Negative electrode for lithium secondary battery and lithium secondary battery

Abstract

A negative electrode for a lithium secondary battery, which is a negative electrode for a lithium secondary battery having a negative electrode active material layer formed on a current collector, the negative electrode active material comprising a phosphorus-carbon composite negative electrode material containing a phosphorus atom and a carbon atom, the area proportion of the black portion of a binary image obtained by the following method with respect to the entire negative electrode active material layer being 0.05% or more and 12% or less. [Method for obtaining binary image] The surface of the negative electrode active material layer is imaged at a photographing magnification of 40 times using a scanning electron microscope to obtain a negative electrode surface image. The negative electrode surface image is subjected to adaptive binary processing to obtain a binary image.

Description

Technical Field

[0001] This invention relates to a negative electrode for lithium secondary batteries and lithium secondary batteries.

[0002] This application claims priority based on Japanese Patent Application No. 2024-027419 filed on February 27, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Lithium-ion batteries are used as power sources for small electronic devices such as mobile phones and laptops. In recent years, lithium-ion batteries have also made progress in their practical application in medium- or large-scale power sources, such as automotive applications and energy storage.

[0004] Carbon materials are known as negative electrode active materials for lithium secondary batteries. Previously, with the aim of improving battery performance, negative electrode active materials that further contain phosphorus in carbon materials were known (for example, see Patent Document 1). Regarding the negative electrode active material described in Patent Document 1, by using a negative electrode active material obtained by combining carbon materials with phosphorus, it is possible to produce a negative electrode with excellent charge / discharge capacity.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2009-184861 Summary of the Invention

[0006] The problem that the invention aims to solve As the application fields of lithium-ion rechargeable batteries expand, there is a growing demand for further improvements in battery characteristics. Among these characteristics, capacity retention is a key indicator of degradation caused by repeated charging and discharging; therefore, improving capacity retention is a primary research topic.

[0007] The present invention was made in view of the above circumstances, and the object is to provide a negative electrode for a lithium secondary battery with high capacity retention and a lithium secondary battery using the same.

[0008] Methods for solving problems To address the aforementioned issues, one aspect of the present invention includes the following solution.

[0009] [1] A negative electrode for a lithium secondary battery, wherein a negative electrode active material layer is formed on a current collector, the negative electrode active material layer comprising a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms, and the area ratio of the black part of the binary image of the negative electrode active material layer to the whole is 0.05% or more and 12% or less.

[0010] [Methods for obtaining binarized images] The surface of the aforementioned negative electrode active material layer was photographed using a scanning electron microscope at 40x magnification to obtain an image of the negative electrode surface. The negative electrode surface image was then subjected to adaptive binarization processing to obtain a binarized image.

[0011] [2] According to the negative electrode for lithium secondary batteries described in [1], the binarized image has an island structure in which the black parts are scattered like islands, and the average area of ​​the islands in the island structure is 0.001 mm. 2 Above and 0.03mm 2 the following.

[0012] [3] According to the negative electrode described in [1] or [2], wherein the above-mentioned phosphorus-carbon composite negative electrode material has a peak in XPS spectrum representing the bond between phosphorus atoms and carbon atoms.

[0013] [4] The negative electrode according to any one of [1] to [3], wherein, in the XRD spectrum of the above phosphorus-carbon composite negative electrode material measured using CuKα rays, the intensity I at 2θ=20° is... 20 Intensity I at 2θ = 26.3° 26.3 and the intensity I at 2θ=40° 40 The following equations (1) to (3) are satisfied.

[0014] |P| / |B|<2…(1) P=I 26.3 -I 40 …(2) B = (I 20 -I 40 )×(26.3-40) / (20-40)…(3) [5] The negative electrode according to any one of [1] to [4], wherein the phosphorus-carbon composite negative electrode material has a nuclear particle containing phosphorus atoms and a carbon film covering the surface of the nuclear particle.

[0015] [6] A lithium secondary battery comprising any one of [1] to [5] a negative electrode.

[0016] [7] The lithium secondary battery according to claim 6, wherein the electrolyte comprises a solid electrolyte interface forming agent.

[0017] Invention Effects According to the present invention, a negative electrode for a lithium secondary battery with high capacity retention and a lithium secondary battery using the same can be provided. Attached Figure Description

[0018] Figure 1 This is the XPS spectrum of the PC anode material.

[0019] Figure 2This is a transmission electron microscope (TEM) image of the PC anode material.

[0020] Figure 3 These are the XRD patterns of PC anode materials and PC mixtures.

[0021] Figure 4 This is a schematic diagram illustrating an all-solid-state lithium secondary battery as an example of a battery.

[0022] Figure 5 This is a schematic diagram illustrating an all-solid-state lithium secondary battery as an example of a battery.

[0023] Figure 6 These are images of the negative electrode surface and binarized images of the negative electrode for a lithium secondary battery manufactured in Example 1.

[0024] Figure 7 These are images of the negative electrode surface and binarized images of the negative electrode for a lithium secondary battery manufactured in Example 2.

[0025] Figure 8 These are images of the negative electrode surface and binarized images of the negative electrode for a lithium secondary battery manufactured in Comparative Example 1.

[0026] Figure 9 These are images of the negative electrode surface and binarized images of the negative electrode for a lithium secondary battery manufactured in Comparative Example 2. Detailed Implementation

[0027] <Negative electrode for lithium secondary batteries> This embodiment is a negative electrode for a lithium secondary battery in which a negative electrode active material layer is formed on the current collector.

[0028] The negative electrode active material layer contains a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms as the negative electrode active material.

[0029] Copper or copper alloys can be used as materials for current collectors.

[0030] In the following description, "phosphorus-carbon composite anode material" will sometimes be abbreviated as "PC anode material".

[0031] Generally, electrodes are manufactured by coating a slurry containing electrode material onto a current collector foil, drying it, and then pressing it. The pressing process is performed to make the electrode film thickness uniform and to compact it.

[0032] The raw material (PC anode material) used as the negative electrode active material layer sometimes contains coarse particles. Therefore, the surface of the coating obtained by coating a slurry containing the electrode material and allowing it to dry is expected to have areas with coarse particles that are raised compared to other areas. It is presumed that if such a coating is pressed, the coarse particles that are raised compared to other areas are more easily subjected to pressing pressure and are more easily compacted compared to other areas. As a result, in the obtained negative electrode active material layer, there are areas formed where the coarse particles from the electrode material are compacted during the pressing process, and areas where the pressing pressure is relatively low compared to these areas.

[0033] Later, the "region formed by the compression of coarse particles" was sometimes recorded as "region P", and the "region with relatively low compression pressure compared to region P" was recorded as "region L".

[0034] It is believed that region P is less prone to expansion during charging and less prone to contraction during discharging compared to region L. That is, the volume changes (expansion and contraction) of regions P and L during charging and discharging are different. Therefore, it is speculated that if charging and discharging are repeated, the volume changes of regions P and L will not be interconnected, and cracks are easily generated between regions P and L. At the cracked areas, the contact points between the PC negative electrode materials are easily interrupted, and the conductive path is easily disrupted. At the points where the conductive path is interrupted, lithium ions cannot move, becoming resistance.

[0035] The inventors envisioned the degradation mechanism of electrodes containing PC anode materials as described above. According to this degradation mechanism, it is believed that in the anode active material layer with less P, the area between "region P and region L", which is prone to cracking, is reduced, and the anode is less prone to degradation.

[0036] To verify the degradation mechanism based on the above model, the inventors focused on the surface hue of the negative electrode active material layer. By observing the surface of the negative electrode active material layer after charging and discharging using SEM, a relatively dark area was identified in the SEM image. This "dark area" was considered to be a region formed by strong pressure and compaction, and was thus identified as region P.

[0037] The inventors have confirmed that cracks were generated around the dark-toned areas in the SEM images of the negative electrode active material layer after charge and discharge. Furthermore, the inventors have confirmed that the amount of dark-toned areas in the SEM images is negatively correlated with the capacity retention rate.

[0038] On the other hand, in actual negative electrode active material layers, the method of applying the pressure changes continuously along the surface of the layer, making it impossible to clearly distinguish between "region P" and "region L" as in the model envisioned above. Therefore, evaluating the quantity of region P in actual negative electrode active material layers is difficult.

[0039] Based on the above confirmation results, the inventors conducted in-depth research and came up with the following idea: the amount of region P can be evaluated by binarizing the hue of the surface of the negative electrode active material layer.

[0040] That is, in the binarized image obtained by the following method, black and white areas are observed in the negative electrode active material layer, and the area ratio of the black area to the whole in the binarized image is more than 0.05% and less than 12%.

[0041] [Methods for obtaining binarized images] To obtain the binarized image, the surface of the negative electrode active material layer was photographed using a scanning electron microscope at a magnification of 40x to obtain the negative electrode surface image.

[0042] The surface of the negative electrode active material layer can be observed after the pressing process, or it can be observed by disassembling the assembled lithium secondary battery and removing the negative electrode active material layer. When removing the negative electrode active material layer from the lithium secondary battery, it is preferable to remove it after discharging the lithium secondary battery.

[0043] The scanning electron microscope used was a JCM-7000NeoScope manufactured by Nippon Electron Ltd., with the accelerating voltage set to 15.0kV and the working distance set to 12.6mm.

[0044] In addition, a negative electrode surface image with a pixel count of 2560 pixels × 1920 pixels was obtained as the negative electrode surface image.

[0045] The obtained negative electrode surface image is entered into image processing software, and adaptive binarization processing is performed through the following steps to obtain a binarized image.

[0046] As an image analysis software, it uses Python libraries such as OpenCV and scikit-image (as a module, threshold_sauvola).

[0047] First, for all pixels of the negative electrode surface image, perform the following processing (A) and (B).

[0048] (A): Calculate the threshold using the pixels surrounding the pixel of interest, i.e., the pixels of the local region (specifically, pixels with a vertical × horizontal ratio of 251 × 251). The threshold is calculated using the pixel values ​​of the local region's pixels using the following formula.

[0049] T=m(x,y) (1+k) ((s(x,y) / R)-1)) In the above formula, m(x, y) is the average value of the area of ​​a square with window size W as one side.

[0050] s(x, y) is the standard deviation of the region of a square with window size W as one side. k is a parameter for weighting the standard deviation.

[0051] R is the maximum standard deviation of the grayscale image.

[0052] In addition, the threshold is calculated for each pixel of interest.

[0053] (B): If the pixel value of the pixel of interest is greater than the threshold obtained by (A) above, it is set to white; if it is less than the threshold, it is set to black. This is then binarized.

[0054] In this embodiment, the area ratio of the black portion of the binarized image of the negative electrode active material layer relative to the whole is preferably 0.1% or more and 10% or less, and more preferably 1.5% or more and 8% or less.

[0055] If the area ratio of the black region is below the upper limit mentioned above, then the black region, i.e. region P, which is the cause of crack formation, is small. Even under repeated charging and discharging, the resistance is not easy to increase, so the capacity retention rate is not easy to decrease.

[0056] The smaller the proportion of the black area, the better; however, the lower limit mentioned above is a proportion that is unavoidable and permissible.

[0057] One scheme for obtaining a binarized image using the above method has a black area with an island-like structure. The average area of ​​the islands in the island structure is preferably 0.001 mm. 2 Above and 0.03mm 2 Below, 0.002mm is preferred. 2 Above and 0.02mm 2 Below, 0.003mm is further preferred. 2 Above and 0.01mm 2 the following.

[0058] If the average area of ​​the islands in the island structure is below the aforementioned upper limit, it becomes a layer of negative electrode active material with the least amount of region P. That is, if the area of ​​the islands in the island structure is small, the areas prone to cracking are reduced, making it easier to obtain a negative electrode that is not easily degraded.

[0059] The smaller the average area of ​​the islands in the island structure, the better; however, the lower limit mentioned above is an area that is unavoidable and permissible.

[0060] The average area of ​​an island in a multi-island structure is the numerical average of the area of ​​the entire island obtained through image analysis of the binarized image acquired using the method described above. Image analysis software for calculating the numerical average can use Python libraries such as OpenCV and scikit-image (as a module, threshold_sauvola).

[0061] Phosphorus-carbon composite anode materials The PC anode material used in this embodiment contains phosphorus atoms and carbon atoms.

[0062] In one embodiment of the present invention, the PC negative electrode material is a powder.

[0063] When the PC anode material contains components other than phosphorus atoms and carbon atoms, the proportion of the other components relative to the total amount of the components other than phosphorus atoms and carbon atoms is preferably 1% or more and 15% or less by mass, more preferably 2% or more and 12% or less by mass, and even more preferably 2.5% or more and 8% or less by mass.

[0064] If the proportions of other components are within the above range, the movement of lithium ions is not easily hindered, and the initial capacity of the secondary battery becomes easier to increase.

[0065] PC anode materials can also be composed of more than 60% by mass of phosphorus and carbon atoms, and may further include elements other than phosphorus and carbon atoms.

[0066] Elements other than phosphorus and carbon atoms that can be included in PC anode materials include lithium, silicon, germanium, tin, aluminum, zinc, magnesium, transition metals, nitrogen, oxygen, fluorine, silicon, titanium, niobium, sulfur, and chlorine. These can be sourced from metal oxides, complex metal oxides, metal fluorides, metal sulfides, metal chlorides, silicon oxide, silicates, titanates, and aluminates.

[0067] The content of phosphorus atoms, carbon atoms, and other atoms that can be further included in the PC anode material can be determined by the well-known ICP analysis.

[0068] In the PC anode material, the phosphorus atom content is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more. A high phosphorus content can improve the initial charge-discharge capacity of the PC anode material. Furthermore, in the PC anode material, the phosphorus atom content is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. This is because if the phosphorus atom content is too high, the cycle characteristics of the PC anode material will decrease. The upper and lower limits of the phosphorus atom content can be arbitrarily combined.

[0069] In the PC anode material, the carbon atom content is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. A high carbon atom content improves the cycle characteristics of the PC anode material. Furthermore, in the PC anode material, the carbon atom content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. This is because if the carbon atom content is too high, the initial charge-discharge capacity of the PC anode material decreases. The upper and lower limits of the carbon atom content can be arbitrarily combined.

[0070] Details are described below, but PC anode materials can be manufactured by mixing phosphorus and carbon materials in a ball mill. The inventors conducted detailed analysis and research on the obtained PC anode materials, and the results confirmed that the PC anode material is not a mixture of phosphorus and carbon materials used as raw materials, but rather a novel material in which phosphorus atoms and carbon atoms are chemically bonded (covalently bonded) in the PC anode material, resulting in physical properties different from those of the phosphorus and carbon materials used as raw materials.

[0071] The following section compares PC anode materials with mixtures of phosphorus and carbon materials (hereinafter, sometimes referred to as "PC mixtures") to provide a detailed description of the physical properties of PC anode materials.

[0072] In the following description, an example of a PC anode material is compared with an example of a mixture made by mixing the same raw materials as the PC anode material in a mortar. In the examples shown below, both the raw materials of the PC anode material and the raw materials of the PC mixture contain black phosphorus and carbon materials in a 6:4 (mass ratio). In both the PC anode material and the PC mixture, the carbon material used is CSCNT (stacked cup carbon nanotubes).

[0073] [PPC button presence / absence] PC anode materials exhibit peaks in XPS spectra representing the bonds between phosphorus and carbon atoms. These peaks are known to appear in the XPS spectrum in the range of 132–136 eV. It should be noted that in the following description, the bonds between phosphorus and carbon atoms may sometimes be simply referred to as "PC bonds".

[0074] Figure 1 It is the XPS spectrum of PC anode material and PC mixture. Figure 1 In the diagram, the horizontal axis represents the bonding energy (eV), and the vertical axis represents the number of photoelectrons detected (cps (count per second)). Figure 1 In the diagram, symbol A represents PC anode material, and symbol X represents PC mixture.

[0075] (XPS spectroscopy measurement conditions) XPS spectra were determined under the following conditions.

[0076] • Measurement equipment: XPS unit, ESCA-3400 (manufactured by Shimadzu Corporation) • Radiation source: Mg Kα rays (20mA, 10kV) If a peak is detected in the range of 132–136 eV, it is determined that a PC bond is present.

[0077] like Figure 1 As shown, it was found that no peak representing PC bonds was detected in the range of 132–136 eV for PC mixtures, but a peak representing PC bonds (denoted by the symbol α) was detected for PC anode materials.

[0078] Depend on Figure 1 The results shown suggest that, in terms of PC anode materials, they are substances with chemical bonds between phosphorus atoms and carbon atoms.

[0079] [Appearance] The preferred PC anode material has a core containing phosphorus atoms and a carbon film covering the surface of the core.

[0080] Figure 2 This is a transmission electron microscope (TEM) image of the PC anode material. For example... Figure 2 As shown, the particles 50, which are PC anode materials, exhibit a core-shell structure in which a carbon film 52 covers the surface of the nuclear particles 51 containing phosphorus atoms.

[0081] The presence of phosphorus and carbon atoms in PC anode materials can be confirmed using EDX (Energy Dispersive X-ray Spectroscopy).

[0082] Furthermore, when the PC anode material consists only of phosphorus and carbon atoms, the heavier atoms, namely phosphorus atoms, are captured in greater concentration in the TEM image. Therefore, based on the TEM image, it can be easily determined that it is a core-shell structure in which the nucleus particle 51 contains phosphorus atoms and is covered by a carbon film 52 containing carbon atoms.

[0083] (Conditions for taking TEM photos) TEM photos were taken under the following conditions.

[0084] • TEM apparatus: H-9000NAR transmission electron microscope (manufactured by Hitachi, Ltd.) • Field of view: Maximum 500nm × 500nm. At least a portion of the PC anode material particles placed within the field of view are photographed.

[0085] If the TEM images were taken under the conditions described above, the core-shell structure of the PC anode material could be confirmed.

[0086] In addition to meeting the aforementioned necessary conditions regarding [behavior relative to heat], the preferred PC anode material is a core-shell structure.

[0087] [Crystal State] Figure 3 These are the XRD patterns of PC anode materials and PC mixtures. Figure 3 In the diagram, the horizontal axis represents the diffraction angle (2θ, °), and the vertical axis represents the intensity of the diffracted X-rays (au: arbitrary unit). Figure 3 In the diagram, symbol A represents PC anode material, and symbol X represents PC mixture.

[0088] (XRD spectral determination conditions) XRD patterns were determined under the following conditions.

[0089] • Measuring equipment: Sample horizontal type multi-functional X-ray diffractometer Ultima IV (manufactured by Rigaku Co., Ltd.) • Radiation source: Cu Kα rays • Measurement range (2θ): 10°~90° • Scanning speed: 4° / minute • Sampling: 0.02° Voltage 40kV, Current 40mA like Figure 3 As shown, in the PC mixture, both carbon materials and black phosphorus exhibit a certain degree of crystallinity, displaying diffraction peaks. In contrast, the diffraction peaks observed in the PC anode material are not seen in the PC mixture; only noise can be detected across the entire measurement range. That is, from Figure 3 The results shown suggest that in PC anode materials, the crystallinity of the carbon material used as a raw material disappears, becoming amorphous or, as if its crystalline state cannot be determined, becoming a fine carbon material.

[0090] Here, when the XRD pattern of the PC anode material is measured under the above conditions, the intensity I at 2θ=20° in the XRD pattern measured under the above conditions is... 20 Intensity I at 2θ = 26.3° 26.3 and the intensity I at 2θ=40° 40 Preferably, the following relationships (1) to (3) are satisfied.

[0091] |P| / |B|<2…(1) P=I 26.3 -I 40…(2) B = (I 20 -I 40 )×(26.3-40) / (20-40)…(3) When the XRD spectrum of the carbon material used as a raw material is measured, the peak of the carbon material appears at 2θ=26.3°, which is equivalent to the peak of graphite (002). On the other hand, in the typical XRD spectrum of carbon materials, there are no peaks at 2θ=20° and 2θ=40°. Therefore, in the above equation (1), by taking 2θ=40°, where the peak of the carbon material does not exist, as the reference point, the state of the carbon material can be determined by comparing the intensity of the reference point in the XRD spectrum with the intensity of the peak position (2θ=26.3°) of the carbon material where the raw material exists.

[0092] In the above formula (2), "P" represents the strength I at the reference point. 40 The intensity I of the peak position where carbon materials exist 26.3 The difference represents the difference between the peak at the reference point and the peak at the reference point.

[0093] The “B” in the above formula (3) represents the baseline intensity of 2θ=26.3° estimated from two positions without peaks (2θ=20° and 2θ=40°).

[0094] The ratio of the absolute values ​​of P and B (|P| / |B|) expressed by equation (1) above is used to determine the ratio of the baseline intensity to the peak intensity from the reference point. When |P| / |B| is greater than 2, it indicates the presence of a peak of carbon material.

[0095] On the other hand, when |P| / |B| is less than 2 and equation (1) is satisfied, the peak of the carbon material shrinks, indicating that the crystallinity of the carbon material decreases and the carbon material becomes amorphous or, as if the crystalline state cannot be confirmed, becomes a fine carbon material. Therefore, in addition to satisfying the necessary conditions for [behavior relative to heat] mentioned above, the PC anode material preferably also satisfies the above-mentioned relationships (1) to (3).

[0096] As shown above, the PC anode material and phosphorus (in) which will be used as a raw material Figures 1-3 Compared to mixtures of black phosphorus (in the middle) and carbon materials, it becomes a novel substance that differs from any of the following in terms of thermal behavior, bonding state, appearance, and crystal state.

[0097] (Manufacturing method of PC anode material) PC anode materials are obtained by mixing phosphorus materials with carbon materials. The phosphorus materials and carbon materials are preferably mixed by a mixing and pulverizing process accompanied by compression.

[0098] The carbon materials used as raw materials can be at least one selected from the group consisting of amorphous carbon, graphite, porous carbon, mesophase carbon microspheres (MCMB), fullerenes, carbon nanotubes, graphene, graphene oxide, carbon nitride (C3N4), and carbon nanofibers platelets. All of these carbon materials have a graphite structure.

[0099] As amorphous carbon, examples include carbon black (CB), acetylene black (AB), Ketjen black, hard carbon, and soft carbon.

[0100] As fullerenes, C can be listed as an example. 60 C 72 C 84 wait.

[0101] As examples of carbon nanotubes, single-layer carbon nanotubes (SWCNTs), multilayer carbon nanotubes (MWCNTs), stacked cup carbon nanotubes (CSCNTs), and carbon nanofibers (VGCFs) can be listed.

[0102] They have a structure that extends along a single axis (one-dimensional structure).

[0103] Graphene, graphene oxide, carbon nitride (C3N4), and carbon nanofiber platelets have structures that extend along the surface direction (two-dimensional structures).

[0104] In carbon materials, the ends (edge ​​sites) of the graphite structure are more reactive than the regions outside the edges. Therefore, it is envisioned that most of the PC bonds are formed at the edge sites of the carbon material. Thus, from the viewpoint of facilitating the formation of PC bonds, the carbon material used is preferably one with many edge sites.

[0105] Examples of carbon materials with numerous edge sites include CSCNTs, graphite, mesophase carbon microspheres (MCMB), graphene, graphene oxide, carbon nitride (C3N4), and stacked carbon nanofibers. Among these, CSCNTs are preferred as carbon materials.

[0106] Furthermore, any of the known phosphorus allotropes can be used as the raw material. Black phosphorus is preferred as it is the most chemically stable and electrically conductive of the phosphorus allotropes.

[0107] "Mixed pulverization process accompanied by compression" refers to a process in which multiple powdered raw materials are mixed and pulverized by applying compressive force. It is believed that by subjecting carbon and phosphorus materials to a mixed pulverization process accompanied by compression, a strong impact force is applied to the carbon and phosphorus materials, thereby producing chemical changes that are not achievable in ordinary mixtures while the raw material powders are being mixed and pulverized. The result is believed to be a PC anode material with PC bonds formed that are not present in the raw materials, and a crystalline state not found in the raw materials.

[0108] The "mixing and pulverizing process accompanied by compression" should be continued until the peaks originating from the raw materials disappear in the XRD spectrum of the mixed material. Alternatively, it should be continued until PC bonds can be confirmed in the XPS spectrum of the mixed material.

[0109] Examples of processing devices (pulverizers) capable of performing mixed pulverization with compression include roller mills, jet mills, hammer mills, pin mills, disc mills, rod mills, ball mills, vibratory mills, stirred mills, and bead mills. In the manufacture of PC anode materials, especially considering the ability to simultaneously perform mixing and pulverization, stirred mills with a pulverizing container and a rotating body are preferred. Examples of stirred mills include pin mills, disc mills, rod mills, ball mills, vibratory mills, stirred mills, and bead mills.

[0110] Furthermore, as the aforementioned processing apparatus, a media-stirred pulverizer is preferred from the perspective of being able to apply a strong impact force to carbon materials and phosphorus while mixing and pulverizing the raw material powder. Examples of media-stirred pulverizers include ball mills, vibratory mills, stirred mills, and bead mills. Among these, a ball mill is particularly preferred from the viewpoint of easily controlling the morphological conditions.

[0111] It is believed that if ball milling is used for mixing, phosphorus will first be micronized and carbon materials will decompose, followed by the formation of PC bonds. During these ball milling processes, phosphorus is transformed into the aforementioned nuclei.

[0112] It is believed that, subsequently, a carbon film is formed around the nuclear particles containing phosphorus atoms and then composited to obtain a PC anode material.

[0113] During ball mill mixing, manufacturing conditions can be controlled by adjusting the rotational speed of the ball mill, the amount of media (balls) for the raw materials (ball powder ratio), and the mixing time. That is, by increasing the rotational speed of the ball mill, increasing the amount of media for the raw materials, and extending the mixing time, the mixing of phosphorus and carbon materials can be promoted, making it easier to obtain PC anode materials.

[0114] The spheres are pulverizing media used to crush phosphorus and carbon. The diameter of the sphere refers to its average diameter. The spheres flow at high speed within the pulverizing container of the pulverizer due to its own rotation, colliding with the powdered raw material containing carbon and phosphorus, thereby crushing it into particles with a smaller average particle size. During the pulverizing process, the pulverizing container and the spheres should preferably not experience excessive wear. Therefore, the shape of the spheres is preferably spherical or ellipsoidal.

[0115] The diameter of the sphere is preferably larger than the average particle size of the pulverized PC anode material. By using such a sphere, a large pulverizing energy can be applied to the metal material, thus enabling the efficient production of PC anode material particles in a short time.

[0116] The diameter of the spheres is preferably 0.1–10 mm, more preferably 1–10 mm. Within this diameter range, the formation of PC bonds is promoted, and re-aggregation is inhibited. The diameter of the spheres placed in the grinding container can be uniform or varied.

[0117] Materials that can be used for the spheres include glass, agate, alumina, zirconium oxide, stainless steel, chromium steel, tungsten carbide, silicon carbide, and silicon nitride. Among these, zirconium oxide is preferred because it has relatively high hardness, making it less prone to wear, and its high specific gravity allows for high pulverization energy. Using these spheres allows for the efficient pulverization of raw material powder for PC anode materials.

[0118] The weight ratio of the balls to the raw material powder of the PC anode material is set as the ball-to-powder ratio. By increasing the ball-to-powder ratio, a strong impact force can be applied to the raw material powder of the PC anode material at a high frequency, thus further promoting the formation of PC bonds. If the ball-to-powder ratio is too high, the amount of PC anode material produced per unit operation decreases. Therefore, the preferred ball-to-powder ratio is 0.5 to 500, more preferably 1 to 200, and even more preferably 10 to 200.

[0119] In addition, after the ball milling is completed, the balls are separated from the PC negative electrode material using filters or the like.

[0120] The PC anode material obtained by mixing in a ball mill can be analyzed by measuring the XRD pattern of the mixed material, such as... Figure 1 The disappearance of the peak originating from the raw material, as shown in the diagram, confirms this. The duration of ball mill mixing should preferably be determined through preliminary experiments comparing the relationship between mixing time and the point at which the peak originating from the raw material disappears. In other words, ball mill mixing should ideally continue until the peak originating from the raw material disappears in the XRD pattern of the mixed material.

[0121] Alternatively, the XPS spectrum of the mixed materials can be measured, such as... Figure 1As shown in the diagram, PC bonds were formed to confirm this. In this case, it is advisable to determine the duration of ball mill mixing by conducting preliminary experiments to determine the correspondence between mixing time and the time until PC bonds are formed. In other words, it is advisable to continue ball mill mixing until PC bonds can be confirmed in the XPS spectrum of the mixed material.

[0122] In ball mill mixing, carbon and phosphorus are incorporated through collisions between the media and between the media and the ball mill container, thereby applying strong localized impacts (pressures) to the carbon and phosphorus. Although the details are unclear, it is believed that by applying such impacts, chemical changes that cannot be obtained in ordinary mixtures can occur, resulting in PC anode materials with PC bonds not present in the raw materials and with a crystalline state not seen in the raw materials.

[0123] Manufacturing method of negative electrode for lithium secondary batteries The negative electrode for lithium secondary batteries is manufactured by coating a negative electrode composition containing negative electrode active material onto a current collector, drying it, and then performing any pressing process.

[0124] To achieve the area ratio of the black portion within the aforementioned range, it is preferable to coat the negative electrode composition onto the current collector and dry it without performing a pressing process. Without a pressing process, coarse particles will not be compacted, making it difficult for the black portion to increase.

[0125] When performing the pressing process, by setting the pressing pressure to below 0.3 MPa, coarse particles become less likely to be compacted, and the black portion becomes less likely to increase.

[0126] Furthermore, by using a negative electrode active material with fewer coarse particles of 10 μm or larger, it becomes easier to control the particle size of the black portion within the aforementioned range.

[0127] The negative electrode composition preferably has an adhesive for adhering the negative electrode active material to the current collector. The adhesive may have a known composition.

[0128] As an adhesive, one or a mixture of two or more of polyvinylidene fluoride (hereinafter, sometimes referred to as PVdF), polyimide, polyamide-imide, styrene-butadiene rubber, carboxymethyl cellulose, and acrylic resin may be suitably used.

[0129] The negative electrode composition preferably contains a conductive additive. As a conductive additive, carbon materials such as carbon nanotubes, carbon nanofibers, vapor-grown carbon fibers, mesophase pitch-based carbon fibers, isotropic pitch-based carbon fibers, natural graphite, mesophase carbon microspheres, and other artificial graphite, carbon black (e.g., acetylene black, Ketjen black, and furnace black), graphite particles, graphene, and fullerene can be used. In addition, metal powders such as copper, nickel, aluminum, silver, and gold, and conductive ceramic materials can be used, for example.

[0130] In addition to the components described above, the negative electrode composition may also contain known materials used as negative electrode active materials. Examples of such materials include (i) alloy-based negative electrode active material materials that form with the lithium alloy phase, (ii) transition metal oxides that undergo a decomposition and regeneration reaction (conversion reaction) with lithium ions, (iii) oxides or composite oxides that have activity as negative electrode active materials, and (iv) layered carbon.

[0131] As (i) alloy-based anode active materials, examples include metals such as silicon, germanium, tin, aluminum, zinc, and magnesium, or their alloys.

[0132] Examples of (ii) transition metal oxides include manganese oxides, iron oxides, cobalt oxides, nickel oxides, copper oxides, and magnesium oxides. These oxides may also be complex metal oxides that further contain other metals, such as lithium.

[0133] Examples of (iii) oxides or composite oxides include titanium oxide, lithium titanate, and silicon oxide.

[0134] As (iv) layered carbon, examples include graphite and hard carbon.

[0135] <Lithium secondary batteries> The lithium secondary battery of this embodiment includes the above-described negative electrode for lithium secondary batteries (hereinafter, negative electrode).

[0136] An example of a preferred lithium secondary battery using the negative electrode of this embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte disposed between the positive and negative electrodes.

[0137] An example of a lithium secondary battery includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte disposed between the positive and negative electrodes.

[0138] Figure 4 This is a schematic diagram illustrating an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0139] First, such as Figure 4 As shown in the enlarged partial view, an electrode assembly 4 is formed by stacking and winding a pair of strip-shaped diaphragms 1, a strip-shaped positive electrode 2 with a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 with a negative electrode lead 31 at one end in the order of diaphragm 1, positive electrode 2, diaphragm 1, and negative electrode 3.

[0140] As an example, the positive electrode 2 has a positive active material layer 2a containing a positive active material (hereinafter, CAM) and a positive current collector 2b having the positive active material layer 2a formed on one side. Such a positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing CAM, a conductive material and a binder, and then loading the positive electrode mixture onto one side of the positive current collector 2b to form the positive active material layer 2a.

[0141] As an example, negative electrode 3 can be an electrode (not shown) formed by a negative electrode mixture containing negative electrode active material supported on a negative electrode current collector, or an electrode formed solely by the negative electrode active material, which can be manufactured in the same way as positive electrode 2.

[0142] Next, after accommodating the electrode assembly 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, and the electrolyte 6 is impregnated into the electrode assembly 4, with the electrolyte placed between the positive electrode 2 and the negative electrode 3. Furthermore, by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8, a lithium secondary battery 10 can be manufactured.

[0143] The electrolyte preferably contains a solid electrolyte interface forming agent. Examples of solid electrolyte interface forming agents include carbonate solvents, phosphate solvents, and sulfolane solvents.

[0144] As for the shape of the electrode assembly 4, for example, the cross-sectional shape when the electrode assembly 4 is cut perpendicularly to the winding axis can be a circle, an ellipse, a rectangle, or a columnar shape such as a rectangle obtained by rounding the corners.

[0145] Furthermore, the shape of the lithium secondary battery having such an electrode assembly 4 can adopt the shape specified in the battery standards defined by the International Electrotechnical Commission (IEC), namely IEC 60086 or JIS C 8500. For example, cylindrical or square shapes can be listed.

[0146] Furthermore, lithium secondary batteries are not limited to the above-mentioned wound type structure, but can also be a stacked type structure obtained by repeatedly overlapping the positive electrode, separator, negative electrode, and separator. Examples of stacked lithium secondary batteries include so-called coin-type batteries, button-type batteries, or paper-type (or sheet-type) batteries.

[0147] For the positive electrode, separator, negative electrode and electrolyte constituting a lithium secondary battery, the structure, materials and manufacturing method described in

[0113] to

[0140] of WO2022 / 113904A1 can be used, for example.

[0148] All-solid-state lithium secondary batteries Next, the structure of an all-solid-state lithium secondary battery will be explained, as well as an all-solid-state lithium secondary battery with the aforementioned negative electrode.

[0149] Figure 5 This is a schematic diagram illustrating an example of an all-solid-state lithium secondary battery. Figure 5 The all-solid-state lithium secondary battery 1000 shown has a laminate 100 comprising a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer packaging 200 for housing the laminate 100. Furthermore, the all-solid-state lithium secondary battery 1000 can also be a bipolar structure with a current collector and a negative electrode active material disposed on both sides of the current collector. As a specific example of a bipolar structure, the structure described in JP-A-2004-95400 can be cited.

[0150] The positive electrode 110 has a positive electrode active material layer 111 and a positive electrode current collector 112. The positive electrode active material layer 111 contains the aforementioned CAM and solid electrolyte. In addition, the positive electrode active material layer 111 may also contain a conductive material and a binder.

[0151] The negative electrode 120 has a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains a negative electrode active material. In addition, the negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material.

[0152] The laminate 100 may also have an external terminal 113 connected to the positive current collector 112 and an external terminal 123 connected to the negative current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may also have a separator between the positive electrode 110 and the negative electrode 120.

[0153] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the outer packaging 200, and a seal (not shown) that seals the opening 200a of the outer packaging 200.

[0154] The outer packaging 200 can be a container formed from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. Alternatively, the outer packaging 200 can also be a container formed by processing a laminated film with at least one side treated to be corrosion-resistant into a bag shape.

[0155] The shapes of the all-solid-state lithium secondary battery 1000 can include, for example, coin type, button type, paper type (or sheet type), cylindrical type, square type, or laminated type (bag type).

[0156] As an example, the all-solid-state lithium secondary battery 1000 is shown in a configuration having one stack 100, but this embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may also be configured such that the stack 100 is used as a unit cell and multiple unit cells (stack 100) are sealed inside the outer packaging 200.

[0157] For all-solid-state lithium secondary batteries, for example, the structure, materials and manufacturing methods described in

[0141] to

[0181] of WO2022 / 113904A1 can be used.

[0158] Example The present invention will be described below through embodiments, but the present invention is not limited to these embodiments.

[0159] Example 1 Manufacturing of PC anode materials Black phosphorus manufactured by RASA Industries and CSCNT (stacked cup carbon nanotubes: manufactured by GSI Creos) were weighed at a mass ratio of P:C=6:4 (total weight 1.25g), and mixed using a ball mill under the following conditions to obtain PC anode material 1.

[0160] (Ball mill mixing conditions) Device: Retsch PM-100 Container: 125mL container made of ZrO2 Medium: ZrO2 in 8mm Ball, 150g Atmosphere: Enclosed in argon gas Sample quantity: 1.25g based on the mixture of raw materials. Ball / Powder Ratio: 120 (by weight) Mixing time: 12 hours TEM images of the obtained PC anode material 1 were taken, confirming that it is a core-shell structure in which a carbon film covers the surface of nuclear particles containing phosphorus atoms.

[0161] The obtained PC anode material 1 was charged at a charging rate of 0.2C using lithium metal as the counter electrode. As a result, the average charging potential of PC anode material 1 relative to its capacity (mAh / g) at charging was 0.1V or higher. This confirms that the obtained PC anode material 1 is a material that intercalates lithium ions when using lithium (alkali metal) as the counter electrode and applying a voltage of 0.1V or higher.

[0162] In the obtained PC anode material 1, the content of phosphorus atoms is 60% by mass and the content of carbon atoms is 40% by mass. Since the container used in the above manufacturing process has extremely high airtightness, it is determined that the content of each atom in PC anode material 1 is equal to the ratio of raw materials.

[0163] The obtained PC anode material 1 was measured according to the above (XPS spectroscopy measurement conditions), and the results confirmed the peak representing the bond between phosphorus atoms and carbon atoms.

[0164] For the obtained PC negative electrode material 1, the XRD spectrum was measured according to the above-mentioned (XRD spectrum measurement conditions). In the XRD spectrum, the intensity I at 2θ=20° was... 20 The intensity I is 3063, 2θ = 26.3°. 26.3 The intensity I is 2603 and 2θ = 40°. 40 The value is 1917. Furthermore, |P| / |B| is 0.87. The PC anode material 1, showing these values, satisfies the following equations (1) to (3).

[0165] |P| / |B|<2…(1) P=I 26.3 -I 40 …(2) B = (I 20 -I 40 )×(26.3-40) / (20-40)…(3) [Preparation of the negative electrode composition] PC anode material 1, vapor-phase carbon fiber (manufactured by Resonac, VGCF product name) as a conductive additive, monolayer carbon nanotubes, and binder (vinylidene fluoride PVdF Solef5130 (manufactured by Solvay)) are mixed to obtain anode composition 1 containing 6% by mass of binder.

[0166] [Manufacturing of Negative Electrode 1] The above-mentioned negative electrode composition 1 was mixed with a solvent (NMP (N-methyl-2-pyrrolidone)) using an agate mortar to prepare a negative electrode slurry. At this time, the slurry concentration was adjusted to set the content of PC negative electrode material 1 in the negative electrode slurry to 30-60% by mass.

[0167] The negative electrode slurry was coated onto the copper foil current collector using a doctor blade, and then vacuum dried at 60°C for 1 hour to remove the solvent, resulting in a laminate. The resulting laminate was further vacuum dried at 150°C for 8 hours to obtain negative electrode 1.

[0168] In negative electrode 1, the coating amount (i.e., weight per unit area) of negative electrode composition 1 is 1.9 mg / cm³. 2 .

[0169] It should be noted that the preparation of the negative electrode slurry and the negative electrode were carried out in a glove box under an argon atmosphere.

[0170] The surface of negative electrode 1 was imaged using a scanning electron microscope (JCM-7000) manufactured by Nippon Electron Ltd. at an accelerating voltage of 15kV, a working distance of 13mm, and a magnification of 40x, obtaining a negative electrode surface image with a resolution of 2560 pixels × 1920 pixels. The obtained negative electrode surface image is shown below. Figure 6(a) in.

[0171] The obtained negative electrode surface image is entered into image processing software, and adaptive binarization processing is performed through the following steps to obtain a binarized image.

[0172] As an image analysis software, it uses Python libraries such as OpenCV and scikit-image (module: threshold_sauvola).

[0173] First, for all pixels of the negative electrode surface image, the following processing (A) and (B) are performed. (A): The threshold is calculated using the pixels surrounding the pixel of interest, i.e., the pixels of the local region (specifically, pixels with a vertical × horizontal ratio of 251 × 251). The threshold is calculated using the pixel values ​​of the local region pixels using the following formula.

[0174] T=m(x,y) (1+k) ((s(x,y) / R)-1)) In the above formula, m(x, y) is the average value of the area of ​​a square with window size W as one side.

[0175] s(x, y) is the standard deviation of the region of a square with window size W as one side.

[0176] k is a parameter used to weight the standard deviation.

[0177] R is the maximum standard deviation of the grayscale image.

[0178] More specifically, the binarization process is performed with W=251, k=0.1, and R=256.

[0179] In addition, the threshold is calculated for each pixel of interest.

[0180] (B): If the pixel value of the pixel of interest is greater than the threshold obtained by (A) above, it is set to white; if it is less than the threshold, it is set to black. This is then binarized.

[0181] The resulting binarized image is shown below. Figure 6 (b) in.

[0182] In the binarized image obtained by the above method, the area ratio of the black portion of the negative electrode surface image relative to the whole is calculated. In negative electrode 1, the area ratio of the black portion of the negative electrode surface image relative to the whole is 2.0%. Furthermore, as... Figure 6 As shown in (b), the resulting binarized image exhibits an island-like structure with black areas scattered like islands. Using Python as image analysis software, the average area of ​​the entire island structure was calculated to be 0.0038 mm.2 .

[0183] (The manufacture of a lithium-ion secondary battery for evaluation purposes) The negative electrode, counter electrode, electrolyte, and separator manufactured above are combined to produce a lithium-ion secondary battery (coin-type battery R2032). The battery assembly is carried out in an argon-atmospheric glove box.

[0184] Lithium foil is used as the counter electrode.

[0185] As the electrolyte, a mixture obtained by adding 10% by mass of fluoroethylene carbonate (FEC) to a LiPF6 solution (manufactured by KISHIDA CHEMICAL) was used.

[0186] As a LiPF6 solution, the solution is obtained by dissolving LiPF6 in a mixed solvent in a volume ratio of 30:35:35 for ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) to a concentration of 1 mol / L.

[0187] As a diaphragm, a porous polyethylene membrane diaphragm (12 μm thick) is used.

[0188] (Evaluation of capacity maintenance rate) Using the aforementioned evaluation battery, and maintaining a temperature of 25°C, both charging and discharging were performed with a current setting of 1CA, using constant current and constant voltage charging and constant current discharging. The maximum charging voltage was set to 2.5V, and the minimum discharging voltage was set to 0.01V.

[0189] Next, at a test temperature of 25°C, constant current and constant voltage charging and discharging were repeatedly performed under the following conditions. The number of charge-discharge cycles was 100.

[0190] Charging: Current setting 1CA, maximum voltage 2.5V, constant voltage and constant current charging. Discharge: Battery setting 1CA, minimum voltage 0.01V, constant current discharge. The capacity retention rate is calculated from the discharge capacity of the first cycle and the discharge capacity of the 100th cycle using the following formula. A higher capacity retention rate means that the battery will not deteriorate even after repeated charging and discharging, and will maintain its capacity better, thus indicating that it is a superior battery in terms of performance.

[0191] Capacity retention (%) = Discharge capacity at 100th cycle (mAh / g) / Discharge capacity at 1st cycle (mAh / g) × 100 The capacity retention rate of the lithium secondary battery with negative electrode 1 is 93%.

[0192] Example 2 The negative electrode slurry was coated onto the copper foil current collector using a doctor blade. Afterward, it was vacuum dried at 60°C for 1 hour to remove the solvent. The laminate was then pressed at 0.1 MPa for 10 seconds and further vacuum dried at 150°C for 8 hours. Otherwise, negative electrode 2 was obtained using the same method as in Example 1. An image of the negative electrode surface of negative electrode 2 is shown below. Figure 7 In (a), the binarized image is shown. Figure 7 In (b), in negative electrode 2, the area ratio of the black portion of the negative electrode surface image to the total area is 5.6%. Furthermore, as... Figure 7 As shown in (b), the resulting binarized image exhibits a black area with an island-like structure. The average area of ​​the entire island structure is 0.0225 mm. 2 .

[0193] The capacity retention rate of the lithium secondary battery with negative electrode 2 is 91%.

[0194] Comparative Example 1 Except for pressing the laminate at 0.3 MPa for 10 seconds, the negative electrode 11 was obtained using the same method as in Example 2. An image of the negative electrode surface of the negative electrode 11 is shown below. Figure 8 In (a), the binarized image is shown. Figure 8 In (b), in negative electrode 11, the area ratio of the black portion of the negative electrode surface image to the overall area is 15.9%. Furthermore, as... Figure 8 As shown in (b), the resulting binarized image exhibits an island-like structure with black areas scattered throughout. The average area of ​​the entire island structure is 0.0455 mm. 2 .

[0195] The capacity retention rate of the lithium secondary battery with negative electrode 11 is 59%.

[0196] Comparative Example 2 Except for pressing the laminate at 0.5 MPa for 10 seconds, the negative electrode 12 was obtained using the same method as in Example 2. An image of the negative electrode surface of the negative electrode 12 is shown below. Figure 9 In (a), the binarized image is shown. Figure 9 In (b), in negative electrode 12, the area ratio of the black portion of the negative electrode surface image to the total area is 17.8%. Furthermore, as... Figure 9 As shown in (b), the resulting binarized image exhibits an island-like structure with black areas scattered throughout. The average area of ​​the entire island structure is 0.0487 mm. 2 .

[0197] The capacity retention rate of the lithium secondary battery with negative electrode 12 is 88%.

[0198] As shown in the results above, the capacity retention rates of Examples 1 and 2, with a black area ratio of 2.0% or 5.6%, both exceeded 90%. This is believed to be because: the area formed by the compaction of coarse particles that are prone to cracking is smaller, so the resistance does not easily increase even under repeated charging and discharging, thus maintaining a high capacity retention rate.

[0199] In contrast, Comparative Examples 1 and 2, where the area ratio of the black region exceeds 12%, both exhibited a capacity retention rate of less than 90%. This is believed to be due to the fact that during repeated charging and discharging, cracks form around the areas where coarse particles are compressed, increasing resistance and thus reducing capacity retention.

[0200] Explanation of symbols 50…particles, 51…nuclear particles, 52…carbon film, 100…layers, 120…negative electrode, 121…negative electrode active material layer, 130…solid electrolyte layer

Claims

1. A negative electrode for a lithium secondary battery, wherein a negative electrode active material layer is formed on a current collector. The negative electrode active material layer comprises a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms. The area ratio of the black portion to the total area in the binarized image of the negative electrode active material layer obtained by the following method is greater than 0.05% and less than 12%. Methods for obtaining binarized images: The surface of the negative electrode active material layer was photographed using a scanning electron microscope at a magnification of 40x to obtain a negative electrode surface image; the negative electrode surface image was then subjected to adaptive binarization processing to obtain a binarized image.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein, The binarized image has a black area with an island-like structure, and the average area of ​​the islands in the island structure is 0.001 mm. 2 Above and 0.03mm 2 the following.

3. The negative electrode according to claim 1 or 2, wherein, The phosphorus-carbon composite anode material exhibits peaks in XPS spectra representing the bonds between phosphorus and carbon atoms.

4. The negative electrode according to claim 1 or 2, wherein, In the XRD pattern of the phosphorus-carbon composite anode material measured using CuKα rays, the intensity I at 2θ=20° is... 20 Intensity I at 2θ = 26.3° 26.3 and the intensity I at 2θ=40° 40 The following equations (1) to (3) are satisfied. |P| / |B|<2…(1) P=I 26.3 -I 40 …(2) B=(I 20 -I 40 )×(26.3-40) / (20-40)…(3)。 5. The negative electrode according to claim 1 or 2, wherein, The phosphorus-carbon composite anode material has nuclear particles containing phosphorus atoms and a carbon film covering the surface of the nuclear particles.

6. A lithium secondary battery comprising the negative electrode as described in claim 1 or 2.

7. The lithium secondary battery according to claim 6, wherein, Electrolytes contain solid electrolyte interface forming agents.

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