JP2011048991A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having superior cycle characteristics by which battery life can be extended. <P>SOLUTION: A positive electrode current collector 28, a positive electrode layer 22 which comes into electrical contact with the positive electrode current collector 28 and contains an active material capable of intercalating and releasing lithium, an electrolyte layer 42 containing a nonaqueous electrolytic solution, a negative electrode layer 32 containing the active material capable of intercalating and releasing lithium, and a negative electrode current collector 38 in electrical contact with the negative electrode layer 32 are laminated in this order. The negative electrode layer 32 is movable against the negative electrode current collector concerning the lateral direction H orthogonal against the laminating direction L. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery.

  In lithium ion secondary batteries, lithium ions move from the positive electrode to the negative electrode during charging, and during discharge, the lithium ions move from the negative electrode to the positive electrode, so that the active material expands and contracts, and mechanically acts on the current collector. Stress is added. The mechanical stress may cause deformation or breakage of the current collector, and may reduce battery life due to deterioration of cycle characteristics. Therefore, the current collector is anisotropically absorbed by the expansion and contraction of the active material by providing a large number of holes having a shape having planar anisotropy (see, for example, Patent Document 1).

JP 2005-32524 A

  However, since the expansion and contraction of the active material occurs not only in the longitudinal direction but also in the lateral direction, the absorption effect due to the presence of the hole is not sufficient, for example, the lateral tensile stress exceeding the yield stress of the current collector Is generated, and the current collector is plastically deformed to cause deformation and breakage of the current collector, resulting in a problem of reducing battery life due to deterioration of cycle characteristics.

  The present invention has been made to solve the problems associated with the above-described prior art, and an object thereof is to provide a lithium ion secondary battery that has good cycle characteristics and can extend the battery life.

  To achieve the above object, the present invention includes a positive electrode current collector, a positive electrode layer containing an active material that is in electrical contact with the positive electrode current collector and capable of inserting and removing lithium, and a non-aqueous electrolyte. And a negative electrode layer containing an active material capable of inserting and extracting lithium, and a negative electrode current collector in electrical contact with the negative electrode layer. is there. The positive electrode layer is movable with respect to the positive electrode current collector and / or the negative electrode layer is movable with respect to the negative electrode current collector in a lateral direction perpendicular to the stacking direction. .

  According to the present invention, since at least one of the positive electrode layer and the negative electrode layer is movable in the lateral direction independently of the current collector (contacted but not adhered), the lithium ion When the active material expands and contracts as the electrode moves, and a tensile stress is generated in the lateral direction, the shear force overcomes the friction, so that the electrode layer moves (shifts) in the lateral direction with respect to the current collector. As a result, deformation and breakage of the current collector are suppressed, so that a reduction in battery life due to deterioration of cycle characteristics can be avoided. Therefore, it is possible to provide a lithium ion secondary battery that has good cycle characteristics and can extend the battery life.

It is a perspective view for demonstrating the lithium ion secondary battery which concerns on embodiment of this invention. It is sectional drawing for demonstrating the lithium ion secondary battery which concerns on embodiment of this invention. It is sectional drawing for demonstrating the negative electrode layer shown by FIG. It is sectional drawing for demonstrating the modification 1 which concerns on embodiment of this invention. It is a top view for demonstrating the modification 2 which concerns on embodiment of this invention. It is a top view for demonstrating the modification 3 which concerns on embodiment of this invention. It is sectional drawing for demonstrating the modification 4 which concerns on embodiment of this invention. It is sectional drawing for demonstrating the modification 5 which concerns on embodiment of this invention. It is a top view for demonstrating the modification 6 which concerns on embodiment of this invention. It is a graph for demonstrating the performance evaluation result of the lithium ion secondary battery which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view for explaining a lithium ion secondary battery according to an embodiment of the present invention.

  The lithium ion secondary battery 10 is a laminated nonaqueous electrolyte secondary battery, and includes an outer case 16, a battery main body disposed inside the outer case 16, a positive terminal plate 12, and a negative terminal plate 14.

  The exterior case 16 is used to prevent external impacts and environmental degradation, and is formed by joining a part or all of the outer peripheral portion of the sheet material by thermal fusion. The sheet material is composed of a polymer-metal composite laminate film in which metals (including alloys) such as aluminum, stainless steel, nickel, and copper are covered with an insulator such as a polypropylene film from the viewpoint of weight reduction and thermal conductivity. It is preferable.

  The terminal plates 12 and 14 are made of a highly conductive member, extend from the inside of the exterior case 16 to the outside, and are used to draw current from the battery body. The highly conductive member is, for example, aluminum, copper, titanium, nickel, stainless steel, or an alloy thereof. The terminal plates 12 and 14 are covered with, for example, a heat-resistant insulating heat-shrinkable tube to reliably prevent electrical contact with peripheral devices (for example, automobile parts, particularly electronic devices) and wiring. Is preferred.

  FIG. 2 is a cross-sectional view for explaining a lithium ion secondary battery according to an embodiment of the present invention.

  A battery main-body part is comprised by the battery element 20 which consists of a several cell. The battery element 20 includes a positive electrode layer 22, a positive electrode current collector 28, a negative electrode layer 32, a negative electrode current collector 38, an electrolyte layer 42, a negative electrode lead 46, and a positive electrode lead 44.

  The positive electrode layer 22 contains a positive electrode active material into which lithium can be inserted and removed, is disposed on both surfaces of the positive electrode current collector 28, and is in electrical contact with the positive electrode current collector 28. The negative electrode layer 32 contains a negative electrode active material into which lithium can be inserted and desorbed. The negative electrode layer 32 is disposed on both surfaces of the negative electrode current collector 38 and is in electrical contact with the negative electrode current collector 38.

  The electrolyte layer 42 is made of, for example, a separator containing a nonaqueous electrolytic solution, and is disposed between the positive electrode layer 22 and the negative electrode layer 32. The separator is, for example, a microporous sheet (film) made of polyolefin such as polyethylene or polypropylene.

  The battery element 20 includes a positive electrode layer 22, a positive electrode current collector 28, a positive electrode layer 22, an electrolyte layer 42, a negative electrode layer 32, a negative electrode current collector 38, a negative electrode layer 32, an electrolyte layer 42, a positive electrode layer 22. It is configured by repeating the stacking. The adjacent positive electrode layer 22, electrolyte layer 42 and negative electrode layer 32 constitute one single battery layer.

  The positive electrode lead 44 is made of a highly conductive member, and has one end portion that is continuously integrated with the positive electrode current collector 28 and the other end portion that is fixed to the positive electrode terminal plate 12 that is led out to the outside. It is used to electrically connect the positive electrode current collector 28 and the positive electrode terminal plate 12. The negative electrode lead 46 is made of a highly conductive member, and has one end portion continuously integrated with the negative electrode current collector 38 and the other end portion fixed to the negative electrode terminal plate 14 led out to the outside. It is used to electrically connect the negative electrode current collector 38 and the negative electrode terminal plate 14. As the fixing method, for example, ultrasonic welding or resistance welding is applied.

As the positive electrode active material contained in the positive electrode layer 22, it is preferable to apply a lithium-transition metal composite oxide from the viewpoint of capacity and output characteristics. Lithium - transition metal composite oxide, for example, Li · Co-based composite oxide such as LiCoO _2, Li · Ni-based composite oxide such as LiNiO _2, Li · Mn-based composite oxide such as spinel LiMn ₂ O _4, LiFeO ₂ .

  As the negative electrode active material contained in the negative electrode layer 32, it is preferable to apply a carbon material and an alloy-based negative electrode material from the viewpoint of capacity and output characteristics. Examples of the carbon material include graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon.

  The alloy-based negative electrode material is, for example, silicon, silicon oxide, tin dioxide, silicon carbide, or tin, and preferably includes an element that can be alloyed with lithium. This is because a negative electrode active material made of an alloy-based material containing an element that can be alloyed with lithium has a larger expansion coefficient than a non-alloyed negative electrode active material, so that the mobility of the negative electrode layer is improved.

  The positive electrode layer 22 and the negative electrode layer 32 further contain additives such as a binder and a conductive additive.

  The binder is, for example, polyamic acid, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene. Butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or mixtures thereof.

  The conductive additive is an additive blended to improve the conductivity of the positive electrode layer 22 and the negative electrode layer 32, for example. Carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber.

  The materials of the positive electrode current collector 28 and the negative electrode current collector 38 are, for example, iron, stainless steel, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, aluminum, copper, silver, gold, platinum, and carbon. From the viewpoint of electron conductivity and battery operating potential, aluminum and copper are preferred.

  The nonaqueous electrolytic solution contained in the electrolyte layer 42 is, for example, a liquid electrolyte or a polymer electrolyte.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used as the plasticizer include cyclic carbonates such as propylene carbonate, ethylene carbonate (EC), and vinylene carbonate, and chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate (DEC). . Supporting salt is, for example, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 or an inorganic acid anion salts ₁₀ such as _{Cl, LiCF 3 SO 3, Li} (CF 3 Organic acid anion salts such as SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N.

  The polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which a liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. The ion conductive polymer is, for example, polyethylene oxide (PEO), polypropylene oxide (PPO), and a copolymer thereof.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the above matrix polymer and does not contain an organic solvent that is a plasticizer, so that leakage from the battery is suppressed.

  FIG. 3 is a cross-sectional view for explaining the negative electrode layer shown in FIG.

  The negative electrode layer 32 includes an active material layer 33 that is disposed on the non-aqueous electrolyte side and contains a negative electrode active material, and an electron conductive layer 34 that is disposed on the current collector side and does not contribute to charge / discharge. The electron conductive layer 34 is made of a metal and is movable with respect to a lateral direction H perpendicular to the stacking direction L with respect to the negative electrode current collector 38 that is in electrical contact.

  Since the negative electrode layer 32 is movable in the lateral direction independently of the negative electrode current collector 38 (in contact with but not adhered), the negative electrode active material expands and contracts as lithium ions move. When a tensile stress is generated in the lateral direction, the shearing force overcomes the friction, so that the negative electrode layer 32 moves (displaces) in the lateral direction with respect to the negative electrode current collector 38. Thereby, for example, even when silicon oxide is used as the negative electrode active material and the capacity of the lithium ion secondary battery 10 is increased, deformation and breakage of the negative electrode current collector 38 are suppressed. A decrease in battery life due to deterioration of the battery can be avoided.

  Since the expansion rate of the active material is generally larger than that of the positive electrode layer 22, the negative electrode layer 32 alone is movable in the lateral direction H, thereby simplifying the structure and reducing the deformation of the current collector. It is possible to suppress breakage efficiently.

  Since the electron conductive layer 34 is disposed on the current collector side, it is possible to maintain good electrical contact with the negative electrode current collector 38.

  Since the electron conductive layer 34 is made of metal, it is possible to easily obtain good electron conductivity.

  The size of the negative electrode current collector 38 is set so that it is larger than the size of the movable negative electrode layer 32 and the negative electrode layer 32 moving in the lateral direction is not covered. Therefore, even if the movable negative electrode layer 32 moves in the horizontal direction H, it does not protrude from the corresponding negative electrode current collector 38, and the contact can be reliably maintained, and breakage can be prevented. .

  FIG. 4 is a cross-sectional view for explaining Modification 1 according to the embodiment of the present invention.

  The movable electrode layer is not limited to the negative electrode layer 32, and the positive electrode layer 22 may be movable. In this case, similarly to the negative electrode layer 32, the active material layer 23 that is disposed on the non-aqueous electrolyte side and contains the positive electrode active material, and the electron conductive layer 24 that is disposed on the collector side and does not contribute to charge / discharge. And the positive electrode layer 22 is configured.

  Thereby, since the positive electrode layer 22 is movable in the lateral direction H independently of the positive electrode current collector 28 (in a state where it is in contact but not bonded), the positive electrode active material accompanies the movement of lithium ions. Is expanded and contracted and a tensile stress is generated in the lateral direction, the shear force overcomes the friction, so that the positive electrode layer 22 moves (displaces) in the lateral direction H with respect to the positive electrode current collector 28. Thereby, since the deformation | transformation and fracture | rupture of the positive electrode electrical power collector 28 are suppressed, the fall of the battery life by deterioration of cycling characteristics is avoided. If necessary, only the positive electrode layer 22 can be made movable.

  5 and 6 are plan views for explaining the second modification and the third modification according to the embodiment of the present invention.

  The electron conductive layer 34 is not limited to a form formed by a flat metal plate, and may be configured to have a through hole 35 as necessary. The through-hole 35 can also be formed by applying, for example, a foam metal shown in FIG. 5 or an expanded metal shown in FIG. The through hole 35 can also be formed by machining.

  FIG. 7 is a cross-sectional view for explaining the modification 4 according to the embodiment of the present invention.

  Between the movable negative electrode layer 32 and the negative electrode current collector 38, a layer (metal lithium-containing layer) 34 containing metallic lithium can be disposed. In this case, when the non-aqueous electrolyte is injected, lithium ions from the metal lithium-containing layer are doped into the negative electrode active material contained in the negative electrode layer 32, so that the charge / discharge efficiency of the lithium ion secondary battery 10 is improved. It is possible to improve. In addition, since lithium metal has a small shear stress and a strong force is applied in the lateral direction, the metal lithium is easily allowed to move, so that the mobility of the negative electrode layer 32 is improved. The method for disposing the metal lithium-containing layer is not particularly limited. For example, lithium deposition on the negative electrode current collector 38 can be applied.

  The electron conductive layer 34 of the negative electrode layer 32 preferably has a through hole 35. Since lithium ions from the metal lithium-containing layer pass through the through-hole 35 when the non-aqueous electrolyte is injected, the negative electrode active material contained in the negative electrode layer 32 can be easily doped. It is.

  FIG. 8 is a cross-sectional view for explaining a modification 5 according to the embodiment of the present invention.

  The movable electron conductive layer of the negative electrode layer 32 is not limited to a form made of metal, and a conductive elastic body can be applied as necessary. In this case, since the movable negative electrode layer 32 has the electron conductive layer 34A composed of a conductive elastic body, cracks caused by expansion and contraction of the negative electrode active material can be easily suppressed. The conductive elastic body is, for example, a conductive polymer such as microporous polyethylene.

  FIG. 9 is a plan view for explaining the modification 6 according to the embodiment of the present invention.

  The movable negative electrode layer 32 is divided into a plurality of parts (for example, rectangular and divided into four parts), and can be intermittently disposed on the surface of the negative electrode current collector 38 that is in electrical contact with each other. It is. In this case, since the gap S exists inside the negative electrode layers 32A to 32D and can move (expand) toward the gap, the amount of movement to the outside can be suppressed. The number and shape of the negative electrode layer 32 and the width of the gap S can be set as appropriate.

  FIG. 10 is a chart for explaining the performance evaluation results of the lithium ion secondary battery according to the embodiment of the present invention.

  The performance evaluation of the lithium ion secondary battery according to the present embodiment was performed with respect to the discharge capacity retention rate and distortion after the initial charge / discharge.

  In the initial charge / discharge, (1) charging to 4.2 V at a constant current (0.1 C) and charging at 4.2 V for a total of 12 hours, (2) 30 minutes of discharge pause in an open state, (3 ) Discharge (cut-off) to 2.5 V at a constant current (0.1 C), and (4) 30 minutes of discharge rest in the open state.

  The distortion was evaluated by appearance observation.

  The discharge capacity maintenance rate was evaluated by the ratio of the capacity change to the initial discharge capacity after 50 and 100 cycle tests. In one cycle of the cycle test, (1) charging to 4.2 V at a constant current (0.5 C), charging for a total of 4 hours held at 4.2 V, (2) 30-minute discharge pause in the open state, (3) Discharge (cutoff) to 2.5 V at a constant current (0.5 C), (4) Discharge pause for 30 minutes in the open state was sequentially performed.

  Next, configurations of Examples 1 to 6 and a comparative example applied to performance evaluation will be described.

Example 1
The electron conductive layer according to Example 1 is disposed only on the negative electrode layer as in the case of the electron conductive layer shown in FIG. 3, and the production method of Example 1 will be sequentially described below.

<Preparation of negative electrode slurry>
A solution containing a silicon oxide having a particle diameter of 2 μm and a polyamic acid that is a precursor of polyimide serving as a binder was prepared. Next, using NMP (N-methyl-2-pyrrolidone) as a slurry viscosity adjusting solvent, a solution containing silicon oxide and polyamic acid was added to prepare a negative electrode slurry. The mixing ratio was silicon oxide: polyamic acid = 85: 15 by mass ratio.

<Preparation of negative electrode layer>
The prepared negative electrode slurry was applied onto an aluminum foil having a thickness of 20 μm using a doctor blade. The laminate of the negative electrode slurry and the aluminum foil was held at 80 ° C. for 10 minutes to evaporate NMP, and then vacuum dried at 120 ° C. for 5 hours. And it transferred to a 20-micrometer-thick microporous polyethylene film | membrane (electron conductive layer) on 120 degreeC conditions, and obtained the negative electrode layer. The microporous polyethylene film had a porosity of 32% and contained ketjen black (conductive agent) having an average particle size of 0.1 μm.

<Preparation of negative electrode sheet>
The produced negative electrode layer was cut out so that it might become 20 mm x 100 mm, and two this was prepared. Further, a rolled copper foil (current collector) having a thickness of 20 μm was cut out to 60 mm × 115 mm.

  The double-sided negative electrode sheet was prepared by arranging the negative electrode layer on both sides of the rolled copper foil so that the negative axis side was 5 mm on the short axis side and the long axis side was 10 mm from the end opposite to the tab part. Also. The rolled copper foil and the negative electrode layer were fixed to the rolled copper foil with a polyimide film (for example, Kapton (registered trademark)) at the corner of the negative electrode layer portion on the tab welded portion side. The single-sided negative electrode sheet was prepared by arranging negative electrode layers on both sides of the rolled copper foil so that the minor axis side was 5 mm each, and the major axis side was 5 mm and 10 mm respectively from the end. The 10 mm side in the rolled copper foil is a tab welded portion. The tab corresponds to the negative electrode lead (negative electrode terminal plate).

<Preparation of positive electrode sheet>
Lithium nickelate as a positive electrode active material, acetylene black as a conductive auxiliary agent, and PVdF serving as a binder were prepared. Next, using NMP as a solvent, lithium nickelate, acetylene black, and PVdF were added to prepare a positive electrode slurry. The mixing ratio was lithium nickelate: acetylene black: PVdF = 90: 5: 5 by mass ratio.

  The prepared positive electrode slurry was applied onto an aluminum foil (positive electrode current collector) having a thickness of 15 μm. The resulting positive electrode slurry and aluminum foil laminate was dried at 80 ° C. and then pressed at room temperature (25 ° C.) to adjust the porosity to 35%. And it vacuum-dried at 100 degreeC for 5 hours, it cut out so that a width | variety 49mm, an application part length 99mm, and an uncoated part might be 10 mm, and the positive electrode sheet which used the uncoated part as the welding part for tabs was obtained. The tab corresponds to the positive electrode lead (positive electrode terminal plate).

<Preparation of electrolyte>
EC and DEC were mixed at a volume ratio of 50:50 to obtain a plasticizer (organic solvent) for the electrolytic solution. Next, LiPF ₆ that is a lithium salt was added to the plasticizer so as to have a concentration of 1 M to prepare an electrolytic solution.

<Preparation of separator>
A polypropylene sheet was cut into 62 mm × 102 mm and used as a separator. The polypropylene sheet has a thickness of 25 μm and a porosity of 30%.

<Assembly of secondary battery for evaluation>
Nickel foil and aluminum foil were welded to the negative electrode sheet and the positive electrode sheet, respectively, to form tabs corresponding to the leads (terminal plates). The nickel foil and the aluminum foil are preliminarily provided with a resin made of modified polypropylene, and have a thickness of 300 μm, a width of 60 mm, and a length of 50 mm.

  A positive electrode sheet, a polypropylene separator, a negative electrode sheet, a polypropylene separator, and a positive electrode sheet were laminated in this order. In addition, the negative electrode sheet and the positive electrode sheet are positioned so that the tab of the negative electrode sheet and the tab of the positive electrode sheet are located on the opposite side. Then, the secondary battery for evaluation was completed by arrange | positioning in an aluminum laminate film (exterior case), injecting the adjusted electrolyte solution, and vacuum-sealing in the resin part position of the tip of a tab.

(Example 2)
Example 2 generally corresponds to Modification 2, and a foamed copper foil (see FIG. 5) having a porosity of 70% and a thickness of 100 μm is applied as the electron conductive layer, and the negative electrode layer is produced. The vacuum drying condition is different from Example 1 in that it is 350 hours at 5 hours.

(Example 3)
Example 3 generally corresponds to Modification 3, and differs from Example 2 in that expanded metal (see FIG. 6) is used instead of the foamed copper foil as the electron conductive layer.

Example 4
Example 4 differs from Example 2 in that a rolled copper foil having a thickness of 10 μm was used as the electron conductive layer instead of the foamed copper foil.

(Example 5)
Example 5 generally corresponds to modification 6 (see FIG. 9), and the negative electrode layer that is movable is divided into four parts, and the production of the negative electrode sheet is different from that of Example 1 as shown below. Yes.

<Preparation of negative electrode sheet>
A negative electrode layer produced in the same manner as in Example 3 was cut out to be 24.5 mm × 49 mm, and 8 sheets thereof were prepared. Further, in the same manner as in Example 1, a rolled copper foil (current collector) having a thickness of 20 μm was cut into 60 mm × 115 mm.

  The double-sided negative electrode sheet was prepared by arranging four negative electrode layers on each side (back and front) of the rolled copper foil. At this time, on each surface, the four divided negative electrode layers were arranged so that the minor axis side was 5 mm at a time, and the major axis side was 5 mm from the end opposite to the tab weld. Moreover, among the four corner portions of the divided electrode layer, only one corner portion close to the four corner portions of the rolled copper foil was fixed with a polyimide film.

(Example 6)
Example 6 generally corresponds to Modification 4, and further includes a metallic lithium-containing layer 36 (see FIG. 7) between the expanded metal (electron conductive layer) and the rolled copper foil (current collector). This is different from the third embodiment. The metallic lithium-containing layer was formed by evaporating lithium on a rolled copper foil so as to have a thickness of 5 μm, a width of 50 mm, and a length of 100 mm.

(Comparative example)
The comparative example does not have an electron conductive layer, and is different from Example 1 regarding the production of the negative electrode layer and the production of the negative electrode sheet as shown below.

<Preparation of negative electrode layer>
The negative electrode slurry produced in the same manner as in Example 1 was applied on a rolled copper foil (current collector) having a thickness of 20 μm produced in the same manner as in Example 1 using a doctor blade. The laminate of the negative electrode slurry and the rolled copper foil was held at 80 ° C. for 10 minutes to evaporate NMP. Then, after apply | coating the negative electrode slurry similarly to the back surface, it vacuum-dried at 350 degreeC for 5 hours, and obtained the negative electrode layer.

<Preparation of negative electrode sheet>
The prepared negative electrode layer was cut out so that the applied portion had a width of 50 mm × length of 100 mm, and the uncoated portion had a width of 50 mm × length of 10 to obtain a negative electrode sheet.

  Next, the performance evaluation result of the lithium ion secondary battery according to the present embodiment will be described.

  As shown in FIG. 10, for Examples 1 to 6, the discharge capacity retention rate (%) after 50 cycles is 63 to 75, and the discharge capacity retention rate (%) after 100 cycles is 55 to 71. . On the other hand, regarding the comparative example, the discharge capacity retention rate (%) after 50 cycles is 48, and the discharge capacity retention rate (%) after 100 cycles is 12. That is, Examples 1-6 differ from a comparative example, have a favorable discharge capacity maintenance factor, and the difference becomes remarkable with the increase in the number of cycles.

  In addition, distortion occurs only in the comparative example, and Examples 1 to 6 show good results.

  As described above, in the present embodiment, at least one of the positive electrode layer and the negative electrode layer is movable in the lateral direction independently of the current collector (in contact with but not adhered). Therefore, when the active material expands and contracts along with the movement of lithium ions and a lateral tensile stress is generated, the shear force overcomes the friction, so that the electrode layer moves laterally with respect to the current collector ( Shift). As a result, deformation and breakage of the current collector are suppressed, so that a reduction in battery life due to deterioration of cycle characteristics can be avoided. Therefore, it is possible to provide a lithium ion secondary battery that has good cycle characteristics and can extend the battery life.

  Since the expansion rate of the active material is generally larger than that of the positive electrode layer, when only the negative electrode layer is movable in the lateral direction, the current collector is efficiently deformed or broken while simplifying the structure. It is possible to suppress.

  Since the electron conductive layer is disposed on the current collector side, it is possible to maintain good electrical contact with the negative electrode current collector.

  When the electron conductive layer is made of metal, it is possible to easily obtain good electron conductivity. On the other hand, when the electron conductive layer is composed of a conductive elastic body, it is possible to easily suppress cracks caused by expansion and contraction of the negative electrode active material.

  The size of the negative electrode current collector is set to be larger than the size of the movable negative electrode layer so that the negative electrode layer moving in the lateral direction is not covered. Therefore, even if the movable negative electrode layer moves in the lateral direction, it does not protrude from the corresponding negative electrode current collector, and the contact can be reliably maintained and breakage can be prevented.

  When the movable negative electrode layer is divided into a plurality of parts and arranged on the surface of the negative electrode current collector that is in electrical contact with each other, the gap exists inside the negative electrode layer and moves toward the gap. Since it can expand (expand), the amount of outward movement can be suppressed.

  The negative electrode active material contained in the movable negative electrode layer is preferably made of an alloy-based material containing an element that can be alloyed with lithium. This is because a negative electrode active material made of an alloy-based material containing an element that can be alloyed with lithium has a larger expansion coefficient than a non-alloyed negative electrode active material, so that the mobility of the negative electrode layer is improved.

  It is also possible to arrange a metallic lithium-containing layer between the movable negative electrode layer and the negative electrode current collector. In this case, when the non-aqueous electrolyte is injected, lithium ions from the metal lithium-containing layer are doped into the negative electrode active material contained in the negative electrode layer, thereby improving the charge / discharge efficiency of the lithium ion secondary battery. It is possible. In addition, since metallic lithium has a small shear stress and a strong force is applied in the lateral direction, it can easily be moved, so that the mobility of the negative electrode layer can be improved.

  Moreover, when arrange | positioning a metal lithium content layer, it is preferable that the electron conductive layer of a negative electrode layer has a through-hole. This is because the lithium ion from the metal lithium-containing layer passes through the through-hole when the non-aqueous electrolyte is injected, and thus the negative electrode active material contained in the negative electrode layer can be easily doped. .

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. For example, the modifications 1 to 5 can be appropriately combined. It is also possible to apply to a bipolar secondary battery. In this case, for example, a clad material formed by bonding stainless steel or aluminum and copper is used as the current collector material.

10 Lithium ion secondary battery,
12 Positive terminal plate,
14 negative terminal plate,
16 exterior case,
20 battery elements,
22 positive electrode layer,
23 active material layer,
24 electron conductive layer,
28 positive electrode current collector,
32, 32A negative electrode layer,
33 active material layer,
34, 34A electron conductive layer,
35 through holes,
38 negative electrode current collector,
42 electrolyte layer,
44 positive lead,
46 Negative lead,
50 battery packs,
H lateral direction,
L stacking direction,
S Clearance.

Claims (10)

A positive electrode current collector;
A positive electrode layer containing an active material in electrical contact with the positive electrode current collector and capable of inserting and removing lithium; and
A non-aqueous electrolyte,
A negative electrode layer containing an active material capable of inserting and removing lithium;
A negative electrode current collector in electrical contact with the negative electrode layer;
Are sequentially stacked,
The positive electrode layer is movable with respect to the positive electrode current collector and / or the negative electrode layer is movable with respect to the negative electrode current collector in a lateral direction perpendicular to the stacking direction. A featured lithium ion secondary battery.   The size of the positive electrode current collector and / or the negative electrode current collector in electrical contact with the movable positive electrode layer and / or the negative electrode layer is such that the positive electrode layer moving in the lateral direction and / or The lithium ion secondary battery according to claim 1, wherein the negative electrode layer is set so as not to be covered.   The movable positive electrode layer and / or the negative electrode layer are divided into a plurality of parts, and are arranged on the surfaces of the positive electrode current collector and / or the negative electrode current collector that are in electrical contact with each other and spaced apart from each other. The lithium ion secondary battery according to claim 1 or 2, wherein The positive electrode layer and / or the negative electrode layer, which are movable,
An active material layer disposed on the non-aqueous electrolyte side and containing the active material;
An electron conductive layer that is disposed on the current collector side and is movable with respect to the positive electrode current collector and / or the negative electrode current collector in electrical contact, and does not contribute to charge and discharge;
The lithium ion secondary battery according to any one of claims 1 to 3, wherein:   The lithium ion secondary battery according to claim 4, wherein the electron conductive layer is made of a metal.   The lithium ion secondary battery according to claim 4, wherein the electron conductive layer is made of a conductive elastic body.   7. The lithium ion secondary battery according to claim 1, wherein only the negative electrode layer is movable in the lateral direction.   The lithium ion secondary battery according to claim 7, wherein the active material contained in the movable negative electrode layer is made of an alloy-based material containing an element that can be alloyed with lithium.   9. The lithium according to claim 7, further comprising a layer containing metallic lithium, wherein the layer is disposed between the movable negative electrode layer and the negative electrode current collector. Ion secondary battery. The movable negative electrode layer is disposed on the non-aqueous electrolyte side, disposed on the active material layer containing the active material, and on the negative electrode current collector side, is movable with respect to the negative electrode current collector, and is charged and discharged. An electron conductive layer that does not contribute to
The lithium ion secondary battery according to claim 9, wherein the electron conductive layer has a through hole.

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