Negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Abstract

To provide techniques that can suitably inhibit an inside short circuit and a capacity reduction which are caused by a precipitation of metal Li.SOLUTION: A negative electrode active material layer of a herein disclosed negative electrode contains a chemical compound represented by the general formula (1) in the figure, where each of R1 to R5 is independently selected from the group consisting of hydrogen, an alkyl group, a hydroxy group, a cyano group, an aldehyde group, an ether group, an ester group, an amino group, and a phenyl group, R6 is the alkyl group, and at least one of the R1 to R5 is the hydroxy group. According to the negative electrode containing the chemical compound having the configuration, it is possible to suitably inhibit an occurrence of an inside short circuit and a reduction of a battery capacity which are caused by a precipitation of metal Li.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed herein relates to a lithium ion secondary battery, and more specifically to a negative electrode used in a lithium ion secondary battery and a lithium ion secondary battery using the negative electrode. [Background technology]

[0002] In recent years, lithium-ion secondary batteries have been widely used in various devices, such as electric vehicles and mobile terminals. These lithium-ion secondary batteries include an electrode assembly in which a positive electrode and a negative electrode face each other with a separator interposed therebetween. An electrolyte solution permeates the interior of this electrode assembly (between the positive and negative electrodes). When a lithium-ion secondary battery with this configuration is charged, Li ions, which serve as charge carriers, migrate from the positive electrode to the negative electrode. If overcharging occurs during this process, dendritic metallic Li may precipitate on the negative electrode. This dendritic metallic Li may cause an internal short circuit due to damage to the separator. Furthermore, as the precipitation of metallic Li progresses, the number of Li ions available for charge / discharge reactions decreases, resulting in a decrease in battery capacity. To address these issues, various techniques have been proposed to suppress the precipitation of metallic Li in lithium-ion secondary batteries (e.g., Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-87412 [Patent Document 2] Japanese Patent Application Publication No. 2019-192607 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-123171 Summary of the Invention [Problem to be solved by the invention]

[0004] However, due to the recent increase in demand for battery performance, there is a need for a technology that can more effectively solve the problems caused by the precipitation of metallic Li. The technology disclosed herein has been made in response to such a demand, and aims to provide a technology that can effectively prevent internal short circuits and capacity reduction caused by the precipitation of metallic Li. [Means for solving the problem]

[0005] The negative electrode for a lithium ion secondary battery disclosed herein (hereinafter also simply referred to as "negative electrode") includes a negative electrode core and a negative electrode active material layer applied to the surface of the negative electrode core. The negative electrode active material layer of this negative electrode contains a compound represented by the following general formula (1). In the following general formula (1), R1 to R5 are each independently selected from the group consisting of hydrogen, an alkyl group, a hydroxy group, a cyano group, an aldehyde group, an ether group, an ester group, an amino group, and a phenyl group. R6 in the formula is an alkyl group. The negative electrode disclosed herein is characterized in that at least one of R1 to R5 is a hydroxy group.

[0006] [ka]

[0007] The compound represented by the general formula (1) functions as a Li collector that captures metallic Li deposited on the negative electrode. Specifically, this Li collector is characterized in that at least one of R1 to R5 in the formula is a hydroxy group. This hydroxy group can capture Li after deposition. This makes it possible to prevent internal short circuits due to the growth of metallic Li. Furthermore, since the Li collector having the above configuration has a hydroxy group, which is a hydrophilic group, it is difficult to dissolve in the non-aqueous electrolyte of a lithium-ion secondary battery. However, when hydrogen (H) of the hydroxy group is substituted with lithium (Li) by capturing Li, the Li collector becomes a compound soluble in the non-aqueous electrolyte. This allows the deposited Li to be returned to the non-aqueous electrolyte. As a result, it is possible to prevent a decrease in capacity due to the deposition of metallic Li. Furthermore, after releasing Li, the Li collector becomes a compound having a hydroxy group again, and thus precipitates from the non-aqueous electrolyte. This makes it possible for the Li collector to capture metallic Li again. As described above, the negative electrode disclosed herein can suitably prevent internal short circuits and capacity reduction due to deposition of metallic Li. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view that schematically illustrates a negative electrode for a lithium ion secondary battery according to one embodiment. [Figure 2] FIG. 2 is a diagram illustrating the collection of Li in the negative electrode shown in FIG. [Figure 3] FIG. 3 is a diagram illustrating deposition of the Li trapping material in the negative electrode shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a lithium ion secondary battery according to one embodiment. [Figure 5] FIG. 5 is a perspective view showing an electrode body of a lithium ion secondary battery according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the technology disclosed herein will be described in detail with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., detailed manufacturing methods for negative electrodes) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are designated by the same reference numerals.

[0010] In this specification, the term "lithium ion secondary battery" refers to a secondary battery that charges and discharges by transferring Li ions, which are charge carriers, between a positive electrode and a negative electrode. Secondary batteries generally referred to as lithium secondary batteries (or lithium ion batteries) are typical examples of the lithium ion secondary batteries in this specification. In addition, the term "active material" in this specification refers to a substance (compound) that is involved in the absorption and desorption of Li ions on the positive electrode side and the negative electrode side.

[0011] 1. Negative electrodes for lithium-ion secondary batteries First, one embodiment of the negative electrode disclosed herein will be described. Fig. 1 is a cross-sectional view that schematically illustrates the negative electrode for a lithium ion secondary battery according to this embodiment. Fig. 2 is a diagram that illustrates the capture of Li in the negative electrode shown in Fig. 1. Fig. 3 is a diagram that illustrates the deposition of a Li capture material in the negative electrode shown in Fig. 1.

[0012] 1, the negative electrode 10 according to this embodiment includes a negative electrode substrate 12 and a negative electrode active material layer 14. Each component will be described below.

[0013] (1) Negative electrode substrate The negative electrode core 12 is a foil-shaped conductive member. Any conventionally known conductive member that can be used as a negative electrode core for a lithium-ion secondary battery can be used for the negative electrode core 12 without any particular restrictions. In other words, the negative electrode disclosed herein is not limited by the configuration of the negative electrode core. An example of the negative electrode core 12 is a copper foil having a thickness of 5 μm to 30 μm.

[0014] (2) Negative electrode active material layer The negative electrode active material layer 14 is applied to the surface of the negative electrode core 12. This negative electrode active material layer 14 contains a negative electrode active material and various additives (binder, etc.). Furthermore, the negative electrode active material layer 14 in this embodiment contains a Li capture material 14a. The components of the negative electrode active material layer 14 will be described below.

[0015] (a) Negative electrode active material The negative electrode active material is a granular material capable of absorbing and releasing lithium ions. There are no particular limitations on the material for the negative electrode active material, and any conventionally known material for a negative electrode active material can be used without particular limitations. Suitable examples of the material for the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon (hard carbon), easily graphitizable carbon (soft carbon), and carbon nanotubes. Other suitable examples of the material for the negative electrode active material include Si-based materials such as silicon (Si) and silicon compounds. The content of the negative electrode active material relative to the total mass (100 wt%) of the negative electrode active material layer 14 is preferably 90 wt% to 99.5 wt% (more preferably 95 wt% to 99 wt%).

[0016] (b) Additives Examples of additives other than the negative electrode active material include binders and thickeners. Examples of binders include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyethylene (PE), and polyacrylic acid (PAA). Examples of thickeners include carboxymethyl cellulose (CMC) and methyl cellulose (MC). The total content of the additives relative to the total mass of the negative electrode active material layer 14 is preferably 0.5 wt% to 10 wt% (more preferably 1 wt% to 5 wt%).

[0017] (c) Li trapping material The negative electrode active material layer 14 in this embodiment contains a compound (Li trapping material 14a) represented by the following general formula (1).

[0018] [ka]

[0019] Here, R1 to R5 in the general formula (1) are each independently selected from the group consisting of hydrogen, an alkyl group, a hydroxy group, a cyano group, an aldehyde group, an ether group, an ester group, an amino group, and a phenyl group. The Li trapping material 14a in this embodiment is characterized in that at least one of R1 to R5 is a hydroxy group. The negative electrode 10 including the Li trapping material 14a having such a configuration can effectively prevent the deposition of metallic Li during charging of a lithium-ion secondary battery. This will be explained in detail below.

[0020] First, as described below, the negative electrode 10 of a typical lithium-ion secondary battery is used while immersed in a nonaqueous electrolyte solution. Since the Li trapping material 14a has a hydrophilic hydroxyl group (-OH), it is difficult to dissolve in the nonaqueous electrolyte solution containing an organic solvent. Therefore, the Li trapping material 14a in a typical charge / discharge reaction is present in the negative electrode active material layer 14 (see FIG. 1). When metallic Li precipitates on the negative electrode 10 as shown in FIG. 2, the Li trapping material 14a traps the metallic Li at the hydroxyl group (-OH). This makes it possible to prevent an internal short circuit due to the growth of metallic Li.

[0021] Next, the hydrogen (H) of the hydroxy group of the Li trapping material 14a that has trapped Li is substituted with lithium (Li), and the Li trapping material 14a becomes an aromatic compound that does not have a hydroxy group. As a result, the Li trapping material 14a dissolves in the non-aqueous electrolyte, as shown in FIG. 3. When the Li trapping material 14a dissolves in the non-aqueous electrolyte, the hydrogen ions (H +) replaces the captured lithium (Li). This allows the once-deposited Li to return to the non-aqueous electrolyte, preventing a decrease in capacity due to the deposition of metallic Li. Meanwhile, the Li capture material 14a becomes an aromatic compound having a hydroxy group again, causing the Li capture material to precipitate from the non-aqueous electrolyte. Then, as shown in FIG. 1, the deposited Li capture material 14a adheres to the negative electrode 10 again, and becomes capable of capturing metallic Li. As described above, the Li capture material 14a represented by the above general formula (1) has two functions: capturing the deposited metallic Li and reusing the captured metallic Li. This effectively prevents both an internal short circuit and a decrease in capacity due to the deposition of metallic Li.

[0022] The hydroxy group (—OH) of the Li trapping material 14a may be present at any one of R1 to R5 in the general formula (1). This sufficiently prevents the occurrence of internal short circuits and a decrease in battery capacity due to the deposition of metallic Li. However, considering the reactivity with metallic Li, the position of the hydroxy group (—OH) is preferably at any one of R1, R2, and R5 in the general formula (1), with R1 being particularly preferred. Specifically, the Li trapping material 14a represented by the general formula (1) has a bulky branched chain containing R6. Hydroxy groups near this branched chain (i.e., R3 and R4) are less likely to react with Li, while hydroxy groups at positions away from this branched chain (i.e., R1, R2, and R5) tend to react more readily with Li.

[0023] Furthermore, the number of hydroxy groups in the Li capture material 14a is not particularly limited and can be appropriately selected in the range of 1 to 5. However, if the number of hydroxy groups is increased too much, the hydroxy groups tend to remain even after capturing metallic Li, making it difficult to reuse Li by dissolving it in a non-aqueous electrolyte. From this perspective, the number of hydroxy groups in the Li capture material 14a is preferably 4 or less, more preferably 3 or less, and even more preferably 2 or less. On the other hand, the lower limit of the number of hydroxy groups is not particularly limited and may be 1 or more.

[0024] Furthermore, R6 in the general formula (1) above is an alkyl group. The alkyl group of R6 affects the solubility in a non-aqueous electrolyte. For example, as the carbon number of the alkyl group of R6 increases, the solubility in a non-aqueous electrolyte during Li capture tends to improve. From this perspective, the number of carbon atoms in the alkyl group of R6 is preferably 1 or more, and more preferably 2 or more. On the other hand, as the carbon number of the alkyl group of R6 decreases, the solubility in a state where Li is not captured tends to decrease. From this perspective, the number of carbon atoms in the alkyl group of R6 is preferably 5 or less, and more preferably 4 or less. Note that in the Li capture material 14a represented by the general formula (1) above, the carboxylic acid group is esterified. This can suppress the reaction between the alkyl group of R6 and Li.

[0025] Specific examples of the Li trapping material 14a include ethyl hydroxybenzoate, methyl hydroxybenzoate, propyl hydroxybenzoate, etc. These aromatic compounds having a hydroxy group can appropriately perform two functions: trapping metallic Li and reusing the trapped metallic Li.

[0026] Furthermore, in a typical lithium-ion secondary battery, metallic Li is likely to be deposited on the surface of the negative electrode active material layer 14. For this reason, it is preferable that the Li trapping material 14a be applied to the surface of the negative electrode active material layer 14. This brings the region where metallic Li is deposited and the position where the Li trapping material 14a is disposed close to each other, thereby improving the Li trapping efficiency. The negative electrode 10 having such a configuration can be produced by applying a slurry containing the Li trapping material 14a to the surface of the negative electrode active material layer 14 and drying it.

[0027] The amount of the Li trapping material 14a added is preferably determined in relation to the unit surface area of ​​the negative electrode active material layer 14. This allows a sufficient amount of the Li trapping material 14a to be present relative to the area of ​​the deposition region of metallic Li, thereby further improving the Li trapping efficiency. In particular, when the amount of the Li trapping material 14a added is 0.02 mg / cm 2It has been confirmed by experiments that the Li capture efficiency is drastically improved when the amount exceeds the above range. From this viewpoint, the amount of the Li capture material 14a added per unit area of ​​the surface of the negative electrode active material layer 14 is set to 0.02 mg / cm. 2 More than 0.03 mg / cm is preferable. 2 More preferably, 0.04 mg / cm or more 2 More preferably, 0.05 mg / cm 2 On the other hand, when the amount of the Li trapping material 14a added exceeds a certain amount, the Li trapping effect saturates. Therefore, the upper limit of the amount of the Li trapping material 14a added is 0.5 mg / cm. 2 Less than 0.4 mg / cm is preferred 2 Less than 0.3 mg / cm is more preferable. 2 More preferably, 0.25 mg / cm 2 The following are particularly preferred:

[0028] 2. Lithium-ion secondary battery Next, a lithium ion secondary battery 1 (hereinafter also simply referred to as "secondary battery 1") having the negative electrode 10 configured as described above will be described. FIG. 4 is a cross-sectional view schematically showing the lithium ion secondary battery according to this embodiment. FIG. 5 is a perspective view showing an electrode body of the lithium ion secondary battery according to this embodiment. In FIG. 4, the symbol X indicates the width direction (of the secondary battery 1), and the symbol Y indicates the height direction (of the secondary battery 1). Note that these directions are defined for the sake of convenience of explanation and are not intended to limit the installation mode of the lithium ion secondary battery disclosed herein.

[0029] 4, the secondary battery 1 according to this embodiment includes an electrode assembly 20 and a non-aqueous electrolyte solution 30. The electrode assembly 20 and the non-aqueous electrolyte solution 30 are housed in a case 40. The specific configuration of the secondary battery 1 will be described below.

[0030] (1) Case As described above, the case 40 is a container that houses the electrode assembly 20 and the nonaqueous electrolyte solution 30. The case 40 shown in FIG. 1 includes a case body 42, which is a box-shaped container having an opening 42a, and a sealing plate 44 that closes the opening 42a. The sealing plate 44 is provided with a positive electrode terminal 46 and a negative electrode terminal 48. The lower end 46a of the positive electrode terminal 46 is electrically connected to the positive electrode 50 inside the case 40. The upper end 46b of the positive electrode terminal 46 is exposed to the outside of the case 40. Meanwhile, the lower end 48a of the negative electrode terminal 48 is electrically connected to the negative electrode 10 inside the case 40. The upper end 48b of the negative electrode terminal 48 is exposed to the outside of the case 40.

[0031] (2) Electrode body As shown in Fig. 5, the electrode assembly 20 has a positive electrode 50 and a negative electrode 10. The positive electrode 50 and the negative electrode 10 face each other with a separator 60 interposed therebetween. The electrode assembly 20 in this embodiment is a wound electrode assembly. Specifically, the electrode assembly 20 is produced by winding a laminate in which the positive electrode 50 and the negative electrode 10 are stacked with the separator 60 sandwiched between them.

[0032] (a) Positive electrode The positive electrode 50 includes a long, foil-like positive electrode core 52 and a positive electrode active material layer 54 applied to the surface of the positive electrode core 52. The positive electrode active material layer 54 contains a positive electrode active material and other additives (such as a binder). One widthwise edge of the positive electrode 50 is not coated with the positive electrode active material layer 54, forming a positive electrode core exposed portion 56 where the positive electrode core 52 is exposed. As shown in FIG. 4, the positive electrode core exposed portion 56 is electrically connected to the lower end portion 46a of the positive electrode terminal 46.

[0033] The positive electrode active material in the positive electrode active material layer 54 is a granular material capable of absorbing and releasing lithium ions. There are no particular limitations on the material of the positive electrode active material, and conventionally known materials can be used without particular limitations. An example of the material of this positive electrode active material is a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium element and one or more transition metal elements. Specific examples of lithium transition metal composite oxides include lithium nickel-based composite oxides (e.g., LiNiO2), lithium cobalt-based composite oxides (e.g., LiCoO2), lithium manganese-based composite oxides (e.g., LiMn2O4), and lithium nickel-manganese-based composite oxides (e.g., LiNi 0.5 Mn 1.5 O4), lithium nickel cobalt manganese composite oxides (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2). Furthermore, polyanion-based (e.g., olivine-based) compounds (e.g., LiFePO4, LiMnPO4) having the general formula LiMPO4 (wherein M is at least one transition metal element selected from Co, Ni, Mn, and Fe) can also be used as the lithium transition metal composite oxide. The term "lithium nickel cobalt manganese composite oxide" as used herein encompasses not only oxides containing only Li, Ni, Co, and Mn as constituent metal elements, but also oxides containing one or more metal elements other than Li, Ni, Co, and Mn. Examples of such metal elements other than Li, Ni, Co, and Mn include transition metal elements other than Ni, Co, and Mn and / or typical metal elements (e.g., Al, Ca, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce). Although detailed explanations are omitted, the terms "lithium nickel composite oxide," "lithium cobalt composite oxide," "lithium manganese composite oxide," and "polyanion compound" also encompass oxides containing one or more other metal elements.

[0034] Other additives in the positive electrode active material layer 54 include a conductive additive, a binder, and the like. These additives are also not particularly limited, and conventionally known additives can be used without any particular restrictions. Examples of conductive additives include carbon-based materials such as carbon powder and carbon fiber. Examples of binders for the positive electrode active material layer 54 include vinyl halide resins such as polyvinylidene fluoride (PVdF) and polyalkylene oxides such as polyethylene oxide (PEO).

[0035] (b) Negative electrode Meanwhile, the secondary battery 1 according to this embodiment uses the negative electrode 10 configured as described above. As described above, this negative electrode 10 includes a Li capture material 14a in the negative electrode active material layer 14. Note that a detailed description of the negative electrode 10 will be omitted to avoid repetition. Also, as shown in FIG. 5 , the negative electrode active material layer 14 is not provided on one side edge in the width direction of the negative electrode 10, and a negative electrode core exposed portion 16 is formed in which the negative electrode core 12 is exposed. As shown in FIG. 4 , this negative electrode core exposed portion 16 is electrically connected to the lower end portion 48a of the negative electrode terminal 48.

[0036] (c) Separator The separator 60 is an insulating sheet interposed between the positive electrode 50 and the negative electrode 10. An example of the material of the separator 60 is a polyolefin resin. The separator 60 also has a plurality of minute pores formed therein. This allows Li ions to move between the positive electrode 50 and the negative electrode 10.

[0037] (3) Non-aqueous electrolyte The nonaqueous electrolyte 30 permeates the inside of the electrode assembly 20. In other words, the nonaqueous electrolyte 30 exists between the positive electrode 50 and the negative electrode 10. When this secondary battery 1 is charged and discharged, Li ions move between the positive electrode 50 and the negative electrode 10 via the nonaqueous electrolyte 30. In addition, in the secondary battery shown in FIG. 4, a portion of the nonaqueous electrolyte 30 exists outside the electrode assembly 20 (typically, between the battery case 40 and the electrode assembly 20) as excess electrolyte 32. This allows the electrode assembly 20 to be replenished with nonaqueous electrolyte 30 when the amount of nonaqueous electrolyte 30 in the electrode assembly 20 decreases.

[0038] The type of nonaqueous electrolyte 30 is not particularly limited, and any conventionally known nonaqueous electrolyte can be used without any particular limitation. Specifically, the nonaqueous electrolyte 30 is prepared by adding a supporting salt to a nonaqueous solvent. Specific examples of nonaqueous solvents include carbonates, ethers, esters, nitriles, sulfones, and lactones. Among these, carbonates are particularly preferred as the solvent for the nonaqueous electrolyte 30 in this embodiment because they can particularly easily dissolve the Li capture material 14a during Li capture. The carbonates may be either chain carbonates or cyclic carbonates. Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). On the other hand, examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), monofluoroethylene carbonate (MFEC), and difluoroethylene carbonate (DFEC). These may be used alone or in combination of two or more. Examples of supporting salts include LiPF, LiBF, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethane)sulfonimide (LiTFSI). The concentration of the supporting salt in the nonaqueous electrolyte 30 is, for example, 0.5 mol / L to 5 mol / L, and preferably 0.7 mol / L to 2.5 mol / L.

[0039] As described above, the secondary battery 1 according to this embodiment includes the negative electrode 10 including the Li trapping material 14a. The Li trapping material 14a has two functions: trapping the deposited metallic Li and reusing the captured metallic Li. This effectively prevents both an internal short circuit and a decrease in capacity due to the deposition of metallic Li.

[0040] 3. Other Embodiments The above describes one embodiment of the technology disclosed herein. The technology disclosed herein is not limited to the above embodiment and includes other embodiments with various modifications. For example, in the above embodiment, a Li trapping material 14a is applied to the surface of the negative electrode active material layer 14 (see FIG. 1 ). However, the location of the Li trapping material does not limit the technology disclosed herein. For example, the Li trapping material may be added to the interior of the negative electrode active material layer. This configuration also effectively prevents the deposition of metallic Li. Specifically, metallic Li is deposited not only on the surface of the negative electrode active material layer but also inside the layer. After capturing Li, the Li trapping material is dissolved in a nonaqueous electrolyte and then re-deposited. Therefore, even if a Li trapping material is added to the negative electrode active material layer during manufacturing, the Li trapping material migrates toward the surface of the negative electrode active material layer as charging and discharging are repeated. This allows a sufficient amount of Li trapping material to be disposed on the surface of the negative electrode active material layer, where metallic Li is likely to deposit.

[0041] [Test example] Test examples relating to the technology disclosed herein will be described below, but the following description is not intended to limit the technology disclosed herein.

[0042] A. First Test In this test, ethyl hydroxybenzoate was prepared as the Li trapping material represented by the general formula (1) above. The solubility and Li trapping performance of this Li trapping material were then investigated. The specific experimental details are as follows:

[0043] First, 10 mL of non-aqueous solvent (ethyl methyl carbonate) was placed in a 25 mL Eppendorf tube. 2000 mg of ethyl hydroxybenzoate was added, followed by shaking with a stirrer (shaking time: 3 minutes, shaking speed: 700 rpm). The amount of ethyl hydroxybenzoate dissolved was 0.05 mg / mL. This indicated that ethyl hydroxybenzoate was poorly soluble in non-aqueous electrolytes.

[0044] Next, 1 g of Li metal pieces was added to this Eppendorf tube and shaken (shaking time: 3 minutes, shaking speed: 700 rpm). As a result, the Li metal pieces disappeared. This indicated that ethyl hydroxybenzoate can capture metallic Li. Furthermore, after capturing Li, the ethyl hydroxybenzoate dissolved in ethyl methyl carbonate. This indicated that ethyl hydroxybenzoate converts into a compound soluble in non-aqueous solvents by capturing metallic Li.

[0045] B. Second Test In this test, the effect of the Li collection material in an actual lithium ion secondary battery was examined. The lithium ion secondary battery (test example) prepared in this test is described below.

[0046] 1. Test examples (1) Test Example 1 In Test Example 1, a lithium ion secondary battery was fabricated without adding a Li collector to the negative electrode active material layer. 1 / 3 Co 1 / 3 Mn 1 / 3 A cathode composite paste was prepared by mixing 02), a conductive material (acetylene black), and a binder (PVdF) in a ratio of 90:8:2 and dispersing the mixture in a dispersion medium (NMP: N-methylpyrrolidone). This cathode composite paste was then applied to both sides of a cathode current collector (aluminum foil), which was then dried and rolled to produce a sheet-shaped cathode. The cathode size was 47 mm x 45 mm. An aluminum cathode terminal was then connected to this cathode.

[0047] Next, in this test example, a negative electrode active material (graphite) and a binder (SBR) were mixed in a ratio of 98:2 and dispersed in a dispersion medium (NMP) to prepare a negative electrode composite paste. This paste was then applied to both sides of a negative electrode substrate (copper foil), dried, and rolled to produce a sheet-shaped negative electrode. The size of the negative electrode was 49 mm x 47 mm. A copper negative electrode terminal was then connected to this negative electrode.

[0048] Next, a laminate was fabricated by disposing a microporous polypropylene separator between the positive and negative electrodes. This laminate was then housed in a pouch-shaped separator, which was then housed inside a laminated exterior. A nonaqueous electrolyte was then poured into the exterior, and the laminated exterior was sealed to construct a lithium-ion secondary battery for evaluation testing (Test Example 1). In this test, a nonaqueous electrolyte solution was used, which was a mixed solvent containing EC, EMC, and DMC in a volume ratio of 3:3:4, and LiPF6 as a supporting electrolyte at a concentration of approximately 1.16 M.

[0049] (2) Test Examples 2 to 7 In Test Examples 2 to 7, lithium ion secondary batteries for evaluation tests were constructed under the same conditions as Test Example 1, except that a Li scavenger (ethyl hydroxybenzoate) was added to the negative electrode active material layer. In Test Examples 2 to 7, a slurry was prepared by mixing EMC and ethyl hydroxybenzoate, and the slurry was applied to the surface of the negative electrode active material layer by a drop casting method. Then, a drying treatment was carried out at 40°C for 120 minutes, thereby adhering the Li scavenger to the surface of the negative electrode active material layer. In these tests, the amount of Li scavenger added relative to the surface area of ​​the negative electrode active material layer (mg / cm 2 ) was varied in Test Examples 2 to 7. Specific amounts of the Li trapping material added are shown in Table 1.

[0050] 2.Evaluation Test Next, in this test example, charge-discharge tests were performed on the lithium ion secondary batteries of Test Examples 1 to 7 to measure the amount of metallic Li precipitated. Specifically, the lithium ion secondary batteries of each test example were subjected to 100 charge-discharge cycles in an environment of -10°C, in which CC charging was performed at a constant current of 3 C from 3 V to 4.2 V, followed by CC discharging at a constant current of 4.2 C (CC discharge) from 4.2 V to 3 V. Then, the batteries after the charge-discharge cycles were disassembled, and the area (mm ) of the region where metallic Li had precipitated on the surface of the negative electrode active material layer (Li precipitate region) was measured. 2 The measurement results are shown in Table 1.

[0051] [Table 1]

[0052] As shown in Table 1, it was confirmed that the area of ​​the Li deposition region was smaller in Test Examples 2 to 7 than in Test Example 1. This shows that adding a Li trapping material to the negative electrode active material layer can suppress the deposition of metallic Li. Furthermore, among Test Examples 2 to 7, the amount of Li deposition was significantly reduced in Test Examples 3 to 7. This suggests that the amount of Li trapping material added was 0.2 mg / cm 2 The above was found to be preferable.

[0053] While specific examples of the technology disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0054] The technology disclosed herein includes the following items 1 to 8. The following items 1 to 8 are not limited to the above-described embodiment.

[0055] <Item 1> a negative electrode core body; a negative electrode active material layer provided on the surface of the negative electrode core; Equipped with The negative electrode for a lithium ion secondary battery, wherein the negative electrode active material layer contains a compound represented by the following general formula (1): [ka] (In the formula, R1 to R5 are each independently selected from the group consisting of hydrogen, an alkyl group, a hydroxy group, a cyano group, an aldehyde group, an ether group, an ester group, an amino group, and a phenyl group; R6 is an alkyl group; and at least one of R1 to R5 is a hydroxy group.)

[0056] <Item 2> 2. The negative electrode according to item 1, wherein R6 is an alkyl group having 1 to 5 carbon atoms.

[0057] <Item 3> 3. The negative electrode according to item 1 or 2, wherein R1 is a hydroxy group.

[0058] <Item 4> 4. The negative electrode according to any one of items 1 to 3, wherein the compound represented by general formula (1) is ethyl hydroxybenzoate.

[0059] <Item 5> 5. The negative electrode according to any one of items 1 to 4, wherein the compound represented by general formula (1) is applied to the surface of the negative electrode active material layer.

[0060] <Item 6> The amount of the compound represented by the general formula (1) added per unit area of ​​the surface of the negative electrode active material layer is 0.02 mg / cm 2 More than 0.25mg / cm 2 6. The negative electrode according to any one of items 1 to 5, wherein:

[0061] <Item 7> an electrode assembly having a positive electrode and a negative electrode; a nonaqueous electrolyte solution that has permeated the interior of the electrode body; It is equipped with A lithium ion secondary battery, wherein the negative electrode is the negative electrode according to any one of items 1 to 6.

[0062] <Item 8> 8. The lithium ion secondary battery according to item 7, wherein the non-aqueous electrolyte solution contains a non-aqueous solvent belonging to carbonates. [Explanation of symbols]

[0063] 1. Lithium-ion secondary battery 10 negative electrode 12 Negative electrode core 14 Negative electrode active material layer 14a Li trapping material 16 Negative electrode core exposed part 20 Electrode body 30 Nonaqueous electrolyte 40 cases 42 Case body 42a opening 44 Sealing plate 46 Positive terminal 48 Negative terminal 50 positive electrode 52 Positive electrode core 54 Cathode active material layer 56 Positive electrode core exposed part 60 Separator

Claims

1. a negative electrode substrate; a negative electrode active material layer provided on the surface of the negative electrode core; Equipped with The negative electrode for a lithium ion secondary battery, wherein the negative electrode active material layer contains a compound represented by the following general formula (1): 【Chemistry 1】 (In the formula, R1 to R5 are each independently selected from the group consisting of hydrogen, an alkyl group, a hydroxy group, a cyano group, an aldehyde group, an ether group, an ester group, an amino group, and a phenyl group; R6 is an alkyl group; and at least one of R1 to R5 is a hydroxy group.)

2. 2. The negative electrode according to claim 1, wherein R6 is an alkyl group having 1 to 5 carbon atoms.

3. The negative electrode according to claim 2 , wherein R 1 is a hydroxy group.

4. 4. The negative electrode according to claim 3, wherein the compound represented by the general formula (1) is ethyl hydroxybenzoate.

5. 2. The negative electrode according to claim 1, wherein the compound represented by general formula (1) is applied to the surface of the negative electrode active material layer.

6. The amount of the compound represented by the general formula (1) added per unit area of ​​the surface of the negative electrode active material layer is 0.02 mg / cm ２ 0.25mg / cm or more ２ 2. The negative electrode of claim 1, wherein:

7. an electrode assembly having a positive electrode and a negative electrode; a nonaqueous electrolyte solution that has permeated the interior of the electrode body; It is equipped with The negative electrode is the negative electrode according to any one of claims 1 to 6. A lithium ion secondary battery.

8. The lithium ion secondary battery according to claim 7 , wherein the non-aqueous electrolyte solution contains a non-aqueous solvent belonging to a carbonate family.

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