JP2005032632A - Manufacturing method of non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery in which the deterioration of cycle characteristics is suppressed. <P>SOLUTION: The manufacturing method of the non-aqueous secondary battery which comprises a negative electrode containing an element capable of alloying with lithium and a positive electrode includes a process of a first charging. The first charging is carried out by a process of the initial stage charging, a middle stage charging, and a last stage charging in this order. In the above process, the negative electrode is pressurized in the thickness direction of the negative electrode, and the initial stage charging and the last stage charging are carried out with a current density of 1.0 mA/cm<SP>2</SP>or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a non-aqueous secondary battery including a negative electrode containing an element that can be alloyed with lithium.

  In recent years, lithium ion secondary batteries have been required to have higher energy density (higher capacity) in accordance with downsizing of devices used, and researches for higher capacity have been actively conducted. Conventionally, a carbon material has been widely used for the negative electrode active material. However, since the carbon material is already used at a capacity close to the theoretical capacity (370 mAh / g), lithium ion secondary material using a carbon material as the negative electrode active material is used. It is difficult to significantly increase the capacity of the secondary battery. As a negative electrode active material capable of further increasing the capacity, a material containing a metal or a semimetal made of an element that can be alloyed with lithium is known. However, the material containing the metal or metalloid has the following problems. The problem will be described below by taking silicon as an example.

When silicon (Si) is alloyed with lithium, it becomes a compound represented by the composition formulas Li _1.7 Si, Li _2.33 Si, Li _3.25 Si, and Li _4.4 Si. For example, it has been calculated by calculation that the volume of Li _1.7 Si is 2.19 times the volume of Si and the volume of Li _4.4 Si is 4.14 times the volume of Si. Therefore, when the negative electrode includes silicon, a silicon compound, or a granular composite material composed of silicon and a conductive material as the negative electrode active material, the volume of the negative electrode expands more than twice that during discharge and expands during charge. When the negative electrode contracts during discharge, large voids are formed between the silicon particles and the silicon particles or between the silicon particles and the conductive additive. If such a charge / discharge cycle is repeated, the electron conduction network is gradually damaged, and the negative electrode active material deviated from the electron conduction network, i.e., the negative electrode active material not involved in alloying with lithium increases. As the cycle progresses, the capacity (charge / discharge capacity) of the negative electrode decreases, and the cycle characteristics of the nonaqueous secondary battery deteriorate.

As a method for solving this problem, the negative electrode active material is composed of metal particles or metalloid particles made of an element that can be alloyed with lithium, and a carbon layer covering the surfaces of the particles, and the carbon particles form metal particles or metalloids. A method of suppressing particle expansion is disclosed. Furthermore, the total charge capacity of the initial charge is set to 1500 mAh / g or less, and in the initial charge process, the initial charge is charged at a constant current density at a predetermined current density, and after reaching the final charge voltage, this potential is maintained and charged. A method of performing constant voltage charging until the amount reaches, for example, 500 to 1000 mAh / g is disclosed (for example, see Patent Document 1).
JP 2000-215887 A (page 5-6)

  However, even if the above method is adopted, there is a difference in reaction progress between the surface side and the center side of the metal particles or metalloid particles, so the surface side of the metal particles or metalloid particles is charged / discharged more than the center side. The degree of expansion and contraction accompanying the above was large, and there was a case where the powder was pulverized by stress due to expansion and contraction. The finely divided metal particles or metalloid particles are out of the electron conduction network, and the deterioration of the cycle characteristics cannot be sufficiently suppressed.

A method for producing a non-aqueous secondary battery of the present invention is a method for producing a non-aqueous secondary battery comprising a negative electrode containing an element that can be alloyed with lithium and a positive electrode, and includes a step of performing initial charge, In the initial charging, initial charging, intermediate charging, and final charging are performed in this order, and in the step, the initial charging and the final charging are performed while the negative electrode is pressed in the thickness direction of the negative electrode. It is characterized by carrying out at a current density of 0 mA / cm ² or less.

  According to the present invention, it is possible to provide a non-aqueous secondary battery in which deterioration of cycle characteristics is suppressed.

  The electrochemical reaction in the battery is a heterogeneous reaction system in which the reaction proceeds at the interface between the electrode and the electrolytic solution. Among them, metal particles or metalloid particles made of an element that can be alloyed with lithium tend to undergo a volume expansion when alloyed with lithium, so that a difference in reaction progress between the surface side and the inner side of the particle tends to occur. . In an electrochemical reaction, the current density and the reaction progress (electric quantity) per unit time are correlated, and the reaction progress increases as the current density is increased. When the reaction progress is large, the volume difference between the reaction part reacted with lithium and the unreacted part that has not reacted is increased for metal particles or metalloid particles containing an element that can be alloyed with lithium. It becomes easy to pulverize. When the particles are pulverized, the electron conduction network in the negative electrode is impaired, and the cycle characteristics of the nonaqueous secondary battery are deteriorated. In particular, when lithium and the negative electrode active material are alloyed for the first time, pulverization tends to occur.

  Therefore, the inventors of the present invention performed the first lithium alloying reaction, that is, in the initial charging step, in the initial charge stage and the final charge stage where the volume change of the particles is large, charging at a low current density to finely pulverize the particles. Suppressing and pressurizing the negative electrode to fill the void in the negative electrode formed by expansion while suppressing the expansion of the negative electrode, and reached the contact between the particles, that is, the retention of the electron conduction network .

That is, the non-aqueous secondary battery manufacturing method of the present embodiment is a non-aqueous secondary battery manufacturing method including a negative electrode containing an element that can be alloyed with lithium and a positive electrode, and is charged for the first time. The initial charge includes a process, and initial charge, intermediate charge, and final charge are performed in this order. In the above process, initial charge and final charge are 1.0 mA while pressing the negative electrode in the thickness direction of the negative electrode. / Cm ² or less current density.

  According to the method for manufacturing a non-aqueous secondary battery of the present embodiment, it is possible to suppress damage to the electron conduction network in the first charging step, and thus provide a non-aqueous secondary battery in which deterioration of cycle characteristics is suppressed. it can.

Although there is no particular limitation on the lower limit value of the current density when performing the initial charging and the final charging, the charging can usually be completed within 24 hours when it is 0.4 mA / cm ² or more. preferable.

  In the present invention, initial charging is charging 0 to 15% (initial region) of the initial charging capacity, and medium-term charging is charging more than 15% and 75% (medium region). Yes, terminal charge is to charge more than 75% and 100% (terminal region).

  The initial charge capacity is the total charge capacity charged in the initial charge step, and is a value determined by the product of the theoretical capacity of the negative electrode and the utilization rate. The utilization rate is a value determined by the type and amount of the negative electrode active material and the positive electrode active material determined at the time of designing the non-aqueous secondary battery, the end-of-charge voltage of the first charge, and the like.

In the step of the first charge, carried out a mid-term charge at a current density of 15 mA / cm ² or less, is charged at a current density of 5~15mA / cm ² at least a portion of the capacitance which is charged by performing metaphase charge It is preferable.

When at least one part or all of the capacity charged by performing the medium-term charge is charged at a current density greater than 15 mA / cm ² , the voltage at the time of performing the final charge at a current density of 1.0 mA / cm ² or less This is because a drop (IR drop) may occur, which may shorten the battery life. On the other hand, charging with a current density smaller than 5 A / cm ² does not cause the above voltage drop, but it takes a long time for charging. Performed metaphase charge 15 mA / cm ² in the following current densities, if charged with a current density of 5~15mA / cm ² at least a portion of the capacitance which is charged by performing metaphase charge, the voltage drop problems The charging time can be shortened without occurring.

  The first charging step is preferably performed at room temperature in order to ensure the performance and life of the battery by uniformly inserting lithium into the negative electrode.

  Although there is no restriction | limiting in particular about the method of pressing a negative electrode in the thickness direction of a negative electrode, For example, what is necessary is just to pressurize a negative electrode and a positive electrode so that a negative electrode and a positive electrode may be approached from the outer side of an exterior case. Specifically, for example, the negative electrode and the positive electrode may be pressurized by curving inward the surface facing the main surface of the negative electrode and the positive electrode of the outer case, or the initial charge is performed between two opposing plates. The previous non-aqueous secondary battery may be disposed, and the negative electrode and the positive electrode may be pressurized by bringing the two plates closer together. The two plates can be brought close to each other using bolts, nuts, clamps and clips. In addition, a method using hydraulic pressure or water pressure may be used.

  The pressure may be appropriately adjusted in consideration of the battery capacity and the like. For example, 196 MPa to 1961 MPa is appropriate for a battery having an initial charge capacity of 500 to 2500 mAh / g.

  The nonaqueous secondary battery produced by the nonaqueous secondary battery manufacturing method of the present embodiment includes the following negative electrode material (negative electrode active material, conductive additive, binder), positive electrode material (positive electrode active material, conductive additive). , Binder), a separator, an electrolytic solution, and the like.

  The negative electrode is prepared by, for example, applying a negative electrode mixture paste obtained by adding an appropriate solvent to the negative electrode material and thoroughly kneading it to a metal mesh, a metal foil, or the like serving as a current collector. It can produce by forming the negative mix layer controlled to the electrode density.

  Similarly to the negative electrode, the positive electrode mixture paste obtained by sufficiently kneading and adding a suitable solvent to the positive electrode material was applied to a metal mesh, a metal foil, etc. as a current collector, with a predetermined thickness. And it can produce by forming the positive mix layer controlled by the predetermined electrode density.

  The negative electrode active material is not particularly limited as long as the material contains an element that can be alloyed with lithium. For example, a metal composed of at least one element selected from the group consisting of Al, Sn, Si, and Zn, or A metalloid, an alloy containing the metal or metalloid, a compound containing the metal or metalloid (hereinafter abbreviated as “metal or metalloid”) can be used. The negative electrode active material may be a composite material including the metal or metalloid and the metal or metalloid and an electrochemically stable insulating material or conductive material. And a composite material containing a conductive substance.

As the insulating material, metal oxides such as Al ₂ O ₃ and SiO ₂ can be used, and as the conductive substance, metals such as carbon or nickel, copper, soot, and aluminum can be used. When the conductive material is carbon, the carbon may cover part or all of the surface of the metal or metalloid. When the conductive material is the above metal, the negative electrode active material is a solid solution, an intermetallic compound, or the like of at least one metal or semimetal selected from the group consisting of Al, Sn, Si and Zn and the above conductive material. The composite material may be used.

  The necessity for the conductive additive for the negative electrode varies depending on the type of the negative electrode active material. For example, when the negative electrode active material is silicon or a silicon compound, a conductive additive is necessary. In the case where the negative electrode active material is a composite material composed of silicon and a conductive material, the negative electrode active material itself has conductivity, so a conductive auxiliary agent is not necessarily required, but the negative electrode active material is electrically conductive with silicon. Even in the case of a composite material composed of a conductive substance, the negative electrode preferably contains a conductive additive in order to further increase the conductivity.

  The conductive auxiliary agent for the negative electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the nonaqueous secondary battery. For example, natural graphite (flaky graphite, earthy graphite, etc.), artificial graphite, Carbon particles such as carbon black, acetylene black, ketjen black, carbon fiber, metal powder (copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivatives, etc. can be used. More than one species may be used.

  It is preferable that the metal and metalloid which consist of an element which can be alloyed with lithium contained in a negative electrode are normally contained in the weight ratio of 5 to 50 weight% with respect to the total weight of negative electrode material.

  The thickness of the negative electrode mixture layer constituting the negative electrode is usually preferably 15 μm or more and 150 μm or less. If the thickness of the negative electrode mixture layer is too thin, the capacity per volume of the battery cannot be secured, and if it is too thick, the negative active material weight increases and the current density per unit weight of the negative active material decreases. Although the current load on the active material is reduced, the diffusion of lithium ions and the increase of overvoltage are further increased by increasing the distance between the surface of the negative electrode mixture layer opposite to the surface in contact with the current collector and the current collector. This is because the charging efficiency decreases.

  As the current collector of the negative electrode, a metal that does not react with Li, preferably Cu, Ni, SUS (stainless steel), or a metal foil (alloy foil) having a thickness of 5 μm to 50 μm mainly composed of these can be used. As this current collector, one having a surface roughness (Ra) of 0.05 μm to 2 μm may be used, and as long as the effective thickness is within 50 μm, unevenness processing may be performed. Shape processing such as inserting a plurality of slits may be performed.

The positive electrode material contains a lithium-containing transition metal oxide, and there are no particular restrictions on the lithium-containing transition metal oxide, and various types can be used, but a composition having a layered structure represented by the composition formula LiMaO ₂ Or a composition having a spinel structure represented by the composition formula LiMb ₂ O ₄ . However, Ma is at least one selected from the group consisting of Mn, Co and Ni, and Mb is at least one selected from the group consisting of Mn, Mg, Fe, Co, Ni, Cu, Zn, Al and Cr. And Mn as a main component (content 20 to 100%). For example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O ₂ , Li _x Ni _{1- y My} O ₂ , _{Li x Mn 2 O 4, Li} x Mn 2-y M y O 4 (M is, Mg, at least one Mn, Fe, Co, Ni, Cu, Zn, is selected from the group consisting of Al and Cr, x, y , Z is preferably a numerical value represented by 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 ≦ z ≦ 2.2).

  The conductive auxiliary agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the charge / discharge potential of the positive electrode material. For example, graphites such as natural graphite (flaky graphite) and artificial graphite Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, and conductive fibers such as carbon fiber and metal fiber may be used singly or in combination. it can. Of these electron conductive materials, artificial graphite, acetylene black, and ketjen black are particularly preferable.

  Examples of the binder used in the negative electrode and the positive electrode include polyacrylic acid, polyacrylic acid Na, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyhydroxy (meth) acrylate, and styrene-maleic acid copolymer. Polymer, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene-diene- Terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal, methyl methacrylate, polyvinyl ester copolymer, styrene Diene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, neoprene rubber, fluororubber, polyethylene oxide, polyester, phenol resin, epoxy resin, starch, carboxymethylcellulose, cellulose, diacetylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc. Polysaccharides, thermoplastic resins, polymers having rubbery elasticity, and the like can be used. In particular, polyacrylate latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are preferable.

  As the electrolytic solution, one prepared by dissolving the following inorganic ion salt in the following solvent can be used.

  Examples of the solvent include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate (MEC), diethylene carbonate (DEC), methyl propionate, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), gamma-butyrolactone ( GBL), ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, and other organic solvents can be used. The solvent may be a molten salt that contains imidazolium cation, quaternary ammonium, phosphonium, or sulfonium as a cation and is liquid at 100 ° C. or lower, or a mixed solvent of these molten salt and the organic solvent.

As the inorganic ion salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group], etc. Can be used. The concentration of the inorganic ion salt in the electrolytic solution is preferably 0.5 to 1.5 mol / dm ³ , particularly preferably 0.9 to 1.25 mol / dm ³ .

  As the separator, a separator having sufficient strength and capable of holding a large amount of electrolytic solution is good. From such a viewpoint, polyethylene, polypropylene, or ethylene-propylene copolymer having a thickness of 10 to 50 μm and an aperture ratio of 30 to 70% is used. A microporous film or a non-woven fabric containing coalescing is preferably used.

  The structure of the electrode group including the positive electrode and the negative electrode is such that the positive electrode and the negative electrode are opposed to each other with the separator and the electrolyte interposed therebetween, and a structure in which flat positive electrodes and negative electrodes are alternately stacked, May have any structure such as a wound structure formed by being rolled up and rolled up.

  The shape of the battery is not particularly limited, and for example, a coin shape, a button shape, a sheet shape, a square shape, or the like can be adopted.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

(Example 1)
90 parts by weight of LiCoO ₂ (positive electrode active material), 6 parts by weight of carbon black (conducting aid) and 4 parts by weight of polyvinylidene fluoride (binder) are uniformly mixed in N-methylpyrrolidone (solvent) to form a positive electrode mixture A paste containing was prepared. The positive electrode mixture-containing paste was applied to one side of a 20 μm-thick aluminum foil serving as a current collector so that the mixture weight per unit area was 30 mg / cm ² and dried. The positive electrode mixture layer was formed on one side of the aluminum foil by adjusting the thickness to 94 μm and the electrode density to 3.2 g / cm ³ . Thereafter, the positive electrode was manufactured by cutting into a shape in which a terminal portion of 20 mm × 5 mm was left at 41 mm × 25.5 mm.

90 parts by weight of a composite material containing silicon particles (negative electrode active material) and carbon particles in a ratio of 1: 1, 5 parts by weight of carbon black (conductive aid), and 5 parts by weight of polyvinylidene fluoride (binder), The mixture was uniformly mixed in N-methyl-2-pyrrolidone (solvent) to prepare a negative electrode mixture-containing paste. The negative electrode mixture-containing paste was applied to both sides of a 10 μm-thick copper foil serving as a current collector so that the weight of the mixture per unit area was 5.0 mg / cm ² and dried. A negative electrode mixture layer was formed by adjusting the negative electrode mixture-containing paste applied to both surfaces of the copper foil to have a thickness of 45 μm and an electrode density of 1.1 g / cm ³ . Thereafter, it was cut into a shape having a terminal portion of 19 mm × 5 mm on 42 mm × 27 mm, and a negative electrode having a thickness of 100 μm was produced.

  Prepare two sheets of the positive electrode, one negative electrode, and a 10 μm thick polypropylene separator (Hoechst Celanese, “Celgard # 2400”), and stack the negative electrode, separator, and positive electrode in this order. Groups were made. The positive electrode terminal portion and the negative electrode terminal portion were welded to the nickel lead by resistance welding, and then inserted into a rectangular aluminum outer case having a thickness of 4.2 mm and a width of 29.4 mm.

Thereafter, the concentration is 1 mol / dm ³ in an organic solvent in which ethylene carbonate (EC) and diethylene carbonate (DEC) are mixed at a volume ratio of 1: 2 between the positive electrode and the negative electrode in the outer case. Then, an electrolyte solution in which LiPF ₆ was dissolved was injected, and the opening of the outer case was sealed by laser welding to obtain a nonaqueous secondary battery.

  As shown in FIG. 1, a non-aqueous secondary battery is sandwiched between two stainless steel plates 3 (thickness 5 mm) provided with screw holes at four positions on each side so that a pressure of 196 MPa is applied to the non-aqueous secondary battery. The first charge was performed with the screw 4 tightened. As the pressure measuring instrument 5, “Load Cell MRD-500N (diameter of sensor tip 3 mm)” manufactured by Showa Seiki was used. In FIG. 1, 2 is an outer case of the battery, and 1 is an electrode group.

The initial charge of the non-aqueous secondary battery is a constant current at a current density of 1.0 mA / cm ^{2 from 0} mAh / g to 300 mAh / g (initial region) of the total charge capacity (2000 mAh / g) of the initial charge. Charge, constant current charging at a current density of 10 mA / cm ² over 300 mAh / g up to 1500 mAh / g (medium region), 1.0 mA / cm ² over 1500 mAh / g up to 2000 mAh / g (terminal region) Constant current charging at a current density of. The initial charge end voltage was 4.25V. Note that the switching of the current density of the charging current was performed by the charging control circuit based on the amount of current passed and the elapsed time.

(Example 2)
By calendering, the thickness of the positive electrode mixture layer was adjusted to 146 μm so that the mixture weight per unit area of the positive electrode was 47 mg / cm ² and the electrode density was 3.2 g / cm ^2. The same conditions as in Example 1 except that the thickness of each negative electrode mixture layer was 70 μm and the thickness of the negative electrode was 150 μm so that the agent weight was 7.7 mg / cm ² and the electrode density was 1.1 g / cm ^2. Then, a non-aqueous secondary battery was prepared and subjected to initial charging in the same manner as in Example 1.

(Example 3)
Of the total charge capacity (2000 mAh / g) of the first charge, constant current charging is performed at a current density of 0.5 mA / cm ^{2 from 0} mAh / g to 300 mAh / g (initial region), and over 300 mAh / g to 1500 mAh / g. Other than charging at a constant current of 5 mA / cm ² up to g (mid-term region) and charging at a constant current of 0.5 mA / cm ² over 1500 mAh / g up to 2000 mAh / g (terminal region) Were tested under the same conditions as in Example 1.

(Example 4)
The initial charge was performed in the same manner as in Example 1 except that the pressure for pressurizing the non-aqueous secondary battery was changed from 196 MPa to 1961 MPa.

(Comparative Example 1)
Of the conditions in Example 1, the initial charge was performed under the same conditions as in Example 1 except that the total charge capacity (2000 mAh / g) of the initial charge was constant current charged at a current density of 5 mA / cm ² .

(Comparative Example 2)
Among the conditions in Comparative Example 1, the thickness of the positive electrode mixture layer was adjusted to 146 μm by calendering so that the mixture weight per unit area of the positive electrode was 47 mg / cm ² and the electrode density was 3.2 g / cm ^2. The thickness of each negative electrode mixture layer was adjusted to 70 μm and the thickness of the negative electrode was adjusted to 150 μm so that the weight of the mixture per unit area of the negative electrode was 7.7 mg / cm ² and the electrode density was 1.1 g / cm ^2. Except for this, the initial charge was performed under the same conditions as in Comparative Example 1.

(Comparative Example 3)
A nonaqueous secondary battery was produced in the same manner as in Example 2 except that the first charge was performed without applying pressure to the negative electrode.

For the nonaqueous secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 to 3, the initial charge efficiency [(discharge capacity / charge capacity) × 100, voltage range 2.5 V to 4.25 V], after 30 cycles The AC resistance and the capacity retention rate after 30 cycles were determined, and the results are shown in Table 1. In the second and subsequent cycles, constant current charging was performed at a current density of 5 mA / cm ^{2 and} the end-of-charge voltage was 4.15V. The alternating current resistance was measured by applying an alternating current of 1 kHz. The capacity retention rate was calculated by the following formula 1. The results are shown in Table 1.

(Equation 1)
Capacity maintenance ratio (%) = (discharge capacity at the 30th cycle / discharge capacity at the second cycle) × 100

実施例と比較例との比較で明らかな様に、実施例は比較例よりも、３０サイクル後の交流抵抗が小さく、３０サイクル後の容量維持率が高い。この結果より、初回充電をする工程において、負極を負極の厚み方向に加圧しながら、初期充電と終期充電とを１．０ｍＡ／ｃｍ²以下の電流密度で行った非水二次電池では、サイクル特性の劣化が抑制されることが確認できた。

As is clear from the comparison between the example and the comparative example, the example has a smaller AC resistance after 30 cycles and a higher capacity retention rate after 30 cycles than the comparative example. As a result, in the non-aqueous secondary battery in which the initial charge and the final charge were performed at a current density of 1.0 mA / cm ² or less while pressing the negative electrode in the thickness direction of the negative electrode in the first charging step, It was confirmed that the deterioration of characteristics was suppressed.

On the other hand, in Comparative Examples 1 and 2 in which rapid charging was performed at the beginning of charging with a large voltage change and at the end of charging with a high operating voltage (initial charging and final charging were performed at a current density greater than 1.0 mA / cm ² ), Since a heterogeneous alloying reaction between silicon and lithium that can be alloyed with silicon is likely to occur, lithium and silicon are partially alloyed by the composition formulas Li _3.25 Si and Li _4.4 Si, and are pulverized. Seems to have occurred. This can also be inferred from the fact that in Comparative Examples 1 and 2, the AC resistance value after 30 cycles is about 1.4 times or more that of the example.

  The method for producing a non-aqueous secondary battery according to the present invention can provide a non-aqueous secondary battery in which deterioration of cycle characteristics is suppressed, and is useful as a method for producing a non-aqueous secondary battery.

Partial sectional drawing explaining an example of the manufacturing method of the non-aqueous secondary battery of this invention

Explanation of symbols

1 Electrode group 2 Exterior case 3 Stainless steel plate 4 Screw 5 Sensor

Claims (6)

A method for producing a non-aqueous secondary battery comprising a negative electrode containing an element that can be alloyed with lithium and a positive electrode,
Including the first charge step,
The initial charge is an initial charge, an intermediate charge, and an end charge in this order,
In the step, the initial charge and the final charge are performed at a current density of 1.0 mA / cm ² or less while pressurizing the negative electrode in the thickness direction of the negative electrode. Method. In the step, performed the metaphase charged at 15 mA / cm ² or less of the current density, charging at a current density of 5~15mA / cm ² at least a portion of the capacity to be charged by performing the medium-term charge billing Item 2. A method for producing a non-aqueous secondary battery according to Item 1.   The non-aqueous secondary battery according to claim 1 or 2, wherein in the step, the non-aqueous secondary battery is disposed between two opposing plates, and the negative electrode is pressurized by bringing the two plates close to each other. Method. The positive electrode includes a lithium-containing transition metal oxide, and the lithium-containing transition metal oxide is a composition represented by a composition formula LiMaO ₂ or a composition represented by a composition formula LiMb ₂ O _4. A method for producing a nonaqueous secondary battery according to any one of the above.
However, Ma is at least one selected from the group consisting of Mn, Co and Ni, and Mb is at least one selected from the group consisting of Mn, Mg, Fe, Co, Ni, Cu, Zn, Al and Cr. Including Mn as a main component.   The method for manufacturing a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the element that can be alloyed with lithium includes at least one selected from the group consisting of Al, Sn, Si, and Zn.   The method for producing a nonaqueous secondary battery according to any one of claims 1 to 5, wherein the negative electrode further includes at least one conductive additive selected from carbon particles and carbon fibers.

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