JP4626105B2 - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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JP4626105B2
JP4626105B2 JP2001234822A JP2001234822A JP4626105B2 JP 4626105 B2 JP4626105 B2 JP 4626105B2 JP 2001234822 A JP2001234822 A JP 2001234822A JP 2001234822 A JP2001234822 A JP 2001234822A JP 4626105 B2 JP4626105 B2 JP 4626105B2
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active
layer
positive electrode
porosity
particle size
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JP2002151055A (en
Inventor
雄児 丹上
英明 堀江
康彦 大澤
止 小川
幹夫 川合
達弘 福沢
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日産自動車株式会社
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Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery with improved power density.
[0002]
[Prior art]
Research has been conducted on various rechargeable batteries that can be used continuously for a long time as a power source for various electronic devices and electric devices. Above all, compared to secondary batteries that are applied as consumer products such as nickel-cadmium storage batteries and nickel-hydrogen storage batteries, lithium ion secondary batteries have characteristics such as high energy density and high output density. Has been actively researched and developed, and has been put into practical use as a power source for portable electronic devices such as mobile phones, camcorders, and notebook computers.
[0003]
In addition, interest in electric vehicles and hybrid vehicles is increasing as an adaptation to the problems of global environmental pollution and global warming, and lithium ion secondary batteries are expected to be applied as power sources for these vehicles. When applied to automobiles, etc., lithium ion secondary batteries have the advantage that they are easy to control and have excellent stability when multiple batteries are connected in series to form a battery pack in order to obtain high output density. Have.
[0004]
Important characteristics of the lithium ion secondary battery include energy density, output density, cycle characteristics, and the like. Japanese Patent Application Laid-Open Nos. 11-31498, 11-297354, and 11-329409 disclose lithium ions. Techniques for improving these characteristics of secondary batteries are disclosed.
[0005]
[Problems to be solved by the invention]
Japanese Patent Application Laid-Open No. 11-31498 discloses a technique for improving capacity and cycle characteristics by adjusting the specific surface area and porosity of an active material of an electrode. However, only the relationship between the specific surface area and the porosity of the active material of the electrode has been discussed, and the interaction between the active material particle size, the electrode thickness, and the porosity has not been sufficiently considered. For this reason, a sufficient output density cannot be obtained depending on the conditions of the electrode thickness and the particle diameter, and there is a limit to improving the performance of the secondary battery by adjusting only the specific surface area and porosity of the active material of the electrode.
[0006]
Japanese Patent Application Laid-Open No. 11-297354 discloses a technique for defining the electrolyte concentration, but does not describe the correlation between the active material particle size or electrode thickness and the electrolyte concentration. For this reason, depending on the conditions of the active material particle size and electrode thickness, even if the electrolyte concentration is increased, the lithium ion conductivity of the electrolytic solution is lowered, so that the output density cannot be effectively improved.
[0007]
Japanese Patent Application Laid-Open No. 11-329409 discloses a technique for improving the output density of a lithium ion secondary battery by defining the coating thickness of the active material of the electrode and the particle size of the active material. However, there is a problem that the energy density is lowered because the configuration emphasizes high output density.
[0008]
The present invention has been completed by taking into consideration various problems of the prior art and intensively studying, and an object of the present invention is to provide a lithium ion secondary battery with improved output density.
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention provides: A positive electrode capable of occluding and releasing lithium ions; a negative electrode capable of occluding and releasing lithium ions; and a lithium ion conductive non-aqueous electrolyte, wherein the active material has a particle size of 5 μm or less, A lithium ion secondary battery having a thickness of 20 to 80 μm and an electrolyte concentration of the non-aqueous electrolyte of 1.5 to 2.5 mol / l .
[0021]
【The invention's effect】
According to the present invention configured as described above, The output density can be improved by defining the particle size of the active material and the thickness of the active material layer within a predetermined range and the electrolyte concentration of the non-aqueous electrolyte within a predetermined range. .
[0029]
DETAILED DESCRIPTION OF THE INVENTION
First, the general form of the lithium ion secondary battery of this invention is demonstrated.
[0030]
A lithium ion secondary battery is a chargeable / dischargeable battery including a positive electrode and a negative electrode made of a material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte having lithium ion conductivity. The positive electrode and the negative electrode are in direct contact with each other. Then, it is separated with a separator so as not to short-circuit. The positive electrode and the negative electrode are usually produced by coating and forming a positive electrode active material and a negative electrode active material on both sides of the positive electrode current collector and the negative electrode current collector, and laminated in layers of positive electrode-separator-negative electrode-separator in this order. A structure or an electrode element structure such as a so-called jelly roll type in which sheets stacked in this order are wound in a spiral shape can be employed.
[0031]
As the positive electrode active material, various known positive electrode active materials such as lithium metal oxides, composite oxides in which a part of the lithium metal oxide is substituted with other elements, and manganese oxides can be appropriately used. Specifically, as the lithium metal oxide, LiCoO 2 , LiNiO 2 LiMnO 2 , LiMn 2 O Four , Li X FeO Y , Li X V Y O Z As the composite oxide in which a part of the lithium metal oxide is substituted with another element, Li X Co Y M Z O 2 (M is Mn, Ni, V, etc.) or Li X Mn Y M Z O 2 (M is Li, Ni, Cr, Fe, Co, etc.) and the like, and the manganese oxide is λ-MnO. 2 , MnO 2 And V 2 O Five Composite, ternary composite oxide MnO 2 XV 2 O Five (0 <x ≦ 0.3).
[0032]
As the negative electrode active material, carbon materials such as hard carbon, soft carbon, graphite and activated carbon, SnB X P Y O Z , Nb 2 O Five , LiTi X O Y LiFe X N Y , LiMn X N Y These metal oxides can be used alone or in combination. Here, hard carbon refers to a carbon material that does not graphitize even when heat-treated at 3000 ° C., and soft carbon refers to a carbon material that graphitizes when heat-treated at 2800 to 3000 ° C. For the production of hard carbon, various known techniques such as a method using a furan resin, an organic material oxygen-crosslinked to a petroleum pitch having an H / C atomic ratio of 0.6 to 0.8, etc. as a starting material are used. Various known techniques such as a method using coal, polymer compounds (polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, etc.), pitch and the like as starting materials can be used for the production of soft carbon.
[0033]
Various known techniques can also be used when the positive electrode active material and the negative electrode active material are formed on the positive electrode current collector and the negative electrode current collector to produce the positive electrode and the negative electrode. For example, when manufacturing a positive electrode, a method of mixing a positive electrode active material with a binder in a solvent to form a paste, coating the paste on a positive electrode current collector, and drying can be used. Similarly, the negative electrode can be formed by mixing a negative electrode active material with a binder in a solvent to form a paste, coating the paste on the negative electrode current collector, and drying. Usually, both sides of the current collector are coated. Applied. A conductive agent such as carbon black, graphite or acetylene black may be added to the paste. The mixing ratio of the active material and the binder is preferably determined appropriately according to the shape of the electrode, and various known methods can be used for coating.
[0034]
As the current collector, various known materials used in lithium ion secondary batteries can be used. Specifically, an aluminum foil or the like is used as a positive electrode current collector, and a copper foil or the like is used as a negative electrode current collector. Is mentioned.
[0035]
Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene, and examples of the solvent include various polar solvents that dissolve the binder. Specific examples include dimethylformamide, dimethylacetamide, methylformamide, N-methylpyrrolidone (NMP) and the like. In addition, when polyvinylidene fluoride is used as a binder, it is preferable to use N-methylpyrrolidone.
[0036]
As the non-aqueous electrolyte, various solutions having lithium ion conductivity are preferable, and cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) may be used alone or in appropriate combination. it can. Further, in order to obtain an electrolytic solution having high electrical conductivity and appropriate viscosity, dimethyl carbonate (DMC), diethyl carbonate (DEC), γ-butyl lactone, γ-valerolactone, ethyl acetate, methyl propionate, etc. May be used in combination.
[0037]
As the electrolyte in the non-aqueous electrolyte, LiPF 6 , LiBF Four LiClO Four , LiAsF 6 , LiCF Three SO Three Etc.
[0038]
As the separator, a microporous film of polyolefin resin such as polyethylene or polypropylene can be used.
[0039]
When the secondary battery according to the present invention is manufactured, the above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator can be appropriately combined. Also, various known materials and shapes can be applied to the battery can and the battery shape.
[0040]
Hereinafter, the invention according to the present application will be described in detail.
[0041]
A first invention of the present application is a lithium ion secondary battery including a positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte. The particle size of the substance is 5 μm or less, more preferably 1 μm or less, and the thickness of the active material layer is 20 to 80 μm, more preferably 20 to 30 μm. In the present invention, the active material layer refers to a layer containing an active material formed on a current collector. For example, the active material layer is prepared by mixing various compositions such as an active material and a binder in a solvent as described above. This is a layer formed by coating the collected paste on the surface of the current collector and drying it. When active material layers are formed on both sides of the current collector in accordance with the usual method, It is preferred to apply the provisions of the invention. Moreover, in this invention, a particle size refers to an average particle diameter.
[0042]
When the particle size of the active material is large, the lithium ion diffusion in the active material particles becomes the rate-determining step rather than the transport of lithium ions in the electrolyte solution in the film thickness direction during large current discharge, and the output density decreases. Cause. Therefore, the particle size of the active material is preferably 5 μm or less. The lower limit value of the particle size of the active material is not particularly specified, but in practice it is suitably 0.1 μm or more. Also, if the film thickness is smaller than 20 μm, the output density is undesirably reduced due to the insufficient amount of active material, and if the film thickness exceeds 80 μm, the internal resistance increases and the output density decreases, which is not preferable.
[0043]
Under the above-mentioned conditions where the active material particle size is small such that the particle size of the active material is 5 μm or less, the transport of lithium ions in the electrolyte solution in the direction of the film thickness is considered to be the rate-limiting step during large current discharge. It is done. Therefore, when the porosity is increased, the amount of the electrolytic solution in the electrode increases, the transport capacity of lithium ions in the electrolytic solution in the electrode in the film thickness direction increases, and the output density can be further improved. However, if the porosity is less than 50%, the amount of the electrolyte corresponding to the amount of the active material cannot be secured, so that the resistance increases and the output density decreases. Therefore, the porosity is preferably 50% or more. In addition, when the porosity exceeds 60%, the output density gradually decreases due to a shortage of the amount of active material, that is, a reduction in the electrode surface area. Therefore, the porosity is more preferably 50 to 60%.
[0044]
Conversely, under conditions where the active material particle size is larger than 5 μm, the diffusion of lithium ions in the active material particles is at the rate-determining stage, so even if the porosity is increased, that is, the amount of electrolyte in the electrode is increased. The output density cannot be improved, and the amount of active material decreases, so the output density decreases.
[0045]
In order to improve the output density by defining the porosity as described above, the thickness of the active material layer is preferably 20 μm or more. This is because when the film thickness is thin, the influence of lithium ion transport in the electrolyte in the electrode in the film thickness direction is small, and the influence of the porosity is small.
[0046]
The active material layer may have a structure in which two active material layers having different porosity are stacked. By using a two-layer structure with different porosity, the output density can be improved without sacrificing the energy density. Specifically, it is preferable to increase the porosity of the active material layer on the separator side and decrease the porosity of the active material layer on the current collector side. By increasing the porosity of the active material layer in the vicinity of the separator, the amount of the electrolyte solution in the vicinity of the separator can be increased, and the lithium ion transport capability can be increased. Further, by reducing the porosity in the vicinity of the current collector, the utilization factor of the active material in the vicinity of the current collector can be improved. Considering such characteristics, the power density can be effectively improved by balancing the diffusion in the active material and the transport in the electrolytic solution. Further, since the energy density is affected by the average porosity and the amount of the active material of the active material layer, the output density can be improved without sacrificing the energy density by appropriately adjusting the energy density. For example, an electrode having a one-layer structure (50% porosity, 60 μm thickness) and a two-layer electrode (40% porosity on the collector side, 30 μm thickness; 60% porosity on the separator side, 30 μm thickness) Are equal in energy density. This is because the average porosity and the amount of active material of these two electrodes are equal.
[0047]
In addition, the thickness of the two active material layers having different porosity is preferably 20 to 30 μm, more preferably 20 to 25 μm, and the thickness of the two active material layers may be different. This is because if the thickness of the active material layer is greater than 30 μm, the energy density tends to decrease, and if it is 30 μm or less, the utilization factor of the active material layer on the current collector side is improved. The porosity of the active material layer on the current collector side is preferably 30% or more and less than 50%, and more preferably 40% or more and less than 50%. The porosity of the active material layer on the separator side is preferably 50 to 60%, more preferably 50 to 55%. By adjusting the porosity in this range, a greater effect can be obtained.
[0048]
A second invention of the present application is a lithium ion secondary battery comprising two active material layers having different active material particle sizes. With such a configuration, the output density can be improved.
[0049]
During large current discharge, the transport of lithium ions in the electrolyte in the electrode in the film thickness direction becomes a rate-determining step, and the electrode active material in the vicinity of the current collector cannot be used effectively, causing the output density to decrease. In order to solve this problem, it is preferable to increase the particle size of the active material in the vicinity of the electrode separator. Thereby, the electrode surface area near the separator is reduced, the utilization factor of the active material near the separator is lowered, and lithium ions can be easily transported to the vicinity of the current collector. For this reason, the utilization factor of the electrode active material in the vicinity of the current collector is improved, and as a total, the utilization factor of the electrode active material is improved, that is, the output density is improved. Further, the output density can be improved without sacrificing the energy density by appropriately adjusting the amounts of active materials in the single-layer battery and the two-layer battery as a whole.
[0050]
The effect of taking the two-layer structure is manifested by increasing the particle size of the active material in the vicinity of the electrode separator and reducing the utilization of the active material in the vicinity of the separator. Therefore, if the thickness of the active material layer on the separator side is thicker than necessary, the utilization factor of the active material in the vicinity of the separator is improved, and the effect of the present invention is reduced. Further, if the thickness of the active material layer on the current collector side is too thick, the output density is lowered, which is not preferable. For this reason, the thickness of each active material layer is preferably 30 μm or less, and more preferably 25 μm or less. The lower limit value of the thickness of the active material layer is preferably 20 μm in order to prevent a decrease in energy density. This is because when the thickness of the active material layer is less than 20 μm, the weight ratio of the current collector and the like in the battery increases.
[0051]
Further, in the two active material layers having different active material particle sizes, the active material particle size of the active material layer on the current collector side is 5 μm or more, or the active material particle size of the active material layer on the separator side is less than 5 μm. This is not preferable because the effect of improving the output density of the present invention is reduced. The lower limit value of the active material particle size on the current collector side is not particularly limited, but in practice it is suitably 0.1 μm or more. In addition, the upper limit of the active material particle size of the active material layer on the separator side is preferably selected as appropriate so long as the active material particle size is not larger than the thickness of the active material layer. From the above viewpoint, the active material particle size of the active material layer on the current collector side is preferably 0.1 μm or more and less than 5 μm, and more preferably 1 μm or more and less than 5 μm. The active material particle size of the active material layer on the separator side is preferably 5 to 20 μm, and more preferably 5 to 10 μm.
[0052]
The particle size of the active material can be adjusted by the particle size of the starting material or classification, and the porosity is applied when a paste containing the active material and a conductive agent is applied to the current collector, dried, and then pressed. It can be adjusted by changing the pressure.
[0053]
In the above description, a two-layer structure has been described as an example, but the present invention can be achieved by adjusting the porosity of the active material layer, the particle size of the active material, and the thickness of the active material layer even in a multilayer structure of three or more layers. It is possible to obtain the effect.
[0054]
In the multilayer structure, first, the first layer can be coated and formed on the current collector, and then the second layer can be coated and formed up to n layers in sequence, and particles having different sizes can be formed. It is also possible to make a multilayer structure by utilizing the difference in sedimentation speed.
[0055]
In the first and second inventions of the present invention, the positive electrode active material is preferably lithium manganese oxide from the viewpoint of obtaining a high power density. Manganese is much cheaper than cobalt and nickel, and is also abundant in terms of resources, so it is preferable from the viewpoint of manufacturing cost. Specific examples of lithium manganese oxide include LiMnO. 2 , LiMn 2 O Four Is mentioned.
[0056]
In the lithium ion secondary battery of the present invention, in order to further improve the output density, in the first and second inventions, the electrolyte concentration of the non-aqueous electrolyte is 1.0 to 3.0 mol / It is preferable that it is 1, and it is more preferable that it is 1.5-2.5 mol / l. By using an electrolyte concentration in such a range, it is possible to balance the diffusion in the active material and the transport in the electrolytic solution, and a suitable output density can be obtained.
[0057]
Under conditions where the particle size of the active material is small or the porosity is large, the transport of lithium ions in the electrolyte solution in the film thickness direction becomes the rate-limiting step during large current discharge. Therefore, when the electrolyte concentration is increased, concentration polarization is suppressed, the transport capacity of lithium ions in the electrolyte solution in the electrode in the film thickness direction is increased, and the output density is improved. If the electrolyte concentration exceeds 3.0 mol / l, the influence of the lithium ion conductivity of the electrolytic solution will appear and the output density will decrease, which is not preferred. If the electrolyte concentration is less than 1.0 mol / l, the internal resistance of the battery will increase. Therefore, it is not preferable. Moreover, the voltage at the time of discharge can be made high and stable by adjusting electrolyte concentration in the range of 1.5-2.5 mol / l.
[0058]
The relationship between the particle size of the active material and the electrolyte concentration can also affect the power density. That is, under the condition that the particle size of the active material is larger than 5 μm, the diffusion of lithium ions in the active material particles becomes the rate-determining step during the large current discharge, rather than the transport of lithium ions in the electrolyte solution in the film thickness direction. . For this reason, there is little influence of electrolyte concentration, and even if it raises the density | concentration of electrolyte, output density does not improve so much. Therefore, when the active material layer has a multilayer structure of two or more layers, it is preferable that the active material particle size of the active material layer on the current collector side be less than 5 μm.
[0059]
The electrolyte is LiPF from the viewpoint of improving the power density by using a compound having high electrical conductivity. 6 Or LiBF Four It is preferable that
[0060]
In the present invention, the particle size of the active material can be measured by a method for measuring various particle size distributions such as a screening test and a sedimentation method, the porosity can be measured by the specific gravity of the constituent material, and the active material layer thickness can be measured by a micrometer. .
[0061]
【Example】
1. Investigation of the effect of active material particle size, active material layer thickness, and porosity on power density
< reference Example 1>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. The specific surface area of this active material is about 3m 2 / G. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A plurality of positive electrodes having a thickness of 60 μm and different active material layer porosity were manufactured. The porosity was adjusted by the amount of solvent, drying conditions, and electrode pressing. Metal lithium is used for the negative electrode active material, and 1M LiPF is used for the electrolyte. 6 A plurality of lithium ion secondary batteries having different porosity of the active material layer of the positive electrode were manufactured using a mixture of PC and DMC (1: 1 volume ratio) in which s.
[0062]
<Comparative Example 1>
Except that the average particle size is 30 μm reference A plurality of lithium ion secondary batteries having different porosity were produced in the same manner as in Example 1.
[0063]
<Comparative Example 2>
Except for the active material layer thickness being 10 μm reference A plurality of lithium ion secondary batteries having different porosity were produced in the same manner as in Example 1.
[0064]
Figure 1 reference The relationship between the porosity of Example 1, Comparative Example 1 and Comparative Example 2 and the output density (relative value when the output density with a porosity of 40% is 1) is shown. reference The power density of the battery of Example 1 was maximized at a porosity of 50 to 60%, whereas the power density of the batteries of Comparative Examples 1 and 2 decreased as the porosity increased.
[0065]
2. Investigation of the effect of making the active material layer into a two-layer structure with different porosity
< reference Example 2>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. The specific surface area of this active material is about 3m 2 / G. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a porosity of 40% and an active material layer thickness of 30 μm was produced. The same positive electrode active material composition was applied to this positive electrode, and an active material layer having an active material layer porosity of 60% and an active material layer thickness of 30 μm was laminated. The porosity was adjusted by the amount of solvent, drying conditions and electrode pressing. In this way, a positive electrode having an active material layer thickness of 60 μm was manufactured, metallic lithium was used as the negative electrode active material, and 1M LiPF was used as the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0066]
< reference Example 3>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. The specific surface area of this active material is about 3m 2 / G. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a porosity of 50% and an active material layer thickness of 60 μm was produced. The porosity was adjusted by the amount of solvent, drying conditions, and electrode pressing. Metal lithium is used for the negative electrode active material, and 1M LiPF is used for the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0067]
< reference Example 4>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. The specific surface area of this active material is about 3m 2 / G. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a porosity of 40% and an active material layer thickness of 20 μm was produced. The same positive electrode active material composition was applied to this positive electrode, and an active material layer having an active material layer porosity of 60% and an active material layer thickness of 40 μm was laminated. The porosity was adjusted by the amount of solvent, drying conditions and electrode pressing. In this way, a positive electrode having an active material layer thickness of 60 μm was manufactured, metallic lithium was used as the negative electrode active material, and 1M LiPF was used as the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0068]
Figure 2 reference Output density of the batteries of Examples 2-4 ( reference (The relative value when the output density of Example 3 is 1). The power density was improved by making the active material layer into a two-layer structure. Moreover, when it was set as 2 layer structure, when the thickness of each active material layer was 30 micrometers or less, the output density could be improved more effectively.
[0069]
In addition, in FIG. reference The energy density of the batteries of Examples 2-4 ( reference The relative value when the energy density of Example 3 is 1 is shown. reference Example 2 and reference The energy density of Example 3 was equal. this is, reference Example 2 and reference This is because the average porosity of Example 3 is equal and the amount of positive electrode active material is equal. reference In Example 4, the active material layer has a single-layer structure. reference Compared with Example 3, the output density was improved, but the energy density was inferior.
[0070]
3. Investigation of the effect of making the active material layer into a two-layer structure with different active material particle sizes
< reference Example 5>
Two types of lithium manganese oxide (LiMnO) having an average particle diameter of 3 μm and 9 μm as positive electrode active materials 2 ) Was used. 75% by mass of an active material having an average particle diameter of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a layer thickness of 30 μm was produced. Similarly, an active material layer having a thickness of 30 μm was laminated on the positive electrode using an active material having an average particle diameter of 9 μm. In this way, a positive electrode having an active material layer thickness of 60 μm was manufactured, metallic lithium was used as the negative electrode active material, and 1M LiPF was used as the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0071]
< reference Example 6>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 )Using, reference A positive electrode having an active material layer thickness of 60 μm was prepared in the same manner as in Example 5, lithium metal was used as the negative electrode active material, and 1M LiPF was used as the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0072]
In FIG. reference Example 5 and reference Output density of Example 6 ( reference (The relative value when the output density of Example 6 is 1). Two-layer structure with different particle sizes reference Example 5 showed a higher power density. In addition, in FIG. reference Example 5 and reference Example 6 energy density ( reference The relative value when the energy density of Example 6 is set to 1 is shown. reference Example 5 and reference In Example 6, the energy density was equal. this is, reference Example 5 and reference This is because the amount of the positive electrode active material in Example and 6 is equal.
[0073]
4). Investigation of the effect of active material layer thickness in a two-layer structure with different active material particle sizes
<Comparative Example 3>
Two types of lithium manganese oxide (LiMnO) having an average particle diameter of 3 μm and 9 μm as positive electrode active materials 2 ) Was used. 75% by mass of an active material having an average particle diameter of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a layer thickness of 20 μm was produced. Similarly, an active material layer having a thickness of 40 μm was laminated on the positive electrode using an active material having an average particle diameter of 9 μm. In this way, a positive electrode having an active material layer thickness of 60 μm was manufactured, metallic lithium was used as the negative electrode active material, and 1M LiPF was used as the electrolyte. 6 A lithium ion secondary battery was manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which the slag was dissolved.
[0074]
FIG. 6 shows Comparative Example 3 and the above reference The output density of Example 6 (relative value when the output density of Comparative Example 3 is 1) is shown. The output density of Comparative Example 3 is low because the active material particle size of the active material layer on the separator side is large, the utilization factor of the active material near the separator is reduced, and the thickness of the active material layer on the separator side is increased. This is because the utilization factor of the active material in the vicinity of the electric body has also decreased. Further, in FIG. reference The energy density of Example 6 (relative value when the energy density of Comparative Example 3 is 1) is shown. Comparative Example 3 reference In Example 6, the energy density was equal. This is similar to Comparative Example 3 reference This is because the positive electrode active material amount is the same as in Example 6.
[0075]
5. Investigation of the effect of active material particle size and electrolyte concentration on power density
<Example 7>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A positive electrode having a thickness of 60 μm was produced. Lithium metal is used for the negative electrode active material, and LiPF with different concentrations is used for the electrolyte. 6 A plurality of lithium ion secondary batteries were manufactured using a mixture of PC and DMC (volume ratio of 1: 1) in which was dissolved.
[0076]
<Comparative example 4>
Lithium manganese oxide (LiMnO) having an average particle size of 30 μm as a positive electrode active material 2 ) Was used to produce a lithium ion secondary battery in the same manner as in Example 7.
[0077]
FIG. 8 shows the relationship between the electrolyte concentration of Example 7 and Comparative Example 4 and the power density (relative value when the power density is 1 when the electrolyte concentration is 1 mol / l). In Example 7, the output density was maximized when the electrolyte concentration was 2 mol / l. In contrast, in Comparative Example 4, the output density was not improved even when the electrolyte concentration was increased.
[0078]
6). Investigation of the effect of active material layer thickness and electrolyte concentration on power density
<Example 8>
Lithium manganese oxide (LiMnO) having an average particle size of 3 μm as a positive electrode active material 2 ) Was used. 75% by mass of an active material having a particle size of 3 μm, 10% by mass of acetylene black as a conductive agent, and 15% by mass of PVDF as a binder are mixed in NMP and applied onto an aluminum foil (current collector). A plurality of positive electrodes having different thicknesses were produced. Lithium metal is used for the negative electrode active material, and LiBF with a concentration of 2 mol / l is used for the electrolyte. Four A plurality of lithium ion secondary batteries having different thicknesses of the active material layer of the positive electrode were manufactured using a mixture of PC and DMC (1: 1 volume ratio) in which the slag was dissolved.
[0079]
< reference Example 9>
1mol / l LiBF in electrolyte 4 A lithium ion secondary battery was produced in the same manner as in Example 8 except that was used.
[0080]
FIG. 9 shows Example 8 and reference Example 9 active material layer thickness and power density ( reference The relationship with the relative value when the output density is set to 1 when the active material layer thickness of Example 9 is 100 μm is shown. The power density of Example 8 with the preferred electrolyte and electrolyte concentration was about twice as high.
[0081]
Example above 7 and 8 , Reference Examples 1-6 and 9, and The structure of Comparative Examples 1-4 is shown to Tables 1-6.
[0082]
[Table 1]
[0083]
[Table 2]
[0084]
[Table 3]
[0085]
[Table 4]
[0086]
[Table 5]
[0087]
[Table 6]

[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between porosity and power density.
[Figure 2] reference It is a graph which shows the relationship between an example and output density.
[Fig. 3] reference It is a graph which shows the relationship between an example and energy density.
[Fig. 4] reference It is a graph which shows the output density of an example.
[Figure 5] reference It is a graph which shows the energy density of an example.
[Fig. 6] reference It is a graph which shows the output density of an example and a comparative example.
[Fig. 7] reference It is a graph which shows the energy density of an example and a comparative example.
FIG. 8 is a graph showing the relationship between electrolyte concentration and power density.
FIG. 9 is a graph showing the relationship between active material layer thickness and power density.

Claims (3)

  1. A positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte,
    The particle size of the active material is 5 μm or less,
    The thickness of the active material layer is 20 to 80 μm,
    The electrolyte concentration of the non-aqueous electrolyte is 1. A lithium ion secondary battery characterized by being 5 to 2.5 mol / l.
  2. The lithium ion secondary battery according to claim 1, wherein the positive electrode active material is lithium manganese oxide.
  3. 3. The lithium ion secondary battery according to claim 1, wherein the electrolyte is LiPF 6 or LiBF 4 .
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