Method for manufacturing secondary battery

Abstract

To provide a method for manufacturing of a secondary battery in which a uniform and excellent coating film is formed on a surface of a negative electrode including a negative electrode active material having a void inside particles.SOLUTION: A method for manufacturing a secondary battery includes: a pore volume acquisition step of acquiring a pore volume of a negative electrode; a battery assembly construction step of constructing a battery assembly in which an electrode body having a positive electrode and a negative electrode is housed in an exterior body; a first charging step of charging a nonaqueous electrolytic solution in the exterior body; a charging electricity quantity estimation step of estimating a charging electricity quantity for forming a coating film derived from the nonaqueous electrolytic solution in a void according to the acquired pore volume; a first conditioning step of charging the battery assembly up to a first voltage corresponding to an estimated charging electricity quantity; a second injection step of injecting the nonaqueous electrolytic solution containing film forming agent into the exterior body; and a second conditioning step of charging the battery assembly up to a second voltage at which a film derived from the film forming agent can be formed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a secondary battery, and more particularly to a method for manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery has an electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent. In such a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte to which a film-forming agent capable of forming a film called a SEI (Solid Electrolyte Interface) film on the surface of a negative electrode active material is preferably used. In a secondary battery using a non-aqueous electrolyte containing a film-forming agent, the film-forming agent is decomposed on the surface of the negative electrode active material mainly during initial charging, and a stable film derived from the decomposed film-forming agent is formed. The film derived from the film-forming agent is preferable because it realizes good movement of charge carriers (typically lithium ions) between the electrolyte and the active material, and suppresses the decomposition of the non-aqueous electrolyte accompanying subsequent charging and discharging, thereby contributing to improvement of the durability (e.g., capacity retention rate) of the battery.

[0003] Patent Document 1 discloses a method for producing a nonaqueous electrolyte secondary battery, including the steps of: preparing an electrode body having a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, wherein the electrode body contains a sodium (Na) component as an unavoidable impurity; housing the electrode body in a battery case; a first injection step of injecting into the battery case a nonaqueous electrolyte solution that does not contain an oxalato complex compound that contains boron (B) as a constituent element; and, after the first injection step, a second injection step of injecting into the battery case a nonaqueous electrolyte solution that contains the oxalato complex compound.

[0004] Patent Document 2 discloses a method for producing a nonaqueous electrolyte secondary battery, which includes: a step of preparing an electrode body (S10); a step of housing the electrode body in a battery case (S20); a first injection step (S30) of injecting into the battery case a nonaqueous electrolyte solution that contains an additive capable of forming a coating on the negative electrode surface and does not contain a component that reacts with a Na component to precipitate a sodium salt in the nonaqueous electrolyte solution; and a second injection step (S40) of injecting into the battery case a nonaqueous electrolyte solution containing lithium bis(oxalato)borate after the first injection step. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-247009 A [Patent Document 2] JP 2016-58338 A Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Documents 1 and 2 describe that by performing the second injection process after the first injection process, it is possible to prevent variation in the amount of coating (thickness, concentration, and amount of coating) formed on the surface of the negative electrode (typically the surface of the negative electrode active material).

[0007] However, according to the study by the present inventors, in the technology described in Patent Documents 1 and 2, when a secondary battery is manufactured using a negative electrode containing a negative electrode active material having voids inside the particles, if the pore volume of the negative electrode exceeds the upper limit of the appropriate range, a problem has been found in that a non-uniform coating with uneven formation is likely to be formed on the surface of the negative electrode active material. If a secondary battery with such an uneven coating is repeatedly charged and discharged, there is a risk that a substance derived from the charge carrier (for example, a metal such as metallic lithium) will precipitate in the part where the resistance is locally increased due to the uneven formation of the coating.

[0008] The present disclosure has been made to solve such problems, and aims to provide a method for manufacturing a secondary battery in which a uniform and excellent coating is formed on the surface of a negative electrode that includes a negative electrode active material having voids inside the particles. [Means for solving the problem]

[0009] A method for manufacturing a secondary battery according to one embodiment includes a pore volume acquisition step of acquiring a pore volume of a negative electrode including a negative electrode active material having voids inside particles; a battery assembly construction step of constructing a battery assembly in which an electrode body having a positive electrode and a negative electrode is housed in an outer casing; a first injection step of injecting a non-aqueous electrolyte solution not containing a film-forming agent capable of forming a film on the surface of the negative electrode active material into the outer casing; a charging quantity estimation step of estimating a charging quantity of electricity for forming a coating derived from the non-aqueous electrolyte solution in the voids based on the acquired pore volume; a first conditioning step of charging the battery assembly up to a first voltage corresponding to the estimated charging quantity of electricity after the first injection step; a second injection step of injecting a non-aqueous electrolyte solution containing a film-forming agent into the outer casing after the first conditioning step; and a second conditioning step of charging the battery assembly up to a second voltage capable of forming a coating derived from the film-forming agent after the second injection step. Effect of the Invention

[0010] The present disclosure can provide a method for producing a secondary battery in which a uniform and excellent coating is formed on the surface of a negative electrode that includes a negative electrode active material having voids inside the particles. [Brief description of the drawings]

[0011] [Figure 1] 4 is a flowchart showing a method for manufacturing the secondary battery according to the first embodiment. [Diagram 2] FIG. 1 is a cross-sectional view showing an outline of a secondary battery. [Diagram 3] 3 is a cross-sectional view showing a part of a negative electrode of the secondary battery shown in FIG. 2. [Figure 4] FIG. 11 is a diagram illustrating an example of first correlation data. [Diagram 5]FIG. 11 is a diagram illustrating an example of second correlation data. [Figure 6] FIG. 11 is a diagram illustrating an example of third correlation data. [Figure 7] FIG. 2 is a cross-sectional view illustrating the effect of the pore volume of the negative electrode on the coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First embodiment Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiment. In addition, in order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is only a part of the whole, and in reality, many other configurations that are not shown are included. Furthermore, in the following description, the same or equivalent elements are given the same reference numerals, and duplicated descriptions are omitted. In the following description, when the structures and members on the positive electrode 30 side and the negative electrode 40 side of the secondary battery 10 are collectively referred to as "positive and negative electrodes", they may be collectively referred to as "positive and negative electrodes".

[0013] An example of a method for manufacturing a secondary battery 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a flowchart showing a method for manufacturing a secondary battery according to the first embodiment. As shown in Fig. 1, the method for manufacturing a secondary battery 10 according to this embodiment includes a pore volume acquisition step (step S1), a battery assembly construction step (step S2), a first injection step (step S3), a charged electric quantity estimation step (step S5), a first conditioning step (step S6), a second injection step (step S8), and a second conditioning step (step S9).

[0014] In a preferred embodiment, the method for producing the secondary battery 10 includes a pore volume determination step (step S4) after the first injection step and before the charged electricity quantity estimation step. Furthermore, in a preferred embodiment, the method for producing the secondary battery 10 includes an electrolyte removal step (step S7) after the first conditioning step and before the second injection step. Furthermore, in a preferred embodiment, the method for producing the secondary battery 10 includes an aging step (step S10) after the second conditioning step.

[0015] The secondary battery 10 manufactured by the method for manufacturing a secondary battery according to this embodiment is a chargeable and dischargeable secondary battery, such as a lithium ion secondary battery, an electric double layer capacitor, etc. Hereinafter, as one preferred embodiment of the method for manufacturing a secondary battery according to this embodiment, a method for manufacturing a lithium ion secondary battery will be specifically described.

[0016] A lithium ion secondary battery is a secondary battery in which charging and discharging are realized by the conduction of lithium ions, which are charge carriers, through an electrolyte between a positive electrode 30 and a negative electrode 40 during an electrochemical reaction. Such lithium ion secondary batteries are suitably used as power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHEVs).

[0017] The secondary battery 10 will now be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a cross-sectional view showing an outline of the secondary battery. Fig. 3 is a cross-sectional view showing a part of the negative electrode of the secondary battery shown in Fig. 2.

[0018] 2, the secondary battery 10 is a battery in which an electrode assembly 20 and a non-aqueous electrolyte are housed in a battery case 11. The battery case 11 is a specific example of an exterior body. The exterior body may be, for example, a pouch made of an aluminum laminate film.

[0019] The battery case 11 has, for example, a flat rectangular parallelepiped shape. The battery case 11 is not limited to a rectangular parallelepiped shape, and may have, for example, a cylindrical shape. The battery case 11 is made of a metal material such as aluminum, an aluminum alloy, or stainless steel. The battery case 11 has a case body 12 having a bottomed square cylinder shape with an open upper end, and a lid 13 having a rectangular flat plate shape. The lid 13 is provided so as to close the opening of the case body 12, and is joined to the case body 12. The lid 13 seals the inside of the battery case 11 with the electrode body 20, which is a power generating element, and the nonaqueous electrolyte solution housed inside the case body 12.

[0020] The lid 13 is provided with an injection port 14, a sealing member 15, a positive electrode terminal 16, and a negative electrode terminal 17. The injection port 14 is used when injecting a non-aqueous electrolyte into the battery case 11, and is a hole penetrating the lid 13. The injection port 14 is airtightly sealed by the sealing member 15. In addition, the lid 13 is provided with a safety valve that opens when the inside of the battery case 11 reaches a predetermined pressure, and discharges gas generated in the battery case 11.

[0021] The positive electrode terminal 16 is electrically connected to the positive electrode 30 via a positive electrode current collector 18 attached to one end of the electrode body 20 where the positive electrode current collector 31 is exposed. The negative electrode terminal 17 is electrically connected to the negative electrode 40 via a negative electrode current collector 19 attached to the other end of the electrode body 20 where the negative electrode current collector 41 is exposed.

[0022] The electrode assembly 20 has a positive electrode 30 and a negative electrode 40. The electrode assembly 20 further has a separator 50 interposed between the positive and negative electrodes 30, 40.

[0023] A wound electrode body in which a long sheet-like positive electrode 30 and a long sheet-like negative electrode 40 are stacked with two long sheet-like separators 50 between them, and then wound in the longitudinal direction and compressed into a flat shape can be suitably used as the electrode body 20. Note that the electrode body 20 is not limited to a wound electrode body, and may be a laminated electrode body in which the positive electrode 30 and the negative electrode 40 are stacked with the separator 50 between them.

[0024] The electrode body 20 has a positive electrode current collector and a negative electrode current collector formed so as to protrude from both ends in the winding axis direction. The positive electrode current collector is one end where the positive electrode mixture layer 33 is not formed and the positive electrode current collector 31 is exposed. The negative electrode current collector is the other end where the negative electrode mixture layer 43 is not formed and the negative electrode current collector 41 is exposed.

[0025] The positive and negative electrode mixture layers 33, 43 and the separator 50 are impregnated with a nonaqueous electrolyte in the battery case 11, and the nonaqueous electrolyte permeates minute gaps formed in the positive and negative electrode mixture layers 33, 43, respectively, thereby transferring Li ions, which are charge carriers, between the electrolyte and each of the positive and negative electrode active materials 42. The electricity stored in the positive and negative electrodes 30, 40 is collected by the positive and negative electrode current collectors 18, 19, respectively, and output from the positive and negative electrode terminals 16, 17.

[0026] The nonaqueous electrolyte of the secondary battery 10 includes a first nonaqueous electrolyte that does not contain a film-forming agent, and a second nonaqueous electrolyte that contains a film-forming agent. As the first nonaqueous electrolyte, a nonaqueous electrolyte in which a Li salt as a supporting salt is dissolved or dispersed in a nonaqueous solvent (organic solvent) can be used. The first nonaqueous electrolyte can include various additives such as an overcharge inhibitor and a freeze inhibitor.

[0027] As the Li salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSO3CF3, etc. can be used alone or in combination. Such supporting salts can be used alone or in combination of two or more.

[0028] The non-aqueous solvent may be an aprotic solvent such as various carbonates, ethers, esters, nitriles, sulfones, or lactones that can decompose at a voltage lower than other components in the non-aqueous electrolyte to form a coating derived from the non-aqueous solvent on the surface of the negative electrode active material 42. The non-aqueous solvent is reductively decomposed on the surface of the negative electrode active material 42 during initial charging to form a solvent-derived coating 51 that is a coating derived from the decomposed non-aqueous solvent. The solvent-derived coating 51 is a specific example of a coating derived from the non-aqueous electrolyte.

[0029] As the non-aqueous solvent, for example, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. Such non-aqueous solvents can be used alone or in combination of two or more.

[0030] The concentration of the supporting salt is not particularly limited, but if it is too low, the amount of Li ions contained in the non-aqueous electrolyte will be insufficient, and the ion conductivity will tend to decrease. On the other hand, if the concentration of the supporting salt is too high, the viscosity of the non-aqueous electrolyte will increase in a temperature range below room temperature (e.g., 0 to 30°C), and the ion conductivity will tend to decrease. Therefore, the concentration of the supporting salt is preferably, for example, 0.1 mol / L to 2 mol / L, and more preferably 0.8 mol / L to 1.5 mol / L.

[0031] The second nonaqueous electrolyte may be a nonaqueous electrolyte in which a Li salt as a supporting salt is dissolved in a nonaqueous solvent (organic solvent) and a film-forming agent is added. The supporting salt and the nonaqueous solvent may be the same as those in the first nonaqueous electrolyte, and it is preferable to appropriately use the same ones as those in the first nonaqueous electrolyte. Typically, the second nonaqueous electrolyte may have the same composition of the supporting salt and the nonaqueous solvent as those in the first nonaqueous electrolyte.

[0032] As the film-forming agent, various compounds that can be decomposed at a voltage lower than that of the nonaqueous solvent and other components in the nonaqueous electrolyte and that can form a film derived from the decomposed film-forming agent on the surface of the negative electrode active material 42 can be used. The film-forming agent is reductively decomposed on the surface of the negative electrode active material 42 during initial charging, and forms a film derived from the film-forming agent 52, which is a film derived from the decomposed film-forming agent. By including the film-forming agent in the nonaqueous electrolyte, it is possible to suppress a decrease in durability (e.g., capacity retention rate) of the secondary battery 10 due to decomposition of the nonaqueous solvent.

[0033] Examples of the film-forming agent include oxalato complex compounds and carbonates. Examples of the oxalato complex compounds include (oxalato) borates such as lithium bis(oxalato)borate (LiBOB), fluoro(oxalato) borates such as lithium difluoro(oxalato)borate, and (oxalato) phosphates such as lithium tris(oxalato)phosphate. Examples of the carbonates include vinylene carbonate (VC), vinyl ethyl carbonate (VEC), methyl phenyl carbonate (MPC), and fluoroethylene carbonate (FEC). These film-forming agents can be used alone or in combination of two or more. Among them, LiBOB is particularly preferred because it forms a suitable film.

[0034] Incidentally, when this type of secondary battery is manufactured by a method of injecting a nonaqueous electrolyte solution not containing a film-forming agent (first nonaqueous electrolyte solution) into the battery case 11 containing the electrode body 20, and then injecting a nonaqueous electrolyte solution containing a film-forming agent (second nonaqueous electrolyte solution), when the secondary battery is initially charged, a film 52 derived from the film-forming agent, a film 51 derived from the solvent, and a film 53 derived from other components may be formed on the surface of the negative electrode active material 42. In the following description, when there is no need to distinguish between the film 52 derived from the film-forming agent, the film 51 derived from the solvent, and the film 53 derived from other components, they will be collectively referred to as "films".

[0035] FIG. 7 is a cross-sectional view for explaining the effect of the pore volume of the negative electrode on the coating. As shown in FIG. 7, the coating film-forming agent-derived coating 52 is an SEI coating formed by decomposition of the coating film-forming agent. The solvent-derived coating 51 is an SEI coating formed by decomposition of the non-aqueous solvent in the non-aqueous electrolyte. The other-component-derived coating 53 is an SEI coating formed by decomposition of other components in the non-aqueous electrolyte excluding the coating film-forming agent and the non-aqueous solvent. Note that SEI is an abbreviation for Solid Electrolyte Interface.

[0036] The film-forming agent decomposes at a lower voltage than both the nonaqueous solvent and other components in the nonaqueous electrolyte, and therefore decomposes prior to both the nonaqueous solvent and other components during initial charging, and a film 52 derived from the film-forming agent can be formed in intraparticle voids 46 of the negative electrode active material 42. Furthermore, after the film 52 derived from the film-forming agent is formed on the particle surfaces 47 of the negative electrode active material 42, a film 51 derived from the solvent and a film 53 derived from other components are formed in this order.

[0037] 7 shows a part of a cross section of a negative electrode 401 having a pore volume within the appropriate range. When the pore volume of the negative electrode 401 is within the appropriate range, the coating film 52 derived from the coating agent can be formed in the intraparticle voids 46 and uniformly on the particle surfaces 47.

[0038] However, the present inventors found that, based on data on differential capacity (dQ / dV) when a plurality of secondary batteries manufactured by the same method were initially charged, and on elemental analysis of the coating by ICP (Inductively Coupled Plasma) analysis or the like for each secondary battery after the initial charge, when the negative electrode 402 has a pore volume exceeding the upper limit of the appropriate range, the amount of the coating 52 derived from the coating agent is not uniform, and the resistance increases rapidly. Here, "differential capacity (dQ / dV)" indicates the amount of change in capacity per unit voltage. Differential capacity is an index indicating the reaction amount of the coating formation reaction in which the coating agent, the non-aqueous solvent, etc. are decomposed to form a coating.

[0039] 7 shows a part of a cross section of a negative electrode 402 whose pore volume exceeds the upper limit of the appropriate range. When the pore volume of the negative electrode 402 exceeds the upper limit of the appropriate range, the coating 52 derived from the coating agent is formed in the intraparticle voids 46 and may be formed non-uniformly on the particle surfaces 47. This is thought to be one of the reasons why the coating 52 derived from the coating agent is preferentially formed in the intraparticle voids 46, which are more reactive than the particle surfaces 47, due to the initial charge, since the amount of pores (defects) in the negative electrode active material 42 tends to be greater as the pore volume of the negative electrode 402 increases.

[0040] When the coating film 52 derived from the coating agent is preferentially formed in the intraparticle voids 46, the dispersion of the coating agent in the nonaqueous electrolyte becomes uneven, and the amount of the coating film 52 derived from the coating agent formed on the particle surface 47 may be locally reduced. In this case, in the portion where the amount of the coating film 52 derived from the coating agent is locally reduced, the decomposition reaction of the nonaqueous solvent occurs, and the solvent-derived coating 51 is excessively formed, so that the amount of the solvent-derived coating 51 is locally increased. As a result, a non-uniform coating is easily formed on the surface of the negative electrode 402 including the particle surface 47. Therefore, compared to when the coating film 52 derived from the coating agent is uniformly formed, the resistance of the negative electrode 402 increases, and there is a risk that the durability of the secondary battery, such as the capacity retention rate, may decrease.

[0041] In contrast, the secondary battery 10 manufactured by the manufacturing method for the secondary battery 10 according to the present embodiment has the negative electrode 40 shown in Fig. 3. As shown in Fig. 3, the coating formed on the surface of the negative electrode 40 includes a solvent-derived coating 51 formed in the intra-particle voids 46 by charging in the first conditioning step. The coating formed on the surface of the negative electrode 40 includes a coating-forming agent-derived coating 52, a solvent-derived coating 51, and a coating 53 derived from other components, each of which is uniformly formed on the particle surface 47 by charging in the second conditioning step.

[0042] In this manner, according to the method for manufacturing the secondary battery 10 of this embodiment, the intra-particle voids 46 are filled in advance with the solvent-derived coating 51, and then the coating-forming agent-derived coating 52 is formed, so that a secondary battery 10 can be manufactured in which a uniform and excellent coating is formed on the surface of the negative electrode 40 including the negative electrode active material 42 having the intra-particle voids 46.

[0043] Returning to Fig. 1, an example of each of steps S1 to S10 included in the manufacturing method of the secondary battery 10 will be described in detail. Step S1 is a pore volume acquisition step of acquiring the pore volume of the negative electrode 40 including the negative electrode active material 42 having intra-particle voids 46. In the pore volume acquisition step, first, the negative electrode 40 to be used in the secondary battery 10 to be manufactured is prepared.

[0044] (Negative electrode 40) The negative electrode 40 can be produced, for example, by the following procedure. A paste or slurry-like composition for forming a negative electrode composite layer is prepared by adding a solvent capable of dissolving or dispersing the binder to a powder containing the negative electrode active material 42 and, if necessary, a binder, a thickener, and the like, and kneading the mixture. The composition for forming a negative electrode composite layer thus prepared is applied to at least one surface of the negative electrode current collector 41, except for a portion along one edge in the width direction, dried, and then compressed (pressed), thereby producing the negative electrode 40.

[0045] The produced negative electrode 40 has a negative electrode current collector 41 and a negative electrode mixture layer 43 containing a negative electrode active material 42 formed on the negative electrode current collector 41. As described above, the negative electrode mixture layer 43 may further contain any components such as a binder and a thickener.

[0046] The negative electrode current collector 41 is made of a metal having good electrical conductivity (for example, copper, a copper alloy, etc.). In this embodiment, a copper foil is used as the sheet-like negative electrode current collector 41, but the shape of the negative electrode current collector 41 is not limited to a sheet shape and can be appropriately changed according to the shape of the secondary battery 10, etc.

[0047] The negative electrode active material 42 is a particulate material capable of absorbing and releasing lithium ions. The negative electrode active material 42 has a large number of voids (pores) inside the particles. Intra-particle voids 46, which are voids formed inside the particles of the negative electrode active material 42, include micropores. The micropores refer to pores with a pore diameter of 2 nm or less. As such a negative electrode active material 42, for example, carbon materials such as graphite, hard carbon, soft carbon, etc. can be used alone or in combination. In addition, the surface of the negative electrode active material 42 may be coated with an amorphous carbon film.

[0048] Graphite is preferable as the negative electrode active material 42 because it has advantages such as a relatively high capacity per unit volume, excellent cost and durability. Examples of graphite include natural graphite and artificial graphite. Examples of natural graphite include flake graphite and spheroidized natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite.

[0049] The average particle size (D50) of the negative electrode active material 42 is not particularly limited, but is preferably, for example, 7.0 μm to 14 μm. The average particle size (D50) of the negative electrode active material 42 can be determined, for example, by particle size distribution measurement using a laser diffraction scattering method.

[0050] As the binder, any binder that can be used in a lithium ion secondary battery can be used without any particular limitation. As the binder, for example, rubbers such as styrene butadiene rubber (SBR), polyethylene oxide (PEO), styrene acrylic acid ester (St-Ac), vinyl acetate copolymer, etc. can be suitably used. In addition, additives such as a thickener can be used as appropriate. As the thickener, for example, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), polyvinyl alcohol (PVA), etc. can be used.

[0051] The solvent is appropriately selected depending on the binder used. Examples of the solvent include non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK), dimethylformamide (DMF), and toluene, mixed solvents of non-aqueous solvents, and aqueous solvents such as water or mixed solvents mainly composed of water.

[0052] The density of the negative electrode mixture layer 43 is not particularly limited, but is, for example, 1.0 g / cm 3 ~1.6g / cm 3 The thickness of negative electrode mixture layer 43 is not particularly limited, but is preferably, for example, 20 μm to 150 μm.

[0053] In the negative electrode 40, the pore volume derived from pores having a pore diameter of 0.26 nm to 0.74 nm (hereinafter, sometimes referred to as micropores) determined by the MP method is preferably, for example, 0.0020 mL / g to 0.0023 mL / g. When the pore volume is within this range, the coating is formed uniformly, and the performance of the negative electrode active material 42 can be suitably exhibited. The pore volume of the negative electrode 40 can be determined, for example, by pore distribution measurement using a gas adsorption method.

[0054] For example, a plurality of measurement samples may be cut from the negative electrode 40, and the pore volume of the negative electrode 40 may be obtained by measuring the specific surface area and pore distribution of the cut measurement samples using a specific surface area and pore distribution measuring device. In the gas adsorption method, the measurement sample is first evacuated and N2 is enclosed to adsorb N2 to the measurement sample. As the amount of N2 enclosed increases, N2 is adsorbed in multiple layers on the surface of the measurement sample. Then, based on the relationship between the amount of N2 adsorbed in the measurement sample and the pressure change, the pore volume of the negative electrode 40 can be calculated from the BET (Brunauer Emmett Teller) formula. The pore volume of the negative electrode 40 obtained in this way differs for each negative electrode 40.

[0055] [Battery assembly construction process (step S2)] Step S2 is a battery assembly construction process in which a battery assembly is constructed in which an electrode body 20 having a positive electrode 30 and a negative electrode 40 is housed in a battery case 11 as an exterior body. In the battery assembly construction process, in addition to the negative electrode 40 prepared in step S1, a positive electrode 30 and a separator 50 to be used in the secondary battery 10 to be manufactured are prepared.

[0056] (positive electrode 30) The positive electrode 30 can be produced, for example, by the following procedure. A paste or slurry-like composition for forming a positive electrode composite layer is prepared by adding a solvent capable of dissolving or dispersing the binder to a powder containing a positive electrode active material and, if necessary, a conductive material, a binder, etc., and kneading the mixture. The composition for forming a positive electrode composite layer thus prepared is applied to at least one surface of the positive electrode current collector 31, except for a portion along one edge in the width direction, dried, and then compressed (pressed), thereby producing the positive electrode 30.

[0057] The produced positive electrode 30 has a positive electrode current collector 31 and a positive electrode mixture layer 33 containing a positive electrode active material formed on the positive electrode current collector 31. As described above, the positive electrode mixture layer 33 may further contain any component such as a conductive material and a binder.

[0058] The positive electrode current collector 31 is made of a metal having good electrical conductivity (for example, aluminum, an aluminum alloy, etc.). In this embodiment, an aluminum foil is used as the sheet-like positive electrode current collector 31, but the shape of the positive electrode current collector 31 is not limited to a sheet shape and can be appropriately changed according to the shape of the secondary battery 10, etc.

[0059] As the positive electrode active material, any positive electrode active material that can absorb and release lithium ions and can be used in a lithium ion secondary battery can be used without any particular limitation. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), etc. can be used alone or in combination. In addition, other metal elements may be added to the positive electrode active material.

[0060] The average particle size (D50) of the positive electrode active material is not particularly limited, but is preferably 3.0 μm to 8.0 μm, and more preferably 4.0 μm to 6.0 μm. The average particle size (D50) of the positive electrode active material can be measured by particle size distribution measurement using, for example, a laser diffraction scattering method.

[0061] As the conductive material, any conductive material that can be used in a lithium ion secondary battery can be used without any particular limitation. For example, carbon black such as acetylene black, activated carbon, graphite, carbon materials such as carbon nanotubes, etc. can be used alone or in combination.

[0062] The binder can be any binder that can be used in lithium ion secondary batteries without any particular limitations. The binder can be, for example, a vinyl halide resin such as polyvinylidene fluoride (PVDF) or a polyalkylene oxide such as polyethylene oxide (PEO). The solvent is appropriately selected according to the binder used, and can be the same as that of the negative electrode 40.

[0063] The density of the positive electrode mixture layer 33 is not particularly limited, but is, for example, 1.8 g / cm 3 ~3.0g / cm 3 The thickness of positive electrode mixture layer 33 is not particularly limited, but is preferably, for example, 20 μm to 130 μm.

[0064] (Separator 50) The separator 50 is made of a porous insulating resin sheet such as polyethylene (PE) or polypropylene (PP). Such a porous resin sheet may have a single layer structure or a laminated structure of two or more layers. In addition, the resin sheet may have a porous heat-resistant layer on a part of its surface.

[0065] (Electrode body 20) The electrode body 20 is produced using the positive electrode 30, the negative electrode 40, and the separator 50 prepared as described above. In producing the electrode body 20, the positive electrode 30, the negative electrode 40, and two separators 50 are first stacked together so that the positive electrode mixture layer 33 and the negative electrode mixture layer 43 face each other through the separator 50. At this time, the positive electrode 30 and the negative electrode 40 are stacked together with a slight shift in the width direction so that the exposed parts of the positive and negative electrode current collectors 31 and 41 protrude outward from both sides of the separator 50 in the width direction. Next, the stacked positive electrode 30, the negative electrode 40, and the two separators 50 are wound in the longitudinal direction, and compressed into a flat shape having a predetermined thickness to form the electrode body 20 (wound electrode body) in a flat tube shape.

[0066] Next, the positive electrode current collector 18 connected to the positive electrode terminal 16 is joined to the positive electrode current collector, and the negative electrode current collector 19 connected to the negative electrode terminal 17 is joined to the negative electrode current collector. This electrically connects the positive and negative electrodes 30, 40 of the electrode body 20 to the positive and negative electrode terminals 16, 17. Note that the joining of the positive and negative electrodes 30, 40 to the positive and negative electrode terminals 16, 17 can be performed by using a method such as ultrasonic welding or resistance welding.

[0067] Then, the electrode body 20 is accommodated inside the case body 12 through the opening of the prepared case body 12. Thereafter, the opening of the case body 12 is closed with the lid 13, and these are joined together to form the battery case 11. In this manner, a battery assembly in which the electrode body 20 is accommodated in the battery case 11 can be constructed.

[0068] [First injection step (step S3)] Step S3 is a first injection step of injecting a nonaqueous electrolyte solution that does not contain a film-forming agent capable of forming a film on the surface (including the particle surface 47 and the wall surface of the intra-particle void 46) of the negative electrode active material 42 into the battery case 11 of the battery assembly. In the first injection step, the above-mentioned first nonaqueous electrolyte solution is prepared as a nonaqueous electrolyte solution that does not contain a film-forming agent.

[0069] After the first nonaqueous electrolyte solution is injected, the pressure inside the battery case 11 may be appropriately reduced as necessary to impregnate the first nonaqueous electrolyte solution into the electrode body 20. After the first nonaqueous electrolyte solution is injected, the injection port 14 may be temporarily sealed using the sealing member 15 until removal of the first nonaqueous electrolyte solution is started or until the second nonaqueous electrolyte solution is injected.

[0070] [Pore volume determination step (step S4)] Step S4 is a pore volume determination step in which, if it is determined that the acquired pore volume exceeds the upper limit of the appropriate range, the process proceeds to a charged electricity quantity estimation step. In the pore volume determination step, first correlation data is acquired that can determine whether the pore volume acquired in the pore volume acquisition step exceeds the upper limit of the appropriate range.

[0071] Fig. 4 is a diagram showing an example of the first correlation data. As shown in Fig. 4, the first correlation data is data showing the correlation between the pore volume and the resistance. Such first correlation data can be obtained in advance by an experiment, a simulation, or the like.

[0072] Specifically, first, a plurality of test battery assemblies having different pore volumes in the negative electrode 40 are prepared. Next, each test battery assembly is charged with a required amount of the second nonaqueous electrolyte, and then aged as necessary, and the resistance of each test battery assembly is measured. Based on the results of such resistance measurements, a correlation between the pore volume of the negative electrode 40 and the resistance of the test battery assembly is obtained, whereby the first correlation data can be created.

[0073] The test battery assembly prepared here has the same configuration as the battery assembly constructed in the pore volume acquisition step and the battery assembly construction step when manufacturing the target secondary battery 10.

[0074] In this embodiment, based on the measurement result of the resistance, the range in which the resistance does not increase suddenly is set as the appropriate range of the pore volume of the negative electrode 40. In the pore volume determination step, it is determined whether the pore volume acquired in the pore volume acquisition step exceeds the upper limit of the appropriate range, and if it is determined that it exceeds the upper limit of the appropriate range, the process proceeds to the charging electricity amount estimation step described later. On the other hand, in the pore volume determination step, if it is determined that the pore volume acquired in the pore volume acquisition step does not exceed the upper limit of the appropriate range, the process proceeds to the second injection step described later. By providing the pore volume determination step, multiple steps can be omitted when the pore volume of the negative electrode 40 is within the appropriate range.

[0075] [Charged electricity amount estimation process (step S5)] Step S5 is a charge quantity estimation step for estimating a charge quantity for forming a solvent-derived coating 51 in the intra-particle void 46 according to the acquired pore volume. In the charge quantity correction step, first, the resistance of the battery assembly is estimated based on the pore volume acquired in the pore volume acquisition step. The resistance of the battery assembly can be calculated (estimated) by referring to the pore volume acquired in the pore volume acquisition step with first correlation data as data showing the correlation between the pore volume and resistance acquired in advance.

[0076] Next, second correlation data corresponding to the estimated resistance is obtained. FIG. 5 is a diagram showing an example of the second correlation data. As shown in FIG. 5, the second correlation data is data showing the correlation between the charged electric quantity and the resistance. Such second correlation data can be obtained in advance by an experiment, a simulation, or the like.

[0077] Specifically, first, a plurality of test battery assemblies are prepared, each of which has a specific pore volume in the negative electrode 40. Next, each test battery assembly is charged with a required amount of the first nonaqueous electrolyte, and the first nonaqueous electrolyte is removed as necessary. In this charging, the plurality of test secondary battery assemblies are charged to a voltage corresponding to a different amount of charge electricity. Next, each test battery assembly is charged with a required amount of the second nonaqueous electrolyte, and then the test secondary battery assemblies are charged with a predetermined amount of charge, and then the test secondary battery assemblies are aged as necessary, and the resistance of each test secondary battery assemblies is measured. Based on the measurement results of such resistance, the correlation between the amount of charge electricity and the resistance of the test battery assemblies is obtained, and the second correlation data can be created. The test battery assemblies prepared here have the same configuration as the battery assemblies constructed by the pore volume acquisition process and the battery assembly construction process when manufacturing the secondary battery 10 to be manufactured.

[0078] The charged quantity of electricity for forming the solvent-derived coating 51 in the intra-particle voids 46 is a charged quantity of electricity that can correct the difference between the target resistance and the estimated resistance. The charged quantity of electricity can be calculated (estimated) by referring to the target resistance and second correlation data, which is data indicating the correlation between the charged quantity of electricity and resistance obtained in advance.

[0079] Alternatively, in the charging quantity of electricity estimation step, third correlation data may be acquired as data showing the correlation between the pore volume and the charging quantity of electricity based on the above-mentioned first correlation data and second correlation data. FIG. 6 is a diagram showing an example of the third correlation data. The graph in FIG. 6 can be created by taking the pore volume on the horizontal axis and the charging quantity of electricity acquired for each pore volume on the vertical axis after acquiring the charging quantity of electricity that can correct the above-mentioned difference for each pore volume.

[0080] The third correlation data shown in Fig. 6 indicates that when the pore volume of the negative electrode 40 exceeds the upper limit of the appropriate range, the required amount of charging electricity increases as the pore volume increases. When the third correlation data is used, the amount of charging electricity can be calculated (estimated) by referring to the pore volume acquired in the pore volume acquisition step as data showing the correlation between the pore volume acquired in advance and the amount of charging electricity. By using the third correlation data, it is not necessary to estimate the resistance of the battery assembly, and the amount of charging electricity can be easily obtained from the acquired pore volume.

[0081] [First conditioning step (step S6)] Step S6 is a first conditioning step in which the battery assembly is charged (initial charging) to a first voltage corresponding to the estimated charged quantity of electricity after the first injection step. The first conditioning step causes the nonaqueous solvent to be decomposed on the wall surface of the intra-particle voids 46, and a solvent-derived coating 51 can be formed in the intra-particle voids 46.

[0082] In the first conditioning step, for example, an external power source is connected between the positive and negative terminals 16, 17 of the battery assembly into which the first nonaqueous electrolyte has been injected, and charging is performed at room temperature (usually 25°C ± 5°C) until the voltage between the positive and negative terminals 16, 17 reaches a first voltage. The charging in the first conditioning step includes at least CV charging (constant voltage charging) in which the first voltage is maintained for a predetermined time. In the first conditioning step, a solvent-derived coating 51 is formed in the intra-particle voids 46 in an amount of CV capacity equivalent to the amount of charged electricity when CV charging is performed. Since CV charging is easy to maintain a low rate (small current value) while controlling the voltage to be suitable for the formation of the solvent-derived coating 51, the solvent-derived coating 51 can be reliably formed in the intra-particle voids 46.

[0083] The charging in the first conditioning step is preferably CCCV charging (constant current constant voltage charging) including CC charging (constant current charging) for increasing the voltage until it reaches the first voltage, and CV charging for maintaining the first voltage for a predetermined time. By carrying out such CCCV charging in the first conditioning step, charging at the first voltage can be stably carried out, and a suitable solvent-derived coating 51 can be easily formed in the intra-particle voids 46.

[0084] From the viewpoint of forming a suitable solvent-derived coating 51, the time of CV charging in the first conditioning step is preferably 1 hour or more, and more preferably 3 hours or more. Moreover, the holding voltage of the CV charging in the first conditioning step is preferably in the range of 2.3 V to 2.5 V, and more preferably in the range of 2.3 V to 2.4 V.

[0085] The current value when CC charging in the first conditioning step is performed is not particularly limited and can be set as appropriate as long as it can form the solvent-derived coating 51. From the viewpoint of forming a suitable solvent-derived coating 51, the current value when CC charging in the first conditioning step is preferably, for example, 2 A or less, and more preferably 1 A or less.

[0086] [Electrolyte removal process (step S7)] Step S7 is an electrolyte solution removing step in which at least a part of the first nonaqueous electrolyte solution is removed from the battery case 11 after the first conditioning step. By performing the electrolyte solution removing step, it becomes easier to adjust the final concentration of the nonaqueous electrolyte solution. In the electrolyte solution removing step, the first nonaqueous electrolyte solution is discharged from the battery case 11. At this time, it is preferable to disassemble the battery assembly to remove the electrode body 20, and then discharge the first nonaqueous electrolyte solution.

[0087] In the electrolyte removal step, it is preferable to further perform a cleaning process in which the electrode body 20 is cleaned using a cleaning solvent. By such a cleaning process, at least a part of the first nonaqueous electrolyte can be removed from the electrode body 20. The above-mentioned nonaqueous solvents can be used as the cleaning solvent. In order to more reliably remove the first nonaqueous electrolyte from the electrode body 20, it is preferable to repeat the cleaning process multiple times. Note that if the final concentration of the nonaqueous electrolyte can be adjusted taking into account the respective concentrations of the first nonaqueous electrolyte and the second nonaqueous electrolyte, the electrolyte removal step can be omitted.

[0088] [Second injection step (step S8)] Step S8 is a second injection step of injecting a nonaqueous electrolyte solution containing a film-forming agent into the battery case 11 after the first conditioning step or the electrolyte removal step. In the second injection step, the above-mentioned second nonaqueous electrolyte solution is prepared as the nonaqueous electrolyte solution containing a film-forming agent.

[0089] The concentration of the film-forming agent in the second nonaqueous electrolyte may be 0.1% by mass or more, or 0.3% by mass or more, from the viewpoint of appropriately suppressing the decomposition of the nonaqueous solvent. On the other hand, from the viewpoint of suppressing the film-forming agent from remaining after the second conditioning step, the concentration is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less. In addition to the film-forming agent, the second nonaqueous electrolyte may contain various additives such as an overcharge inhibitor and a freeze inhibitor.

[0090] After the second nonaqueous electrolyte is injected, the pressure inside the battery case 11 may be appropriately reduced as necessary to impregnate the second nonaqueous electrolyte into the electrode body 20. After the second nonaqueous electrolyte is injected and before charging in the second conditioning step is started, the injection port 14 is sealed with the sealing member 15 to hermetically seal the battery case 11.

[0091] [Second conditioning step (step S9)] Step S9 is a second conditioning step in which, after the second injection step, the battery assembly is charged (initial charging) to a second voltage at which the film-forming agent-derived film 52 can be formed. The second conditioning step causes the film-forming agent, the non-aqueous solvent, and other components of the non-aqueous electrolyte to be decomposed on the particle surfaces 47, respectively, and allows the film-forming agent-derived film 52, the solvent-derived film 51, and the other component-derived film 53 to be formed on the particle surfaces 47.

[0092] In the second conditioning step, charging may be performed up to an upper limit voltage (for example, 4.0 V to 4.1 V) which is the voltage in a fully charged state. Charging in the second conditioning step may be performed by CC charging, CV charging, or a combination of these, CCCV charging.

[0093] The charging in the second conditioning step is preferably CCCV charging, which includes CC charging for increasing the voltage until it reaches the second voltage and CV charging for maintaining the second voltage for a predetermined time. By carrying out such CCCV charging in the second conditioning step, charging at the second voltage can be stably carried out, and a suitable coating can be easily formed on the inner surface 47 of the particle.

[0094] Regardless of which charging method is adopted, the current value when CC charging is performed is not particularly limited as long as it can form the coating 52 derived from the coating agent, and can be appropriately set in the same manner as in the first conditioning step. From the viewpoint of forming a suitable coating, the current value when CC charging is performed in the second conditioning step is, for example, preferably 10 A or less, and more preferably 5 A or less.

[0095] Furthermore, the above charging may be followed by repeated charging and discharging to a predetermined voltage (e.g., 2 to 5 times). This discharging may be performed by, for example, CC discharging (constant current discharging) in which the voltage between the positive and negative electrode terminals 16, 17 is decreased until it reaches a predetermined voltage (e.g., a lower limit voltage), or by CV discharging (constant voltage discharging) in which the above predetermined voltage is maintained for a predetermined time, or by CCCV discharging (constant current constant voltage discharging) which is a combination of these.

[0096] Regardless of which of the above discharge methods is adopted, the current value during CC discharge is not particularly limited and can be set appropriately. From the viewpoint of forming a suitable coating, the current value during CC discharge is, for example, preferably 10 A or less, more preferably 5 A or less.

[0097] [Aging process (step S10)] Step S10 is an aging step in which aging is performed on the battery assembly after the second conditioning step. The temperature condition for aging is not particularly limited and is, for example, within a range of 15° C. to 80° C. From the viewpoint of further stabilizing the coating, the temperature condition for aging is preferably within a range of 20° C. to 75° C., and more preferably within a range of 25° C. to 70° C.

[0098] The time for leaving the film for aging is not particularly limited, and is, for example, 10 minutes or more and 30 days or less. From the viewpoint of further stabilizing the coating, the time for leaving the film for aging is preferably within the range of 30 minutes or more and 14 days or less, and more preferably within the range of 1 hour or more and 7 days or less. By carrying out aging, the coating can be stabilized.

[0099] The above manufacturing method allows the secondary battery 10 to be manufactured. In the manufacturing method for the secondary battery 10 according to this embodiment, in the first conditioning step, the battery assembly into which the nonaqueous electrolyte solution not containing a film-forming agent is injected is charged up to a first voltage corresponding to the amount of charge electricity estimated according to the pore volume of the negative electrode 40. Therefore, the intra-particle voids 46 can be filled with the solvent-derived film 51.

[0100] As a result, in the second conditioning step, when the battery assembly into which the nonaqueous electrolyte containing the film-forming agent is injected is charged, the film-forming agent-derived film 52 is suppressed from being formed in the intraparticle voids 46. Therefore, compared to the case where the film-forming agent-derived film 52 is formed in the intraparticle voids 46, it is possible to suppress unevenness in the amount of the film-forming agent-derived film 52 formed on the particle surface 47. Furthermore, since the solvent-derived film 51 is formed on the uniformly formed film-forming agent-derived film 52, it is also possible to suppress unevenness in the amount of the solvent-derived film 51 formed. As a result, a uniform and good film can be formed over the entire particle surface 47, and therefore a secondary battery 10 in which a uniform and good film is formed on the surface of the negative electrode 40 can be obtained.

[0101] Next, the present disclosure will be described more specifically based on examples (test examples). Note that the present disclosure is not limited to the examples.

[0102] (Example) A secondary battery for evaluation according to the example was manufactured according to the method for manufacturing the secondary battery 10 according to the present embodiment including the above-mentioned steps S1 to S10, and an evaluation test was carried out to evaluate the resistance of the manufactured secondary battery for evaluation.

[0103] [Pore volume acquisition step (step S1)] The negative electrode 40 was fabricated as follows. Particulate natural graphite (C) was used as the negative electrode active material 42. SBR was used as the binder. CMC was used as the thickener. Ion-exchanged water was used as the solvent.

[0104] C, SBR, and CMC were weighed out so that the mass ratio of C:SBR:CMC was 98:1:1, and a required amount of ion-exchanged water was added and kneaded to prepare a paste-like composition for forming a negative electrode composite layer. The prepared composition for forming a negative electrode composite layer was applied to both sides of copper foil (thickness 8 μm) as a negative electrode current collector 41, and then dried to form a negative electrode composite layer 43 on the copper foil. The composition for forming a negative electrode composite layer had a basis weight of 6.5 mg / cm. 2Furthermore, negative electrode 40 was obtained by pressing using a press machine so that negative electrode mixture layer 43 had a density of 1.1 g / cc.

[0105] Next, the pore distribution of the obtained negative electrode 40 was measured using a specific surface area / pore distribution measuring device (TriStar II, manufactured by Shimadzu Corporation) to obtain a pore distribution with the horizontal axis representing the pore diameter (nm) and the vertical axis representing the pore volume (mL / g). From the obtained pore distribution, the pore volume (0.0024 mL / g) of the negative electrode 40 in the pore diameter range of 0.26 nm to 0.74 nm was calculated.

[0106] [Battery assembly construction process (step S2)] The positive electrode 30 was prepared as follows. The positive electrode active material was LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The NCM with the average composition represented by O2 was used. The conductive material was CNT. The binder was PVDF. The solvent was NMP.

[0107] NCM, CNT, and PVDF were weighed out so that the mass ratio of NCM:CNT:PVDF was 98:1:1, and a required amount of NMP was added and kneaded to prepare a paste-like composition for forming a positive electrode composite layer. The prepared composition for forming a positive electrode composite layer was applied to both sides of an aluminum foil (thickness 15 μm) serving as a positive electrode current collector 31, and then dried to form a positive electrode composite layer 33 on the aluminum foil. The composition for forming a positive electrode composite layer had a basis weight of 10 mg / cm. 2 Furthermore, positive electrode mixture layer 33 was pressed using a press machine so that the coating weight was 2.4 g / cc, thereby obtaining positive electrode 30.

[0108] The positive electrode 30 and the negative electrode 40 were then wound with two separators 50 having a three-layer structure (PE / PP / PE) in which a PE layer and a PP layer were laminated, and the resulting wound structure was pressed in the thickness direction to produce the electrode body 20, which is a flat-shaped wound electrode body.

[0109] The electrode body 20 thus produced was electrically connected to the positive electrode terminal 16 and the negative electrode terminal 17, and then the electrode body 20 was housed inside the case body 12 of an aluminum battery case 11. The case body 12 was then sealed with the lid 13 to construct a battery assembly in which the electrode body 20 was housed in the battery case 11.

[0110] [First injection step (step S3)] A first nonaqueous electrolyte was injected into the battery case 11 of the battery assembly through the injection port 14, and then the injection port 14 was temporarily sealed with a sealing member 15. Then, the electrode body 20 was impregnated with the first nonaqueous electrolyte under reduced pressure. The first nonaqueous electrolyte was prepared by dissolving LiPF6 as a supporting salt in EC as a nonaqueous solvent at a concentration of 1 mol / L.

[0111] [Pore volume determination step (step S4)] The first correlation data shown in FIG. 4 was created in the following manner.

[0112] Four test battery assemblies, sample Nos. 1 to 4, having different pore volumes in the negative electrode 40, were constructed by the same pore volume acquisition step and battery assembly construction step as in the examples. A second nonaqueous electrolyte solution containing LiBOB as a film-forming agent was injected into the battery case 11 of each test battery assembly constructed in this manner through the injection port 14, and then the injection port 14 was sealed with a sealing member 15 to hermetically seal the battery case 11. Then, the electrode body 20 was impregnated with the second nonaqueous electrolyte solution under reduced pressure. The second nonaqueous electrolyte solution used was the same as that used in the examples.

[0113] Next, each test battery assembly into which the second nonaqueous electrolyte was injected was subjected to CCCV charging at a current value of 5 A up to a voltage of 4.1 V under a temperature condition of 25° C. Then, aging was performed by the same aging step (step S10) as in the example, and the resistance was measured in the same manner as in the example. The graph of FIG. 4 was created as data showing the correlation between the pore volume of the negative electrode 40 and the resistance by plotting the pore volume on the horizontal axis and the resistance on the vertical axis.

[0114] The horizontal axis of the graph shown in Fig. 4 indicates the pore volume (%) of the negative electrode 40 of Sample Nos. 1 to 4 expressed as a relative percentage when the pore volume value of the negative electrode 40 of Sample No. 1 is set as the reference (100%). The vertical axis of the graph shown in Fig. 4 indicates the resistance (%) of the test battery assemblies of Samples Nos. 1 to 4 expressed as a relative percentage when the resistance value of the test battery assembly of Sample No. 1 is set as the reference (100%), and it can be said that the higher the percentage value, the higher the resistance.

[0115] As shown in FIG. 4, the pore volumes and resistances of Samples Nos. 1 to 4 were as follows. Sample No. 1: Pore volume 100%, resistance 100% Sample No. 2: Pore volume 110%, resistance 100% Sample No. 3: Pore volume 120%, resistance 120% Sample No. 4: Pore volume 130%, resistance 140% As can be seen from this result, it was confirmed that when the pore volume of the negative electrode 40 increases by more than 10% from the reference, the resistance increases rapidly. Therefore, the upper limit of the appropriate range of the pore volume of the negative electrode 40 was set to 110%. And, when the resistance value of the test battery assembly of sample No. 1 is expressed as a relative percentage when the resistance value is set as the reference (100%), the pore volume of the negative electrode 40 obtained in the example is 113%. Therefore, it can be determined that the pore volume of the negative electrode 40 obtained in the example exceeds the upper limit of the appropriate range, and therefore the charging electricity amount estimation process was carried out.

[0116] [Charged electricity amount estimation process (step S5)] By referring to the pore volume (113%) of the negative electrode 40 obtained in the example in the first correlation data obtained as described above, it was estimated that if the pore volume increases by 3% beyond the upper limit of the appropriate range (110%), the resistance will increase by 5%.

[0117] In addition, the second correlation data shown in FIG. 5 was created in the following manner. Four test battery assemblies, sample Nos. 5 to 8, in which the negative electrode 40 has a specific pore volume (113%), were constructed by the same pore volume acquisition step and battery assembly construction step as in the embodiment. Next, the first nonaqueous electrolyte was injected into the battery case 11 of each of the constructed test battery assemblies through the injection port 14 by the same first injection step as in the embodiment, and then the injection port 14 was temporarily sealed with the sealing member 15. Then, the electrode body 20 was impregnated with the first nonaqueous electrolyte under reduced pressure. The first nonaqueous electrolyte was the same as in the embodiment. Then, CCCV charging was performed at a current value of 5A for each of the test battery assemblies, into which the first nonaqueous electrolyte was injected, up to a voltage corresponding to any one of the charge electric quantities of 45mAh, 90mAh, and 105mAh. At this time, the test battery assembly of sample No. 5 was not charged.

[0118] Next, the first nonaqueous electrolyte was removed and each test battery assembly was reconstructed by the electrolyte removal step similar to that of the embodiment. Next, in the second injection step, a second nonaqueous electrolyte containing LiBOB as a film-forming agent was injected from the injection port 14 into the battery case 11 of each reconstructed test battery assembly, and then the injection port 14 was sealed with a sealing member 15 to hermetically seal the battery case 11. Then, the electrode body 20 was impregnated with the second nonaqueous electrolyte under reduced pressure. The second nonaqueous electrolyte used was the same as that of the embodiment.

[0119] Then, each test battery assembly into which the second nonaqueous electrolyte was injected was subjected to CCCV charging at a current value of 5 A up to a voltage of 4.1 V under a temperature condition of 25° C. Furthermore, the resistance was measured after aging in the same aging process as in the examples. The graph in FIG. 5 was created as data showing the correlation between the charged amount of electricity and the resistance by plotting the horizontal axis of the charge electric charge and the vertical axis of the resistance.

[0120] The horizontal axis of the graph shown in FIG. 5 indicates the amount of charge electricity (mAh) of the charge performed on each of the test battery assemblies of samples No. 5 to No. 8 into which the first nonaqueous electrolyte was injected. However, in the case of the test battery assembly of sample No. 5, which was not charged, the amount of charge electricity is set to 0 mAh. The vertical axis of the graph shown in FIG. 5 indicates the resistance (%) of the test battery assemblies of samples No. 5 to No. 8 expressed as a relative percentage when the resistance value of the test battery assembly of sample No. 5 is set as the reference (100%), and it can be said that the smaller the percentage value, the more the resistance is reduced. Here, in this embodiment, the target resistance was set to 100%.

[0121] As shown in FIG. 5, the charged electric quantity and resistance of Samples Nos. 5 to 8 were as follows. Sample No. 5: Charged electricity amount 0mAh, resistance 105% Sample No. 6: Charged electricity amount 45mAh, resistance 105% Sample No. 7: Charged electricity amount 90mAh, resistance 100% Sample No. 8: Charged electricity amount 105mAh, resistance 115% From the results of sample No. 7, it was confirmed that the resistance could be reduced by 5% when the charging amount of electricity was set to 90 mAh.

[0122] Then, by referring to the target resistance (100%) in the second correlation data obtained in the manner described above, the amount of charging electricity that can correct the difference (5% increase) between the estimated resistance and the target resistance was estimated to be 90 mAh.

[0123] [First conditioning step (step S6)] The first voltage was set to 2.4 V corresponding to a charge quantity of 90 mAh. After the first injection step was completed, the battery assembly into which the first nonaqueous electrolyte solution had been injected was subjected to CC charging at a current value of 1 A up to a voltage of 2.4 V under a temperature condition of 25° C., and then to CV charging in which the voltage was maintained at 2.4 V for 3 hours.

[0124] [Electrolyte removal process (step S7)] After the first conditioning step was completed, the battery assembly was disassembled, the electrode body 20 was removed, and the first nonaqueous electrolyte was discharged from the battery case 11. Furthermore, the removed electrode body 20 was subjected to a cleaning treatment using EMC as a cleaning solvent. In this manner, the first nonaqueous electrolyte was removed from the battery case 11. Then, the battery assembly was reconstructed using the electrode body 20 after the cleaning treatment.

[0125] [Second injection step (step S8)] A second nonaqueous electrolyte containing LiBOB as a film-forming agent was injected from the injection port 14 into the battery case 11 of the reconstructed battery assembly, and then the injection port 14 was sealed with a sealing member 15 to hermetically seal the battery case 11. The second nonaqueous electrolyte was then impregnated into the electrode body 20 under reduced pressure. The second nonaqueous electrolyte was prepared by dissolving 1 mol / L of LiPF6 and 0.5 mass% of LiBOB as a supporting salt in EC as a nonaqueous solvent. The injection amounts of the first nonaqueous electrolyte and the second nonaqueous electrolyte were 50% mass% when the total amount [g] of the nonaqueous electrolyte injected into the battery case 11 was taken as 100 mass%.

[0126] [Second conditioning step (step S9)] The second voltage was set to 4.1 V, which corresponds to the amount of charge electricity in a fully charged state. The battery assembly into which the second nonaqueous electrolyte was injected was subjected to CC charging at a current value of 5 A up to a voltage of 4.1 V under a temperature condition of 25° C., and then subjected to CV charging at a voltage of 4.1 V. When the current value decreased to a cut-off current of 1 A, charging was terminated, and the battery was fully charged.

[0127] [Aging process (step S10)] After the second conditioning step, aging was performed by leaving the battery assembly for 5 hours under a temperature condition of 60° C. In this manner, a secondary battery for evaluation according to the example was manufactured.

[0128] [Evaluation test] After the aging process was completed, the impedance of the evaluation secondary battery adjusted to SOC 60% was measured in a temperature environment of -30°C. The resistance (Ω) was calculated from the arc of the Nyquist plot. The impedance measurement was performed at -30°C, a frequency of 10 6 The test was performed under conditions of 0.01 Hz and a current amplitude of 0.2 A.

[0129] As a result of the evaluation test, by setting the amount of charge electricity during charging in the first conditioning step to 90 mAh, the resistance of the evaluation secondary battery according to the example could be reduced to 100%, which is the target resistance.

[0130] The present disclosure is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present disclosure. [Explanation of symbols]

[0131] 10 Secondary battery 11 Battery case 12 Case body 13 Lid 14 Inlet 15 Sealing member 16 Positive terminal 17 Negative terminal 18 Positive current collector 19 Negative current collector 20 Electrode body 30 positive electrode 31 Positive electrode current collector 33 Positive electrode mixture layer 40 negative electrode 41 Negative electrode current collector 42 Negative electrode active material 43 Negative electrode composite layer 46 Intraparticle voids 47 Particle surface 50 Separator 51 Solvent-derived coatings 52 Films derived from film-forming agents 53 Films derived from other components 401, 402 negative electrode

Claims

1. a pore volume acquiring step of acquiring a pore volume of a negative electrode including a negative electrode active material having voids inside particles; a battery assembly construction step of constructing a battery assembly in which an electrode body having a positive electrode and the negative electrode is housed in an outer casing; a first injection step of injecting a non-aqueous electrolyte solution that does not contain a film-forming agent capable of forming a film on a surface of the negative electrode active material into the exterior body; a charging electricity quantity estimating step of estimating a charging electricity quantity required for forming a coating film derived from the nonaqueous electrolyte in the pores based on the obtained pore volume; a first conditioning step of charging the battery assembly to a first voltage corresponding to the estimated charged quantity of electricity after the first injection step; a second injection step of injecting a nonaqueous electrolyte solution containing the film-forming agent into the exterior body after the first conditioning step; a second conditioning step of charging the battery assembly to a second voltage at which a film derived from the film-forming agent can be formed, the second conditioning step being performed after the second injection step; A method for manufacturing a secondary battery having the above structure.

2. The method for producing a secondary battery according to claim 1 , further comprising a pore volume determining step of proceeding to the charged electric quantity estimating step when it is determined that the acquired pore volume exceeds an upper limit of an appropriate range.

3. The method for manufacturing a secondary battery according to claim 1 , further comprising an aging step of subjecting the battery assembly to aging after the second conditioning step.

4. The method for producing a secondary battery according to claim 1 , wherein the charged quantity of electricity is calculated by referring to previously acquired data showing a correlation between the pore volume and the charged quantity of electricity.

5. 2. The method for manufacturing a secondary battery according to claim 1, wherein the charging in the first conditioning step includes CC charging in which the voltage is increased until it reaches the first voltage, and CV charging in which the first voltage is maintained for a predetermined period of time.

6. 2. The method for manufacturing a secondary battery according to claim 1, wherein the charging in the second conditioning step includes CC charging in which the voltage is increased until it reaches a second voltage, and CV charging in which the second voltage is maintained for a predetermined period of time.

7. The method for producing a secondary battery according to claim 1 , wherein the negative electrode active material contains graphite.

8. The method for producing a secondary battery according to claim 1 , wherein the film-forming agent contains lithium bis(oxalato)borate.

9. The method for producing a secondary battery according to claim 1 , wherein the non-aqueous electrolyte contains ethylene carbonate as a non-aqueous solvent.

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