Method for manufacturing a lithium-ion secondary battery and lithium-ion secondary battery

Abstract

The present invention provides a method for manufacturing a lithium-ion secondary battery that suppresses the increase in ESR, and a lithium-ion secondary battery. [Solution] A method for manufacturing a lithium-ion secondary battery includes a Si coating step, a negative electrode formation step, and a battery assembly step. In the Si coating step, SiO x or SiO x (OH) 4-2X (0

Description

[Technical Field]

[0001] This invention relates to lithium-ion secondary batteries and methods for manufacturing them. [Background technology]

[0002] A lithium-ion secondary battery consists of a positive electrode and a negative electrode facing each other via a separator within an electrolyte layer containing an electrolyte, a solid electrolyte, or a combination thereof. It charges and discharges according to the direction of lithium ion absorption and release between the positive and negative electrodes. In a lithium-ion secondary battery, lithium ions are released from the positive electrode and absorbed into the negative electrode during charging and discharging, and released from the negative electrode and absorbed into the positive electrode during discharging. This lithium-ion secondary battery has the advantages of being able to operate at high voltages and having a high energy density.

[0003] A lithium-ion secondary battery comprises a positive electrode and a negative electrode containing an active material that reversibly absorbs and releases lithium ions, and an electrolyte layer of lithium salt. The positive electrode and the negative electrode are each formed by integrating the active material layer with a current collector. The positive electrode active material and the current collector, and the negative electrode active material and the current collector, are each joined via a binder using crimping or a doctor blade method.

[0004] For example, lithium-ion secondary batteries typically use lithium nickelate or lithium cobaltate as the positive electrode active material, graphite as the negative electrode active material, lithium hexafluoride phosphate as the electrolyte, and a non-aqueous solvent as the solvent for the electrolyte (see, for example, Patent Document 1).

[0005] In recent years, the development of electric vehicles (EVs) and hybrid electric vehicles (HEVs), which use electric motors to assist in part of the drive system, has been rapidly progressing at various automobile manufacturers. The lithium-ion secondary batteries used in these vehicles require high rate characteristics; that is, they must be capable of charging and discharging at high currents. The technological fields requiring high rate characteristics for lithium-ion secondary batteries extend far beyond automotive applications such as electric vehicles and hybrid electric vehicles.

[0006] Therefore, a method has been proposed to increase the BET specific surface area of ​​the negative electrode active material particles by bonding the secondary particles of the negative electrode active material particles to form a three-dimensional network structure, for example (see, for example, Patent Document 2). The negative electrode active material particles with an increased BET specific surface area have appropriate voids, which allows the electrolyte to be impregnated. As a result, the movement of ions in the electrolyte within the electrode becomes smoother. This enables charging and discharging with high currents. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2011-204571 [Patent Document 2] Japanese Patent Publication No. 2016-115912 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] For example, Li4Ti5O 12 Our diligent research has revealed that by using lithium titanate, represented by [formula], the BET specific surface area of ​​the negative electrode active material particles can be increased to the extent that the initial ESR is reduced. Moreover, lithium titanate has a charge / discharge potential of approximately 1.55V (vs. Li / Li) compared to graphite and hard carbon. + It has high performance, excellent safety, and stable battery characteristics even after a large number of charge-discharge cycles.

[0009] However, it became clear that increasing the BET specific surface area to the extent possible by using lithium titanate results in a large amount of moisture adhering to the negative electrode active material particles. This large amount of moisture then degrades the ESR of the lithium-ion secondary battery at a charge-discharge cycle count where lithium titanate is advantageous in terms of battery characteristic stability.

[0010] Therefore, even if the BET specific surface area is increased and the initial ESR is reduced by using lithium titanate, when the number of charge cycles reaches a range where lithium titanate is advantageous, the ESR increases and the rate performance deteriorates. Moreover, the operation of reducing the once-attached moisture is inefficient.

[0011] For example, when a negative electrode is formed by the same manufacturing method, during the formation process of this negative electrode, the negative electrode active material particles with a BET specific surface area of 9.6 m 2 / g contained 4000 ppm of moisture. On the other hand, the negative electrode active material particles with a BET specific surface area increased to 58 m 2 / g using lithium titanate contained as much as 9000 ppm of moisture. And even when dried at 160°C for 12 hours, the negative electrode active material particles with a BET specific surface area increased to 58 m 2 / g using lithium titanate still had more than 733 ppm of moisture remaining. For the negative electrode active material particles with a BET specific surface area of 9.6 m 2 / g, it decreased to about 470 ppm under the same drying conditions.

[0012] The present invention has been proposed to solve the above problems, and its object is to provide a method for manufacturing a lithium-ion secondary battery and a lithium-ion secondary battery in which an increase in ESR is suppressed.

Means for Solving the Problems

[0013] To solve the above problems, the method for manufacturing a lithium-ion secondary battery according to this embodiment is SiO x or SiO x (OH) 4-2XAn Si coating step of producing a negative electrode active material powder containing lithium titanate particles to which a silicon oxide of (0 < x ≤ 2) is attached, a negative electrode forming step of forming a negative electrode by laminating a negative electrode active material layer containing the negative electrode active material powder on a negative electrode current collector, and a battery assembling step of opposing the negative electrode to a positive electrode and interposing an electrolyte between the positive electrode and the negative electrode, wherein in the negative electrode forming step, a negative electrode active material powder having a water content of 15,000 ppm or less with respect to the negative electrode active material powder and having the silicon oxide of 0.73 wt% or more and 2.9 wt% or less attached to the negative electrode active material powder is used for formation.

[0014] In the Si coating step, the silicon oxide of 2.4 wt% or more and 2.9 wt% or less with respect to the negative electrode active material powder may be attached to the lithium titanate particles.

[0015] The Si coating step may include a mixing step of mixing the lithium titanate particles and a raw material of the silicon oxide, and a firing step of firing the powder obtained by the mixing step at 300°C or higher and 600°C or lower.

[0016] The Si coating step may be such that the silicon oxide is attached to the lithium titanate particles having a BET specific surface area of 40 m 2 / g or more.

[0017] Also, in order to solve the above problems, a lithium ion secondary battery of the present embodiment includes a positive electrode, a negative electrode having a negative electrode active material layer containing a negative electrode active material powder, and an electrolyte, and the negative electrode active material powder contains lithium titanate particles to which a silicon oxide such as SiO x or SiO x (OH) 4-2X (0 < x ≤ 2) is attached, and the negative electrode active material layer is formed using the negative electrode active material powder having a BET specific surface area of 40 m 2 / g or more, a water content of 15,000 ppm or less, and a content of the silicon oxide of 0.73 wt% or more and 2.9 wt% or less with respect to the negative electrode active material powder.

Effects of the Invention

[0018] According to the present invention, it is possible to suppress the increase in ESR associated with the charge-discharge cycle of lithium-ion secondary batteries. [Modes for carrying out the invention]

[0019] The following describes a lithium-ion secondary battery and a manufacturing method according to an embodiment of the present invention. However, the present invention is not limited to the embodiments described below.

[0020] (Negative electrode active material powder) A lithium-ion secondary battery comprises a positive electrode and a negative electrode arranged opposite each other, and an electrolyte interposed between the positive and negative electrodes. A separator, through which the electrolyte can penetrate, is provided between the positive and negative electrodes. The separator isolates the positive and negative electrodes to prevent short circuits and also holds the electrolyte. The positive and negative electrodes are Faraday reaction electrodes in which lithium ions are reversibly inserted and removed. The positive and negative electrodes are each formed by integrating layers of active material with a current collector. The positive electrode active material and current collector, and the negative electrode active material and current collector, are joined via a binder using crimping or a doctor blade method, respectively.

[0021] The negative electrode active material layer is formed by laminating negative electrode active material powder on the current collector. In addition to the negative electrode active material powder, the negative electrode active material layer may contain a binder, a conductive additive, or both. The negative electrode active material powder is an aggregate of negative electrode active material particles and contains moisture. The negative electrode active material particles have the general formula Li α Ti β O γ These are lithium titanate particles represented by [formula], with silicon oxide attached to them.

[0022] Lithium titanate particles are preferably Li 4+w Ti5O 12 This is a spinel-type lithium titanate represented by (0 ≤ w ≤ 3). w represents the insertion and removal of lithium ions, and Li4Ti5O 12 As an intercalation compound, it has a rock salt-type structure Li7Ti5O in the reversible insertion and deinsertion of lithium.12 It forms.

[0023] These lithium titanate particles have an energy storage function through the insertion and removal of lithium ions. Because the volume change due to insertion and removal is approximately 1%, there is little capacity degradation. Furthermore, the lithium titanate particles have a charge / discharge potential of approximately 1.5V (vs Li / Li). + Therefore, side reactions such as electrolyte decomposition and lithium metal deposition due to rapid charging and discharging are less likely to occur, and it inherently has excellent cycle characteristics.

[0024] Lithium titanate particles are granules having a three-dimensional network structure formed by the interconnected arrangement of primary particles. In this three-dimensional network structure, some or all of the primary particles are connected without grain boundaries at their bonding interfaces. However, minute pores exist at the boundary-less bonding interfaces between primary particles. Furthermore, the three-dimensional network structure contains voids surrounded by rows of primary particles connected without grain boundaries. These lithium titanate particles with this three-dimensional network structure have electron paths formed by the interconnected primary particles at boundary-less bonding interfaces, electrolyte storage areas in the voids, and ion paths that pass through the pores between primary particles towards the voids.

[0025] The void ratio in the cross-section of the three-dimensional network structure is preferably in the range of 7 to 50%. If the void ratio is less than 7%, the surface area in contact with the electrolyte is small, which affects the movement of ions in the electrolyte. If the void ratio exceeds 50%, the bonding between primary particles becomes looser, making it difficult to form a three-dimensional network structure.

[0026] The average particle diameter of lithium titanate primary particles is in the range of 5 to 300 nm. The method for calculating the average particle diameter is as follows: Using a scanning electron microscope, observe the primary particles and take an image containing at least 150 primary particles. Measure the major and minor axes of the elliptical images of the primary particles contained in the captured field of view (image). Calculate the average of these major and minor axes for each primary particle, add the average values ​​of each primary particle, and divide the sum by the number of primary particles measured. The result should fall within the range of 5 to 300 nm.

[0027] When the primary particles in this range combine to form a three-dimensional network structure, the lithium titanate particles acquire many nano-sized pores between the primary particles without grain boundaries. This fine pore contains many fine pores especially with a size of 40 nm or less. In the differential pore volume converted from the pore size distribution measured by the nitrogen gas adsorption measurement method for the lithium titanate particles, the differential pore volume in the pore size range of 10 to 40 nm has a value of 0.01 cm 3 / g or more, and particularly has a value of 0.02 cm 3 / g or more.

[0028] It is preferable to form a three-dimensional network structure so that the lithium titanate particles have a BET specific surface area of 40 m 2 / g or more. A lithium ion secondary battery using lithium titanate particles having a BET specific surface area of 40 m 2 / g or more as a negative electrode active material has a low initial ESR and enables charge and discharge with a large current.

[0029] However, the structure of the lithium titanate particles is not limited, and lithium titanate particles having a BET specific surface area of less than 40 m 2 / g may be used as a negative electrode active material, and an effect of suppressing the change in ESR over time can be obtained. However, the three-dimensional network structure enables the production of lithium titanate particles having a BET specific surface area of 40 m 2 / g or more, the initial ESR is low, and the effect of suppressing the change in ESR over time becomes remarkable.

[0030] The silicon oxide adhering to the lithium titanate particles is SiO x or SiO x (OH) 4-2X (0 < x ≦ 2). The silicon oxide adheres to at least a part of the surface of the lithium titanate particles. It is preferable that the silicon oxide also adheres to the inner surface forming the voids of the internal structure of the lithium titanate particles, that is, the three-dimensional network structure. However, it remains without completely filling the voids of the three-dimensional network structure. That is, the lithium titanate particles containing silicon oxide have 0.002 dV with respect to a pore diameter of 10 nm or less p / drp It has an ultra-high pore volume change rate. Furthermore, lithium titanate particles containing silicon oxide are solid compared to lithium titanate particles without silicon oxide attached. 1 Among the peaks obtained by 1H-NMR, the integrated intensity reduction rate of the peak located at 5-8 ppm is 25% or more.

[0031] Furthermore, it is preferable that the Si coating layer made of silicon oxide be amorphous. The amorphous Si coating layer improves the bonding with lithium titanate particles. The amorphous Si coating layer adheres uniformly and closely to the lithium titanate particles, suppressing the dissolution of the Si coating layer by the electrolyte or the like.

[0032] This silicon oxide is attached to lithium titanate particles in an amount of 0.73 wt% to 2.9 wt% relative to the negative electrode active material powder. First, within this attachment ratio range, the porosity is 0.002 dV for pore sizes of 10 nm or less. p / dr p It has an ultra-low pore volume change rate, and the thickness of the Si coating layer is controlled so that the voids do not become clogged with silicon oxide. p indicates the pore volume, r p This indicates the pore size (nm), and dV p / dr p This indicates the rate of change in pore volume.

[0033] Furthermore, by using lithium titanate particles with a large BET specific surface area within the range of 0.73 wt% to 2.9 wt% of the negative electrode active material powder, the change in ESR over time in the lithium-ion secondary battery is suppressed even if it contains a large amount of moisture. In other words, this lithium-ion secondary battery has a low initial ESR, and the increase in ESR is suppressed even after repeated charge-discharge cycles.

[0034] Preferably, silicon oxide is attached to the negative electrode active material powder in an amount of 2.4 wt% to 2.9 wt%. When silicon oxide is attached to the lithium titanate particles in this range, the capacity degradation of the lithium-ion secondary battery is suppressed even after repeated charge-discharge cycles.

[0035] The moisture content of the negative electrode active material powder is 15,000 ppm or less. If the moisture content is 15,000 ppm or less, the increase in ESR can be suppressed even after repeated charge-discharge cycles by attaching silicon oxide to the lithium titanate particles in a range of 0.73 wt% to 2.9 wt% relative to the negative electrode active material powder. If silicon oxide is attached to the lithium titanate particles in a ratio of 4.1 wt% or more relative to the negative electrode active material powder, even if the moisture content is significantly below 15,000 ppm, the increase in ESR due to repeated charge-discharge cycles is unavoidable, and the ESR will worsen compared to the case where silicon oxide is not attached.

[0036] (Si coating process) Such negative electrode active material powder is produced by following a mixing step of mixing lithium titanate particles and silicon oxide, a calcination step after the mixing step, and a moisture adjustment step to adjust the moisture content of the negative electrode active material powder, in this order.

[0037] (Mixing process) In the mixing process, a mixed solution is prepared by mixing a negative electrode active material powder, which is an aggregate of lithium titanate particles and does not have silicon oxide attached, with a silicon oxide raw material. A silane coupling agent containing silicon atoms can be used as the silicon oxide raw material. Specifically, a solvent is added to a mixture of the negative electrode active material powder (without silicon oxide attached) and the silane coupling agent to form a mixed solution. Alternatively, the silane coupling agent solution may be impregnated into the negative electrode active material powder (without silicon oxide attached) under reduced pressure. Alternatively, the silane coupling agent solution may be sprayed onto the negative electrode active material powder (without silicon oxide attached) while stirring and mixing.

[0038] The silane coupling agent is preferably mixed in a ratio of 3.6 to 14.1 wt% relative to the anode active material powder that does not have silicon oxide attached. It is preferable that 0.73 to 2.9 wt% of silicon oxide, when converted to silicon oxide relative to the anode active material powder, is attached to the lithium titanate particles.

[0039] While there are no particular limitations on silane coupling agents, typical examples include compounds represented by the general formulas below, or salts thereof. [ka] (In the formula, X1 is an atomic group having a vinyl group, amino group, epoxy group, chlor group, mercapto group, ketimine group, acryloyl group, metachloroyl group, styryl group, phenyl group, isocyanate group, alkyl group, or alkoxy group; X2-X4 are alkyl group, alkoxy group, chlor group, or hydroxyl group.)

[0040] Examples of these silane coupling agents include tetraethoxysilane, vinyltrimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane hydrochloride.

[0041] As a solvent, any liquid that does not adversely affect the reaction can be used without particular limitations, and water, methanol, ethanol, isopropyl alcohol, etc., can be suitably used. Two or more solvents may also be mixed and used. The mixed solution is thoroughly stirred using a homogenizer or the like so that the negative electrode active material powder and silane coupling agent are dispersed in the mixed solution. This stirring causes the silane coupling agent to adhere to the surface of the lithium titanate particles and the inner surface of the voids in the three-dimensional network structure. The mixed solution is then allowed to stand, and the negative electrode active material powder and silane coupling agent dispersed in the mixed solution are agglomerated to recover the mixed powder of negative electrode active material powder and silane coupling agent.

[0042] Here, an alkaline compound may be further added to the mixed solution. By adding an alkaline compound, the amount of silicon oxide adhering to the silicon oxide raw material added in the manufacturing process increases, and the rate of increase in internal resistance after charging and discharging can be more effectively suppressed with a smaller amount of silane coupling agent. Alternatively, if the same suppression effect as when no alkaline compound is added is to be obtained, the amount of silicon oxide raw material added in the manufacturing process can be reduced, leading to a reduction in cost. The amount of alkaline compound added is preferably in the range of 0.05 to 5 mmol per 10 g of negative electrode active material powder.

[0043] Examples of alkali compounds include hydroxides, acetates, sulfates, carbonates, nitrates, chlorides, inorganic alkaline agents, and organic alkaline agents of alkali metals or alkaline earth metals. Examples of alkali metals and alkaline earth metals include lithium, sodium, potassium, and calcium. Examples of inorganic alkaline agents include aqueous ammonia. Examples of organic alkaline agents include amines such as triethylamine, diethylamine, pyridine, and tetramethylguanidine. These alkali compounds may be added to the mixed solution one or more of them.

[0044] Preferred alkali compounds include lithium salts, which are of the same type as the raw materials for the negative electrode active material powder or the electrolyte in the electrolyte solution, and which do not become impurities in the properties of the negative electrode active material powder, or which are removed by heat treatment during the manufacturing process and do not remain in the negative electrode active material powder.

[0045] In addition to the method of further adding an alkaline compound to the mixed solution, the negative electrode active material powder may also be pre-treated with an alkaline compound before proceeding to the mixing step with the silane coupling agent. In the pre-treatment step, the alkaline compound and the negative electrode active material powder are mixed with a solvent, filtered, and dried. The filtered and dried mixture is then used for the mixing step. After mixing, it may be left to stand at a temperature of 30 to 100°C for 1 to 100 hours. Pre-treating the negative electrode active material powder with an alkaline compound, as in this method, can further effectively suppress the increase in internal resistance after charging and discharging. The solvent and alkaline compound used in this method can be the same as those used in the method of further adding an alkaline compound to the mixed solution.

[0046] (Firing process) In the calcination process, the mixed powder obtained in the mixing process is subjected to heat treatment. The calcination treatment is carried out, for example, at a temperature range of 300 to 600°C for 1 to 24 hours. During this calcination process, silicon oxide derived from the silane coupling agent is formed in an amorphous state and adheres to the lithium titanate particles.

[0047] Furthermore, before the firing process, the aggregates obtained in the mixing process may be collected and subjected to a drying treatment. Drying is preferably done by heating, with the aggregates heated to 20-180°C. The heating time should be 6-48 hours. Through this drying process, a mixed powder is obtained in which the negative electrode active material powder and silane coupling agent are mixed, with the solvent contained in the aggregates evaporated by heating.

[0048] (moisture adjustment process) After the firing process, the moisture content of the negative electrode active material powder is adjusted. There are no particular limitations on the method of moisture adjustment, but the moisture content may be adjusted by drying, which involves leaving the powder undisturbed for a predetermined time in an environment where the atmospheric pressure, temperature, and humidity are controlled.

[0049] Here, when lithium titanate particles are coated with silicon oxide at a ratio of 0.73 wt% to 2.9 wt% relative to the negative electrode active material powder, dehydration from the negative electrode active material powder becomes easier, and the amount of moisture in the negative electrode active material powder can be adjusted to the desired amount by setting the temperature and residence time of the standing environment. If silicon oxide is not attached, the BET specific surface area is 40 m². 2 It is difficult to set the desired moisture content of the negative electrode active material powder, which is an aggregate of lithium titanate particles of a certain magnitude ( / g or more).

[0050] By fabricating a negative electrode using a negative electrode active material powder produced through a Si coating process that includes this moisture adjustment step, the increase in ESR is suppressed even as the number of charge-discharge cycles of the lithium-ion secondary battery increases.

[0051] (Lithium-ion rechargeable battery) (Negative electrode formation process) The negative electrode is formed using a negative electrode active material powder manufactured in a Si coating process, containing a moisture content of 15,000 ppm or less relative to the negative electrode active material powder, and having 0.73 wt% to 2.9 wt% of silicon oxide attached to it. The current collector of the negative electrode is typically a conductive material such as aluminum, copper, iron, nickel, titanium, steel, or carbon. In particular, aluminum or copper, which have high thermal and electronic conductivity, are preferred. The shape of the current collector can be any shape, such as film, foil, plate, mesh, expanded metal, or cylindrical.

[0052] A slurry of negative electrode active material powder and a binder is applied to this current collector, forming a negative electrode in which a layer of negative electrode active material containing the negative electrode active material powder is laminated onto the current collector. The slurry is dispersed using a mixer, jet mixing, ultracentrifugation, or other ultrasonic treatments. The slurry is then applied to the cathode foil by slurry casting, doctor blade method, or spray atomization method.

[0053] Examples of binders include rubbers such as fluoropolymers, diene-based rubbers, and styrene-based rubbers; fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride; celluloses such as carboxymethylcellulose and nitrocellulose; and other materials such as polyolefin resins, polyimide resins, acrylic resins, nitrile resins, polyester resins, phenolic resins, polyvinyl acetate resins, polyvinyl alcohol resins, and epoxy resins. These binders may be used individually or in mixtures of two or more types.

[0054] The negative electrode active material layer may contain a conductive additive. The conductive additive is fibrous carbon, carbon powder, or a mixture thereof. Fibrous carbon includes carbon nanotubes, carbon nanofibers, etc. Carbon nanotubes may be single-walled carbon nanotubes with one layer of graphene sheet, or multi-walled carbon nanotubes (MWCNTs) with two or more layers of graphene sheet rolled coaxially to form a multi-layered tube wall. Carbon powder can be natural plant tissue such as coconut shell, synthetic resins such as phenol, activated carbon derived from fossil fuels such as coal, coke, and pitch, carbon black such as Ketjenblack, acetylene black, and channel black, carbon nanohorns, non-graphitizable carbon, artificial graphite, natural graphite, pyrolysis carbons, cokes such as pitch coke, needle coke, and petroleum coke, graphites, glassy carbons, or sintered organic polymer compounds obtained by sintering phenolic resins or furan resins at an appropriate temperature.

[0055] The negative electrode active material layer may be pressure-molded into pellets by a press process, then rolled onto the current collector, or bonded to it using an adhesive. The pressure applied to the active material layer by the rolling process is generally 50,000 to 1,000,000 N / cm². 2 Preferably 100,000 to 500,000 N / cm² 2 This is within the specified range. Furthermore, there are no special restrictions on the temperature of the rolling process; the process may be carried out at room temperature or under heated conditions.

[0056] (Positive electrode formation process) The positive electrode active material is a metallic compound particle capable of intercalating and releasing lithium ions. Examples of metallic compound particles used as positive electrode active materials include layered rock salt type LiMO2, layered Li2MnO3-LiMO2 solid solution, and spinel type LiM2O4 (where M represents Mn, Fe, Co, Ni, or a combination thereof). Specific examples of these include LiCoO2, LiNiO2, and LiNi 4 / 5 Co 1 / 5 O2, LiLiLi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiLiLi 1 / 2 Mn 1 / 2 O2, LiFeO2, LiMnO2, Li2MnO3-LiCoO2, Li2MnO3-LiNiO2, Li2MnO3-LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li2MnO3-LiNi 1 / 2 Mn 1 / 2 O2, Li2MnO3-LiNi 1 / 2 Mn 1 / 2 O2-LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, LiMn 3 / 2 Ni 1 / 2 O4 is one example.

[0057] Metal compound particles used as positive electrode active materials include sulfur and Li2S, TiS2, MoS2, FeS2, VS2, and Cr. 1 / 2 V 1 / 2Sulfides such as S2, selenides such as NbSe3, VSe2, NbSe3, Cr2O5, Cr3O8, VO2, V3O8, V2O5, V6O 13 In addition to oxides such as LiNi 0.8 Co 0.15 Al 0.05 O2, LiVOPO4, LiV3O5, LiV3O8, MoV2O8, Li2FeSiO4, Li2MnSiO4, LiFePO4, LiFe 1 / 2 Mn 1 / 2 Examples include composite oxides such as PO4, LiMnPO4, and Li3V2(PO4)3.

[0058] By coating a current collector with a slurry of this positive electrode active material and a binder, a positive electrode is formed in which a layer of positive electrode active material is laminated onto the current collector. A conductive additive may be added to the slurry to contain the conductive additive within the positive electrode active material layer. The positive electrode active material layer may be pressure-molded into pellets by a press process, and then rolled onto the current collector or bonded to it using an adhesive.

[0059] (Battery assembly process) Lithium-ion secondary batteries are manufactured by placing the positive and negative electrodes opposite each other during the battery assembly process and interposing an electrolyte between them. The electrolyte is held in place by a separator. The separator is interposed between the positive and negative electrodes, holding the electrolyte between them while also insulating them from each other.

[0060] Examples of separators include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; and acrylic resins. These resins can be used individually or in mixtures.

[0061] Electrolytes can be solids, liquids, or both. Examples of electrolytes include non-aqueous electrolytes containing lithium salts that serve as lithium ion sources. Lithium salts include LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2C2F5)2, CF3SO3Li, LiC(SO2CF3)3, and LiPF3(C2F5)3, or mixtures thereof.

[0062] In addition to lithium salts, quaternary ammonium salts or quaternary phosphonium salts having a quaternary ammonium cation or a quaternary phosphonium cation can be included in the electrolyte. For example, examples of cations include tetraethylammonium, triethylmethylammonium, diethyldimethylammonium, ethyltrimethylammonium, methylethylpyrrolidinium, spirobipyrrolidinium, spiro-(N,N')-bipyrrolidinium, 1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, etc., and examples of anions include BF4. - PF6 - ClO4 - AsF6 - SbF6 - AlCl4 - , or RfSO3 - (RfSO2)2N - , RfCO2 - Examples include (where Rf is a fluoroalkyl group having 1 to 8 carbon atoms), and salts or mixtures thereof can be used.

[0063] The following solvents can be used as the electrolyte. These solvents may be used individually or in mixtures of two or more. Examples include cyclic carbonate esters, linear carbonate esters, phosphate esters, cyclic ethers, linear ethers, lactone compounds, linear esters, nitrile compounds, amide compounds, sulfone compounds, etc. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, and 4-(trifluoromethyl)-1,3-dioxolan-2-one, with ethylene carbonate and propylene carbonate being preferred.

[0064] Examples of chain-like carbonate esters include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl n-propyl carbonate, methyl isopropyl carbonate, n-butyl methyl carbonate, diethyl carbonate, ethyl n-propyl carbonate, ethyl isopropyl carbonate, n-butyl ethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, di-n-butyl carbonate, fluoroethyl methyl carbonate, difluoroethyl methyl carbonate, and trifluoroethyl methyl carbonate. Preferably, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate are used.

[0065] Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, and diethylmethyl phosphate. Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of linear ethers include dimethoxyethane. Examples of lactone compounds include γ-valerolactone and γ-butyrolactone. Examples of linear esters include methylpropionate, methyl acetate, ethyl acetate, and methylformate. Examples of nitrile compounds include acetonitrile. Examples of amide compounds include dimethylformamide. Examples of sulfone compounds include sulfolane, methylsulfolane, dimethylsulfone, ethylmethylsulfone, and isopropylsulfone, but are not limited to these.

[0066] The electrolyte can be impregnated into the element by stacking the positive and negative electrodes with a separator in between, and then immersing the element, which consists of the positive electrode, negative electrode, and separator, in the electrolyte. [Examples]

[0067] The present invention will be described in more detail below based on the following examples. However, the present invention is not limited to the following examples.

[0068] (Example 1) A lithium-ion secondary battery was fabricated using the manufacturing method of Example 1. First, a Si coating process was performed using a negative electrode active material powder (manufactured by Teika Co., Ltd.) consisting of lithium titanate particles.

[0069] First, the median diameter of the secondary particles of lithium titanate was measured beforehand. The median diameter was measured by laser analysis and scattering. Approximately 10 mg of negative electrode active material powder was added to 10 mL of pure water and subjected to ultrasonic dispersion treatment. The dispersed solution was transferred to a measurement cell. The particle size distribution of the measurement cell was measured using a laser diffraction / scattering particle size distribution analyzer (HORIBA, LA-950). From the obtained particle size distribution curve, the median diameter of the secondary particles of lithium titanate was calculated. As a result, the median diameter of the lithium titanate particles in Example 1 was 7 μm.

[0070] Furthermore, the BET specific surface area of ​​the secondary lithium titanate particles was measured. The BET specific surface area was measured using the BET method in accordance with JIS Z8830:2013. The pretreatment temperature was set to 150°C, and nitrogen gas was introduced as the measurement gas into the surface of the lithium titanate particles and into the pores formed inside that communicate with the surface. The amount of nitrogen gas adsorbed was then measured using a gas adsorption measurement device (Microtrac-Bell). The pressure of the introduced nitrogen gas was gradually increased, and the amount of nitrogen gas adsorbed against each equilibrium pressure was plotted to obtain an adsorption isotherm curve. Next, the specific adsorption amount was calculated from the adsorption amount using the BET formula, and the BET specific surface area was calculated from the molecular cross-sectional area and Avogadro's constant. As a result, the BET specific surface area of ​​the lithium titanate particles in Example 1 was 55 m². 2 It was / g.

[0071] In the mixing step of the Si coating process, 1000 g of negative electrode active material powder was impregnated with a silane coupling agent. The silane coupling agent has a glycidoxy group, and its Si content is 12 wt% relative to the weight of the silane coupling agent. 3.6 wt% of the silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. During the impregnation process, the silane coupling agent was diluted with water. The impregnation was carried out under reduced pressure with stirring.

[0072] After impregnating lithium titanate particles with a silane coupling agent, the negative electrode active material powder was vacuum-dried for 1 hour at a temperature of 150°C. This caused the water in the silane coupling solution to volatilize from the negative electrode active material powder.

[0073] In the Si coating process, the process proceeded from the mixing step to the firing step. During the firing step, the negative electrode active material powder was exposed to a temperature environment of 400°C for 2 hours. As a result, an amorphous coating layer, in which the silane coupling agent was converted to silicon oxide, adhered to the lithium titanate particles.

[0074] In the Si coating process, the moisture adjustment process followed the firing process. In the moisture adjustment process, the material was exposed to an inert gas atmosphere with nitrogen gas and a temperature of 100°C for 2 hours.

[0075] After the Si coating process was completed, the SiO2 content of the negative electrode active material powder in Example 1 was measured. A fluorescence X-ray analyzer was used to measure the SiO2 content. Specifically, a pressure-molded negative electrode active material pellet was prepared, and the SiO2 content was quantified using the fundamental parameter method (FP method). As a result, the lithium titanate particles in Example 1 had 0.73 wt% SiO2 attached relative to the weight of the negative electrode active material powder.

[0076] Furthermore, the moisture content of the negative electrode active material powder of Example 1 was measured after the Si coating process was completed. The moisture content was measured using the Karl Fischer method. 0.4 g of the negative electrode active material powder was placed in a measurement cell heated to 140°C, and argon gas was flowed as a carrier gas at a flow rate of 200 mL / min. The moisture content up to a measurement temperature of 300°C was measured using a Karl Fischer trace moisture analyzer (manufactured by Mitsubishi Chemical Analytec Co., Ltd.) and a moisture vaporizer. As a result, the moisture content of the negative electrode active material powder of Example 1 was 13,000 ppm after the Si coursing process was completed.

[0077] Thus, in the negative electrode active material powder of Example 1, the BET specific surface area of ​​the lithium titanate particles is 55 m². 2The amount of silicon oxide adhering to the lithium titanate particles was 0.73 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 13,000 ppm.

[0078] A negative electrode formation process was carried out using this negative electrode active material powder to form a negative electrode. In the negative electrode formation process, additives were added to a dispersion containing N-methylpyrrolidone and thoroughly kneaded to form a slurry. 97.5 wt% of the additives were negative electrode active material powder, and 2.5 wt% were polyvinylidene fluoride, which served as a binder. The slurry was applied to aluminum foil, which served as the current collector for the negative electrode, and dried to remove the solvents N-methylpyrrolidone and water from the dispersion, thereby obtaining the negative electrode.

[0079] In the positive electrode formation process, LiMn2O4 and LiNi are used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 A mixture of O2 was used. The weight ratio was LiMn2O4 and LiNi 0.6 Co 0.2 Mn 0.2 O2 was mixed with a larger proportion of LiMn2O4 in a 4:1 ratio. Acetylene black was also included as a conductive additive in the positive electrode active material layer. In this positive electrode formation process, the positive electrode active material, conductive additive, and polyvinylidene fluoride as a binder were added to a dispersion containing N-methylpyrrolidone and thoroughly mixed to form a slurry. 92 wt% of the additives were positive electrode active material, 6 wt% were conductive additives, and 2 wt% were polyvinylidene fluoride. The slurry was applied to aluminum foil, which served as the current collector for the positive electrode, and dried to remove the N-methylpyrrolidone and water, which were the solvents in the dispersion, thereby obtaining the negative electrode.

[0080] After forming the positive and negative electrodes, the battery assembly process began. A separator was placed between the positive and negative electrodes, and the two electrodes were then overlapped and wound together. The separator was a cellulose separator primarily made of rayon. This wound material was then impregnated with an electrolyte. The electrolyte was lithium tetrafluoroborate (LiBF4), the solvent was propylene carbonate, and the molar concentration of the electrolyte was 1.0 M. This resulted in the fabrication of a wound lithium-ion secondary battery with a diameter of 16 mm and a length of 35 mm.

[0081] (Example 2) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 2. The manufacturing method of Example 2 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, 6.8 wt% of silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder.

[0082] In this Example 2 negative electrode active material powder, the BET specific surface area of ​​the lithium titanate particles is 53 m². 2 The amount of silicon oxide adhering to the lithium titanate particles was 1.4 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 13,000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0083] (Example 3) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 3. The manufacturing method of Example 3 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, 12.2 wt% of silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder.

[0084] In this Example 3 negative electrode active material powder, the BET specific surface area of ​​the lithium titanate particles is 55 m². 2 / g, and the amount of silicon oxide attached to the lithium titanate particles was 2.5 wt% based on the weight of the negative electrode active material powder. The amount of moisture contained in the negative electrode active material powder at the stage after the Si coating process was 15,000 ppm. Using this negative electrode active material powder, the process moved on to the negative electrode forming process.

[0085] (Example 4) A lithium ion secondary battery was fabricated by the manufacturing method of Example 4. The manufacturing method of Example 4 was the same method and same conditions as the manufacturing method of Example 1. However, in the mixing process within the Si coating process, 14.1 wt% of a silane coupling agent based on the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder.

[0086] In the negative electrode active material powder of this Example 4, the BET specific surface area of the lithium titanate particles was 63 m 2 / g, and the amount of silicon oxide attached to the lithium titanate particles was 2.9 wt% based on the weight of the negative electrode active material powder. The amount of moisture contained in the negative electrode active material powder at the stage after the Si coating process was 10,000 ppm. Using this negative electrode active material powder, the process moved on to the negative electrode forming process.

[0087] (Example 5) A lithium ion secondary battery was fabricated by the manufacturing method of Example 5. The manufacturing method of Example 5 was the same method and same conditions as the manufacturing method of Example 1. However, in the mixing process within the Si coating process, 12.2 wt% of a silane coupling agent based on the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. Also, in the moisture adjustment process, it was exposed for 5 hours under an inert gas atmosphere with nitrogen gas and at a temperature environment of 100°C.

[0088] In the negative electrode active material powder of this Example 5, the BET specific surface area of the lithium titanate particles was 51 m 2 / g, and the amount of silicon oxide attached to the lithium titanate particles was 2.5 wt% based on the weight of the negative electrode active material powder. The amount of moisture contained in the negative electrode active material powder at the stage after the Si coating process was 4,000 ppm. Using this negative electrode active material powder, the process moved on to the negative electrode forming process.

[0089] (Example 6) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 6. The manufacturing method of Example 6 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, 11.7 wt% of silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. In addition, in the moisture adjustment step, the material was exposed to an inert gas atmosphere with nitrogen gas and a temperature environment of 100°C for 5 hours.

[0090] In the negative electrode active material powder of this Example 6, the BET specific surface area of ​​the lithium titanate particles is 53 m². 2 The amount of silicon oxide adhering to the lithium titanate particles was 2.5 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 5000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0091] (Example 7) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 7. The manufacturing method of Example 7 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, 12.2 wt% of silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. In addition, in the moisture adjustment step, the material was exposed to an inert gas atmosphere with nitrogen gas and a temperature environment of 100°C for 5 hours.

[0092] In the negative electrode active material powder of this Example 7, the BET specific surface area of ​​the lithium titanate particles is 52 m². 2 The amount of silicon oxide adhering to the lithium titanate particles was 2.5 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 6000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0093] (Example 8) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 8. The manufacturing method of Example 8 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, 11.3 wt% of silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. In addition, in the moisture adjustment step, the material was exposed to an inert gas atmosphere with nitrogen gas and a temperature environment of 100°C for 5 hours.

[0094] In the negative electrode active material powder of this Example 8, the BET specific surface area of ​​the lithium titanate particles is 62 m². 2 The amount of silicon oxide adhering to the lithium titanate particles was 2.4 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 9000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0095] (Example 9) A lithium-ion secondary battery was manufactured using the manufacturing method of Example 9. The manufacturing method of Example 9 is the same as that of Example 1 in terms of method and conditions. However, in the mixing step within the Si coating process, a silane coupling agent having a methyl group and containing 21 wt% of Si relative to the weight of the silane coupling agent was used, and 5.0 wt% of the silane coupling agent relative to the weight of the negative electrode active material powder was impregnated into the negative electrode active material powder. In addition, in the moisture adjustment step, the material was exposed to an inert gas atmosphere with nitrogen gas and a temperature environment of 100°C for 5 hours.

[0096] In the negative electrode active material powder of this Example 9, the BET specific surface area of ​​the lithium titanate particles is 60 m². 2 The amount of silicon oxide adhering to the lithium titanate particles was 2.5 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 8000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0097] (Comparative Example 1) A lithium-ion secondary battery was fabricated by the manufacturing method of Comparative Example 1. In the negative electrode active material powder of Comparative Example 1, silicon oxide was not adhered to the lithium titanate particles. That is, only the moisture adjustment step was carried out, and the mixing step and the firing step were omitted. In the moisture adjustment step, it was exposed for 5 hours under an inert gas atmosphere with nitrogen gas and at a temperature environment of 100 °C.

[0098] In this negative electrode active material powder of Comparative Example 1, the BET specific surface area of the lithium titanate particles was 58 m 2 / g, and the moisture content contained in the negative electrode active material powder at the stage after the moisture adjustment step was 9000 ppm. The negative electrode formation step was carried out using this negative electrode active material powder.

[0099] (Comparative Example 2) A lithium-ion secondary battery was fabricated by the manufacturing method of Comparative Example 2. The manufacturing method of Comparative Example 2 was the same method and the same conditions as those of the manufacturing method of Example 1. However, in the mixing step in the Si coating step, the negative electrode active material powder was impregnated with 20 wt% of a silane coupling agent based on the weight of the negative electrode active material powder. Also, in the moisture adjustment step, it was exposed for 5 hours under an inert gas atmosphere with nitrogen gas and at a temperature environment of 100 °C.

[0100] In this negative electrode active material powder of Comparative Example 2, the BET specific surface area of the lithium titanate particles was 48 m 2 / g, the adhesion amount of silicon oxide to the lithium titanate particles was 4.1 wt% based on the weight of the negative electrode active material powder, and the moisture content contained in the negative electrode active material powder at the stage after the Si coating step was 6000 ppm. The negative electrode formation step was carried out using this negative electrode active material powder.

[0101] (Comparative Example 3) A lithium-ion secondary battery was fabricated by the manufacturing method of Comparative Example 3. The manufacturing method of Comparative Example 3 was the same method and the same conditions as those of the manufacturing method of Example 1. However, in the mixing step in the Si coating step, the negative electrode active material powder was impregnated with 11.7 wt% of a silane coupling agent based on the weight of the negative electrode active material powder. For Comparative Example 3, the moisture adjustment step was omitted.

[0102] In this comparative example 3, the negative electrode active material powder has a BET specific surface area of ​​55 m² of lithium titanate particles. 2 The amount of silicon oxide adhering to the lithium titanate particles was 2.4 wt% relative to the weight of the negative electrode active material powder, and the moisture content of the negative electrode active material powder after the Si coating process was 22,000 ppm. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0103] (Reference example 1) A lithium-ion secondary battery was fabricated using the manufacturing method of Reference Example 1. In the negative electrode active material powder of Reference Example 1, the BET specific surface area of ​​lithium titanate particles was 9.6 m². 2 The value is / g. The mixing and calcination processes were omitted, and silicon oxide was not attached to the lithium titanate particles. Only the moisture adjustment process was performed. In the moisture adjustment process, the particles were exposed to an inert gas atmosphere with nitrogen gas and a temperature of 100°C for 5 hours.

[0104] In this Reference Example 1 negative electrode active material powder, the BET specific surface area of ​​the lithium titanate particles is 9.6 m². 2 The moisture content of the negative electrode active material powder after the moisture adjustment process was 4000 ppm / g. The negative electrode formation process was then carried out using this negative electrode active material powder.

[0105] (Battery characteristics test) The lithium-ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were charged and discharged over 4000 cycles. After 4000 cycles, the ESR (equivalent series resistance) and the rate of change in capacity were measured.

[0106] The charging and discharging method over 4000 cycles was as follows: Charging was performed using the CCCV (Constant Current Constant Voltage) method. During constant current charging, charging was performed at a C rate of 10C, and constant voltage charging was terminated when the C rate reached 0.5C. During discharging, constant current discharge was performed at a C rate of 10C. The upper limit of the charging voltage was set to 2.7V, and the lower limit of the discharging voltage was set to 1.8V. The ambient temperature for charging and discharging was set to 60°C. This charging and discharging process was repeated 4000 times.

[0107] ESR was measured using a battery high tester (HIOKI BT3562A) at a measurement current frequency of 1 kHz, with the State of Charge (SOC) of the lithium-ion secondary battery adjusted to 50% and the ambient temperature set to 25°C.

[0108] The capacity change rate is the rate of change in the cell capacity of the lithium-ion secondary battery before and after 4000 charge-discharge cycles. The discharge capacity was measured after charging with a current of 5C and a voltage of 2.7V using CCCV charging (CCCV stands for Constant Current, Constant Voltage, and CV is a 0.05C current cutoff), and then discharging with a constant current of 5C and a voltage of 1.8V.

[0109] (Test results) Table 1 below shows the ESR and volume change rates for Examples 1 to 4 and Comparative Examples 1 to 3. (Table 1) TIFF2026067096000002.tif71166

[0110] As shown in Table 1 above, when the negative electrode formation process was carried out using the negative electrode active material powders of Examples 1 to 4, the ESR after 4000 charge-discharge cycles of the lithium-ion secondary battery was kept lower than that of Comparative Examples 1 to 3.

[0111] In Examples 1 to 4, although the moisture content is higher than in Comparative Example 1, the increase in ESR is suppressed because the SiO2 content is 0.73 wt% or more. In Comparative Example 2, SiO2 is attached to the lithium titanate particles, but because the SiO2 content is 4.1 wt%, the increase in ESR after 4000 charge-discharge cycles is not suppressed. Moreover, although Comparative Example 2 has a lower moisture content than Comparative Example 1, the presence of 4.1 wt% SiO2 actually worsens the increase in ESR after 4000 charge-discharge cycles. In Comparative Example 3, the SiO2 content is the same as in Example 3, but when the moisture content reaches 22000 ppm, the increase in ESR after 4000 charge-discharge cycles cannot be suppressed.

[0112] Thus, in the negative electrode formation process, the negative electrode was formed using negative electrode active material powder containing a moisture content of 15,000 ppm or less relative to the negative electrode active material powder, and having 0.73 wt% to 2.9 wt% of silicon oxide attached to the negative electrode active material powder. As a result, even when lithium titanate particles are used as negative electrode active material particles and the BET specific surface area is increased, the increase in ESR of the lithium-ion secondary battery after 4,000 charge-discharge cycles can be suppressed. Therefore, it was confirmed that a lithium-ion secondary battery with low initial ESR and excellent battery characteristics can be achieved even when using high-rate charge-discharge cycles.

[0113] Furthermore, the ESR and volume change rates for Examples 1 to 7 and Example 9 are shown in Table 2 below. (Table 2) TIFF2026067096000003.tif73164

[0114] As shown in Table 2 above, Examples 3 to 7 and Example 9 exhibit smaller capacity changes after 4000 charge-discharge cycles compared to Examples 1 and 2. Thus, it was confirmed that by attaching 2.4 wt% to 2.9 wt% of silicon oxide to the lithium titanate particles relative to the negative electrode active material powder in the Si coating process, the capacity change of the lithium-ion secondary battery can be kept low even when using high-rate charge-discharge cycles.

[0115] (Moisture adjustment test) The negative electrode active material powders of Reference Example 1, Comparative Example 1, and Examples 3 and 8 were further dried by exposing them to a temperature environment of 160°C for 12 hours, following the moisture adjustment process. After this drying, the moisture content was measured using the Karl Fischer method. 0.4 g of negative electrode active material powder was placed in a measurement cell heated to 140°C, and argon gas was flowed as a carrier gas at a flow rate of 200 mL / min. The moisture content up to a measurement temperature of 250°C was measured using a Karl Fischer trace moisture analyzer (manufactured by Mitsubishi Chemical Analytec Co., Ltd.) and a moisture vaporization device.

[0116] Table 3 below shows the results of further moisture adjustment tests on the negative electrode active material powders of Reference Example 1, Comparative Example 1, Examples 3 and 8. (Table 3) TIFF2026067096000004.tif51108

[0117] As shown in Table 3 above, the water content in Examples 3 and 8 is higher than that in Reference Example 1. Furthermore, in Examples 3 and 8, the BET specific surface area of ​​the lithium titanate particles is 40 m². 2 The amount is greater than / g and easily contains moisture. Even in Examples 3 and 8, if the SiO2 content is between 2.4 wt% and 2.9 wt%, the BET specific surface area of ​​the lithium titanate particles is 40 m². 2 Even if the BET specific surface area is 9.6m² or more, 2 This product surpasses Reference Example 1, which contains lithium titanate particles at 250°C, by demonstrating a lower water content at 250°C.

[0118] On the other hand, Comparative Example 1 could not reduce the water content at 250°C as in Examples 3 and 8. Specifically, the BET specific surface area of ​​the lithium titanate particles was 40 m². 2 Even when using a negative electrode active material powder that is more than / g and easily contains moisture, it was confirmed that if the SiO2 content is between 2.4 wt% and 2.9 wt%, the moisture content in the negative electrode active material powder can be easily adjusted, and it can be easily reduced to, for example, 15,000 ppm, which can suppress the increase in ESR.

Claims

1. SiO ｘ or SiO ｘ (OH) ４－２Ｘ A Si coating process for producing a negative electrode active material powder containing lithium titanate particles to which silicon oxide (0 < x ≤ 2) is attached, A negative electrode forming step involves stacking a negative electrode active material layer containing the aforementioned negative electrode active material powder on a negative electrode current collector to form a negative electrode, A battery assembly process in which the negative electrode is placed opposite the positive electrode and an electrolyte is interposed between the positive electrode and the negative electrode, Includes, In the negative electrode formation step, the negative electrode active material powder is formed using a negative electrode active material powder that contains a moisture content of 15,000 ppm or less relative to the negative electrode active material powder, and to which 0.73 wt% to 2.9 wt% of silicon oxide is attached relative to the negative electrode active material powder. A method for manufacturing lithium-ion secondary batteries characterized by the following.

2. In the Si coating step, 2.4 wt% to 2.9 wt% of the silicon oxide is attached to the lithium titanate particles relative to the negative electrode active material powder. A method for manufacturing a lithium-ion secondary battery according to claim 1, characterized by the above.

3. The Si coating process described above is: A mixing step of mixing the lithium titanate particles and the silicon oxide raw material, A firing step is performed in which the powder obtained in the mixing step is fired at a temperature of 300°C to 600°C. Including, A method for manufacturing a lithium-ion secondary battery according to claim 1, characterized by the above.

4. The Si coating process described above has a BET specific surface area of ​​40 m². ２ To attach the silicon oxide to the lithium titanate particles in a quantity of / g or more, A method for manufacturing a lithium-ion secondary battery according to claim 1 or 2, characterized by the above.

5. The device comprises a positive electrode, a negative electrode having a negative electrode active material layer containing negative electrode active material powder, and an electrolyte. The negative electrode active material powder is composed of silicon oxide such as SiO ｘ or SiO ｘ (OH) ４－２Ｘ It contains lithium titanate particles with silicon oxide attached (0 < x ≤ 2), The negative electrode active material layer has a BET specific surface area of ​​40 m². ２ The negative electrode active material powder is formed using a negative electrode active material powder that has a concentration of 15,000 ppm or less, a moisture content of 15,000 ppm or less, and a silicon oxide content of 0.73 wt% to 2.9 wt% relative to the negative electrode active material powder. A lithium-ion secondary battery characterized by the following features.

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