Method for activating non-aqueous electrolyte secondary battery and method for manufacturing non-aqueous electrolyte secondary battery

Abstract

To perform activation of a non-aqueous electrolyte secondary battery with low internal resistance and a long life.SOLUTION: In a nonaqueous electrolyte secondary battery, which includes a positive electrode, a negative electrode, a third electrode for charging the negative electrode, a separator for isolating the positive electrode, the negative electrode, and the third electrode, and a nonaqueous electrolyte, the negative electrode contains graphite, and the nonaqueous electrolyte contains LiB(C2O4)2 as an additive, and an activation method for a non-aqueous electrolyte secondary battery includes an initial charging step (S81) of performing initial charging using a positive electrode and a negative electrode, a negative electrode charging step (S82) of performing charging using the negative electrode and the third electrode, an aging step (S83), and a negative electrode discharging step (S84) using the negative electrode and the third electrode.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a method for activating a nonaqueous electrolyte secondary battery and a method for manufacturing a nonaqueous electrolyte secondary battery, and more particularly to a method for activating a nonaqueous electrolyte secondary battery having low internal resistance and a long life, and a method for manufacturing a nonaqueous electrolyte secondary battery. [Background technology]

[0002] In non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, a film of SEI (Solid Electrolyte Interphase) is formed to protect the negative electrode during initial charging. However, this SEI increases the reaction resistance. Since the SEI film has a high resistance, it is desirable for it to be thin and have a low reaction resistance.

[0003] In addition, in such lithium ion secondary batteries, the capacity of the battery is determined by the amount of lithium inserted and removed from the positive electrode. On the other hand, the decomposition reaction of the electrolyte occurs in the negative electrode, and lithium is consumed for the formation of SEI, etc., so the capacity of the battery decreases. For this reason, a nonaqueous electrolyte with a low decomposition rate is desirable.

[0004] For this purpose, it has been found that adding an additive such as LiB(C2O4)2 to a non-aqueous electrolyte reduces the reaction resistance of the SEI and suppresses the decomposition of the non-aqueous electrolyte at the negative electrode, thereby improving storage characteristics. Furthermore, when such an additive is added, high-temperature aging at a higher SOC [%] can significantly reduce the reaction resistance of the SEI and suppress the decomposition of the non-aqueous electrolyte at the negative electrode, thereby improving storage characteristics.

[0005] However, if the SOC [%] of a cell is increased during high-temperature aging, the positive electrode potential will rise, and transition metals in the positive electrode active material will dissolve, which may lead to a so-called chemical short circuit in the negative electrode. Therefore, it is not desirable to increase the SOC [%] of the entire battery cell.

[0006] Therefore, it is possible to increase only the SOC [%] of the negative electrode by lowering the counter capacity ratio CR, which is the ratio of the negative electrode capacity to the positive electrode capacity. However, if the counter capacity ratio CR is set below a certain value, the so-called high-rate performance and resistance to overcharging may deteriorate.

[0007] In Patent Document 1, the imbalance in the amount of carrier ions inserted and removed between the positive electrode and the negative electrode caused by decomposition of the electrolyte in the negative electrode is adjusted or improved to suppress the decrease in the capacity of the electricity storage device. The electricity storage device has a positive electrode, a negative electrode, and an electrolyte, and further has a third electrode, and after charging the electricity storage device using the positive electrode and the negative electrode, additional charging is performed using the third electrode and the negative electrode.

[0008] Patent Document 2 describes a lithium-ion battery system that includes a positive electrode, a negative electrode, an electrolyte, and a third electrode that uses a material containing lithium as an active material. At least one of the third electrode and the positive electrode and the third electrode and the negative electrode has a connection part that can be switched between an electrically connected state and an electrically disconnected state. The system avoids the deposition of metallic lithium in the negative electrode or overdischarge in the positive electrode, and appropriately replenishes lithium ions.

[0009] As described above, there is a technique for performing different processes on the positive electrode and the negative electrode by using a third electrode different from the positive electrode and the negative electrode. Such a method using a third electrode makes it possible to perform different treatments on the positive electrode and the negative electrode. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2014-143184 A [Patent Document 2] JP 2016-051570 A Summary of the Invention [Problem to be solved by the invention]

[0011] However, the invention described in Patent Document 1 is to adjust or improve the imbalance in the amount of carrier ions inserted and removed between the positive electrode and the negative electrode caused by decomposition of the electrolyte in the negative electrode to suppress the decrease in the capacity of the electricity storage device, but is not an adjustment in the activation process. Also, the invention described in Patent Document 2 is to avoid the deposition of metallic lithium in the negative electrode or overdischarge in the positive electrode and appropriately replenish lithium ions, but is also not an adjustment in the activation process. In the first place, there was no recognition of the issues of reducing internal resistance and extending the life in the activation process.

[0012] The problem to be solved by the method for activating a nonaqueous electrolyte secondary battery and the method for producing a nonaqueous electrolyte secondary battery of the present invention is to activate a nonaqueous electrolyte secondary battery so as to reduce internal resistance and extend the battery life. [Means for solving the problem]

[0013] In order to solve the above problems, the method for activating a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a third electrode for charging the negative electrode, a separator separating the positive electrode, the negative electrode, and the third electrode, and a non-aqueous electrolyte, wherein the negative electrode contains graphite and the non-aqueous electrolyte contains LiB(C2O4)2 as an additive, and the method includes a first charging step of performing initial charging using the positive electrode and the negative electrode, a second charging step of performing charging using the negative electrode and the third electrode, an aging step, and a first discharging step of performing discharging using the negative electrode and the third electrode.

[0014] Furthermore, following the first discharging step, a second discharging step can be included in which discharging is performed using the positive electrode and the negative electrode. In this case, the additive to the non-aqueous electrolyte may contain at least one of FSO3Li and LiPO2F2.

[0015] The third electrode may contain any one of metallic lithium, a ternary positive electrode material containing nickel, manganese and cobalt, lithium iron phosphate (LiFePO4), LiMn2O4 and Al.

[0016] The electrode body of the nonaqueous electrolyte secondary battery is configured as a wound body in which the positive electrode, the negative electrode and the separator are laminated and wound, and the third electrode can be disposed around the wound body.

[0017] Alternatively, the third electrode may be a metal case of the nonaqueous electrolyte secondary battery. The method for activating a nonaqueous electrolyte secondary battery may include a method for producing a nonaqueous electrolyte secondary battery, which can be suitably carried out when the nonaqueous electrolyte secondary battery is a lithium ion secondary battery. Effect of the Invention

[0018] The method for activating a nonaqueous electrolyte secondary battery and the method for producing a nonaqueous electrolyte secondary battery of the present invention have the effect of enabling activation of a nonaqueous electrolyte secondary battery with low internal resistance and long life. [Brief description of the drawings]

[0019] [Figure 1] 1 is a perspective view showing an outline of the configuration of a lithium ion secondary battery according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a schematic diagram showing the configuration of a wound electrode body and a third electrode. [Diagram 3] FIG. 2 is a schematic diagram showing the functions of a positive electrode, a negative electrode, and a third electrode. [Figure 4] FIG. 2 is a schematic diagram showing the relationship between a negative electrode active material and a coating of an SEI. [Diagram 5] 1 is a graph for determining a degradation slope DC indicating degradation of a lithium ion secondary battery. [Figure 6] 1 is a graph showing the relationship between the negative electrode SOC [%] and the degradation slope of the negative electrode in an aging process. [Figure 7]1 is a graph showing the relationship between the negative electrode SOC [%] and the reaction resistance [mΩ] of the negative electrode in the aging process. [Figure 8] 1 is a graph showing the capacity of a battery cell of a lithium ion secondary battery and the potentials of the negative electrode and positive electrode when the opposed capacity ratio CR, which is the ratio of the negative electrode capacity to the positive electrode capacity, is changed. [Figure 9] 2 is a flowchart showing an example of a method for manufacturing the lithium ion secondary battery according to the present embodiment. [Figure 10] 3 is a flowchart showing the procedure of a method for activating a lithium ion secondary battery according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A method for activating a non-aqueous electrolyte secondary battery and a method for manufacturing a non-aqueous electrolyte secondary battery according to the present invention will be described with reference to one embodiment of a method for manufacturing a lithium ion secondary battery 1 with reference to FIGS. (Principle of the invention of this embodiment) As described in the Background Art, since the SEI coating has a high resistance, it is desirable that it is thin, has a low reaction resistance, and has a low decomposition rate of the nonaqueous electrolyte. For this purpose, it has been found that adding an additive such as LiB(C2O4)2 to the nonaqueous electrolyte reduces the reaction resistance of the SEI and suppresses the decomposition of the nonaqueous electrolyte at the negative electrode, thereby improving storage characteristics. Furthermore, when such an additive is added, high-temperature aging at a higher SOC [%] can significantly reduce the reaction resistance of the SEI and suppress the decomposition of the nonaqueous electrolyte at the negative electrode, thereby improving storage characteristics.

[0021] <Negative electrode active material NA and SEI> 4 is a schematic diagram showing the relationship between the negative electrode active material NA and the SEI. The coating of the SEI is formed by mixing the negative electrode active material NA made of graphite particles GP with the nonaqueous electrolyte 13 and lithium ions Li decomposed during the initial charge. + The lithium ion Li + Electron - is exchanged between the nonaqueous electrolyte 13 and the graphite particles GP which are the negative electrode active material NA.

[0022] <Deterioration gradient D C > FIG. 5 is a graph showing the degradation slope D of the battery cell capacity Cc [Ah] of the lithium-ion secondary battery 1 over time ΔT [days]. C The horizontal axis indicates the number of days of storage T [days], and the vertical axis indicates the battery cell capacity Cc [Ah]. C " is an index showing the degree of deterioration [Ah / day] of the battery cell capacity Cc [Ah] caused mainly by the decomposition of the non-aqueous electrolyte on the negative electrode surface. Deterioration is accelerated under the conditions of a specified high temperature (75[°C] in this case) and a specified high SOC [%] (80[%] in this case). "Deterioration gradient D C " is D C Here, graph L2 is derived from graph L1 by the "deterioration slope D C " is larger. From this, it can be said that the rate of deterioration per unit time of graph L2 is faster than that of graph L1.

[0023] <Negative electrode SOC [%] and degradation slope D C > FIG. 6 shows the degradation slope D when the negative electrode SOC [%] is changed during the aging process (FIG. 10: S83). C The horizontal axis of the graph in FIG. 6 is the SOC [%] of the negative electrode during the aging process, and the vertical axis is the "deterioration slope D C Although not shown in the figure, the degradation slope D C The graph L4 was obtained by plotting the points and performing multiple regression analysis. Graph L4 shows the coefficient of determination R 2 = 0.85, showing a strong correlation. From this graph, we can see that the higher the negative electrode SOC [%] in the aging process, the more resistant the lithium-ion secondary battery that can be manufactured is to degradation.

[0024] <Negative electrode SOC [%] and negative electrode reaction resistance R A [mΩ]> Figure 7 shows the relationship between the negative electrode SOC [%] and the negative electrode reaction resistance R during the aging process. A 4. The horizontal axis is the SOC [%] of the negative electrode during the negative electrode aging process, and the vertical axis is the reaction resistance R A Although not shown in the figure, the reaction resistance R when the negative electrode SOC [%] is changed in many cases A By plotting the points of [mΩ] and performing multiple regression analysis, graph L5 was obtained. Graph L5 shows the coefficient of determination R 2 = 0.84, which shows a strong correlation. From this graph, it can be seen that the larger the negative electrode SOC [%] during the aging process, the greater the reaction resistance R A It was found that it is possible to manufacture a lithium ion secondary battery 1 with a small resistance [mΩ].

[0025] <About positive electrode SOC> For the reasons mentioned above, the higher the SOC [%] of the negative electrode during high-temperature aging, the more the deterioration of the negative electrode can be suppressed and the reaction resistance RA [mΩ] can be suppressed. For this reason, it is possible to increase the SOC [%] of the cell battery itself during high-temperature aging. If the SOC [%] of the cell battery itself is increased, the SOC [%] of the negative electrode increases and the potential [V] of the positive electrode also increases. If the potential [V] of the positive electrode increases, the transition metal in the positive electrode active material dissolves into the nonaqueous electrolyte 13. The dissolved transition metal precipitates as a metal in the negative electrode, causing so-called chemical short circuits and causing short circuits. For these reasons, there are problems with increasing the SOC [%] of the entire cell battery.

[0026] <Positive electrode capacity and negative electrode capacity> Figure 8 shows the positive electrode capacity C P Negative electrode capacity C versus [Ah] N The opposing capacity ratio C, which is the ratio of [Ah] R The capacity C of a lithium-ion secondary battery cell when C The horizontal axis shows the capacity C [Ah] and the vertical axis shows the positive electrode potential V P [V], negative electrode potential V N [V] and the cell battery voltage V CIndicates [V].

[0027] Graph L6 shows the capacitance of the positive electrode, C P [Ah] and positive electrode potential V P [V]. Graph L8 shows the standard negative electrode capacity C N1 [Ah] and negative electrode potential V N [V] relationship, graph L7 is the adjusted negative electrode capacity C N2 [Ah] and negative electrode potential V N [V] relationship.

[0028] Here, C P [Ah] is the positive electrode capacity, C N1 [Ah] is the standard negative electrode capacity, C N2 [Ah] indicates the adjusted negative electrode capacity. C [Ah] indicates the capacity of the cell battery. In this graph, C C [Ah] is the positive electrode capacity C P It is equal to [Ah].

[0029] In Figure 8, V C [V] indicates the voltage of the cell battery. At points P1 and P2, the positive electrode potential is V P [V], and the negative electrode potential is V N [V]. Cell battery voltage V C [V] is V C =V P -V N As shown in the figure.

[0030] The positive electrode capacity C shown in Figure 8 P [Ah] and standard negative electrode capacity C N1 [Ah], the negative electrode capacity C N1 In this way, the positive electrode capacity C P [Ah] Negative electrode capacity C N1 The reason why [Ah] is large is as follows. When the capacity of the negative electrode is insufficient during charging and the negative electrode is overcharged, the nonaqueous electrolyte 13 decomposes and lithium ions Li + In order to prevent the negative electrode from being overcharged, the negative electrode capacity C N1This is because there is a margin in [Ah]. In other words, the cell battery capacity C C [Ah] is the positive electrode capacity C P It is set as a so-called "positive regulation" regulated by [Ah].

[0031] < Opposing capacitance ratio C R > Here, the negative electrode capacity C N [Ah] vs. Positive electrode capacity C P The ratio of [Ah] is called the "opposite capacity ratio C R " and is calculated using the following formula:

[0032] "Opposed capacitance ratio C R ” = negative electrode capacity C N [Ah] / positive electrode capacity C P [Ah] And the positive electrode capacity C P Negative electrode capacity C versus [Ah] N1 The ratio of [Ah] is called the "opposite capacity ratio C R1 "

[0033] Then, the initial capacitance ratio C R1 teeth, C R1 =C N1 / C P It is calculated by:

[0034] On the other hand, the positive electrode capacity C P Anode capacity C adjusted for [Ah] N2 The ratio of [Ah] is called the "opposite capacity ratio C R2 Then, the opposing capacitance ratio C R2 , C R2 =C N1 / C P It is calculated by:

[0035] In this case, the positive electrode capacity C P [Ah] is constant, Negative electrode capacity C N1 >Negative electrode capacity C N2 Therefore, Opposing capacitance ratio CR1 > Opposing capacitance ratio C R2 It becomes.

[0036] As mentioned above, the opposing capacitance ratio C R1 The opposing capacitance ratio C R2 The negative electrode capacity C N1 The negative electrode capacity C N2 In this case, there is no change in the positive electrode SOC [%] or the cell battery SOC [%] at point P1 on graph L6.

[0037] On the other hand, the negative electrode capacity C N1 The negative electrode capacity C N2 In this case, the negative electrode SOC [%] at point P2 in graph L8 becomes relatively large. As a result, as shown in FIG. 6 and FIG. 7, the negative electrode SOC [%] becomes relatively high, and the deterioration gradient D C [Ah / day] becomes smaller and the reaction resistance [mΩ] also becomes smaller.

[0038] In other words, if the positive electrode SOC [%] is constant, the opposing capacity ratio C R The smaller the value, the higher the negative electrode SOC [%]. Therefore, in this embodiment, the opposing capacity ratio C R is set to be 190[%] or less.

[0039] However, although the negative electrode capacity is originally set to a certain extent as a positive electrode regulation, the capacity of the negative electrode decreases with use. In this case, if the negative electrode is overcharged, the cell battery may deteriorate significantly.

[0040] Therefore, in this embodiment, the opposed capacity ratio CR, which is the ratio of the negative electrode capacity to the positive electrode capacity, is set to 120% or more. <3rd electrode> Fig. 1 is a perspective view showing the outline of the configuration of a lithium ion secondary battery 1 of this embodiment. Fig. 2 is a schematic diagram showing the configuration of an electrode body 12 to be wound.

[0041] The opposing capacitance ratio C R However, there is a limit to how much the SOC [%] of the negative electrode can be increased by adjusting the positive electrode potential. Therefore, the present inventors solved this problem by using a lithium-ion secondary battery 1 equipped with a third electrode.

[0042] The lithium ion secondary battery 1 of this embodiment includes a negative electrode plate 3, a positive electrode plate 2, a third electrode plate 5 for charging the negative electrode, a separator 4, and a non-aqueous electrolyte 13. The negative electrode plate 3 contains graphite, which is a negative electrode active material, and constitutes the negative electrode. The positive electrode plate 2 constitutes the positive electrode. The third electrode plate 5 constitutes a third electrode for charging the negative electrode. The separator 4 separates the positive electrode plate 2, the negative electrode plate 3, and the third electrode plate 5. The non-aqueous electrolyte 13 contains LiB(C2O4)2 as an additive.

[0043] <Activation Method of Lithium-Ion Secondary Battery 1 of the Present Embodiment> FIG. 10 is a flow chart showing the procedure of the activation method of the lithium ion secondary battery 1 of this embodiment (FIG. 9: S8). On the premise of the above-mentioned configuration, in the activation method of the lithium ion secondary battery 1 of this embodiment, an initial charging step (first charging step) is performed using the negative electrode plate 3 and the positive electrode plate 2 (S81). Then, a negative electrode charging (second charging step) is performed in which charging is performed using the negative electrode plate 3 and the third electrode plate 5 (S82). Then, an aging step (S83) is performed. After the aging step (S83) is completed, a negative electrode discharging (first discharging step) is performed in which discharging is performed using the negative electrode plate 3 and the third electrode plate 5. Then, a cell discharging (second discharging step) is performed, and the activation step (FIG. 9: S8) is completed.

[0044] By carrying out such a process, aging can be carried out in a state where the negative electrode SOC [%] is high, and activation can be carried out to obtain a lithium ion secondary battery 1 with low internal resistance and long life.

[0045] (Configuration of this embodiment) The activation method for the lithium ion secondary battery 1 according to this embodiment will be described in detail below. <Configuration of lithium-ion secondary battery 1> 1 is a perspective view showing the outline of the external configuration of a lithium-ion secondary battery 1 according to the present embodiment. First, the configuration of the lithium-ion secondary battery 1 according to the present embodiment, which is an example of the present invention, will be described.

[0046] As shown in FIG. 1, the lithium ion secondary battery 1 is configured as a cell battery. The lithium ion secondary battery 1 includes a battery case 11 in the shape of a plate-like rectangular parallelepiped having an opening on the upper side. An electrode body 12 is accommodated inside the battery case 11. A nonaqueous electrolyte 13 is filled into the battery case 11 through a filling hole (not shown). The battery case 11 is made of a metal such as an aluminum alloy, and forms a battery container sealed by a lid. The lithium ion secondary battery 1 also includes a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power. The positive electrode external terminal 14 is electrically connected to a positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to a negative electrode current collector terminal 17 inside the battery case 11 via the lid. The positive electrode current collector terminal 16 is electrically connected to a positive electrode current collector part 23 (see FIG. 4) of the electrode body 12. Moreover, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector portion 33 of the electrode body 12 (see FIG. 4).

[0047] The configuration of this embodiment is characterized by having a third electrode. The lithium ion secondary battery 1 of this embodiment is provided with a third electrode external terminal 18 used for charging and discharging power. The third electrode external terminal 18 is electrically connected to a third electrode current collector terminal 19 inside the battery case 11 via a lid body. The third electrode current collector terminal 19 is electrically connected to the third electrode plate 5 of the electrode body 12.

[0048] <Electrode body 12> 2 is a schematic diagram showing the configuration of the wound electrode assembly 12. The electrode assembly 12 is formed by stacking a large number of positive electrode plates 2 and negative electrode plates 3 with separators 4 disposed therebetween. This embodiment is characterized in that it further includes a third electrode plate 5 on the outermost side.

[0049] <Negative plate 3 and positive plate 2> The stacked positive electrode plate 2, negative electrode plate 3, and separator 4 are wound to form a flat plate. The negative electrode plate 3 has a negative electrode composite layer 32 formed on a negative electrode current collector 31 made of copper foil as a base material. A negative electrode current collector 33 is provided on one end side in a width direction W (winding axis direction) perpendicular to the winding direction (winding direction L). The negative electrode current collector 33 has a configuration in which the negative electrode composite layer 32 is not formed and the negative electrode current collector 31 is exposed.

[0050] In the positive electrode plate 2, a positive electrode composite layer 22 is formed on a positive electrode collector 21 made of aluminum foil as a base material. As shown in Fig. 4, a positive electrode collector 23 is provided on the other end side (opposite to the negative electrode collector 33) in a width direction W (winding axis direction) perpendicular to the direction in which the positive electrode collector 21 is wound (winding direction L). No positive electrode composite layer 22 is formed on the positive electrode collector 23, and the metal of the positive electrode collector 21 is exposed.

[0051] <Layer structure of electrode body 12> As shown in FIG. 2, the basic configuration of an electrode assembly 12 of a lithium ion secondary battery 1 includes a positive electrode plate 2, a negative electrode plate 3, and a separator 4.

[0052] The positive electrode plate 2 includes a positive electrode mixture layer 22 on both sides of a positive electrode current collector 21 serving as a positive electrode base material. The other end of the positive electrode current collector 21 serves as a positive electrode current collector 23 where the metal is exposed. The negative electrode plate 3 includes a negative electrode mixture layer 32 on both sides of a negative electrode current collector 31 serving as a negative electrode base material. One end of the negative electrode current collector 31 serves as a negative electrode current collecting portion 33 where the metal is exposed.

[0053] A laminate is formed by stacking the positive electrode plate 2 and the negative electrode plate 3 with a separator 4 interposed therebetween. As shown in Fig. 2, this laminate is wound in the longitudinal direction around the winding axis to form a wound-type electrode assembly 12 that is shaped flat as shown in Fig. 1.

[0054] <Laminated Structure of Third Electrode Plate 5> As shown in Fig. 1, the electrode body 12 of this embodiment further includes a third electrode plate 5 at its outermost portion. As shown in Fig. 2, a separator 4 is disposed at the outermost portion of the wound body of the negative electrode plate 3 and the positive electrode plate 2. The third electrode plate 5 is laminated on the separator 4 while being insulated by the separator 4. That is, the third electrode plate 5 is disposed so as to wrap the wound body of the positive electrode plate 2 and the negative electrode plate 3. An insulating resin sheet (not shown) is disposed on the inner surface of the Al battery case 11, so that the third electrode plate 5 and the battery case 11 are also insulated from each other.

[0055] 1, a third electrode current collecting terminal 19 is electrically connected to the third electrode plate 5. In addition, the third electrode current collecting terminal 19 is electrically connected to a third electrode external terminal 18 via the lid of the battery case 11.

[0056] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of the lithium ion secondary battery 1 of this embodiment shown in FIG. 1 is a composition in which a lithium salt is dissolved in an organic solvent. As the lithium salt, LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. can be used. As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used. As the non-aqueous electrolyte 13, one or more of these can be mixed and used. The composition of the non-aqueous electrolyte 13 is not limited to this.

[0057] <Additives> In the non-aqueous electrolyte 13 of this embodiment, LiB(C2O4)2 is added as an additive. Therefore, during the initial charge, the reaction resistance [mΩ] of the SEI coating formed on the surface of the graphite particles GP, which are the negative electrode active material of the negative electrode, can be reduced, and the decomposition of the non-aqueous electrolyte 13 can be suppressed. For the same purpose, the additive of the non-aqueous electrolyte 13 can further contain either or both of FSO3Li and LiPO2F2 in addition to LiB(C2O4)2. Of course, the additive is not limited to these. Furthermore, it can contain various additives that are added for various purposes, although not exemplified.

[0058] <Components of electrode body 12> Next, the components constituting the electrode assembly 12, that is, the positive electrode plate 2, the negative electrode plate 3, the separator 4, and the third electrode plate 5, will be described.

[0059] <Negative electrode plate 3> As shown in Fig. 2, negative electrode mixture layers 32 are formed on both sides of negative electrode current collector 31, which is a negative electrode base material, to form negative electrode plate 3. In a source process (Fig. 9: S1), negative electrode mixture layer 32 is formed by applying a negative electrode mixture paste to negative electrode current collector 31. After that, negative electrode plate 3 is completed through a drying process, a pressing process, and a cutting process.

[0060] <Negative electrode current collector 31> In this embodiment, the negative electrode current collector 31 is made of Cu foil. The negative electrode current collector 31 serves as a base for the aggregate of the negative electrode mixture layer 32, and also functions as a current collecting member that collects electricity from the negative electrode mixture layer 32. One end of the negative electrode current collector 31 serves as a negative electrode current collecting part 33 where the negative electrode mixture layer 32 is not formed and the metal surface is exposed. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode current collector 31, the negative electrode current collecting part 33, and the negative electrode current collecting terminal 17.

[0061] <Negative electrode composite layer 32> The negative electrode mixture layer 32 is composed of a negative electrode active material as a raw material, a binder (binding material) as a secondary material, additives, etc. The raw materials and secondary materials are kneaded with an organic solvent, etc. to generate a negative electrode mixture paste. This negative electrode mixture paste is applied to the negative electrode current collector 31. The applied negative electrode mixture paste is dried and shaped and pressed to complete the negative electrode plate 3.

[0062] <Negative electrode active material NA> In this embodiment, the negative electrode active material is powdered graphite particles GP made of graphite having a layered structure, and lithium ions Li + It is a material that can absorb and release energy.

[0063] <Positive electrode current collector 21> 2, a positive electrode mixture layer 22 is formed on both sides of a positive electrode current collector 21, which is a positive electrode base material, to form a positive electrode plate 2. In this embodiment, the positive electrode current collector 21 is made of Al foil. The positive electrode current collector 21 serves as a base material for the positive electrode mixture layer 22, and also functions as a current collecting member that collects electricity from the positive electrode mixture layer 22.

[0064] First, the positive electrode base material constituting the positive electrode current collector 21 is exemplified as an Al foil, but may be made of a conductive material made of a metal having good conductivity. As a material having good conductivity, for example, in addition to Al foil, a material containing an Al alloy may be used. The configuration of the positive electrode current collector 21 is not limited to this.

[0065] <Positive electrode mixture layer 22> Positive electrode mixture layer 22 is formed by applying and drying a positive electrode mixture paste to positive electrode current collector 21. Positive electrode mixture layer 22 contains additives such as a conductive assistant, a binder, and a dispersant in addition to positive electrode active material particles.

[0066] <Composition of positive electrode active material> The positive electrode active material particles contain a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment is exemplified by a ternary system called NCM having a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0067] The positive electrode active material of the present embodiment is not limited to a lithium transition metal oxide containing all of Ni, Co, and Mn, and may also be a composition containing, for example, Al in addition to these.

[0068] <Separator 4> The separator 4 is a highly insulating nonwoven fabric made of polypropylene or the like, which is a porous resin for holding the nonaqueous electrolyte 13 between the positive electrode plate 2 and the negative electrode plate 3. As the separator 4, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, and a porous polyvinyl chloride membrane, or a lithium ion or ion conductive polymer electrolyte membrane can be used alone or in combination.

[0069] <Third electrode plate 5> The third electrode plate 5 is made of a metal having a positive potential relative to the negative electrode plate 3, such as metallic lithium, a ternary positive electrode material containing nickel, manganese, and cobalt, lithium iron phosphate (LiFePO4), LiMn2O4, or Al. In this embodiment, the third electrode plate 5 is made of a metal foil made of metallic lithium.

[0070] The third electrode plate 5 transfers lithium ions Li to the negative electrode by utilizing the potential difference during the aging process (FIG. 10: S83). + Therefore, unlike the positive electrode plate 2 and the negative electrode plate 3, a composite layer is not formed on a current collector serving as a base material, but the electrode plate can be made of only metal foil.

[0071] <Method of Manufacturing Lithium-Ion Secondary Battery 1> FIG. 9 is a flow chart showing an example of a method for manufacturing the lithium ion secondary battery 1 of this embodiment. The method for manufacturing the lithium ion secondary battery 1 of this embodiment will be briefly described below. In the lithium ion secondary battery 1, which is a cell battery, first, in the source step (S1), the positive electrode plate 2, the negative electrode plate 3, the separator 4, and the third electrode plate 5, which are power generating elements, are produced. After the positive electrode plate 2, the negative electrode plate 3, the separator 4, and the third electrode plate 5 are produced in the source step (S1), the positive electrode plate 2 and the negative electrode plate 3 are stacked and integrated with each other via the separator 4 in the stacking step (S2). The stack produced in this way is wound in the winding step (S3) in the winding direction L as shown in FIG. 2. The stack wound in the winding step (S3) is roughly plate-shaped. The third electrode plate 5 is further stacked so as to wrap the outermost part of this wound body. Such a wound body is pressed in the thickness direction by the pressing surface of the opposing press machine in the wound body pressing step (S4). In the wound body pressing step (S4), the wound body is pressed until it reaches a specified thickness [mm] so that the electrode body 12 is accommodated without any gaps in the battery case 11 shown in FIG.

[0072] In the winding pressing step (S4), when the thickness of the electrode body 12 is adjusted, an assembly step (S5) is performed. In the assembly step (S5), as shown in FIG. 1, a negative electrode current collector terminal 17, a positive electrode current collector terminal 16, and a third electrode current collector terminal 19 are attached to the electrode body 12, and further, a negative electrode external terminal 15, a positive electrode external terminal 14, and a third electrode external terminal 18 are attached via a lid. Then, the electrode body 12 is housed in a battery case 11. Then, the lid is welded to the battery case 11 to seal the opening. At this stage, the liquid injection port (not shown) of the lid is open, so the cell is heated in a cell drying step (S6) to dry the inside of the cell. After the inside of the cell is dried in the cell drying step (S6), a nonaqueous electrolyte 13 is injected in a liquid injection / sealing step (S7), and the liquid injection port is sealed and hermetically sealed. This completes the assembly of the lithium ion secondary battery 1.

[0073] Then, an SEI film is formed by initial charging (S81 in FIG. 10) in the activation step (S8). In addition, the battery is stored at high temperature for a long time in the aging step (S83) to eliminate micro-short circuits. Details of this activation step (S81 to S85 in FIG. 10) will be described later.

[0074] Once this activation process (S8) is complete, an inspection process (S9) is carried out to check the battery capacity, internal resistance, self-discharge, OCV, etc., and those that pass are shipped as products. <Activation method for lithium-ion secondary batteries> 10 is a flow chart showing in detail the procedure of the activation step (S8) of the lithium ion secondary battery of this embodiment. The activation step (S8) of the lithium ion secondary battery of this embodiment includes an initial charging step (S81), a negative electrode charging step (S82), an aging step (S83), a negative electrode discharging step (S84), and a cell discharging step (S85).

[0075] <Initial charging process (S81)> 3 is a schematic diagram showing the functions of the positive electrode, the negative electrode, and the third electrode, where the arrows indicate the direction of current flow.

[0076] The initial charging step (first charging step) (S81) is the first charging performed on the lithium ion secondary battery 1 after assembly. As shown by the arrows of "Charge 1" in FIG. 3, the positive electrode of a power source (not shown) is connected to the positive electrode external terminal 14, and the negative electrode of the power source is connected to the negative electrode external terminal 15, and a current is applied. In other words, the third electrode external terminal 18 is not connected to the power source. By charging, lithium ions Li+ released from the positive electrode are inserted into graphite, which is the negative electrode active material NA. At this time, the graphite is decomposed into a non-aqueous electrolyte. However, an SEI film is formed at the same time as charging, and thus the graphite is protected from erosion by the non-aqueous electrolyte 13 during subsequent charging.

[0077] By the initial charging, the SOC [%] of the cell battery increases, and the positive electrode SOC [%] and the negative electrode SOC [%] also increase accordingly. For example, the battery is charged to 3.8 [V] or more and 4.0 [V] or less (or the negative electrode SOC is 100 [%]). In the initial charging process (S81) of this embodiment, the battery is charged to 3.97 [V].

[0078] <Negative electrode charging process (S82)> In the negative electrode charging step (second charging step) (S82), as shown by the arrows of "Charge 2" in Fig. 3, a current is applied by connecting the positive electrode of a power source to the third electrode external terminal 18 and the negative electrode of a power source to the negative electrode external terminal 15. In other words, the positive electrode external terminal 14 is not connected to the power source. In this state, charging is performed at a potential at which the negative electrode active material NA of the negative electrode is further reduced.

[0079] In this embodiment, charging is performed until the negative electrode SOC [%] reaches 100 [%]. Alternatively, the voltage [V] between the third electrode and the negative electrode potential may be managed, and charging may be performed from 0 [V] to 0.01 [V].

[0080] <Aging process (S83)> After the negative electrode charging step (S82) is completed, in the aging step (S83), aging is performed with the negative electrode SOC at 100[%] or less.

[0081] The aging conditions were a storage temperature [°C] of 60°C or higher and a storage time of 10 to 30 hours. In this embodiment, the storage temperature [°C] was 65°C and the storage time was 25 hours.

[0082] <Negative electrode discharge process (S84)> After the aging step (S83) is completed, the negative electrode discharge step (first discharge step) (S84) is first performed. In the negative electrode discharge step (S84), the cell is discharged until the cell voltage becomes the cell voltage [V] at the start of aging.

[0083] In the negative electrode discharge step (first discharge step) (S84), as shown by the arrow of "Discharge 1" in Fig. 3, a load is connected to the third electrode external terminal 18 and the negative electrode external terminal 15 to discharge a current. In other words, the positive electrode external terminal 14 is not connected to a load. In this state, the negative electrode active material NA of the negative electrode is oxidized to a normal potential.

[0084] Aging is performed with the negative electrode SOC [%] high, and the negative electrode SOC [%] is lowered to a normal SOC [%] while the positive electrode SOC [%] is kept unchanged in the negative electrode discharge step (S84), thereby adjusting the balance between the positive electrode and the negative electrode. This completes the activation method for the lithium ion secondary battery 1 of this embodiment.

[0085] <Cell discharge process (S85)> The activation process (S8 in FIG. 9) of the lithium ion secondary battery 1 in this embodiment is completed by the negative electrode discharging process (S84), but a cell discharging process (second discharging process) (S85) is performed to equalize the shipping state of the product. Here, a load is connected to the positive electrode external terminal 14 and the negative electrode external terminal 15 to discharge the current, as indicated by the arrows of "Discharge 2" in FIG. 3. In other words, no power source is connected to the third electrode external terminal 18.

[0086] In this way, we aim to standardize the product's shipping condition. When the activation process (FIG. 10: S81 to S85) is completed as described above, the process proceeds to the inspection process (S9) in FIG.

[0087] (Action of this embodiment) As shown in FIG. 10, in the activation method for the lithium ion secondary battery 1 of this embodiment, assuming a configuration including a third electrode, an initial charging step (first charging step) is performed using the negative electrode plate 3 and the positive electrode plate 2 (S81). Then, a negative electrode charging (second charging step) is performed in which charging is performed using the negative electrode plate 3 and the third electrode plate 5 (S82). Then, an aging step (S83) is performed. After the aging step (S83) is completed, a negative electrode discharging (first discharging step) is performed in which discharging is performed using the negative electrode plate 3 and the third electrode plate 5. Then, a cell discharging (second discharging step) is performed, and the activation step (FIG. 9: S8) is completed.

[0088] By carrying out such a process, aging can be carried out in the aging step (S83) in a state where the negative electrode SOC [%] is high, and the lithium ion secondary battery 1 having low internal resistance and long life can be activated.

[0089] (Effects of this embodiment) (1) The method for producing the lithium ion secondary battery 1 of the present embodiment has the advantage of being able to activate the lithium ion secondary battery so as to reduce the internal resistance and extend its life.

[0090] (2) The nonaqueous electrolyte 13 contains LiB(C2O4)2 as an additive, and can fully demonstrate its performance during high-temperature aging. As a result, it has the effect of forming an SEI coating with low reaction resistance and excellent storage characteristics.

[0091] (3) In particular, the provision of the third electrode has the effect of sufficiently increasing the SOC [%] of the negative electrode without adversely affecting the positive electrode. (4) Furthermore, even if the negative electrode deteriorates with use, the deterioration can be restored by using a third electrode.

[0092] (5) The activation process can be performed simply by switching the electrodes, so it can be easily implemented in existing manufacturing equipment. (6) Moreover, since the activation can be performed simply by controlling charging and discharging, appropriate activation can be easily achieved.

[0093] (Another example) In this embodiment, the invention is embodied by the third electrode plate 5 provided on the outer periphery of the electrode body 12, but is not limited thereto. It goes without saying that the shape and position of the third electrode plate 5 can be optimized according to the configuration of the battery by a person skilled in the art. For example, the third electrode plate 5 can use the battery case 11 of the lithium ion secondary battery 1 itself as an electrode.

[0094] In this case, the battery case 11 can function as a third electrode by being made of Al or the like. In this case, in order to suppress electrical corrosion of the battery case 11, the battery case 11 can be configured to guide the charge / discharge current to a specific portion by using a protrusion shape or the like.

[0095] The exemplified additives are not limited to these, and any additives can be used as long as the invention can be carried out. Furthermore, the material of the third electrode is not limited to the examples given, and any material can be used as long as the invention can be implemented.

[0096] In this embodiment, a rectangular plate-shaped lithium ion secondary battery cell is exemplified as a non-aqueous electrolyte secondary battery, but the present invention is not limited to this. The shape is not limited to a cylindrical shape, etc. Furthermore, the shapes of the positive electrode external terminal 14, the negative electrode external terminal 15, the third electrode external terminal 18, etc. are not limited to the shapes shown in the drawings.

[0097] The numerical values ​​and numerical ranges exemplified in the present embodiment are merely examples and may be optimized by those skilled in the art. Other materials for lithium ion secondary batteries are also merely examples and are not limited thereto.

[0098] The flowcharts shown in Figures 9 and 10 are an example of an implementation procedure, and a person skilled in the art can add or delete steps, change the order, or modify the steps as appropriate. In addition, those skilled in the art may add, delete, or modify the configuration without departing from the scope of the claims. [Explanation of symbols]

[0099] C C [Ah]…(cell battery) capacity C P [Ah]…Positive electrode capacity C N1 [Ah]…Negative electrode capacity C N2 [Ah]…Negative electrode capacity C R ,C R1 , C R2 … Opposing capacitance ratio D C [Ah / day]…(Capacity over time) Deterioration rate GP: Graphite particles NA…Negative electrode active material RA [mΩ]…Reaction resistance SEI...SEI coating V C [V]…Cell battery voltage V P [V]…Positive electrode potential V N [V]…Negative electrode potential 1...Lithium-ion secondary battery (cell battery) 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15...Negative external terminal 16…Positive current collecting terminal 17...Negative current collecting terminal 18...Third electrode external terminal 19...Third electrode collector terminal 2…Positive electrode plate 21...Positive electrode current collector 22...Positive electrode mixture layer 23…Positive electrode current collector 3...Negative electrode plate 31...Negative electrode current collector 32...Negative electrode composite material layer 33...Negative electrode current collector 4…Separator 5…Third electrode plate

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a third electrode for charging the negative electrode, a separator separating the positive electrode, the negative electrode, and the third electrode, and a non-aqueous electrolyte, The negative electrode contains graphite, and the non-aqueous electrolyte contains LiB(C ２ O ４ ) ２ Including, a first charging step of performing an initial charging using the positive electrode and the negative electrode, a second charging step of performing charging using the negative electrode and the third electrode, an aging step, and a first discharging step of performing discharging using the negative electrode and the third electrode. A method for activating a non-aqueous electrolyte secondary battery, comprising:

2. Following the first discharge step, a second discharge step is performed in which discharging is performed using the positive electrode and the negative electrode.

2. The method for activating a non-aqueous electrolyte secondary battery according to claim 1, further comprising the steps of:

3. The additive of the non-aqueous electrolyte is FSO ３ Li, LiPO ２ F ２ 2. The method for activating a non-aqueous electrolyte secondary battery according to claim 1, further comprising at least one of the steps of:

4. The third electrode is made of a ternary positive electrode material containing metallic lithium, nickel, manganese, and cobalt, and lithium iron phosphate (LiFePO ４ ), LiMn ２ O ４ 2. The method for activating a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery contains either one of Al and Mn.

5. 2. The method for activating a nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode body of the nonaqueous electrolyte secondary battery is configured as a wound body in which the positive electrode, the negative electrode and the separator are stacked and wound, and the third electrode is disposed around the wound body.

6. 2. The method for activating a non-aqueous electrolyte secondary battery according to claim 1, wherein the third electrode is a metal case of the non-aqueous electrolyte secondary battery.

7. A method for producing a nonaqueous electrolyte secondary battery, comprising the method for activating a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6.

8. 8. The method for producing a non-aqueous electrolyte secondary battery according to claim 7, wherein the non-aqueous electrolyte secondary battery is a lithium ion secondary battery.

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