Negative electrode and battery

Abstract

As a subject, the main purpose of the present disclosure is to provide a negative electrode with good capacity retention. In the present disclosure, the subject is solved by providing the following negative electrode. The negative electrode is a negative electrode having a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, the negative electrode active material layer having a Li complex layer containing a Li complex, the Li complex containing a Li element and a doping element, and in the Li complex layer, when the concentration of the doping element in the first surface opposite to the negative electrode collector side is recorded as C1 and the concentration of the doping element in the second surface on the negative electrode collector side is recorded as C2, C2 is greater than C1.

Description

Technical Field

[0001] The present disclosure relates to negative electrodes and batteries. Background Art

[0002] In recent years, with the rapid spread of electronic devices such as personal computers and mobile phones, the development of batteries to serve as their power sources has been progressing. Furthermore, the automotive industry is also developing batteries for use in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). Among these batteries, lithium-ion secondary batteries have the advantage of high energy density.

[0003] Batteries represented by lithium-ion secondary batteries generally have a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode. The negative electrode, for example, has a negative electrode collector and a negative electrode active material layer (negative electrode layer) disposed on the negative electrode collector. For example, Patent Document 1 discloses a negative electrode layer for an all-solid-state secondary battery comprising a sulfide-based solid electrolyte. Patent Document 1 discloses that the first negative electrode active material layer comprises a lithium metal complex, and the lithium metal complex comprises lithium metal and an inorganic negative electrode active material (such as lithium fluoride). In addition, Patent Document 2 discloses an all-solid-state battery in which the reaction of the negative electrode utilizes the precipitation-dissolution reaction of metallic lithium. Patent Document 2 discloses that the negative electrode layer comprises a β single-phase alloy of metallic lithium and metallic magnesium as the negative electrode active material.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-077640

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-184513 Summary of the Invention

[0008] It is desirable to obtain a battery with less capacity loss associated with charge and discharge. The present disclosure has been made in view of the above-mentioned actual situation, and its main object is to provide a negative electrode with good capacity retention.

[0009] In the present disclosure, a negative electrode is provided, which has a negative electrode collector and a negative electrode active material layer arranged on the above-mentioned negative electrode collector, the above-mentioned negative electrode active material layer has a Li complex layer containing a Li complex, and the Li complex contains a Li element and a doping element. In the above-mentioned Li complex layer, when the concentration of the above-mentioned doping element in the first surface opposite to the above-mentioned negative electrode collector side is recorded as C1 and the concentration of the above-mentioned doping element in the second surface on the above-mentioned negative electrode collector side is recorded as C2, the above-mentioned C2 is greater than the above-mentioned C1.

[0010] According to the present disclosure, a negative electrode having a good capacity retention ratio is obtained by using a Li complex containing a Li element and a doping element, wherein the concentration of the doping element satisfies the relationship C2>C1.

[0011] In the above disclosure, the concentration of the doping element in the Li complex layer may decrease stepwise or continuously in the direction from the second surface toward the first surface.

[0012] In the above disclosure, the above C1 may be greater than 0 atomic %.

[0013] In the above disclosure, the ratio of the above C2 to the above C1 (C2 / C1) may be 1.25 or more and 100 or less.

[0014] In the above disclosure, the above C1 may be 0 atomic %.

[0015] In the above disclosure, the Li complex layer may contain at least one of Mg, Al, Zn, Ag, Au, Si, Sn, In, Bi, Pd, and Rh as the doping element.

[0016] In addition, in the present disclosure, a battery is provided, which is a battery having a positive electrode, a negative electrode and an electrolyte layer, the positive electrode has a positive electrode collector and a positive electrode active material layer, the negative electrode has a negative electrode collector and a negative electrode active material layer, the electrolyte layer is arranged between the positive electrode active material layer and the negative electrode active material layer, and the negative electrode is the above-mentioned negative electrode.

[0017] According to the present disclosure, a battery with excellent cycle characteristics can be obtained by using the above-mentioned negative electrode.

[0018] The negative electrode in the present disclosure achieves a good capacity retention effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an explanatory diagram illustrating the negative electrode in the present disclosure.

[0020] Figure 2 It is an explanatory diagram for explaining the Li complex layer in the present disclosure.

[0021] Figure 3 It is an explanatory diagram for explaining the Li complex layer in the present disclosure.

[0022] Figure 4 It is an explanatory diagram for explaining the Li complex layer in the present disclosure.

[0023] Figure 5 It is an explanatory diagram for explaining the Li complex layer in the present disclosure.

[0024] Figure 6It is an explanatory diagram for explaining the Li complex layer in the present disclosure.

[0025] Figure 7 This is a schematic cross-sectional view illustrating a battery in the present disclosure.

[0026] Figure 8 These are the results of SEM-EDX measurement of the negative electrode obtained in Example 13.

[0027] Description of Reference Numerals

[0028] 1…Negative electrode current collector

[0029] 2…Negative electrode active material layer

[0030] 10…Negative electrode

[0031] 11…Positive electrode current collector

[0032] 12…Positive electrode active material layer

[0033] 20…positive electrode

[0034] 21…Li complex layer

[0035] 30…Electrolyte layer

[0036] 100…batteries DETAILED DESCRIPTION

[0037] The negative electrode and battery of the present disclosure are described in detail below. In this specification, when expressing the arrangement of another component relative to a certain component, simply stating "on" includes both the arrangement of the other component directly above the certain component in contact with the certain component and the arrangement of the other component above the certain component with the other component interposed therebetween, unless otherwise specified.

[0038] A. Negative electrode

[0039] Figure 1 (a) is a schematic cross-sectional view illustrating the negative electrode in the present disclosure. Figure 1 The negative electrode 10 shown in (a) includes a negative electrode current collector 1 and a negative electrode active material layer 2 disposed on the negative electrode current collector 1. The negative electrode active material layer 2 includes a Li complex layer 21 containing a Li complex containing a Li element and a dopant element. Figure 1 (b) is an example Figure 1 (a) is a graph showing the concentration distribution of the doping elements. Figure 1As shown in (a) and (b), in the Li composite layer 21, the concentration of the doping element in the first surface S1 opposite to the negative electrode current collector 1 is denoted as C1, and the concentration of the doping element in the second surface S2 on the negative electrode current collector 1 side is denoted as C2. In the present disclosure, C2 is greater than C1.

[0040] According to the present disclosure, by using a Li complex containing Li and a doping element, and wherein the concentration of the doping element has a relationship of C2>C1, a negative electrode with good capacity retention is achieved. The inventors initially anticipated that, from the perspective of capacity retention, it is preferable that the concentration distribution of the doping element in the Li complex layer be uniform (e.g., C1=C2). The reason for this is that it is speculated that when the concentration distribution of the doping element is non-uniform, the interface of the composition with different concentrations (the interface with slightly different crystal structures) becomes the starting point for cracking caused by the volume change associated with charge and discharge, causing Li to slip or isolate.

[0041] In contrast, by setting the concentration of the doping element to C2>C1, it was unexpectedly confirmed that the capacity retention rate was improved. It is speculated that the reason is that by increasing the concentration C2 of the doping element in the surface on the negative electrode collector side and reducing the concentration C1 of the doping element in the surface on the opposite side of the negative electrode collector, the stress caused by the volume change of Li associated with charging and discharging is alleviated, and the occurrence of cracks is suppressed. In addition, as described in the examples described later, by setting the concentration of the doping element to C2>C1, it was confirmed that the battery resistance was reduced. It is speculated that the reason is that by increasing the concentration C2 of the doping element in the surface on the negative electrode collector side and reducing the concentration C1 of the doping element in the surface on the opposite side of the negative electrode collector, the diffusion rate of Li ions is increased.

[0042] 1. Negative electrode active material layer

[0043] The negative electrode active material layer in the present disclosure has a Li complex layer containing a Li complex, and the Li complex contains a Li element and a doping element. The doping element is usually an element other than the Li element, and is an element that can form a solid solution (such as an interstitial solid solution or a substitutional solid solution) or an intermetallic compound with metallic Li. That is, the Li complex is usually a solid solution containing the Li element and the doping element, or an intermetallic compound containing the Li element and the doping element. The doping element is typically a metal element, and the Li complex is typically a Li alloy.

[0044] As doping elements, for example, Mg, Al, Zn, Ag, Au, Si, Sn, In, Bi, Pd, and Rh can be cited. The Li complex may contain only one doping element or two or more doping elements. The Li complex may contain only Li element and a doping element, or may contain other elements (elements that do not form a solid solution or an intermetallic compound with metallic Li) in addition to Li element and doping element. The total ratio of Li element and doping element in the Li complex is, for example, 75 atomic % or more, 85 atomic % or more, or 95 atomic % or more.

[0045] like Figure 1 As shown in (a) and (b), in the Li composite layer 21, the concentration of the doping element in the first surface S1 opposite to the negative electrode current collector 1 is denoted as C1, and the concentration of the doping element in the second surface S2 on the negative electrode current collector 1 side is denoted as C2. The concentration of the doping element can be determined by measurement using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX).

[0046] From the perspective of improving accuracy, it is preferable to calculate C1 from the average concentration of the doping element in a predetermined region including the first surface S1. Specifically, Figure 2 As shown, it is preferable to measure the average concentration of the doping element in the predetermined region 21x including the first surface S1. For example, when the thickness of the Li complex layer 21 is 4 μm or more, the region 21x is, for example, a region from the first surface S1 to a position 2 μm away from the first surface S1. Similarly, from the perspective of improving accuracy, it is preferable to calculate C2 from the average concentration of the doping element in the predetermined region including the second surface S2. Specifically, as Figure 2 As shown, it is preferable to measure the average concentration of the doping element in a predetermined region 21y including the second surface S2. For example, when the thickness of the Li composite layer 21 is 4 μm or greater, the region 21y is, for example, a region from the second surface S2 to a position 2 μm away from the second surface S2.

[0047] C1 may be 0 atomic % or greater than 0 atomic %. In the latter case, C1 is, for example, 0.005 atomic % or greater, 0.01 atomic % or greater, 0.1 atomic % or greater, or 1 atomic % or greater. On the other hand, C1 is, for example, 80 atomic % or less, or 70 atomic % or less.

[0048] C2 is greater than C1. C2 is, for example, 0.5 atomic % or greater, 1 atomic % or greater, or 5 atomic % or greater. On the other hand, C2 may be 100 atomic % or less, or less than 100 atomic %. In the latter case, C2 is, for example, 95 atomic % or less, 90 atomic % or less, or 85 atomic % or less.

[0049] When C1 is greater than 0 atomic %, the ratio of C2 to C1 (C2 / C1) is, for example, 1.03 or greater, 1.05 or greater, 1.08 or greater, or 1.25 or greater. When C2 / C1 is 1.25 or greater, the capacity retention rate is particularly high. On the other hand, C2 / C1 is, for example, 1000 or less, 700 or less, 200 or less, or 100 or less. When C2 / C1 is 100 or less, the capacity retention rate is particularly high.

[0050] The concentration of the doping element in the Li complex layer may decrease gradually from the second surface toward the first surface. Figure 3 The Li complex layer 21 shown in (a) has a first region 21a including a first surface S1 and a second region 21b including a second surface S2, and the first region 21a and the second region 21b are in contact at a boundary B. There is no interface (solid / solid interface) between the first region 21a and the second region 21b, and both are formed continuously. Figure 3 As shown in (b), the concentration of the doping element in the first region 21a is uniform and is C1. Similarly, the concentration of the doping element in the second region 21b is uniform and is C2. Figure 3 In the direction from the second surface S2 to the first surface S1, the concentration of the doping element in the Li complex layer 21 gradually decreases. Figure 3 The concentration of the doping element changes stepwise (sharply) at the boundary B, but the concentration of the doping element may also change continuously near the boundary B.

[0051] exist Figure 3 In the embodiment, the concentration of the doping element decreases in stages in the direction from the second surface S2 to the first surface S1 in two stages, C2 and C1. In the present disclosure, the concentration of the doping element may also decrease in stages in three or more stages in the direction from the second surface to the first surface. For example, the concentration of the doping element may decrease in stages in the order of C2, C3, and C1 in the direction from the second surface to the first surface. In this case, C3 satisfies C2>C3>C1.

[0052] The concentration of the doping element in the Li complex layer may also decrease continuously from the second surface to the first surface. Figure 1 As shown in (b), the concentration of the doping element can be continuously reduced from C2 to C1 in the direction from the second surface S2 to the first surface S1. Figure 1 In (b), the concentration of the doping element decreases linearly from C2 to C1. Figure 4As shown in (a) and (b), the concentration of the doping element can also decrease linearly from C2 to C1.

[0053] As mentioned above, C1 may be 0 atomic %. For example, Figure 5 The Li complex layer 21 shown in (a) includes a third region 21c. The third region 21c includes the first surface S1, and the concentration of the doping element in the third region 21c is 0 atomic %. The third region 21c is preferably a layer containing only Li. The thickness of the third region 21c is, for example, 100 nm or more, 1 μm or more, or 5 μm or more. Figure 5 The Li complex layer 21 shown in (a) includes a third region 21c and a fourth region 21d containing a Li complex, and the third region 21c and the fourth region 21d are in contact at a boundary B. There is no interface (solid / solid interface) between the third region 21c and the fourth region 21d, and both are formed continuously.

[0054] like Figure 5 As shown in (a) and (b), the concentration of the doping element at the boundary B is recorded as C4. C4 is usually greater than 0 atomic %. The preferred range of the C4 value is the same as the preferred range of the C1 value mentioned above. In addition, the preferred range of the ratio of C2 to C4 (C2 / C4) is the same as the preferred range of the C2 / C1 value mentioned above. Preferably, the concentration of the doping element in the Li complex layer decreases in stages or continuously in the direction from the second surface to the boundary B. In the direction from the second surface to the boundary B, the concentration of the doping element can be gradually reduced in two stages, or in three or more stages. In addition, in the case where the concentration of the doping element continuously decreases in the direction from the second surface to the boundary B, the concentration of the doping element can decrease linearly from C2 to C4, or can decrease curvedly from C2 to C4.

[0055] The Li complex layer in the present disclosure may be a laminated body in which a plurality of members are laminated. Figure 6 The Li complex layer 21 shown in (a) includes a first member 21α having a first surface S1 and a second member 21β having a second surface S2, and the first member 21α and the second member 21β are in contact at an interface I. Figure 6 As shown in (b), the concentration of the doping element in the first member 21α is uniform and is C1. Similarly, the concentration of the doping element in the second member 21β is uniform and is C2. Figure 6In the embodiment, the concentration of the doping element in the Li complex layer 21 decreases stepwise from the second surface S2 toward the first surface S1. Although not specifically shown, the Li complex layer may include a first member having a first surface, a second member having a second surface, and one or more third members disposed between the first and second members.

[0056] As the shape of the Li complex layer, for example, a foil (film) can be cited. The Li complex layer is preferably a layer having a foil (film)-shaped Li complex. The Li complex layer can also be a vapor-deposited layer of a Li complex. In addition, the Li complex layer is usually not a layer containing a particulate Li complex.

[0057] The thickness of the Li composite layer is not particularly limited, and may be, for example, 1 μm or greater, 5 μm or greater, or 10 μm or greater. Meanwhile, the thickness of the Li composite layer may be, for example, 1000 μm or less, 500 μm or less, or 300 μm or less. The method for forming the Li composite layer is not particularly limited, and examples thereof include PVD methods such as vacuum deposition, sputtering, and ion plating.

[0058] The negative electrode active material layer in the present disclosure may include only the Li complex layer, or may include other layers that contribute to the charge-discharge capacity in addition to the Li complex layer.

[0059] 2. Negative electrode collector

[0060] The negative electrode current collector in the present disclosure collects current from the negative electrode active material layer. Examples of materials for the negative electrode current collector include stainless steel (SUS), copper, nickel, and carbon. Examples of shapes for the negative electrode current collector include foil and mesh. The negative electrode current collector is, for example, positioned on the side opposite the electrolyte layer relative to the negative electrode active material layer.

[0061] 3. Negative electrode

[0062] The negative electrode in the present disclosure includes the above-mentioned negative electrode active material layer and a negative electrode current collector. The negative electrode is preferably used in a battery.

[0063] B.Battery

[0064] Figure 7 This is a schematic cross-sectional view illustrating a battery in the present disclosure. Figure 7 The battery 100 shown includes a positive electrode 20 having a positive electrode collector 11 and a positive electrode active material layer 12, a negative electrode 10 having a negative electrode collector 1 and a negative electrode active material layer 2, and an electrolyte layer 30 disposed between the positive electrode active material layer 12 and the negative electrode active material layer 2. The negative electrode 10 is the negative electrode described in "A. Negative Electrode" above.

[0065] According to the present disclosure, a battery with excellent cycle characteristics can be obtained by using the above-mentioned negative electrode.

[0066] 1. Negative electrode

[0067] Regarding the negative electrode in this disclosure, since the contents are the same as those described in "A. Negative Electrode" above, the description here is omitted. The Li complex layer and the electrolyte layer in the negative electrode may be in contact. In addition, a Li precipitation layer may be arranged between the Li complex layer and the electrolyte layer in the negative electrode. The Li precipitation layer is a layer of Li deposited during charging.

[0068] 2. Positive electrode

[0069] The positive electrode in the present disclosure has a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer contains at least a positive electrode active material. Examples of the positive electrode active material include LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 and other rock salt layered active materials, LiMn2O4, Li4Ti5O 12 、Li(Ni 0.5 Mn 1.5 )O4 and other spinel active materials, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 and other olivine active materials.

[0070] The positive electrode active material layer may also contain at least one of an electrolyte, a conductive material and a binder. The details of the electrolyte are described in the following "3. Electrolyte Layer". As the conductive material, for example, a carbon material can be cited. As the carbon material, for example, a particulate carbon material such as acetylene black (AB), Ketjen black (KB), a fibrous carbon material such as carbon fiber, carbon nanotube (CNT), carbon nanofiber (CNF), etc. can be cited. As the binder, for example, a fluorine-containing binder such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. can be cited. In addition, the thickness of the positive electrode active material layer is, for example, not less than 0.1 μm and not more than 1000 μm.

[0071] The positive electrode current collector collects current from the positive electrode active material layer. Examples of materials for the positive electrode current collector include stainless steel (SUS), aluminum, nickel, iron, titanium, and carbon. Examples of shapes for the positive electrode current collector include foil and mesh. The positive electrode current collector is, for example, positioned on the side opposite the electrolyte layer relative to the positive electrode active material layer.

[0072] 3. Electrolyte layer

[0073] The electrolyte layer in the present disclosure contains at least an electrolyte. Examples of the electrolyte include liquid electrolytes (electrolyte solutions), gel electrolytes, and solid electrolytes. The battery in the present disclosure is preferably a liquid battery in which the electrolyte layer contains a liquid electrolyte (electrolyte solution). This is because, as described in the Examples below, it is effective in reducing battery resistance.

[0074] The electrolyte solution includes, for example, a lithium salt and a solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiC(SO2CF3)3. Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0075] Gel electrolytes are typically obtained by adding a polymer to an electrolyte. Examples of polymers include polyethylene oxide and polypropylene oxide. Examples of solid electrolytes include organic solid electrolytes such as polymer electrolytes, and inorganic solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes. The thickness of the electrolyte layer is, for example, 0.1 μm to 1000 μm. The electrolyte layer may also include a separator.

[0076] 4.Battery

[0077] The battery disclosed herein is typically a lithium-ion secondary battery. Examples of battery applications include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. Furthermore, the battery disclosed herein may also be used as a power source for mobile vehicles other than vehicles (e.g., trains, ships, and aircraft), or as a power source for electrical products such as information processing devices.

[0078] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiments having substantially the same configuration and achieving the same functions and effects as the technical concepts described in the claims of the present disclosure are encompassed within the technical scope of the present disclosure.

[0079] Example

[0080] [Example 1]

[0081] (Fabrication of negative electrode)

[0082] Using the vacuum evaporation method, a Li complex layer containing Li and Mg elements (doping elements) was formed on the negative electrode collector (Cu foil). Specifically, a crucible equipped with Li metal and a crucible equipped with Mg metal were prepared, and these crucibles were subjected to electron beam heating. By electron beam heating, Li and Mg were volatilized in the vacuum evaporation device, and were evaporated on the surface of the Cu foil to form a Li complex layer (thickness 40μm). At this time, the evaporation conditions were adjusted so that the desired Li complex layer (the concentration C2 of the Mg element in the second surface is 30 atomic%, and the concentration C1 of the Mg element in the first surface is 20 atomic%) can be obtained. Specifically, the concentration of the Li element and the concentration of the Mg element are adjusted by controlling the temperature of the crucible (that is, the volatilization rate of the element). In this way, a negative electrode having a negative electrode collector and a Li complex layer was obtained.

[0083] (Production of positive electrode)

[0084] The positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), a conductive material (acetylene black), a binder (polyvinylidene fluoride), and a dispersant. These materials are mixed with N-methylpyrrolidone to form a positive electrode slurry. This slurry is applied to a positive electrode current collector (Al foil) and dried to produce a positive electrode.

[0085] (Battery Production)

[0086] As the electrolyte, a solution of a supporting electrolyte (LiPF6) dissolved at a concentration of 1M in a non-aqueous solvent (a mixed solvent of equal volumes of EC and DMC) was prepared. Separately, a three-layer porous film of polypropylene (PP), polyethylene (PE), and polypropylene (PP) was prepared as the separator. Using these components, the aforementioned negative and positive electrodes, a wound-type battery was fabricated.

[0087] [Comparative Example 1]

[0088] A negative electrode was produced in the same manner as in Example 1 except that Mg metal was not used. A battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

[0089] [Comparative Example 2]

[0090] A negative electrode was fabricated in the same manner as in Example 1, except that the vapor deposition conditions were adjusted so that a Li composite layer having a Mg element concentration C2 of 20 atomic % on the second surface and a Mg element concentration C1 of 30 atomic % on the first surface was obtained. A battery was fabricated in the same manner as in Example 1, except that the obtained negative electrode was used.

[0091] [evaluate]

[0092] (Capacity retention rate)

[0093] The batteries obtained in Example 1 and Comparative Examples 1 and 2 were used to measure capacity retention after 200 cycles. Charge and discharge conditions were constant current charge and discharge, a current rate of 1C, a voltage range of 3.3V to 4.2V, and an ambient temperature of 60°C. The ratio of the discharge capacity at the 200th cycle to the discharge capacity at the 1st cycle was defined as the capacity retention. The results are shown in Table 1.

[0094] (Battery resistance)

[0095] The battery resistance of the batteries obtained in Example 1 and Comparative Examples 1 and 2 was measured. Specifically, the open circuit voltage (OCV) of the battery was adjusted to 3.70 V, and then discharged under the conditions of an ambient temperature of -5°C, a current rate of 5C, and a discharge time of 8 seconds. The voltage drop ΔV caused by this discharge was obtained, and the battery resistance was calculated using the following formula.

[0096] Battery resistance = ΔV / (5C current value)

[0097] The results are shown in Table 1. The battery resistance values ​​in Table 1 are relative values ​​when the battery resistance of Comparative Example 1 is set to 1.00.

[0098] Table 1

[0099]

[0100] As shown in Table 1, Example 1 exhibits a higher capacity retention rate than Comparative Examples 1 and 2. This is presumably because the Li composite layer contains a dopant element in addition to Li, and the concentration of the dopant element has a C2>C1 relationship. This mitigates the stress caused by the volume change of Li associated with charge and discharge, thereby suppressing the occurrence of cracks. Furthermore, Example 1 exhibits lower battery resistance than Comparative Examples 1 and 2. This is presumably because the Li composite layer contains a dopant element in addition to Li, and the concentration of the dopant element has a C2>C1 relationship. This facilitates the conduction of Li ions via the dopant element (increasing the Li carrier concentration).

[0101] [Examples 2 to 13]

[0102] A negative electrode was produced in the same manner as in Example 1 except that C1 and C2 were changed to the values ​​shown in Table 2. A battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

[0103] [evaluate]

[0104] The capacity retention rate and battery resistance were determined in the same manner as above using the batteries obtained in Examples 2 to 13. The results are shown in Table 2. The battery resistance values ​​in Table 2 are relative values ​​when the battery resistance of Comparative Example 1 is set to 1.00.

[0105] Table 2

[0106]

[0107] As shown in Table 2, in Examples 2 to 13, both the capacity retention rate and the battery resistance were good. In particular, in Examples 4 to 11, a high capacity retention rate of 80% or more was obtained. Similarly, in Examples 4 to 11, the battery resistance was particularly low. In addition, the cross section of the negative electrode obtained in Example 13 was observed using SEM-EDX. Figure 8 The results are shown in . Figure 8 As shown in FIG. 1 , it was confirmed that the concentration of the doping element in the Li complex layer had a relationship of C2>C1.

[0108] [Examples 14 to 23]

[0109] A negative electrode was produced in the same manner as in Example 1, except that the doping element was changed to the element shown in Table 3. A battery was produced in the same manner as in Example 1, except that the obtained negative electrode was used.

[0110] [evaluate]

[0111] The capacity retention rate and battery resistance were determined in the same manner as above using the batteries obtained in Examples 14 to 23. The results are shown in Table 3. The battery resistance values ​​in Table 3 are relative values ​​when the battery resistance of Comparative Example 1 is set to 1.00.

[0112] Table 3

[0113]

[0114] As shown in Table 3, in Examples 14 to 23, the capacity retention rate and battery resistance were good, similarly to Example 1. In other words, it was confirmed that the same effect can be obtained even when an element other than Mg is used as the doping element.

[0115] [Example 24]

[0116] A negative electrode was produced in the same manner as in Example 1 except that C1 and C2 were changed to the values ​​shown in Table 4. A battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

[0117] [evaluate]

[0118] The capacity retention rate and battery resistance were determined in the same manner as above using the battery obtained in Example 24. The results are shown in Table 4. The battery resistance values ​​in Table 4 are relative values ​​when the battery resistance of Comparative Example 1 is set to 1.00.

[0119] Table 4

[0120]

[0121] As shown in Table 4, in Example 24, the capacity retention rate and battery resistance were both good, similarly to Example 1. In other words, it was confirmed that the same effect can be obtained even when C1 is 0 atomic %.

Claims

1. A negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, The negative electrode active material layer includes a Li complex layer containing a Li complex, wherein the Li complex contains only Li element and a doping element, and the doping element is Mg. In the Li composite layer, when the concentration of the doping element in the first surface opposite to the negative electrode current collector side is recorded as C1, and the concentration of the doping element in the second surface on the negative electrode current collector side is recorded as C2, C2 is greater than C1, C1 is greater than 0 atomic %, and the ratio of C2 to C1, i.e., C2 / C1, is greater than 1.25 and less than 100.

2. The negative electrode according to claim 1, The concentration of the doping element in the Li complex layer decreases stepwise or continuously in a direction from the second surface toward the first surface.

3. A battery comprising a positive electrode, a negative electrode and an electrolyte layer, The positive electrode comprises a positive electrode current collector and a positive electrode active material layer. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer. The electrolyte layer is disposed between the positive electrode active material layer and the negative electrode active material layer. The negative electrode is the negative electrode according to claim 1 or 2.

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