such as defects 3F and transitions 3G as shown in FIGS. 12 and 13, they diffuse into the carbon layer 2C more quickly than the prior art described later.
[0095]
On the other hand, in the conventional crystal lattice 3D of FIG. 11, when Li ions are released, it is disturbed by the deformed portion 3E lacking the regularity of the crystal and cannot move to the carbon layer 2C, and the discharge efficiency is lowered. The same applies to the case where Li ions are inserted from the carbon layer 2C into the composite oxide layer 3C.
[0096]
Thus, the lithium secondary battery using the composite oxide layer 3C containing Li and Mn of the present invention has good reversibility of Li insertion / release, and can maintain almost 100% in charge / discharge efficiency.
[0097]
[Example 9]
A battery was produced in the same manner as in Example 1. Other conditions were within the optimum range specified by the present invention. Regarding the negative electrode discharge capacity, the capacity of the negative electrode single electrode was evaluated using Li metal as a counter electrode. FIG. 14 shows the relationship between the cycle life and the negative electrode discharge capacity with respect to the negative electrode true density of the negative electrode carbon. From the figure, the negative electrode true density is 1.2 g / cm. ^Three Larger than 1.8g / cm ^Three In a smaller range, the cycle life and the negative electrode discharge capacity showed good characteristics.
[0098]
Furthermore, in the unit cell, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, the input density is in the range of 300 to 1800 W / kg, and the output density is 500 to 3500 W / kg. Was in range.
[0099]
In the case of an assembled battery in which 96 batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 200 to 1300 W / kg. Yes, the power density was in the range of 360-2520 W / kg.
[0100]
[Example 10]
A battery was produced in the same manner as in Example 1. Other conditions were within the optimum range specified by the present invention. The relationship between the negative electrode carbon crystal thickness Lc, the input density, and the output density was evaluated. When the crystal thickness Lc of the negative electrode carbon is in the range of 5 to 150 mm, the input density and the output density show good characteristics. In the unit cell, the temperature is in the range of -10 ° C to 50 ° C, and the discharge depth is in the range of 30 to 80%. The input density was in the range of 1000-1800 W / kg, and the output density was in the range of 2500-3500 W / kg.
[0101]
In the case of an assembled battery in which 96 of these batteries are connected in series, the temperature is in the range of −10 ° C. to 50 ° C., the depth of discharge is in the range of 30 to 80%, and the input density is in the range of 800 to 1300 W / kg. The power density was in the range of 2000-2520 W / kg.
[0102]
【The invention's effect】
According to the present invention, a long-life lithium secondary battery could be obtained by using the long-life material of the present invention at a high temperature of 50 ° C. In addition, the lithium secondary battery using the composite oxide containing Li and Mn according to the present invention can supply power promptly in response to load fluctuations.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a cycle life and a discharge capacity with respect to a Li / Mn ratio of a lithium secondary battery of the present invention.
FIG. 2 is a graph showing the relationship between the cycle life and the discharge capacity with respect to the lattice constant of the positive electrode active material of the lithium secondary battery of the present invention.
FIG. 3 is a graph showing the relationship between the half-value width of a (400) peak and the cycle life of the positive electrode active material of the lithium secondary battery of the present invention.
FIG. 4 is a graph showing the relationship between the cycle life and the rapid discharge efficiency with respect to the specific surface area of the secondary particles of the positive electrode active material of the lithium secondary battery of the present invention.
FIG. 5 is a graph showing the relationship between the cycle life and the rapid discharge efficiency with respect to the average primary particle diameter of the positive electrode active material of the lithium secondary battery of the present invention.
FIG. 6 is a graph showing the relationship between the cycle life and the negative electrode discharge capacity with respect to the negative electrode density of the lithium secondary battery of the present invention.
FIG. 7 is a graph showing the relationship between the number of cycles and discharge capacity of a lithium secondary battery.
FIG. 8 is a partial cross-sectional view of the lithium secondary battery of the present invention.
FIG. 9 is a schematic explanatory view illustrating the relationship between the positive electrode and the negative electrode used.
FIG. 10 is a schematic perspective view showing a crystal structure of a used composite oxide layer.
FIG. 11 is a schematic perspective view showing a crystal structure of a conventional complex oxide layer.
FIG. 12 is a schematic perspective view showing a crystal structure of a composite oxide layer.
FIG. 13 is a schematic perspective view showing a crystal structure of a complex oxide layer.
14 is a graph showing the relationship between the cycle life and the negative electrode discharge capacity with respect to the negative electrode true density of the negative electrode carbon of the lithium secondary battery of the present invention. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Separator, 2 ... Load, 3 ... Positive electrode, 3C ... Composite oxide layer, 4 ... Battery can, 5 ... Insulating part, 6 ... Positive electrode terminal, 7 ... Negative electrode terminal.

Claims (1)

In a lithium secondary battery having a negative electrode, a non-aqueous electrolyte, and a positive electrode, the negative electrode active material contains amorphous carbon, and the negative electrode density is greater than 0.95 g / cm ^{3 and} less than 1.5 g / cm ³ ,
The active material of the positive electrode has a half width of the 2θ angle of the (400) peak of the X-ray diffraction pattern smaller than 0.2 °,
A composite oxide containing Li and Mn having a spinel crystal structure, wherein the Li / Mn atomic ratio of the composite oxide is larger than 0.55 and smaller than 0.8;
The lattice constant in the spinel crystal structure is greater than 8.031 and less than 8.230
The specific surface area of secondary particles of the composite oxide is smaller than the larger 1.5 m ² / g than 0.1 m ² / g,
The lithium secondary battery, wherein an average particle size of primary particles of the composite oxide is larger than 1 μm and smaller than 20 μm.

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