JP6455726B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Japanese Patent Laying-Open No. 2015-060802 discloses an invention relating to a method for manufacturing a non-aqueous electrolyte secondary battery including a positive electrode having a positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher. . Here, as examples, fluoroethylene carbonate (hereinafter referred to as “FEC” as appropriate) as fluorinated cyclic carbonate and methyl (2,2,2-trifluoroethyl) carbonate as fluorinated chain carbonate. (Hereinafter referred to as “MTFEC” where appropriate) is used in a mixed solvent ratio of FEC: MTFEC = 50: 50 (paragraph 0021).

Japanese Patent Laying-Open No. 2015-060802

By the way, in a non-aqueous electrolyte secondary battery including a positive electrode having a positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher, the non-aqueous electrolyte is decomposed in a high potential region, and gas is generated. There's a problem. It is desirable to suppress the generation of gas while maintaining the performance of such a non-aqueous electrolyte secondary battery high.

The proposed non-aqueous electrolyte secondary battery includes a positive electrode having a positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher, a negative electrode having a negative electrode active material, a non-aqueous electrolyte, And a case containing a positive electrode, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte is composed of a solvent and an additive. The solvent is composed only of a fluorinated chain carbonate, and the additive contains an alkyl-based additive or a boron-based additive. According to this non-aqueous electrolyte secondary battery, the capacity retention rate can be kept high and the amount of gas generated can be kept low.

FIG. 1 is a cross-sectional view of a lithium ion secondary battery 10. FIG. 2 is a graph showing the relationship between the VC addition amount and gas generation amount of Samples 1-9. FIG. 3 is a graph showing the relationship between the VC addition amount and the capacity retention rate of Samples 1 to 9.

  Hereinafter, an embodiment of the nonaqueous electrolyte secondary battery proposed here will be described. The embodiments described herein are, of course, not intended to limit the present invention in particular. The invention is not limited to the embodiments described herein unless specifically stated.

<Configuration Example of Lithium Ion Secondary Battery 10>
FIG. 1 is a cross-sectional view of a so-called prismatic lithium-ion secondary battery 10 showing a configuration example of the proposed nonaqueous electrolyte secondary battery. The lithium ion secondary battery 10 includes, for example, a wound electrode body 40 obtained by winding a positive electrode sheet 50 and a negative electrode sheet 60 with separators 72 and 74 interposed therebetween. In the lithium ion secondary battery 10, the wound electrode body 40 and the electrolytic solution 80 are accommodated in the case 20.

  The positive electrode sheet 50 includes a positive electrode current collector foil 51 and a positive electrode active material layer 53 held on both surfaces of the positive electrode current collector foil 51. The positive electrode active material layer 53 is a layer in which, for example, positive electrode active material particles and a conductive additive are bound by a binder. The positive electrode active material layer 53 has a required gap so that the electrolyte can permeate appropriately between the particles.

  The negative electrode sheet 60 includes a negative electrode current collector foil 61 and negative electrode active material layers 63 held on both surfaces of the negative electrode current collector foil 61. The negative electrode active material layer 63 is a layer in which, for example, negative electrode active material particles and a conductive additive are bound by a binder. The negative electrode active material layer 63 has a required gap so that the electrolyte can permeate appropriately between the particles.

  In the form shown in FIG. 1, the positive electrode current collector foil 51 is a belt-like sheet (for example, an aluminum foil). The positive electrode active material layer 53 is formed on both surfaces of the positive electrode current collector foil 51 except for the exposed portion 52 set on one side in the width direction of the positive electrode current collector foil 51. The negative electrode current collector foil 61 is a belt-like sheet (for example, copper foil). The negative electrode active material layer 63 is formed on both surfaces of the negative electrode current collector foil 61 except for the exposed portion 62 set on one side in the width direction of the negative electrode current collector foil 61.

  The positive electrode sheet 50 and the negative electrode sheet 60 are aligned so that the length direction is aligned, and the positive electrode active material layer 53 and the negative electrode active material layer 63 are opposed to each other with the separators 72 and 74 interposed therebetween. At this time, the exposed portion 52 of the positive electrode current collector foil 51 protrudes on one side of the separators 72 and 74 in the width direction, and the exposed portion 62 of the negative electrode current collector foil 61 protrudes on the opposite side of the separators 72 and 74 in the width direction. The positive electrode sheet 50 and the negative electrode sheet 60 are stacked. The positive electrode sheet 50, the negative electrode sheet 60, and the separators 72 and 74 are wound around the winding axis WL set along the short width of the positive electrode sheet 50 in the state of being stacked as described above. The exposed portion 52 of the positive electrode current collector foil 51 protrudes from the separators 72 and 74 on one side of the wound electrode body 40 along the winding axis WL. On the opposite side, the exposed portion 62 of the negative electrode current collector foil 61 protrudes from the separators 72 and 74. The wound electrode body 40 has a flat shape along one plane including the winding axis WL, and is housed in a rectangular case 20 having a flat rectangular housing region. In addition, an insulating film (not shown) is interposed between the case 20 and the wound electrode body 40 accommodated in the case 20, and the case 20 and the wound electrode body 40 are preferably insulated.

  In the example shown in FIG. 1, the case 20 includes a case main body 21 and a sealing plate 22. Here, the case main body 21 has a bottomed rectangular parallelepiped shape whose one surface is open. The sealing plate 22 is a member that closes the opening of the case body 21. The sealing plate 22 is welded to the peripheral edge of the opening of the case body 21 to form a substantially hexahedral case 20. In the example shown in FIG. 1, the sealing plate 22 is provided with a positive external terminal 25 and a negative external terminal 26. The external terminals 25 and 26 are electrically connected to internal terminals 23 and 24 that extend into the case 20. An exposed portion 52 of the positive electrode current collector foil 51 is welded to the distal end portion 23a of the internal terminal 23 of the positive electrode. The exposed portion 62 of the negative electrode current collector foil 61 is welded to the tip 24 a of the negative internal terminal 24.

  The positive electrode current collector foil 51 is electrically connected to an external device through the internal terminal 23 and the external terminal 25. The negative external terminal 26 is electrically connected to the internal terminal 24. The negative electrode current collector foil 61 is electrically connected to an external device through the internal terminal 24 and the external terminal 26. The sealing plate 22 is provided with a safety valve 30 and a liquid injection hole 32, and a cap material 33 is attached to the liquid injection hole 32.

  The electrolytic solution 80 accommodated in the case 20 enters the electrode body 40 from both sides in the axial direction of the winding shaft WL. The electrolytic solution 80 sufficiently permeates the voids of the positive electrode active material layer 53 and the negative electrode active material layer 63 inside the wound electrode body 40. The electrolyte solution 80 contains lithium ions as electrolyte ions that can contribute to the battery reaction of the lithium ion secondary battery 10. In FIG. 1, the amount of the electrolytic solution 80 is not strict.

  As mentioned above, although the structural example of the lithium ion secondary battery 10 was illustrated as an example of the nonaqueous electrolyte secondary battery proposed here, about the general material of the member which comprises the lithium ion secondary battery 10, Since there are various known documents, detailed description is omitted here. Moreover, the structure of the lithium ion secondary battery 10 is not limited to this form. For example, the case 20 may be a cylindrical case. The case 20 may have a bag shape or a so-called laminate-type exterior body. Moreover, the electrode body does not necessarily have a wound structure. For example, a positive electrode sheet and a negative electrode sheet may be laminated via a separator.

By the way, this inventor is considering providing the lithium ion secondary battery which operate | moves at high potential, using the positive electrode active material which has an operating potential of 4.3V (vsLi / Li ^<+> ) or more. In the examination, there arises a problem that gas is generated, an unnecessary film is formed on the negative electrode and resistance is increased, and on the contrary, a required film is not formed and the capacity retention rate is greatly reduced. The present inventor believes that one of the causes is that the electrolyte is decomposed by being exposed to a high potential.

Examples of the positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher include LiNi _0.5 Mn _1.5 O ₄ having a spinel structure (hereinafter referred to as “LNM” as appropriate). It is done. Note that the positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher is not limited to LNM. For example, a lithium composite metal oxide disclosed in paragraph 0011 of Patent Document 1 may have a working potential of 4.3 V (vsLi / Li ⁺ ) or higher.

  For example, according to the knowledge of the present inventor, the fluorinated cyclic carbonate used as the solvent of the non-aqueous electrolyte is decomposed to generate gas in a high potential battery having an operating potential of 4.3 V or higher, An unnecessary film is formed on the negative electrode to increase the resistance. In addition, when only the chain carbonate is used as a solvent, a necessary film is not formed, so that the capacity retention rate is greatly reduced. Furthermore, an attempt was made to use only fluorinated chain carbonate as a solvent. In this case, the oxidation resistance of the non-aqueous electrolyte is improved and, for example, gas is hardly generated even when exposed to a high potential of 4.3 V or higher (for example, about 5.0 V). However, with only the fluorinated chain carbonate, a necessary film is not formed, and there remains a problem that the capacity retention rate is greatly reduced. Thus, in a high potential battery having an operating potential of 4.3 V or higher, it is difficult to use the electrolytic solution used in a battery having an operating potential of about 4 V as it is.

  For example, ethylene carbonate (EC) can be decomposed when exposed to a high potential of 4.3 V or higher in a high potential battery having an operating potential of 4.3 V or higher. In addition, fluoroethylene carbonate (FEC) is less likely to be decomposed when exposed to a high potential of 4.3 V or higher than ethylene carbonate (EC). For this reason, fluoroethylene carbonate (FEC) can be used for a high potential battery having an operating potential of 4.3 V or higher, but there is room for further improvement in terms of suppressing gas generation. Thus, in the high potential battery having an operating potential of 4.3 V or higher, the electrolytic solution is exposed to a higher potential than a battery having an operating potential of about 4 V. The present inventor wants to further reduce the amount of gas generated due to the electrolyte and maintain a high capacity retention rate in such a high potential battery having an operating potential of 4.3 V or higher.

  Based on the recognition of such a problem, the present inventor conducted further studies and added an additive capable of forming a necessary film on the negative electrode to a solvent composed only of fluorinated chain carbonate, thereby generating gas. It reached | attained to make suppression and the fall suppression of a capacity | capacitance maintenance rate compatible. Here, the solvent of the non-aqueous electrolyte proposed by the present inventor consists only of fluorinated chain carbonate. An additive capable of forming a film on the negative electrode surface is added to the solvent. Here, examples of the additive capable of forming a film on the negative electrode surface include an alkyl-based additive and a boron-based additive. The additive is not limited to an alkyl-based additive or a boron-based additive, and may be any additive that can form a required film on the negative electrode surface. Here, the solvent does not include a high dielectric constant solvent such as ethylene carbonate (EC) or fluoroethylene carbonate (FEC). According to such a configuration, in a high potential battery exposed to a high potential of 4.3 V or higher, gas generation is suppressed because the electrolyte solution (solvent) is not easily decomposed even when exposed to a high potential. Moreover, since an appropriate film is formed on the surface of the negative electrode active material by the additive, the capacity retention rate can be maintained high.

  Here, the fluorinated chain carbonate has a property that it is not decomposed even when exposed to a high potential of about 4.3 V to 5.0 V in a temperature environment of about -30 ° C. to 60 ° C., for example. Is preferred. A typical example is methyl (2,2,2 trifluoroethyl) carbonate (MTFEC). Other specific examples of the fluorinated chain carbonate include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, fluoromethyl difluoromethyl carbonate, bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (Trifluoromethyl) carbonate, (2-fluoroethyl) methyl carbonate, ethylfluoromethyl carbonate, (2,2-difluoroethyl) methyl carbonate, (2-fluoroethyl) fluoromethyl carbonate, ethyl difluoromethyl carbonate, (2, 2-Difluoroethyl) fluoromethyl carbonate, (2-fluoroethyl) difluoromethyl carbonate, ethyl trifluoromethyl carbonate Ethyl- (2-fluoroethyl) carbonate, ethyl- (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, ethyl- (2,2,2-trifluoroethyl) carbonate, ethyl- (2 , 2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2′-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2′-fluoro Ethyl carbonate, 2,2,2-trifluoroethyl-2 ′, 2′-difluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, pentafluoroethyl methyl carbonate, pentafluoroethyl fluoromethyl carbonate, Pentafluoroethyl ethyl carbo Over DOO, such as bis (pentafluoroethyl) carbonate.

  Examples of the alkyl-based additive include vinylene carbonate (hereinafter referred to as “VC” where appropriate), vinylethylene carbonate (hereinafter referred to as “VEC” as appropriate)), and the like. . Examples of the boron-based additive include lithium difluorooxalate borate (hereinafter referred to as “LiDFOB”), which is also an oxalate-based additive, and lithium bisoxalate borate (Lithium bis ( oxalate) borate, hereinafter referred to as “LiBOB” where appropriate.

The amount of additive, for example, 0.03 mmol / ^{m 2} or more of the surface area of the negative electrode active material, for example 0.08 mmol / ^{m 2} or more, 0.64 mmol / ^{m 2} or less for example 0.32 mmol / ^{m 2} It may be the following. Desirably, an appropriate film is formed on the surface of the negative electrode active material depending on the addition amount. The surface area of the negative electrode active material can be calculated from the weight of the negative electrode active material layer, the weight ratio of the negative electrode active material in the negative electrode active material layer, and the average surface area per unit weight of the negative electrode active material. Moreover, in the electrolytic solution, the additive amount of the additive with respect to the solvent composed only of the fluorinated chain carbonate is preferably, for example, 0.01 mol / L or more and 0.4 mol / L or less.

  A suitable example of the solvent of the non-aqueous electrolyte proposed here consists only of methyl (2,2,2 trifluoroethyl) carbonate (MTFEC) as the fluorinated chain carbonate. The solvent does not contain a high dielectric constant solvent such as ethylene carbonate (EC) or fluoroethylene carbonate (FEC). Then, an additive containing an alkyl-based additive (for example, VC, VEC) or a boron-based additive (for example, LiDFOB, LiBOB) is added to the solvent. According to the proposed nonaqueous electrolytic solution, in a high potential battery exposed to a high potential of 4.3 V or higher, even when the electrolytic solution (solvent) is exposed to a high potential, gas generation is suppressed. The reduction in the capacity maintenance rate can be suppressed.

  Examples of the lithium ion secondary battery proposed here will be described below. In addition, the lithium ion secondary battery proposed here is not limited by the lithium ion secondary battery mentioned here unless there is particular mention. Here, an evaluation battery manufactured by changing the conditions of the electrolytic solution and making the other conditions the same was manufactured and the performance was evaluated.

For the production of the positive electrode of the evaluation battery, LiNi _0.5 Mn _1.5 O ₄ (LNM) is used as the positive electrode active material, acetylene black (AB) is used as the conductive additive, and polyvinylidene fluoride (PVDF) is used as the binder. It was. Here, the positive electrode active material, the conductive auxiliary agent, and the binder are dispersed in a weight ratio of positive electrode active material (LNM): conductive auxiliary agent (AB): binder (PVDF) = 87: 10: 3. It mixed with N-methyl-2-pyrrolidone (NMP) as a solvent to obtain a mixed slurry. The obtained mixed slurry was applied onto an aluminum foil (15 mm thickness) as a positive electrode current collector foil and dried. Thereby, a positive electrode active material layer is formed on the positive electrode current collector foil. And the sheet | seat obtained by the roll press was pressed until the density of the formed positive electrode active material layer became 2.3 g / cm < ³ >, and the positive electrode sheet was produced.

For the production of the negative electrode, as a negative electrode active material, a natural graphite system having an average particle diameter of 10 μm (D50), an average surface area of 4.8 m ² / g (D50), a lattice constant C ₀ = 0.67 nm, and a crystallite diameter Lc = 27 nm Material used. Further, a styrene butadiene copolymer (SBR) is used as a binder, and carboxymethyl cellulose (CMC) is used as a thickener. The weight ratio of the negative electrode active material, the binder, and the thickener is as follows: negative electrode active material: binder (SBR): thickener (CMC) = 98: 1: 1, and mixed with water as a dispersion solvent. A mixed slurry was obtained. The obtained mixed slurry was applied onto a copper foil (10 mm thickness) as a negative electrode current collector foil and dried. Thereby, a negative electrode active material layer is formed on the negative electrode current collector foil. And the sheet | seat obtained by roll press was pressed until the density of the formed negative electrode active material layer became 1.2 g / cm < ³ >, and the negative electrode sheet was produced.

  Here, the positive electrode active material layer of the produced positive electrode sheet and the negative electrode active material layer of the negative electrode sheet were opposed to each other through a separator to produce an electrode body. The produced electrode body was housed together with an electrolytic solution, and a laminate type evaluation battery sealed with a laminate was produced.

The electrolytic solution was prepared using MTFEC as a solvent, a mixed solvent obtained by mixing MTFEC and FEC, and the presence or absence of an additive and the type of additive (VC, LiDFOB) were prepared to prepare a plurality of electrolytic solutions. Here, a mixed solvent prepared by mixing MTFEC and FEC at a volume ratio of MTFEC: FEC = 70: 30 was prepared. In addition, each electrolyte, the electrolyte concentration such that 1 mol / L, and the LiPF ₆ was added as an electrolyte. Table 1 shows the configuration of the electrolyte solutions of Samples 1 to 9 and the evaluation results for evaluating the performance of the evaluation battery.

As shown in Table 1, in the electrolyte solution of Sample 1, VC (about 0.1% relative to the electrolyte solution) was obtained in a solvent consisting of only MTFEC so that the total surface area of the negative electrode in the battery was 0.08 mmol / m ² . 1 mol / L) is added.
In sample 2, VC (about 0.2 mol / L with respect to the electrolytic solution) is added to a solvent composed only of MTFEC so that the total surface area of the negative electrode in the battery is 0.16 mmol / m ² .
In sample 3, VC (about 0.4 mol / L with respect to the electrolytic solution) is added to a solvent composed only of MTFEC so that the total surface area of the negative electrode in the battery is 0.32 mmol / m ² .
In sample 4, Li DF OB (about 0.2 mol / L with respect to the electrolyte) was added to a solvent consisting only of MTFEC so that the total surface area of the negative electrode in the battery was 0.1 mmol / m ^2. Yes.
In sample 5, a solvent consisting only of MTFEC is used, but no additive is added.
In Sample 6, a mixed solvent of MTFEC and FEC is used, but no additive is added.
In Sample 7, VC (about 0.1 mol / L with respect to the electrolyte) is added to the mixed solvent of MTFEC and FEC so that the total surface area of the negative electrode in the battery is 0.08 mmol / m ² . .
In Sample 8, VC (about 0.04 mol / L with respect to the electrolytic solution) is added to a solvent composed only of MTFEC so that the total surface area of the negative electrode in the battery is 0.03 mmol / m ² .
In Sample 9, VC (about 0.8 mol / L with respect to the electrolytic solution) is added to a solvent composed only of MTFEC so that the total surface area of the negative electrode in the battery is 0.64 mmol / m ² .

  Here, for each sample of the evaluation batteries 1 to 9, the initial charge was performed by the CCCV method in the initial charge. Specifically, in the initial charging, charging is performed at a constant current of 1/5 C to 4.9 V, and then constant voltage charging is performed until the current value reaches 1/50 C while maintaining 4.9 V. Charged. Thereafter, the battery was discharged at a constant current up to 3.5 V at a current value of 1/5 C, and the discharge capacity at that time was defined as the initial capacity. The initial capacity was measured in a temperature environment of 25 ° C.

  The SOC of the battery was adjusted to 60% by charging the electric capacity corresponding to 60% of the initial capacity at a current value of 1/5 C from the state after discharge for measuring the initial capacity. The adjustment here was performed in a temperature environment of 25 ° C. Then, after standing for 3 hours in a thermostat adjusted to 0 ° C., charging and discharging were performed at a constant current of 1 / 3C, 1C, and 3C at SOC 60% for 5 seconds, respectively, and measured at the time of charging and discharging, respectively. The measured overvoltage was measured. Then, the resistance was calculated by dividing the measured overvoltage by the current value, and the average value (arithmetic average) of the calculated resistance was defined as the initial DC resistance. The initial resistance in Table 1 is the initial DC resistance measured here.

  Moreover, the cycle test which repeats charge and discharge from 3.5V to 4.9V was implemented about the sample of each evaluation battery in a 60 degreeC temperature environment. Charging and discharging were each a constant current method, and the current rate was 2C. After 200 cycles of such charging and discharging, CCCV charging was used to achieve a full charge of 4.9 V in the same manner as the above initial capacity, and then CCCV discharging was performed to 3.5 V, and the capacity after cycling was measured. . And about each sample, the capacity | capacitance maintenance factor of Table 1 was obtained by remove | dividing the capacity | capacitance after the obtained cycle by an initial stage capacity | capacitance.

  The amount of gas generated in Table 1 was measured by the Archimedes method. First, the laminate cell immediately after assembly was immersed in a container filled with a fluorine-based inert liquid (for example, 3M Japan Co., Ltd., “Fluorinert”), and the initial volume was measured from the change in weight before and after the immersion. Furthermore, the volume after the cycle was measured by the same method after 200 cycles, and a value obtained by subtracting the initial volume from the volume after the cycle was defined as a gas generation amount.

  Here, FIG. 2 is a graph showing the relationship between the VC addition amount and the gas generation amount of Samples 1-9. FIG. 3 is a graph showing the relationship between the VC addition amount and the capacity retention rate of Samples 1 to 9.

  As shown in FIG. 2, as shown in Table 1, in the sample 5 in which the solvent of the electrolytic solution is composed only of MTFEC but no VC is added, the gas generation amount is 1.27 mL, which is another sample. It is relatively high compared to In this regard, the present inventor presumes that VC is not added and a necessary film is not formed on the surface of the negative electrode active material. In addition, for the samples 6 and 7 in which the mixed solvent containing FEC is used, the gas generation amounts are slightly increased to 1.33 mL and 1.31 mL, respectively. The inventor believes that the amount of gas generated in Samples 6 and 7 is slightly higher because a mixed solvent containing FEC is used.

  Also, as shown in FIG. 3, in terms of capacity maintenance rate, sample 5 made of only MTFEC but not added with VC at all has a capacity maintenance rate of 32%, which is relatively poor compared to other samples. This is also presumed to be because a necessary film is not formed on the surface of the negative electrode active material. Further, as in sample 4, not only VC as an alkyl additive but also LiDFOB as a boron additive may be used as the additive. Although not illustrated here, according to the knowledge of the present inventor, other boron-based additives such as LiBOB may be used instead of LiDFOB. Further, instead of VC, other alkyl additives may be used.

  Thus, in a high potential battery that is exposed to a high potential of about 4.3 V to 5.0 V, the solvent of the non-aqueous electrolyte is a fluorinated chain carbonate (here, methyl (2, 2, 2 (Trifluoroethyl) carbonate (MTFEC)), and an additive containing an alkyl-based additive or a boron-based additive may be added to the solvent (for example, Samples 1-4, 8, and 9). . Here, it is preferable that the solvent does not contain a solvent that can generate gas upon being exposed to a high potential of 4.3 V or higher, such as ethylene carbonate (EC). Furthermore, it is preferable that a high dielectric constant solvent such as fluoroethylene carbonate (FEC) is not included. As a result, the solvent of the electrolytic solution consists only of MTFEC, but when an additive containing an alkyl-based additive or a boron-based additive is not added (for example, Sample 5), or the solvent is fluoroethylene carbonate (FEC). Compared with the case where the high dielectric constant solvent is included (for example, samples 6 and 7), the amount of gas generated can be remarkably reduced. Also, from the viewpoint of the capacity retention rate, the solvent of the electrolytic solution is composed only of MTFEC, but compared with the case where no additive containing an alkyl-based additive or a boron-based additive is added (for example, Sample 5). The maintenance rate can be maintained high.

In addition, when an additive containing an alkyl-based additive or a boron-based additive is added to a solvent composed only of MTFEC, if the additive amount is small, the effect of maintaining a high capacity is reduced. In some cases (eg, sample 8). In addition, when the additive amount increases, the initial resistance may increase (for example, Sample 9). According to the knowledge of the present inventor, in such a viewpoint, for example, when the additive is VC, the addition amount is preferably 0.03 mmol / m ² or more and 0.64 mmol / m, with respect to the surface area of the negative electrode active material. m ² may or less. As a result, the capacity maintenance rate can be kept high and the amount of gas generated can be kept low. In addition, for example, in terms of maintaining the capacity higher, the additive amount may be 0.08 mmol / m ² or more (for example, Sample 1), and more preferably 0.16 mmol / m ² or more. There should be (for example, sample 2). Further, from the viewpoint of suppressing the gas generation amount to a small amount, the additive amount is preferably 0.32 mmol / m ² or less (for example, Sample 3).

  The non-aqueous electrolyte secondary battery proposed here has been variously described, but the embodiments and examples given here do not limit the present invention unless otherwise specified.

For example, the non-aqueous electrolyte secondary battery proposed here is typically a lithium ion secondary battery. However, as described above, the non-aqueous electrolyte having high potential resistance is the main component, and lithium ion secondary batteries are used. It can be applied to other than secondary batteries. In other words, the configuration of the nonaqueous electrolyte secondary battery proposed here is a nonaqueous solution in which a positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher is used in addition to the lithium ion secondary battery. It is widely applicable to electrolyte secondary batteries.

10 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
20 Case 21 Case body 22 Sealing plate 23, 24 Internal terminal 25, 26 External terminal 30 Safety valve 32 Injection hole 33 Cap material 40 Winding electrode body 50 Positive electrode sheet 51 Positive electrode current collector foil 52 Exposed portion 53 Positive electrode active material layer 60 Negative electrode Sheet 61 Negative electrode current collector foil 62 Exposed portion 63 Negative electrode active material layers 72 and 74 Separator 80 Electrolytic solution (nonaqueous electrolytic solution)
WL winding axis

Claims (1)

A positive electrode having a positive electrode active material having an operating potential of 4.3 V (vsLi / Li ⁺ ) or higher;
A negative electrode having a negative electrode active material;
A non-aqueous electrolyte,
A case containing the positive electrode, the negative electrode, and the non-aqueous electrolyte;
The non-aqueous electrolyte comprises a solvent and an additive,
The solvent consists only of fluorinated chain carbonate,
The additive contains at least one of vinylene carbonate, vinyl ethylene carbonate, lithium difluorooxalate borate and lithium bisoxalate borate .
Non-aqueous electrolyte secondary battery.

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