Method and system for charging and discharging non-aqueous electrolyte secondary battery

Abstract

A charge and discharge method for a nonaqueous secondary battery, which is provided with a positive electrode, a negative electrode comprising a negative electrode collector, and a nonaqueous electrolyte, wherein lithium metal is deposited on the negative electrode during the charge and lithium metal is dissolved in the nonaqueous electrolyte during the discharge, comprises a charge step and a discharge step that is carried out after the charge step. The charge step comprises: a first step wherein constant current charge is carried out at a first current I1 having a current density of 1.0 mA / cm2 or less; and a second step wherein constant current charge is carried out at a second current I2 that is larger than the first current I1 after the first step. In the discharge step, an electric quantity corresponding to from 20% to 80% of the full charge quantity is discharged.

Description

[Technical field]

[0001] The present invention relates to a method and system for charging and discharging a non-aqueous electrolyte secondary battery. [Background technology]

[0002] 2. Description of the Related Art Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, have high energy density and high output and are considered promising for use as power sources for mobile devices such as smartphones, power sources for vehicles such as electric vehicles, storage devices for natural energy such as solar power, and the like.

[0003] Meanwhile, with the aim of increasing the capacity of batteries, nonaqueous electrolyte secondary batteries in which lithium metal is deposited on the negative electrode current collector during charging and the lithium metal dissolves during discharging are being considered (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-243957 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is difficult to control the morphology of lithium metal deposition, and the suppression of dendrite formation is insufficient. Lithium metal deposited in a dendrite shape on the negative electrode current collector during charging begins to dissolve from the negative electrode current collector side during discharging, so some of the deposited lithium metal is easily isolated from the negative electrode (conductive network) during discharging. As charging and discharging are repeated, the lithium metal becomes increasingly isolated from the negative electrode, and the cycle characteristics tend to deteriorate. [Means for solving the problem]

[0006] In view of the above, one aspect of the present invention relates to a method for charging and discharging a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte, in which lithium metal is deposited on the negative electrode during charging and the lithium metal is dissolved in the non-aqueous electrolyte during discharging, the method comprising a charging step and a discharging step carried out after the charging step, the charging step being carried out at a current density of 1.0 mA / cm 2 The first current I 1 A first step of constant current charging with the first current I 1 A second current I 2 and a second step of performing constant current charging at a constant current of 100 V. In the discharging step, an amount of electricity equivalent to 20% or more and 80% or less of the fully charged amount is discharged.

[0007] Another aspect of the present invention provides a non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode having a negative electrode current collector; and a non-aqueous electrolyte; lithium metal is deposited on the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharging; the charge / discharge device comprises a charge control unit and a discharge control unit; and the charge control unit controls the charge / discharge device to charge the negative electrode at a current density of 1.0 mA / cm. 2 The first current I 1 After the first constant current charging, the first current I 1 A second current I 2 and the discharge control unit controls discharging so as to discharge an amount of electricity equivalent to 20% or more and 80% or less of a fully charged amount. Effect of the Invention

[0008] According to the present invention, the cycle characteristics of a non-aqueous electrolyte secondary battery can be improved. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief description of the drawings]

[0009] [Figure 1] These are scanning electron microscope (SEM) images of the negative electrode of a non-aqueous electrolyte secondary battery during constant current charging. Figure 1(a) shows the deposition state of lithium metal on the negative electrode current collector at a charge rate of 50% when the charging current value is 0.05C. Figure 1(b) shows the deposition state of lithium metal on the negative electrode current collector at a charge rate of 50% when the charging current value is 0.2C. [Diagram 2] 1 is a schematic configuration diagram of a charge / discharge system for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. [Diagram 3] 1 is a schematic perspective view, with a portion cut away, of a nonaqueous electrolyte secondary battery used in a charge / discharge method and a charge / discharge system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Method of charging and discharging non-aqueous electrolyte secondary battery] A method for charging and discharging a non-aqueous electrolyte secondary battery according to one embodiment of the present invention relates to a method for charging and discharging a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte, in which lithium metal is deposited on the negative electrode during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging. The charging and discharging method includes a charging step and a discharging step performed after the charging step. The charging step is performed at a current density of 1.0 mA / cm. 2 The first current I 1 The first step is constant current charging at I 1 A second current I 2 and a second step of constant current charging at 100%. In the discharge step, an amount of electricity equivalent to 20% to 80% of the fully charged amount is discharged. In other words, the battery is discharged until the discharge rate described below is 20% to 80%.

[0011] The current density (mA / cm 2 ) is the unit opposing area between the positive and negative electrodes (1 cm 2) and is obtained by dividing the current value applied to the battery by the total area of ​​the positive electrode composite layer (or positive electrode active material layer) facing the negative electrode (hereinafter also referred to as the effective total area of ​​the positive electrode). For example, when the positive electrode has a positive electrode composite layer on both sides of the positive electrode current collector, the effective total area of ​​the positive electrode is the total area of ​​the positive electrode composite layer on both sides (i.e., the total of the projected areas of the positive electrode composite layers on both sides onto one and the other surfaces of the positive electrode current collector).

[0012] Usually, the charging step brings the battery to a fully charged state. A fully charged battery means a battery that has been charged to a voltage (e.g., 4.1V) estimated to be charged to the rated capacity. A fully charged amount means the amount of electricity charged when a fully discharged battery is charged to a fully charged state. A fully discharged battery means a battery that has been discharged to a voltage (e.g., 3V) estimated to be discharged to the rated capacity. Hereinafter, the ratio of the amount of electricity charged to the fully charged amount is referred to as the charging rate. The ratio of the amount of electricity discharged to the fully charged amount is referred to as the discharging rate. When the battery is fully charged, the charging rate is 100%. When the battery is fully discharged, the discharging rate is 100%.

[0013] When the above-mentioned charging step and discharging step are performed, isolation of lithium metal from the negative electrode during discharge is suppressed, and the capacity reduction due to the isolation is suppressed. The deterioration of cycle characteristics due to the progression of the isolation with repeated charging and discharging is suppressed.

[0014] In the first step (initial charging), the first current I 1 When the current density is 1.0mA / cm 2 The first current I is small, and lithium metal is likely to precipitate in clumps (granules) on the negative electrode current collector. Clumped Li is not likely to become isolated during discharge. In the second step, the charge rate can be made higher than in the first step, making it possible to shorten the charging time. In the second step, dendrite-shaped lithium metal precipitates to a certain extent, but it precipitates on the clumped Li precipitated in the early stages of charging (mainly in the first step), and tends to be firmly integrated with the clumped Li, suppressing the isolation of Li during discharge. First current I 1 may be 0.1C or less.

[0015] When discharging an amount of electricity equivalent to 20% or more and 80% or less of the full charge amount, it is easy to leave a sufficient amount of lump Li on the surface of the negative electrode current collector at the end of the discharging step. This allows good quality lump Li to be maintained on the negative electrode current collector throughout charging and discharging, and lithium metal is reliably precipitated on the good quality lump Li during charging and is firmly integrated with the lump Li, suppressing the isolation of Li during discharging. The discharge rate at the end of the discharging step may be 50% or more and 80% or less, or 50% or more and 75% or less.

[0016] Note that (1 / X)C represents the current value when a quantity of electricity equivalent to the rated capacity is charged or discharged at a constant current for X hours. For example, 0.1C is the current value when a quantity of electricity equivalent to the rated capacity is charged or discharged at a constant current for 10 hours.

[0017] (Charging steps) In the first step, an amount of electricity equivalent to 5% or more and 15% or less of the total amount of charge electricity in the charging step (total amount of electricity charged in the charging step) may be charged. In this case, it is easy to sufficiently deposit block Li. In addition, in this case, by combining with a discharging step in which the battery is discharged to a discharge rate of 20% or more and 80% or less, a sufficient amount of good-quality block Li is easily maintained on the negative electrode current collector throughout charging and discharging. For example, when the charging and discharging steps do not include a preliminary charging step described later, an amount of electricity equivalent to a full charge amount may be charged in the first charging step, and the total amount of charge electricity in the above charging steps may be the full charge amount.

[0018] The charging step is the third current I 3 When the constant current charging in the first to third steps is performed, the second current I 2 Current density J 2 is the first current I 1 Current density J 1 and 4.0mA / cm 2 and the third current I 3 Current density J 3 is the second current I 2Current density J 2 and 4.0mA / cm 2 The second current I 2 is the first current I 1 and is equal to or less than 0.4 C, and the third current I 3 is the second current I 2 and may be equal to or greater than 0.4 C. When the charging steps include the first to third steps and the first to third currents are appropriately set, the cycle characteristics are likely to be improved.

[0019] The third step is set and the current density J 2 4.0mA / cm 2 By making the current density smaller than 0.1V, the generation of dendrites in the second step is suppressed. 2 is 2.0mA / cm 2 In the following cases, bulk Li may precipitate. By increasing the current value in the second and third steps, charging can be performed efficiently in a short time. Current density J 3 is 4.0mA / cm 2 In the above cases, it is easy to shorten the charging time while maintaining excellent cycle characteristics.

[0020] 1st current I 1 Current density J 1 is, for example, 0.1mA / cm 2 More than 0.8mA / cm 2 may be less than 0.1 mA / cm 2 More than 0.5mA / cm 2 The second current I 2 Current density J 2 is, for example, 1.0 mA / cm 2 More than 2.0mA / cm 2 The third current I 3 Current density J 3 For example, 8.0mA / cm 2 More than 10.0mA / cm 2 It may be the following. 1st current I1 The second current I may be, for example, 0.01 C or more and 0.08 C or less, or 0.01 C or more and 0.05 C or less. 2 The third current I may be, for example, 0.1 C or more and 0.2 C or less. 3 may be 0.8C or more and 1.0C or less.

[0021] From the viewpoint of performing a balanced and efficient three-step constant current charging, the first current I 1 The second current I 2 Ratio of:I 2 / I 1 For example, the second current I 2 The third current I 3 Ratio of:I 3 / I 2 may be, for example, 3 or more, or 3 or more and 10 or less.

[0022] The timing to end each step of constant current charging may be controlled, for example, by the charging time, the amount of charged electricity, or the voltage, or by the ratio of the amount of charged electricity to the total amount of charged electricity in the charging step, or by the charging rate. The amount of charged electricity (charging rate) may be estimated by the voltage. The amount of charged electricity (charging rate) may be estimated by the voltage based on the relationship between the amount of charged electricity and the voltage when an initial battery is charged at a constant current up to the rated capacity (charging rate 100%), and the charging end voltage may be set at each step. For example, the charging end voltage of the final step of constant current charging may be set to a voltage at which an amount of electricity equivalent to the rated capacity has been charged based on the relationship between the amount of charged electricity and the voltage when an initial battery is charged at a constant current up to the rated capacity.

[0023] In the first step, constant current charging may be performed so that the amount of charge electricity in the first step is 15% or less of the total amount of charge electricity in the charging steps. When constant current charging is performed in the first to third steps, constant current charging may be performed in the second step so that the total amount of charge electricity in the first and second steps is 50% or less of the total amount of charge electricity in the charging steps. In this case, it is easy to perform the first to third steps in a well-balanced manner, and it is easy to obtain an effect of improving cycle characteristics.

[0024] In order to perform charging more reliably, the above charging step may further include a constant voltage charging step in which charging is performed at a constant voltage after the constant current charging step. The constant voltage charging is performed, for example, until the current reaches a predetermined value (e.g., 0.02 C). When the final step of constant current charging is performed until a predetermined voltage (e.g., 4.1 V) is reached, constant voltage charging may be performed at that voltage.

[0025] FIG. 1 is a SEM image showing the state of the negative electrode during constant current charging of a nonaqueous electrolyte secondary battery. FIG. 1(a) shows the state of the negative electrode during constant current charging of a nonaqueous electrolyte secondary battery when the charging current value was 0.05 C (0.5 mA / cm 2 ) at a charging current of 0.2 C (2.0 mA / cm ). 2 ) shows the deposition state of lithium metal on the negative electrode current collector at a charge rate of 50%.

[0026] For the negative electrode in Figure 1(a), the charging current density was 0.5 mA / cm 2 On the other hand, in the negative electrode shown in Fig. 1(b), the charging current density is 2.0 mA / cm 2 and a large amount of dendrite-like lithium metal is deposited on the negative electrode current collector.

[0027] (Discharge step) In the discharge step, an amount of electricity equivalent to 20% to 80% of the full charge amount is discharged. The discharge may be a constant current discharge or a constant power discharge. The timing to end the discharge step may be controlled, for example, by the amount of electricity discharged (discharge rate) or the voltage. The amount of electricity discharged (discharge rate) may be estimated by the voltage. In the case of constant current discharge, the amount of electricity discharged (discharge rate) may be estimated by the voltage based on the relationship between the amount of electricity discharged and the voltage when an initial battery in a fully charged state is discharged at a constant current up to the rated capacity (discharge rate of 100%), and the discharge end voltage may be set. In the case of discharging to a discharge rate of 20% to 80%, the discharge end voltage is set to, for example, 3.5 V to 3.8 V. The discharge current density in the discharge step is, for example, 2.0 mA / cm 2 More than 20.0mA / cm 2 The discharge current value in the discharge step is, for example, 0.2 C or more and 2 C or less.

[0028] (Pre-charging step) The above charge / discharge method further includes a step in which the current density is 0.5 mA / cm before the first charge step. 2 The current I 0 The pre-charging step may include a constant current charging step at a current I. By performing the pre-charging step, a large amount of good quality Li clumps can be formed on the negative electrode current collector, as shown in the negative electrode in the SEM image of FIG. 1(a). 0 is, for example, 0.05C or less.

[0029] From the viewpoint of forming good quality Li chunks, the current I 0 Current density J 0 is 0.1mA / cm 2 More than 0.5mA / cm 2 may be less than 0.2 mA / cm 2 More than 0.5mA / cm 2 From the viewpoint of forming good quality lump Li, the current I 0 may be 0.01C or more and 0.05C or less, or 0.02C or more and 0.05C or less. When a preliminary discharge step described later is performed, an amount of electricity equivalent to the rated capacity may be charged in the preliminary charge step to obtain a negative electrode with a charge rate of 100%. When a preliminary discharge step described later is not performed, a negative electrode with a charge rate of, for example, 80% or more and 100% or less may be obtained in the preliminary charge step.

[0030] (Pre-discharge step) The above-mentioned charge / discharge method may further include a preliminary discharge step, after the preliminary charge step and before the first charge step, in which discharging is performed so that a part of the lithium metal deposited during charging in the preliminary charge step remains. The discharge may be a constant current charge or a constant power discharge. By performing the preliminary discharge step, it is possible to efficiently leave a better quality chunk of Li on the negative electrode current collector.

[0031] For example, the battery may be charged to a charge rate of 100% in the preliminary charge step, and discharged to a discharge rate of 20% to 80% in the preliminary discharge step. In this case, the discharge cut-off voltage is set to, for example, 3.5 V to 3.8 V. The discharge current density in the preliminary discharge step is, for example, 2.0 mA / cm 2 More than 20.0mA / cm 2 The discharge current value in the preliminary discharge step is, for example, 0.2 C or more and 2 C or less.

[0032] [Charge and discharge system for non-aqueous electrolyte secondary batteries] A charge / discharge system for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a non-aqueous electrolyte secondary battery and a charge / discharge device. The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte, and lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging. The charge / discharge device includes a charge control unit and a discharge control unit. The charge control unit controls the charge / discharge device to charge the non-aqueous electrolyte when the current density is 1.0 mA / cm. 2 The first current I 1 After the first constant current charging, the first current I 1 A second current I 2The charging is controlled so that the second constant current charging is performed at the first current I. The discharge control unit controls the discharging so that the amount of electricity corresponding to 20% to 80% of the fully charged amount is discharged. In the first constant current charging, the amount of electricity corresponding to 5% to 15% of the fully charged amount may be charged. 1 may be 0.1C or less.

[0033] The charging control unit charges the battery at a third current I after the second constant current charging. 3 In this case, the charging may be controlled so that the third constant current charging is performed at the second current I 2 Current density J 2 is the first current I 1 Current density J 1 and 4.0mA / cm 2 The third current I 3 Current density J 3 is the current density J 2 and 4.0mA / cm 2 The second current I 2 is the first current I 1 The third current I 3 is the second current I 2 and may be 0.4C or more.

[0034] The charging control unit may control charging so that when the amount of charged electricity reaches a first threshold during the first constant current charging, the first constant current charging is terminated and a second constant current charging is initiated, and when the amount of charged electricity reaches a second threshold during the second constant current charging, the second constant current charging is terminated and a third constant current charging is initiated. The first threshold may be an amount of charged electricity equivalent to 15% or less of the total amount of charged electricity. The second threshold may be an amount of charged electricity equivalent to 50% or less of the total amount of charged electricity.

[0035] Here, FIG. 2 shows an example of a charge / discharge system according to an embodiment of the present invention. The charge / discharge system includes a nonaqueous electrolyte secondary battery 11 and a charge / discharge device 12. An external power source 13 that supplies power to the charge / discharge device 12 is connected to the charge / discharge device 12. An external load 14 is connected to the nonaqueous electrolyte secondary battery 11. The nonaqueous electrolyte secondary battery 11 is a secondary battery that includes a positive electrode, a negative electrode including a negative electrode current collector, and a nonaqueous electrolyte, in which lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves in the nonaqueous electrolyte during discharging. The charge / discharge device 12 includes a charge control unit 15 including a charging circuit, and a discharge control unit 16 including a discharging circuit.

[0036] The charging control unit 15 controls the current density to be 1.0 mA / cm 2 The first current I 1 The first constant current charge is performed at I 1 A second current I 2 In the first constant current charging, an amount of electricity equivalent to 5% or more and 15% or less of the total charged amount of electricity is charged.

[0037] The charge / discharge device 12 includes a voltage detection unit 17 that detects the voltage of the nonaqueous electrolyte secondary battery 11. The voltage detection unit 17 may include a calculation unit that calculates a charged amount of electricity (charging rate) based on the voltage. Based on the voltage detected by the voltage detection unit 17 (the charged amount of electricity calculated by the calculation unit), the charge control unit 15 switches from the first constant current charging to the second constant current charging or terminates the second constant current charging.

[0038] After the second constant current charging, the charging control unit 15 performs constant voltage charging at a predetermined voltage (e.g., an end voltage of the second constant current charging). The charging / discharging device 12 includes a current detection unit 18 that detects a current. The charging control unit 15 may perform control so as to end the constant voltage charging when the current detected by the current detection unit 18 reaches a threshold value.

[0039] 2, the timing of termination of the first constant current charging and the second constant current charging is controlled by the voltage detected by voltage detection unit 17, but it may also be controlled by the charging time. For example, the termination of the first constant current charging may be controlled by the charging time, and the termination of the second constant current charging may be controlled by the voltage.

[0040] The discharge control unit 16 controls the discharge so as to discharge an amount of electricity equivalent to 20% or more and 80% or less of the full charge amount (constant current discharge or constant power discharge). The voltage detection unit 17 may include a calculation unit that calculates the discharged amount of electricity (discharge rate) based on the voltage. The discharge control unit 16 controls the discharge so as to end the discharge when the voltage detected by the voltage detection unit 17 (the discharged amount of electricity (discharge rate) calculated by the calculation unit) reaches a threshold value.

[0041] Before the initial first constant current charge, the charge control unit 15 controls the current density to be 0.5 mA / cm 2 The current I 0 The discharge control unit 16 may control charging so that a constant current charge (preliminary charge) is performed after the preliminary charge and before the initial first constant current charge. The discharge control unit 16 may control discharging so that a part of the lithium metal deposited during the preliminary charge remains (preliminary discharge).

[0042] Hereinafter, each of the components of the nonaqueous electrolyte secondary battery will be described in more detail. [Negative electrode] The negative electrode includes a negative electrode current collector. In a lithium secondary battery, for example, lithium metal is deposited on the surface of the negative electrode current collector by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode current collector by charging, becoming lithium metal, and depositing on the surface of the negative electrode current collector. The lithium metal deposited on the surface of the negative electrode current collector dissolves as lithium ions in the non-aqueous electrolyte by discharging. The lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied from the positive electrode active material by charging, or may be both of them.

[0043] The negative electrode current collector may be a conductive sheet. The conductive sheet may be a foil, a film, etc. The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0044] The surface of the conductive sheet may be smooth. This makes it easier for lithium metal from the positive electrode to deposit evenly on the conductive sheet during charging. "Smooth" means that the maximum height roughness Rz of the conductive sheet is 20 μm or less. The maximum height roughness Rz of the conductive sheet may be 10 μm or less. The maximum height roughness Rz is measured in accordance with JIS B 0601:2013.

[0045] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloy. The conductive material may be a metallic material such as a metal or an alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form any alloy or intermetallic compound with lithium is preferable. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with a basal surface preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among them, copper and / or copper alloys having high conductivity are preferable.

[0046] [Positive electrode] The positive electrode includes a positive electrode active material capable of absorbing and releasing lithium ions. The positive electrode active material may be, for example, a composite oxide including lithium and a metal other than lithium, Me. The metal Me includes at least a transition metal. The composite oxide is advantageous in that it has low manufacturing costs and a high average discharge voltage.

[0047] The lithium contained in the composite oxide is released as lithium ions from the positive electrode during charging and precipitates as lithium metal at the negative electrode. During discharging, the lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the composite oxide of the positive electrode. That is, the lithium ions involved in charging and discharging are generally derived from the solute (lithium salt) in the non-aqueous electrolyte and the positive electrode active material. Therefore, the molar ratio of the total amount of lithium mLi contained in the positive and negative electrodes to the amount of metal Me mMe contained in the positive electrode: mLi / mMe may be, for example, 1.1 or less.

[0048] The transition metal may include nickel (Ni) and at least one element selected from the group consisting of cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), chromium (Cr), titanium (Ti), niobium (Nb), zirconium (Zr), vanadium (V), tantalum (Ta), tungsten (W) and molybdenum (Mo).

[0049] The metal Me may include a metal other than a transition metal. The metal other than a transition metal may include at least one selected from the group consisting of aluminum (Al), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn) and silicon (Si). In addition, the composite oxide may further include boron (B) and the like in addition to the metal.

[0050] From the viewpoint of increasing capacity, the composite oxide has a layered rock salt type crystal structure, and the metal Me other than lithium preferably contains at least nickel as a transition metal, and the atomic ratio of Ni to metal Me: Ni / Me may be 0.65 or more. In the case of a nickel-based composite oxide with Ni / Me of 0.65 or more, the initial charge / discharge efficiency is smaller than that of lithium cobalt oxide, and lithium metal (mainly lump Li at the beginning of charging) deposited on the negative electrode current collector during discharge is likely to remain. When the amount of remaining lithium metal is large, it can exert the same effect as the lump Li remaining by discharging to a discharge rate of 20% or more and 80% or less, or the lump Li deposited on the negative electrode current collector in the above preliminary charge. In the composite oxide, the atomic ratio of Ni to metal Me: Ni / Me is preferably 0.65 or more and less than 1, more preferably 0.7 or more and less than 1, and even more preferably 0.8 or more and less than 1.

[0051] From the viewpoint of increasing capacity and improving output characteristics, the metal Me preferably contains Ni and at least one selected from the group consisting of Co, Mn and Al, and more preferably contains Ni, Co, Mn and / or Al. When the metal Me contains Co, the phase transition of the composite oxide containing Li and Ni during charging and discharging is suppressed, the stability of the crystal structure is improved, and the cycle characteristics are likely to be improved. When the metal Me contains Mn and / or Al, the thermal stability is improved.

[0052] The composite oxide has the general formula (1): Li a Ni b M 1-b O 2 (satisfying 0.9≦a≦1.2 and 0.65≦b≦1, where M is at least one element selected from the group consisting of Co, Mn, Al, Ti, Fe, Nb, B, Mg, Ca, Sr, Zr, and W). The proportion of Ni in the metals other than Li is large, and chunks of Li tend to remain during discharge. In this case, the capacity is easily increased, and the effects of Ni and element M are well balanced.

[0053] The composite oxide is represented by the general formula (2): Lia Ni 1-y-z Co y Al z O 2 (0.9 ≤ a ≤ 1.2, 0 < y ≤ 0.2, 0 < z ≤ 0.05, and y + z ≤ 0.2). When y, which represents the composition ratio of Co, is greater than 0 and less than or equal to 0.2, it is easy to maintain high capacity and high output, and the stability of the crystal structure during charge and discharge is likely to be improved. When z, which represents the composition ratio of Al, is greater than 0 and less than or equal to 0.05, it is easy to maintain high capacity and high output, and the thermal stability is likely to be improved. (1 - y - z), which represents the composition ratio of Ni, satisfies 0.8 or more and less than 1. In this case, the proportion of Ni in the metal other than Li is large, and it is easy to control the precipitation form of Li. Also, in this case, it is easy to achieve high capacity, and the effects of Ni, Co, and Al can be obtained in a well-balanced manner.

[0054] In addition to the above composite oxide, for example, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. may be used as the positive electrode active material.

[0055] The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer may be formed on one surface of the positive electrode current collector or on both surfaces. The positive electrode can be obtained, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the surface of the positive electrode current collector, drying the coating film, and then rolling it.

[0056] The conductive agent is, for example, a carbon material. Examples of the carbon material include carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0057] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber-like polymers, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0058] The positive electrode current collector may be a conductive sheet. The conductive sheet may be a foil, a film, or the like. The surface of the positive electrode current collector may be coated with a carbon material. The thickness of the positive electrode current collector is not particularly limited, and is, for example, 5 μm or more and 300 μm or less.

[0059] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0060] [Separator] A separator may be disposed between the positive electrode and the negative electrode. A porous sheet having ion permeability and insulating properties is used for the separator. Examples of the porous sheet include a thin film having micropores, a woven fabric, and a nonwoven fabric. The material of the separator is not particularly limited, but may be a polymer material. Examples of the polymer material include an olefin resin, a polyamide resin, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The separator may contain an additive as necessary. Examples of the additive include an inorganic filler.

[0061] [Non-aqueous electrolyte] The non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent, and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0062] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0063] The gelled non-aqueous electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. For the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin.

[0064] The lithium salt or anion may be any known material used in non-aqueous electrolytes for lithium secondary batteries. 4 - , ClO 4 - , P.F. 6 - , C.F. 3 SO 3 - , C.F. 3 CO 2 - , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO 2 F) 2 - , N(SO 2 CF 3 ) 2 - , N(C m F 2m+1 SO 2 ) x (C n F 2n+1 SO 2 )y - (m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, and x+y=2 is satisfied.) The anion of the oxalate complex may contain boron and / or phosphorus. The anion of the oxalate complex may be a bisoxalate borate anion: B(C 2 O 4 ) 2 - , difluorooxalate borate anion: BF 2 (C 2 O 4 ) - , P.F. 4 (C 2 O4 ) - , P.F. 2 (C 2 O 4 ) 2 - The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0065] From the viewpoint of suppressing lithium metal from being precipitated in a dendritic form, the non-aqueous electrolyte preferably contains at least an anion of an oxalate complex. Among them, difluorooxalate borate anion is more preferable. Due to the interaction between the anion of the oxalate complex and lithium, lithium metal is easily precipitated uniformly in a lump (particulate) form. Therefore, it is easy to suppress localized precipitation of lithium metal. The anion of the oxalate complex may be combined with another anion. The other anion may be PF 6 - and / or N(SO 2 F) 2 - The anion may be an imide anion such as

[0066] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and halogen-substituted products thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of the halogen-substituted products include fluorides.

[0067] Examples of esters include carbonate esters and carboxylate esters. Examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Examples of chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylate esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylate esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0068] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0069] The non-aqueous solvent may contain a small amount of a component such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethyl carbonate (VEC), etc. In this case, a coating derived from the above-mentioned component is formed on the negative electrode, and the coating suppresses the formation of dendrites.

[0070] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0071] An example of the structure of the non-aqueous electrolyte secondary battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and a non-aqueous electrolyte are housed in an exterior body. Alternatively, instead of a wound type electrode group, an electrode group of another form, such as a stacked type electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, may be applied. The non-aqueous electrolyte secondary battery may be in any form, such as a cylindrical type, a square type, a coin type, a button type, a laminate type, or the like.

[0072] FIG. 3 is a schematic perspective view of a partly cutaway nonaqueous electrolyte secondary battery according to one embodiment of the present invention. The battery includes a bottomed prismatic battery case 4, and an electrode group 1 and a non-aqueous electrolyte (not shown) housed within the battery case 4. The electrode group 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed between them to prevent direct contact. The electrode group 1 is formed by winding the negative electrode, positive electrode, and separator around a flat plate-shaped winding core and then removing the winding core.

[0073] One end of the negative electrode lead 3 is attached to the negative electrode collector of the negative electrode by welding or the like. The other end of the negative electrode lead 3 is electrically connected to a negative electrode terminal 6 provided on the sealing plate 5 via a resin insulating plate (not shown). The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. One end of the positive electrode lead 2 is attached to the positive electrode collector of the positive electrode by welding or the like. The other end of the positive electrode lead 2 is connected to the back surface of the sealing plate 5 via an insulating plate. That is, the positive electrode lead 2 is electrically connected to the battery case 4 which also serves as the positive electrode terminal. The insulating plate separates the electrode group 1 and the sealing plate 5, and separates the negative electrode lead 3 and the battery case 4. The periphery of the sealing plate 5 is fitted into the open end of the battery case 4, and the fitting portion is laser welded. In this way, the opening of the battery case 4 is sealed with the sealing plate 5. The injection hole for the non-aqueous electrolyte provided in the sealing plate 5 is closed with a sealing plug 8 .

[0074] [Example] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples.

[0075] Example 1 [Preparation of positive electrode] Lithium nickel composite oxide (LiNi 0.9 Co 0.05 Al 0.05 O 2), acetylene black, and polyvinylidene fluoride (PVdF) were mixed in a mass ratio of 95:2.5:2.5, N-methyl-2-pyrrolidone (NMP) was added, and the mixture was stirred to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to the surface of an Al foil serving as a positive electrode current collector, the coating was dried, and then the mixture was rolled to form a positive electrode mixture layer (density 3.6 g / cm) on both sides of the Al foil. 3 ) was formed on the positive electrode.

[0076] [Preparation of negative electrode] An electrolytic copper foil (thickness: 10 μm) was cut to a predetermined electrode size to obtain a negative electrode current collector.

[0077] [Preparation of non-aqueous electrolyte] A non-aqueous electrolyte was prepared by dissolving a lithium salt in a mixed solvent. The mixed solvent was a mixture of fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of FEC:EMC:DMC=20:5:75. The lithium salt was LiPF 6 And LiN (FSO 2 ) 2 (hereinafter referred to as LiFSI) and LiBF 2 (C 2 O 4 ) (hereinafter referred to as LiFOB) and LiPF in a non-aqueous electrolyte 6 The concentration of LiFSI in the non-aqueous electrolyte was 0.5 mol / L. The content of LiFOB in the non-aqueous electrolyte was 1 mass %.

[0078] [Battery assembly] An Al positive electrode lead was attached to the positive electrode obtained above, and an Ni negative electrode lead was attached to the negative electrode obtained above. In an inert gas atmosphere, the positive electrode and the negative electrode were spirally wound with a polyethylene thin film (separator) interposed therebetween to produce a wound electrode group. The electrode group was housed in a bag-shaped exterior body formed of a laminate sheet having an Al layer, and the nonaqueous electrolyte was injected, and then the exterior body was sealed to produce a nonaqueous electrolyte secondary battery. When the electrode group was housed in the exterior body, a part of the positive electrode lead and the negative electrode lead were each exposed to the outside from the exterior body.

[0079] Since all of the lithium contained in the electrode group originated from the positive electrode, the molar ratio mLi / mMe of the total amount of lithium mLi contained in the positive and negative electrodes to the amount mMe of metal Me (here, Ni, Co, and Al) contained in the positive electrode was 0.8.

[0080] [Pre-charge / discharge] The obtained battery was subjected to the following preliminary charge and discharge in an environment of 25°C. (Pre-charge) 0.05C (0.5mA / cm2) until the voltage reaches 4.1V (100% charge). 2 ) current I 0 The battery was charged at a constant current. (Pre-discharge) After 10 minutes of rest, discharge at 0.6C (6.0mA / cm2) until the voltage reaches 3.75V (discharge rate 50%). 2 ) constant current discharge was performed.

[0081] [Charge / discharge cycle test] The following charge-discharge cycle test was carried out in a 25° C. environment using the battery after the preliminary charge-discharge.

[0082] (charging) First, the following first and second steps of constant current charging were carried out. 1st step: 0.05C (0.5mA / cm2) from 50% charge to 57.5% charge 2 ) first current I 1 Constant current charging Second step: 0.2C (2.0mA / cm2) from 57.5% charge to 100% charge 2 ) the second current I 2 Constant current charging

[0083] The end of the first step was controlled by the charging time. The charging time (hr) was calculated as (1 / I) x (X / 100) when charging an amount of electricity equivalent to a charging rate of X (%) at a current value of I (C). The end of the second step was controlled by the voltage. Specifically, in the second step, constant current charging was performed until the voltage reached 4.1V, which is estimated as a charging rate of 100%.

[0084] Furthermore, after the above constant current charging, constant voltage charging was performed at a voltage of 4.1 V until the current reached 0.02 C.

[0085] (discharge) After 10 minutes of rest, discharge at 0.6C (6.0mA / cm2) until the voltage reaches 3.75V (discharge rate 50%). 2 ) constant current discharge was performed.

[0086] [evaluation] The above charge and discharge cycle was counted as one cycle, and 100 cycles were performed. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the capacity retention rate.

[0087] Example 2 The nonaqueous electrolyte secondary battery used was the same as that used in Example 1. In the preliminary discharge, the battery was discharged at 0.6 C (6.0 mA / cm) until the voltage reached 3.6 V (up to a discharge rate of 75%). 2 Preliminary charge and discharge were carried out in the same manner as in Example 1, except that constant current discharge was carried out at 0.05 C (0.5 mA / cm) from a charge rate of 25% to 36.25% in the first constant current charge step of the charge-discharge cycle test. 2 ) first current I 1 In the second step, the charge rate was increased from 36.25% to 100% at a constant current of 0.2C (2.0mA / cm 2 ) the second current I 2The battery was charged at a constant current of 0.6 C (6.0 mA / cm2) until the voltage reached 3.6 V (75% discharge rate). 2 A charge-discharge cycle test was carried out in the same manner as in Example 1, except for the above, and evaluation was carried out.

[0088] Comparative Examples 1 and 2 The nonaqueous electrolyte secondary battery used was the same as that used in Example 1. Preliminary charging and discharging was performed in the same manner as in Example 1. In the constant current charging step, the battery was charged at 0.4 C (4.0 mA / cm) until the voltage reached 4.1 V (up to a charging rate of 100%). 2 The charge-discharge cycle test was carried out and evaluated in the same manner as in Example 1, except that constant-current charging was performed at a current of 1.0 V, and the discharge cut-off voltage was set to the value shown in Table 1. When the discharge cut-off voltage in Comparative Example 3 was 3.0 V, discharging was performed to a discharge rate of 100%.

[0089] The evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

[0090] In Examples 1 and 2, a higher capacity retention rate was obtained compared to Comparative Examples 1 and 2. In Example 1, a higher capacity retention rate was obtained.

[0091] In Comparative Example 1, the charging current density at the initial stage of charging was 4.0 mA / cm 2 In Comparative Example 2, the charge current density was 4.0 mA / cm at the initial charging stage, and many dendrites were formed on the negative electrode current collector, which led to the isolation of Li and reduced cycle characteristics. 2 Since the discharge cut-off voltage was low and the battery was discharged to a discharge rate of 100%, the cycle characteristics were significantly reduced.

[0092] [Table 1]

[0093] Example 3 The nonaqueous electrolyte secondary battery used was the same as that used in Example 1. Current I 0 0.02C (0.2mA / cm 2) Preliminary charging and discharging were performed in the same manner as in Example 1, and a charge-discharge cycle test was performed and evaluated.

[0094] Example 4 The nonaqueous electrolyte secondary battery used was the same as that used in Example 1. No preliminary charge / discharge was performed. In the first step of the first cycle of the charge / discharge cycle test, the charge rate was increased from 0% to 15% at 0.05 C (0.5 mA / cm 2 ) first current I 1 In the second step, the charge rate was increased from 15% to 100% at a constant current of 0.2C (2.0mA / cm 2 ) the second current I 2 In the first step of the second cycle onwards, the charge rate was increased from 50% to 57.5% at a constant current of 0.05C (0.5mA / cm 2 ) first current I 1 In the second step, the charge rate was increased from 57.5% to 100% at a constant current of 0.2C (2.0mA / cm 2 ) the second current I 2 A charge-discharge cycle test was carried out in the same manner as in Example 1 except for the above, and evaluation was carried out.

[0095] The evaluation results of Examples 3 and 4 are shown in Table 2. Table 2 also shows the evaluation results of Example 1.

[0096] A high capacity retention rate was obtained in all of Examples 1, 3, and 4. In Examples 1 and 3, in which preliminary charging and discharging was performed, a higher capacity retention rate was obtained. 2 In Example 3, an even higher capacity retention rate was obtained.

[0097] [Table 2] [Industrial Applicability]

[0098] The method for charging and discharging a nonaqueous electrolyte secondary battery according to the present invention is suitably used for a nonaqueous electrolyte secondary battery of the type in which lithium metal is deposited on the negative electrode current collector during charging and the lithium metal dissolves during discharging. Although the present invention has been described with respect to the presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be interpreted to cover all variations and modifications without departing from the true spirit and scope of the present invention. [Explanation of symbols]

[0099] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug, 11: nonaqueous electrolyte secondary battery, 12: charge / discharge device, 13: external power source, 14: external load, 15: charge control unit, 16: discharge control unit, 17: voltage detection unit, 18: current detection unit

Claims

1. A battery comprising: a positive electrode; a negative electrode having a negative electrode current collector; and a non-aqueous electrolyte; A method for charging and discharging a non-aqueous electrolyte secondary battery, in which lithium metal is precipitated on the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharging, comprising the steps of: A charging step and a discharging step performed after the charging step, The charging step is performed at a current density of 1.0 mA / cm ２ The first current I １ A first step of performing constant current charging with the first current I １ A second current I ２ and a second step of performing constant current charging at In the discharging step, an amount of electricity equivalent to 20% or more and 80% or less of a fully charged amount is discharged.

2. In the first step, the first current I １ The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 1 , wherein constant current charging is performed at a constant current of 100 V.

3. 3. The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 1, wherein in the first step, an amount of electricity corresponding to 5% or more and 15% or less of a total amount of electricity charged in the charging step is charged.

4. The charging step includes, after the second step, a third current I ３ A third step of constant current charging is performed at The second current I ２ is the first current I １ and the current density is 4.0 mA / cm ２ is as follows: The third current I ３ is the second current I ２ and the current density is 4.0 mA / cm ２ That's all. A method for charging and discharging the nonaqueous electrolyte secondary battery according to claim 1 or 2.

5. In the second step, constant current charging is performed at the second current I2, which is larger than the first current I1 and is equal to or less than 0.4 C; 5. The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 4, wherein in the third step, constant current charging is performed at the third current I3 that is larger than the second current I2 and is 0.4 C or more.

6. In the first step, constant current charging is performed so that the amount of charge in the first step is 15% or less of the total amount of charge in the charging step; In the second step, constant current charging is performed so that the total amount of charge electricity in the first step and the second step is 50% or less of the total amount of charge electricity in the charging step. The method for charging and discharging the nonaqueous electrolyte secondary battery according to claim 4 or 5.

7. Furthermore, before the first charging step, the current density is 0.5 mA / cm ２ The current I ０ The method for charging and discharging a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, further comprising a preliminary charging step of performing constant current charging at a constant current of 100 V.

8. 8. The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 7, wherein in the preliminary charging step, constant current charging is performed at the current I0 of 0.05 C or less.

9. A method for charging and discharging a non-aqueous electrolyte secondary battery as described in claim 7 or 8, comprising a pre-discharge step of discharging an amount of electricity equivalent to 20% or more and 80% or less of a fully charged amount after the pre-charge step and before a first charging step.

10. The positive electrode has a layered rock salt type crystal structure and contains a composite oxide containing lithium and nickel, The composite oxide has the general formula (1): Li ａ Ni ｂ M １－ｂ O ２ wherein in general formula (1), 0.9≦a≦1.2 and 0.65≦b≦1 are satisfied, and M is at least one element selected from the group consisting of Co, Mn, Al, Ti, Fe, Nb, B, Mg, Ca, Sr, Zr, and W.

11. The method for charging and discharging a nonaqueous electrolyte secondary battery according to any one of claims 1 to 10, wherein the negative electrode current collector is a copper foil or a copper alloy foil.

12. The first step is a process for precipitating the lithium metal in a lump form on the negative electrode current collector, The second step is a step of depositing further lithium metal on the lump of lithium metal, 12. The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 1, wherein in the discharging step, at least a portion of the lump of lithium metal is left on the negative electrode current collector.

13. The present invention includes a non-aqueous electrolyte secondary battery and a charge / discharge device, The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte, and lithium metal is deposited on the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharging. The charging / discharging device includes a charging control unit and a discharging control unit, The charging control section has a current density of 1.0 mA / cm ２ The first current I １ After the first constant current charging, the first current I １ A second current I ２ and controlling the charging so as to perform a second constant current charging at The discharge control unit controls the discharge so as to discharge an amount of electricity equivalent to 20% or more and 80% or less of a fully charged amount. A charging and discharging system for non-aqueous electrolyte secondary batteries.

14. 14. The charge / discharge system for a nonaqueous electrolyte secondary battery according to claim 13, wherein the first constant current charging charges an amount of electricity equivalent to 5% or more and 15% or less of a total charged amount of electricity.

15. The charging control unit controls the charging of the battery at a third current I ３ and controlling the charging so as to perform a third constant current charging at The second current I ２ is the first current I １ and the current density is 4.0 mA / cm ２ is as follows: The third current I ３ is the second current I ２ and the current density is 4.0 mA / cm ２ That's all. The charge / discharge system for a non-aqueous electrolyte secondary battery according to claim 13.

16. the charging control unit controls charging so that, when a charging amount of electricity reaches a first threshold value in the first constant current charging, the first constant current charging is terminated and the second constant current charging is started, and, when a charging amount of electricity reaches a second threshold value in the second constant current charging, the second constant current charging is terminated and the third constant current charging is started; The first threshold value is a charged amount of electricity equivalent to 15% or less of a total charged amount of electricity, The second threshold value is a charging amount of electricity equivalent to 50% or less of the total charging amount of electricity. The charge / discharge system for a non-aqueous electrolyte secondary battery according to claim 15.

17. The charge control unit controls the current density to be 0.5 mA / cm before the initial first constant current charge. ２ The current I ０ The charge / discharge system for a non-aqueous electrolyte secondary battery according to any one of claims 13 to 16, wherein charging is controlled so as to perform constant current charging at a constant current of 100 V.

18. The charge / discharge system for a non-aqueous electrolyte secondary battery as described in claim 17, wherein the charge control unit controls discharging so that, after constant current charging at the current I0, before an initial first constant current charging, an amount of electricity equivalent to 20% or more and 80% or less of a fully charged amount is discharged.

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