JP6600938B2 - Lithium ion secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

  Conventionally, a lithium ion secondary battery including a positive electrode and a negative electrode, an electrolytic solution serving as a medium for ions to move between the positive electrode and the negative electrode, and a separator for preventing a short circuit between the positive electrode and the negative electrode is widely known. It has been. When manufacturing this battery, it is common to apply a certain pressure to the electrode plate group in which the positive electrode having the positive electrode active material layer, the separator, and the negative electrode having the negative electrode active material layer are stacked, so that the electrode plate group has a specified thickness. Is. Furthermore, in Patent Document 1, a constant pressure is applied in the thickness direction of the electrode plate group so that the thickness of the positive electrode and / or the negative electrode, and consequently the electrode plate group, does not increase due to the expansion of the active material during charging and discharging of the battery. Continued batteries have been proposed.

  Here, in the case of a battery that is regulated so as not to increase the thickness of the electrode plate group, if the active material expands during charging / discharging in the active material layer, the electrolyte retained in the active material layer is removed from the active material layer. Pushed out. If it does so, the quantity of the electrolyte solution which exists in the active material vicinity will reduce, and there exists a possibility that the performance of a battery may fall as a result.

  Patent Document 2 discloses a lithium ion secondary battery in which a heat-resistant porous layer is formed on a negative electrode active material layer in order to suppress the expansion of a short-circuit portion at the time of an internal short circuit. Patent Document 2 discloses that the heat-resistant porous layer has an electrolyte solution holding ability, and that the content of the electrolyte solution of the negative electrode can be increased by disposing the heat-resistant porous layer on the negative electrode active material layer. It is disclosed. However, Patent Document 2 does not describe restraining the electrode plate group in the thickness direction so that the thickness does not increase. In general, a battery in which some layer is formed on the surface of the active material layer may cause a decrease in output due to an increase in resistance or the like.

JP 2014-82157 A JP 2007-200755 A

  The present invention has been made in view of such circumstances, and suppresses deterioration of battery performance in a lithium ion secondary battery in which the electrode plate group is constrained in the thickness direction so as not to increase the thickness. Objective.

  As a result of intensive studies, the inventors of the present invention have arranged a coating layer on the surface of the negative electrode active material layer, and the thickness of the coating layer is 0.03 or more and 0.15 or less with respect to the thickness of the negative electrode active material layer. In the lithium ion secondary battery in which the electrode plate group is restrained in the thickness direction so as not to increase the thickness, it has been found that the battery performance can be prevented from deteriorating.

  That is, the lithium ion secondary battery of the present invention is a lithium ion secondary battery including an electrode plate group including a positive electrode, a separator, and a negative electrode, and an electrolyte solution. The negative electrode includes a current collector and a surface of the current collector. The negative electrode active material layer is disposed on the surface of the negative electrode active material layer, and the coating layer includes inorganic particles, a binder for the coating layer, and a void. The electrode plate group is constrained in the thickness direction so as not to increase in thickness.

  The porosity of the coating layer is preferably 35% to 85%.

  The thickness of the coating layer is preferably 1 μm or more and 15 μm or less.

  The method for producing a lithium ion secondary battery according to the present invention is a method for producing a lithium ion secondary battery having an electrolyte solution, wherein the surface of the negative electrode active material layer formed on the surface of the current collector is coated with inorganic particles, A negative electrode forming step for forming a coating layer containing a binder for the layer and voids, an electrode plate group forming step for forming an electrode plate group having a positive electrode, a separator, and a negative electrode obtained in the negative electrode forming step; A constraining step of constraining the electrode plate group in the thickness direction so that the thickness does not increase in the lithium ion secondary battery, and the thickness of the coating layer in the negative electrode forming step is equal to the thickness of the negative electrode active material layer in the negative electrode forming step On the other hand, it is 0.03 or more and 0.15 or less.

  In the lithium ion secondary battery of the present invention, the electrode plate group is constrained in the thickness direction so that the thickness does not increase. Therefore, when the negative electrode active material expands during charge / discharge, the electrolyte retained in the negative electrode active material layer may be pushed out of the negative electrode active material layer. In the lithium ion secondary battery of the present invention, the coating solution having a specific thickness is disposed on the surface of the negative electrode active material layer, so that the electrolyte solution retained in the negative electrode active material layer during charge / discharge is the negative electrode active material layer. Even if it is pushed out, the electrolyte solution is retained in the voids contained in the coating layer, so the electrolyte solution contained in the coating layer can be used by the nearby negative electrode active material, and the deterioration of battery performance is suppressed. The

It is a schematic diagram explaining the negative electrode before charging / discharging of the lithium ion secondary battery of this embodiment. It is a schematic diagram explaining the negative electrode at the time of charging / discharging of the lithium ion secondary battery of this embodiment. It is a schematic diagram explaining the electrode group of the lithium ion secondary battery of this embodiment. It is a schematic diagram explaining the example of a restriction | limiting of the electrode group of the lithium ion secondary battery of this embodiment. It is a graph which shows the relationship between the ratio with respect to the thickness of the negative electrode active material layer of the thickness of a coating layer, the charging resistance of a lithium ion secondary battery, and a capacity | capacitance maintenance factor.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention includes an electrode plate group including a positive electrode, a separator, and a negative electrode, and an electrolytic solution. The electrode plate group is constrained in the thickness direction so that the thickness does not increase. The negative electrode includes a current collector, a negative electrode active material layer, and a coating layer. The coating layer includes inorganic particles, a binder for the coating layer, and voids, and the thickness of the coating layer is 0.03 or more and 0.15 or less with respect to the thickness of the negative electrode active material layer.

(Negative electrode)
The negative electrode includes a current collector, a negative electrode active material layer disposed on the surface of the current collector, and a coating layer disposed on the surface of the negative electrode active material layer and including inorganic particles, a binder for the coating layer, and voids. Have.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As a current collector material, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, or stainless steel The metal material can be exemplified. The current collector may be covered with a known protective layer. Moreover, you may use what processed the surface of the electrical power collector by the well-known method as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

The negative electrode active material layer includes a negative electrode active material, and includes a binder and / or a conductive aid as necessary.
As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. Therefore, the negative electrode active material is not particularly limited as long as it is a simple substance, alloy, or compound that can occlude and release lithium ions. The negative electrode active material generally expands and contracts as lithium ions are stored and released.

Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element capable of being alloyed with lithium, a compound having an element capable of being alloyed with lithium, or a polymer material. Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, natural graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature. Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable. As the compound having an element that can be alloyed with lithium, specifically, ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 or LiSnO, and SiO _x (0.5 ≦ x ≦ 1.5) is particularly preferable. Moreover, tin compounds (Cu-Sn alloy, Co-Sn alloy, etc.) can be illustrated as a compound which has an element which can be alloyed with lithium. Specific examples of the polymer material include polyacetylene and polypyrrole.

The negative electrode active material is preferably in powder form. When the negative electrode active material is in a powder form, the average particle diameter D ₅₀ of the negative electrode active material is preferably 0.5 μm or more and 30 μm or less, and more preferably 1 μm or more and 20 μm or less. When the average particle diameter D ₅₀ of the negative electrode active material is too small, the specific surface area of the powder of the negative electrode active material is increased, it increases the contact area of the powder of the anode active material and the electrolyte solution, proceed decomposition of the electrolyte solution As a result, the cycle characteristics may be deteriorated. If the average particle diameter D ₅₀ of the negative electrode active material is too large, if the conductivity using a low negative electrode active material, conductive entire electrode becomes uneven, charging and discharging characteristics may deteriorate.

The average particle diameter D ₅₀ can be measured by particle size distribution measurement method. The average particle diameter D ₅₀ is that the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D ₅₀ means the median size measured by volume.

  The binder plays a role of binding the active material to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and poly (meth) acrylic acid. Known resins such as acrylic resins, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, styrene butadiene rubber, and alkoxysilyl group-containing resins can be used. These binders can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a binder, The range of 1-50 mass parts of binders with respect to 100 mass parts of active materials is preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  A conductive additive is added to increase conductivity. Examples of the conductive assistant include carbon black, graphite, acetylene black, ketjen black (registered trademark), and vapor grown carbon fiber (Vapor Grown Carbon Fiber) which are carbonaceous fine particles. These conductive assistants can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a conductive support agent, For example, it can be set as 1-30 mass parts of conductive support agents with respect to 100 mass parts of active materials.

  In order to form the negative electrode active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. The negative electrode active material may be applied directly on the surface. Specifically, a composition for forming an active material layer containing a negative electrode active material and, if necessary, a binder and / or a conductive aid is prepared, and an appropriate solvent is added to the composition to obtain a paste-like liquid. And A solution in which a binder is dissolved in a solvent in advance or a dispersed suspension may be used. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. The paste-like liquid is applied to the surface of the current collector and then dried. Drying may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set drying temperature suitably, and the temperature beyond the boiling point of the said solvent is preferable. What is necessary is just to set drying time suitably according to an application quantity and drying temperature. In order to increase the density of the negative electrode active material layer, a compression step may be added to the dried current collector on which the negative electrode active material layer is formed.

The coating layer is disposed on the surface of the negative electrode active material layer and includes inorganic particles, a binder for the coating layer, and voids.
This coating layer has voids between the inorganic particles, between the inorganic particles and the binder for the coating layer, between the inorganic particles and the negative electrode active material layer, and the like. In the lithium ion secondary battery, the electrolytic solution is held in this gap. Since the volume of the inorganic particles does not change during charging / discharging of the lithium ion secondary battery, the amount of the electrolyte solution in the gap does not change due to charging / discharging. That is, the electrolytic solution retained in the coating layer is not reduced by charge / discharge. Therefore, the nearby negative electrode active material can be easily used for the electrolyte contained in the coating layer. Therefore, deterioration of the battery capacity and capacity retention rate of the lithium ion secondary battery having the electrode plate group constrained in the thickness direction can be suppressed.

  In addition, since the coating layer is disposed on the surface of the negative electrode active material layer, direct contact between the negative electrode active material layer and the electrolytic solution is reduced. The electrolytic solution is decomposed by direct contact between the electrolytic solution and the negative electrode active material. Therefore, decomposition | disassembly of electrolyte solution can be suppressed with a coating layer. In addition, since the surface of the negative electrode active material layer is covered with the coating layer, deposition of a metal component eluate or a decomposition product of the electrolyte contained in the electrolyte is suppressed on the surface of the negative electrode active material layer. As a result, deterioration of the cycle characteristics of the lithium ion secondary battery can be suppressed.

Examples of the inorganic particles include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, kaolinite, CaSO ₄ , MgSO _4. , BaSO ₄ , CaO, ZnO, and particles composed of one or more inorganic compounds selected from zeolite. As the material for the inorganic particles, Al ₂ O ₃ , SiO ₂ , and TiO ₂ are preferable from the viewpoint of easy availability, and Al ₂ O ₃ is particularly preferable.

The particle size of the inorganic particles, the average particle size _{D 50} thereof is preferably 0.1 to 10 [mu] m, more preferably a 0.2 to 5 .mu.m, those of 0.5~3μm is particularly preferred. When the average particle diameter D ₅₀ is too small, there are cases where forming a gap capable of holding the electrolytic solution becomes difficult. Since the thickness of the average particle diameter D ₅₀ is too large the coating layer increases, resulting due to the increase in thickness the resistance is likely to adversely affect the battery output.

  As the binder for the coating layer, the binder described in the description of the active material layer may be employed alone or in combination. As the binder for the coating layer, polyvinylidene fluoride is particularly preferable from the viewpoint of electrochemical stability.

  A preferable mass ratio of the inorganic particles and the binder for the coating layer is 5: 1 to 200: 1, more preferably 10: 1 to 150: 1, and particularly preferably 15: 1 to 100: 1. .

  The thickness of the coating layer is 0.03 or more and 0.15 or less, more preferably 0.05 or more and 0.11 or less with respect to the thickness of the negative electrode active material layer. Although mentioned later in an Example, it can be set as the lithium ion secondary battery which satisfies both charging resistance and a capacity | capacitance maintenance factor by making ratio of the thickness of a coating layer with respect to the thickness of a negative electrode active material layer into this range. If the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer is too large, the resistance of the electrode may be increased too much. If the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer is too small, the lithium ion secondary battery There is a risk that the capacity maintenance rate will deteriorate.

The thickness of the coating layer is not particularly limited, but is preferably 1 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less.
Although the density of the coating layer is not particularly limited but is preferably ^{0.1g / cm 3 ~3g / cm 3} , more preferably ^{0.3g / cm 3 ~2.5g / cm 3} , 0.6g / cm 3 ~2g / Cm ³ is particularly preferred.
The porosity of the coating layer is not particularly limited, but is preferably 5% to 95%, more preferably 20% to 90%, and further preferably 35% to 85%.

  In order to provide a coating layer on the negative electrode active material layer, for example, a step of preparing a coating layer forming composition by dispersing inorganic particles and a coating layer binder in a solvent, and a coating layer forming composition, What is necessary is just to implement a drying process, after implementing the process apply | coated on a negative electrode active material layer. The total amount of the inorganic particles and the binder for the coating layer in the composition for forming a coating layer is preferably in the range of 10% by mass to 50% by mass. Examples of the solvent used for preparing the composition for forming a coating layer include N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. In the coating process, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. The drying step may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set a drying temperature suitably in the range which the binder for coating layers does not decompose | disassemble, and the temperature beyond the boiling point of the said solvent is preferable. What is necessary is just to set drying time suitably according to an application quantity and drying temperature.

  Here, the effect of the coating layer will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a negative electrode before charging / discharging of the lithium ion secondary battery of this embodiment. FIG. 2 is a schematic diagram for explaining the negative electrode during charging and discharging of the lithium ion secondary battery of the present embodiment.

  As shown in FIG. 1, the negative electrode active material layer 11 is disposed on the surface of the negative electrode current collector 10, and the coating layer 12 is disposed on the surface of the negative electrode active material layer 11. As shown by arrows A and B in FIG. 1, a binding force is applied to the negative electrode current collector 10, the negative electrode active material layer 11, and the coating layer 12 in the thickness direction. The negative electrode active material layer 11 includes a negative electrode active material 111 and an electrolytic solution 5. The negative electrode active material layer 11 also includes a binder and a conductive auxiliary agent, which are omitted in FIG. The coating layer 12 includes inorganic particles 121 and the electrolytic solution 5. The coating layer 12 also includes a coating layer binder, but is omitted in FIG. In the negative electrode shown in FIG. 1, since the negative electrode active material 111 is not expanded because it is before charging and discharging, the negative electrode active material layer 11 holds the electrolytic solution 5 in the vicinity of the negative electrode active material 111.

  FIG. 2 shows a state where the negative electrode active material 111 is expanded during charging / discharging of the lithium ion secondary battery. As shown in FIG. 2, the negative electrode active material 111 is expanded in the negative electrode active material layer 11, and the electrolytic solution 5 is pushed out from the negative electrode active material layer 11. In FIG. 2, since the binding force is applied in the directions of arrows A and B shown in FIG. 2, the thickness of the negative electrode active material layer 11 is not changed in the thickness direction, and the binding force is not applied. For example, the electrolytic solution 5 is extruded in the direction of arrow C which is a direction perpendicular to the thickness direction. In the coating layer 12, the inorganic particles 121 do not expand at the time of charging / discharging, so the void volume in the coating layer does not decrease and the coating layer 12 holds the electrolytic solution 5 as before charging / discharging. Therefore, the negative electrode active material 111 in the vicinity of the coating layer 12 can use the electrolytic solution 5 retained in the coating layer 12 even when the amount of the electrolytic solution 5 in the vicinity is small during charging and discharging. When the coating layer 12 is not disposed, the electrolyte solution 5 is insufficient in the vicinity of the negative electrode active material 111, and the battery capacity may be reduced. By disposing the coating layer 12 on the surface of the negative electrode active material layer 11, it is possible to suppress the electrolyte withering near the negative electrode active material even when a binding force is applied in the thickness direction. It is possible to suppress a decrease in capacity and a decrease in capacity maintenance rate of the lithium ion secondary battery due to the electrolyte withering.

(Positive electrode)
The positive electrode has a current collector and a positive electrode active material layer disposed on the surface thereof. The positive electrode active material layer includes a positive electrode active material, and includes a binder and / or a conductive aid as necessary.
As the current collector, the binder, and the conductive auxiliary agent, the same materials as those described for the negative electrode can be used.

As the positive electrode active material, a lithium-containing oxide or another metal oxide can be used. As the lithium-containing oxides include a lithium-cobalt composite oxide having a layered structure, the lithium nickel composite oxide having a layered structure, the lithium manganese composite oxide having a spinel structure represented by the general _{formula: Li a Co p Ni q Mn} r D _s O _x (D is at least one selected from Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, and p + q + r + s = 1, 0 <p <1, 0 ≦ q <1, Lithium cobalt-containing composite metal having a layered structure represented by 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) oxides of the general formula: olivine-type lithium phosphate compound oxide represented by LiMPO ₄ (at least one M is selected Mn, Fe, Co and Ni), the general _formula: Li 2 _MPO 4 F Fluoride olivine-type lithium phosphate compound oxide represented (at least one M is selected Mn, Fe, Co and Ni), the general _formula: Li 2 MSiO silicate lithium composite oxide represented by ₄ ( M may be at least one selected from Mn, Fe, Co, and Ni. Examples of other metal oxides include titanium oxide, vanadium oxide, and manganese dioxide.

The positive electrode active material is preferably made of a lithium-containing oxide represented by the chemical formula: LiMO ₂ (M is at least one selected from Ni, Co, and Mn), and further has a general formula: Li _a Co _p Ni _{q Mn r D s O x (} D is at least one selected Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, p + q + r + s = 1,0 <p <1,0 ≦ Lithium having a layered structure represented by q <1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) It is preferably made of a cobalt-containing composite metal oxide.

Examples of the lithium-containing oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _{0. 3} O ₂ , LiCoO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiCoMnO ₂ can be used. Among these, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are preferable in terms of thermal stability.

The positive electrode active material preferably has an average particle diameter _{D 50} is a powder form of 1 m to 20 m. When the average particle diameter D ₅₀ of the positive electrode active material is small, the specific surface area of the positive electrode active material is increased. Thus, the reaction area of the average particle diameter D ₅₀ of the positive electrode active material is too small and the positive electrode active material and the electrolyte becomes excessive increase it, as a result, are accelerated decomposition of the electrolytic solution, the lithium ion secondary The cycle characteristics of the battery may be deteriorated. When the average particle diameter D ₅₀ of the positive electrode active material is too large resistance of the lithium ion secondary battery increases, there is a possibility that the output characteristics of the lithium ion secondary battery decreases.
In order to form the positive electrode active material layer on the surface of the current collector, a method similar to the method for forming the negative electrode active material layer described above for the negative electrode may be used.

(Separator)
The separator separates the positive electrode and the negative electrode, and allows ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, a known one used in each lithium ion secondary battery may be used. For example, a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyester, and polyamide. Or the porous film made from ceramics can be illustrated. The separator made of synthetic resin may have a single layer structure using a single synthetic resin or a laminated structure in which a plurality of synthetic resin layers are stacked. The thickness of the separator is not particularly limited, but is preferably in the range of 5 μm to 100 μm, more preferably in the range of 10 μm to 50 μm, and particularly preferably in the range of 15 μm to 30 μm.

(Plate group)
A separator is sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched.

  FIG. 3 is a schematic diagram for explaining an electrode plate group of the lithium ion secondary battery of the present embodiment. As shown in FIG. 3, a separator 3 is sandwiched between a negative electrode 1 and a positive electrode 2 to form an electrode plate group 4. The negative electrode 1 includes a negative electrode current collector 10, a negative electrode active material layer 11 disposed on the surface of the negative electrode current collector 10, and a coating layer 12 disposed on the surface of the negative electrode active material layer 11. The positive electrode 2 includes a positive electrode current collector 20 and a positive electrode active material layer 21 disposed on the surface of the positive electrode current collector 20.

  The electrode plate group is constrained in the thickness direction so that the thickness does not increase. It is preferable that the increase rate of the thickness of the electrode plate group divided by the original thickness of the electrode plate group × 100 is increased to 10% or less.

  The pressure applied in the thickness direction of the electrode plate group (hereinafter referred to as the restraining pressure) is 0 MPa or more and does not reduce the thickness of the electrode plate group. The restraining pressure may be applied to the electrode plate group by a container that encloses the electrode plate group, or is applied to the electrode plate group by a restraining means that applies the restraining pressure to the electrode plate group through a container that encloses the electrode plate group. May be.

  If the electrode plate group is disposed in a container made of a material that has an internal dimension that does not allow the electrode plate group to become thick and does not deform due to expansion of the electrode plate group, a restraining pressure is applied from the container to the electrode plate group. . Examples of the restraining means include a pair of plates that sandwich the container in the thickness direction, and a rod and a nut that fasten the pair of plates. In addition, the restraining means may use an elastic body such as rubber or a spring, a hydraulic device, or an electric device instead of the configuration in which the bolt and the nut are fastened.

  FIG. 4 is a schematic diagram for explaining a constraint example of the electrode plate group of the lithium ion secondary battery of the present embodiment. The form shown in FIG. 4 is an example, and the present invention is not limited to this. In FIG. 4, the electrode plate group 4 is contained in a container 6. The container 6 is sandwiched between the pair of plates 71 and 72 in the thickness direction of the electrode plate group 4. The pair of plates 71 and 72 are fastened at four corners with bolts and nuts. As shown in FIG. 4, bolts 81 are installed through the right ends of the pair of plates 71 and 72, and both ends of the bolt 81 are fastened with nuts 91 and 92. Further, a bolt 82 is installed through the left end of the pair of plates 71 and 72, and both ends of the bolt 82 are fastened with nuts 93 and 94. The plate group 4 is given a restraining pressure in the thickness direction through the container 6 by these plates, nuts, and bolts.

(Electrolyte)
The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.
As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters that can be used include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. As ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane can be used.

As the electrolyte dissolved in the electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

As an electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate, or the like is from 0.5 mol / l to 1.7 mol / l. A solution dissolved at a certain concentration can be used.

The container is not particularly limited. The material of the container is preferably a material that is not easily deformed by expansion of the electrode plate group, and examples of the material of the container include a metal material.
The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, and a coin shape can be adopted.

  An example of the manufacturing method of the lithium ion secondary battery of this invention is shown. First, a positive electrode and a negative electrode are prepared by the method described above. Next, a separator is sandwiched between both electrodes to form an electrode plate group. Next, between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal that communicate with the outside are connected by current collecting leads. Then, the electrode plate group is placed in a container and an electrolyte is added to form a lithium ion secondary battery. The lithium ion secondary battery is constrained in the thickness direction of the electrode plate group. The electrode plate group may be restrained by a container, or a restraining means may be used.

  The manufacturing method of the lithium ion secondary battery of this invention is a manufacturing method of the lithium ion secondary battery which has electrolyte solution, Comprising: A negative electrode formation process, an electrode group forming process, and a restraint process.

  In the negative electrode forming step, a coating layer including inorganic particles, a binder for the coating layer, and voids is formed on the surface of the negative electrode active material layer formed on the surface of the current collector. The electrode plate group forming step forms an electrode plate group having a positive electrode, a separator, and a negative electrode obtained in the negative electrode forming step. The restraining step restrains the electrode plate group in the thickness direction so that the thickness does not increase in the manufactured lithium ion secondary battery. The thickness of the coating layer in the negative electrode forming step is not less than 0.03 and not more than 0.15 with respect to the thickness of the negative electrode active material layer in the negative electrode forming step.

  The lithium ion secondary battery can be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
The battery of the present invention was manufactured as follows.
96 parts by mass of Al ₂ O ₃ having an average particle diameter D ₅₀ of 0.5 μm and 4 parts by mass of polyvinylidene fluoride were mixed to prepare a mixture. N-methyl-2-pyrrolidone was added to the mixture to prepare a coating layer forming composition containing 35% by mass of the mixture.

98 parts by mass of natural graphite having an average particle diameter D ₅₀ of 20 μm, which is a negative electrode active material, and 1 part by mass of styrene butadiene rubber and 1 part by mass of carboxymethyl cellulose, which are binders, were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove water, and then the copper foil was pressed to obtain a bonded product. The mass of the negative electrode active material layer per 1 cm ^{2 of} copper foil was 11.1 mg, and the density of the negative electrode active material layer was 1.4 g / cm ³ . The thickness of the negative electrode active material layer was 79.9 μm. On the negative electrode active material layer of copper foil, the said composition for coating layer formation was apply | coated to the film form using the doctor blade. This was dried at 120 ° C. for 6 hours to obtain a copper foil in which a coating layer having a thickness of 3 μm, a density of 1.2 g / cm ³ and a porosity of 70% was formed on the negative electrode active material layer. This was used as a negative electrode.
(Thickness of coating layer) / (thickness of negative electrode active material layer) was 0.038.

94 parts by mass of a lithium-containing metal oxide having a layered rock salt structure represented by LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having an average particle diameter D ₅₀ of 10 μm as a positive electrode active material, and acetylene as a conductive additive 3 parts by mass of black and 3 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization to obtain an aluminum foil on which a positive electrode active material layer was formed. The mass of the positive electrode active material layer per 1 cm ^{2 of} aluminum foil was 18.4 mg, and the density of the positive electrode active material layer was 3.1 g / cm ³ . The aluminum foil on which this positive electrode active material layer was formed was used as the positive electrode.
A rectangular sheet (112 mm × 136 mm, thickness 25 μm) made of a polyethylene resin film was prepared as a separator.

A separator was sandwiched between the negative electrode and the positive electrode to form an electrode plate group. The electrode plate group was inserted into a metal can (123 mm × 141 mm × 26.5 mm) made of aluminum and having a plate thickness of 3 mm, and an electrolyte was injected into the metal can and sealed to obtain a lithium ion secondary battery. As an electrolytic solution, 1 mol / l of LiPF ₆ was added to a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at EC: EMC: DMC = 30: 30: 40 (volume ratio). A solution dissolved so as to be used was used. The positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the lithium ion secondary battery.

  A lithium ion secondary battery was sandwiched between a pair of aluminum plates. A pair of aluminum plates was fastened using bolts and nuts at four locations near the four corners of the aluminum plate.

  The method for applying the restraint pressure was performed by using a precision universal testing machine Autograph (Shimadzu Corporation), and applying a pressure of 0.52 MPa between a pair of aluminum plates, and fastening and fixing a nut to a bolt.

  The lithium ion secondary battery to which the pressure of 0.52 MPa was applied was used as the lithium ion secondary battery of Example 1.

(Example 2)
A lithium ion secondary battery of Example 2 was fabricated in the same manner as the lithium ion secondary battery of Example 1, except that the thickness of the coating layer was 6 μm, the density was 1.2 g / cm ³ , and the porosity was 70%. (Thickness of coating layer) / (thickness of negative electrode active material layer) in the negative electrode of the lithium ion secondary battery of Example 2 was 0.077.

(Example 3)
A lithium ion secondary battery of Example 3 was fabricated in the same manner as the lithium ion secondary battery of Example 1 except that the thickness of the coating layer was 10 μm, the density was 1.2 g / cm ³ , and the porosity was 70%. (Thickness of coating layer) / (thickness of negative electrode active material layer) in the negative electrode of the lithium ion secondary battery of Example 3 was 0.130.

(Comparative Example 1)
A lithium ion secondary battery of Comparative Example 1 was fabricated in the same manner as the lithium ion secondary battery of Example 1, except that the thickness of the coating layer was 1 μm, the density was 1.2 g / cm ³ , and the porosity was 70%. (Thickness of coating layer) / (thickness of negative electrode active material layer) in the negative electrode of the lithium ion secondary battery of Comparative Example 1 was 0.013.

(Comparative Example 2)
A lithium ion secondary battery of Comparative Example 2 was produced in the same manner as the lithium ion secondary battery of Example 1 except that the thickness of the coating layer was 15 μm, the density was 1.2 g / cm ³ , and the porosity was 70%. In the negative electrode of the lithium ion secondary battery of Comparative Example 2, (the thickness of the coating layer) / (the thickness of the negative electrode active material layer) was 0.191.

<Charging resistance measurement>
The charging resistance of the lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 was measured.
A battery having a charging rate of 85% was charged at a 1.0 C rate for 10 seconds at 25 ° C. The charging resistance (mΩ) was obtained by the following formula.
Charging resistance (mΩ) = | Voltage before charging−Voltage after charging | / Current value Table 1 shows the results.

<Capacity retention measurement>
About the lithium ion secondary battery of Examples 1-3 and Comparative Examples 1-2, the following test was done and the initial stage capacity | capacitance and the capacity | capacitance maintenance factor were measured. The results of the capacity retention rate (%) are shown in Table 1.

  The lithium ion secondary battery to be measured is CCCV charged (constant current constant voltage charge) to 25 ° C., 1C rate, voltage 3.92V, and CCCV discharge (constant current constant voltage discharge) to 3.48V at 1C rate. The discharge capacity at the time of performing was measured, and this discharge capacity was defined as the initial capacity.

  One charge / discharge cycle for CC charge (constant current charge) to 60 ° C, 1C rate, voltage 3.92V, and CC discharge (constant current discharge) to 3.48V at 1C rate for lithium ion secondary batteries This was repeated 2500 cycles. This voltage range is a range in which SOC (State of Charge) is 15% to 85%.

The discharge capacity of the lithium ion secondary battery after 2500 cycles was measured by the same method as the measurement of the initial capacity, and the capacity retention rate was calculated. The capacity retention rate (%) was obtained by the following formula.
Capacity retention rate (%) = 2500 cycles discharge capacity / initial capacity × 100

  FIG. 5 is a graph showing the relationship between the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer and the charging resistance and capacity retention rate of the lithium ion secondary battery. As can be seen from Table 1 and FIG. 5, as the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer increases, the capacity retention rate improves, and the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer decreases. As the charging resistance decreased. In the graph of FIG. 5, the charging resistance is indicated by the reciprocal number, so that the reciprocal number of the charging resistance increases as the ratio of the coating layer thickness to the negative electrode active material layer thickness decreases. From this, it was found that when the thickness of the coating layer is 0.03 or more and 0.15 or less with respect to the thickness of the negative electrode active material layer, the charging resistance does not increase so much and the capacity retention ratio is maintained.

  Even if the electrode plate group of the lithium ion secondary battery is constrained in the thickness direction, the coating layer in which the thickness of the coating layer is 0.03 or more and 0.15 or less with respect to the thickness of the negative electrode active material layer is a negative electrode active material layer It has been found that the negative electrode active material in the vicinity can use the electrolytic solution contained in the coating layer, and the decrease in the capacity retention rate can be suppressed without significantly increasing the resistance.

  In the examples, a carbon material was used as the negative electrode active material. However, it is considered that the same effect can be obtained even if a Si compound or Sn compound that expands more easily during charge / discharge than the carbon material is used as the negative electrode active material.

  1: negative electrode, 2: positive electrode, 3: separator, 4: electrode plate group, 5: electrolyte, 6: container, 10: current collector for negative electrode, 11: negative electrode active material layer, 12: coating layer, 20: positive electrode Current collector, 21: positive electrode active material layer, 111: negative electrode active material, 121: inorganic particles, 71, 72: plate, 81, 82: bolt, 91, 92, 93, 94: nut.

Claims (2)

A laminated lithium ion secondary battery including an electrode plate group including a positive electrode, a separator and a negative electrode, and an electrolyte solution,
The negative electrode is a current collector, a negative electrode active material layer disposed on the surface of the current collector, a coating disposed on the surface of the negative electrode active material layer, including inorganic particles, a binder for the coating layer, and voids And having a layer
The thickness of the coating layer is 0.038 or more and 0.130 or less with respect to the thickness of the negative electrode active material layer,
The coating layer binder is a fluorine-containing resin,
The porosity of the coating layer is 35% to 85%,
Density of the coating layer is ^{0.6g / cm 3 ~2g / cm 3} ,
The coating layer has a thickness of 3 μm or more and 10 μm or less,
In the coating layer, the mass ratio of the inorganic particles and the binder for the coating layer is 15: 1 to 100: 1,
The lithium ion secondary battery, wherein the electrode plate group is constrained in the thickness direction so as not to increase in thickness. A method for producing a laminated lithium ion secondary battery having an electrolyte solution,
A negative electrode forming step of forming a coating layer containing inorganic particles, a binder for the coating layer, and voids on the surface of the negative electrode active material layer formed on the surface of the current collector;
An electrode plate group forming step for forming an electrode plate group having a positive electrode, a separator, and a negative electrode obtained in the negative electrode forming step;
A constraining step of constraining the electrode plate group in the thickness direction so that the thickness does not increase in the manufactured lithium ion secondary battery;
Have
The thickness of the coating layer in the negative electrode forming step is 0.038 or more and 0.130 or less with respect to the thickness of the negative electrode active material layer in the negative electrode forming step, and the porosity of the coating layer is 35% to 85%. , and the density of the coating layer is ^{0.6g / cm 3 ~2g / cm 3} , the thickness of the coating layer has a 3μm or 10μm or less, in the coating layer, consolidating the inorganic particles and the covering layer The mass ratio of the dressing is 15: 1 to 100: 1,
The method for producing a lithium ion secondary battery, wherein the coating layer binder is a fluorine-containing resin.

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