A negative electrode material, a negative electrode sheet, and a battery

Abstract

The application relates to the technical field of lithium ion battery negative electrode materials, in particular to a negative electrode material, a negative electrode sheet and a battery. The negative electrode material comprises a graphite base and a coating layer arranged on at least part of the surface of the graphite base; the negative electrode material comprises a first pore structure and a second pore structure, the pore size D1 of the first pore structure satisfies 2nm<=D1<=5nm, the pore size D2 of the second pore structure satisfies 5nm<D2<=100nm, in the N2 adsorption slit-pore DFT fitting curve of the negative electrode material, the cumulative pore surface area corresponding to the pore with a pore size of >=2nm is S1, the cumulative pore surface area corresponding to the first pore structure is S2, and the cumulative pore surface area corresponding to the second pore structure is S3; wherein 0<=S2 / S1*100%<=5%, and S3 / S1*100%>=75%. The negative electrode material can improve the interface stability and consider the ion transmission performance at the same time, and is beneficial to solving the problem that the existing modified graphite negative electrode is difficult to balance the initial efficiency, the rate performance and the cycle performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery anode material technology, specifically to an anode material, an anode sheet, and a battery. Background Technology

[0002] Graphite anode materials, with their stable layered structure, high conductivity, and excellent reversible active ion insertion / extraction, have become the most critical commercial anode material in current battery systems. However, the surface and near-surface layers of graphite typically contain numerous small micropores or tiny defect pores. These micropores and tiny defect pores easily adsorb and retain electrolyte, and during the first charge / discharge cycle and fast charging, they often become sensitive areas for electrolyte reduction and decomposition, gas generation, and repeated thickening of the SEI film. This results in insufficient interface stability and low initial efficiency, severely limiting the battery's performance under complex operating conditions.

[0003] Existing technologies typically employ surface coating and other modification methods to address this issue. However, existing modification schemes have limited effectiveness in improving interface stability, and enhancing interface stability often leads to increased lithium-ion transport resistance, making it difficult to balance initial efficiency, rate performance, and cycle performance. Summary of the Invention

[0004] This application provides a negative electrode material that can improve interface stability while taking into account ion transport performance, which is beneficial for balancing first-efficiency, rate performance and cycle performance.

[0005] This application provides a negative electrode sheet that is beneficial for improving the initial efficiency, rate performance, and cycle performance of a battery.

[0006] This application provides a battery with superior initial efficiency, rate performance, and cycle performance.

[0007] The negative electrode material provided in this application includes a graphite substrate and a coating layer disposed on at least a portion of the surface of the graphite substrate;

[0008] The negative electrode material includes a first pore structure and a second pore structure. The pore size D1 of the first pore structure satisfies: 2nm ≤ D1 ≤ 5nm, and the pore size D2 of the second pore structure satisfies: 5nm < D2 ≤ 100nm. In the N2 adsorption slit-pore DFT fitting curve of the negative electrode material, the cumulative pore surface area corresponding to pores with a pore size ≥ 2nm is S1, the cumulative pore surface area corresponding to the first pore structure is S2, and the cumulative pore surface area corresponding to the second pore structure is S3.

[0009] Among them, 0≤S2 / S1×100%≤5%, S3 / S1×100%≥75%.

[0010] For the negative electrode material described above, S3 / S1×100%≥90%.

[0011] The negative electrode material described above satisfies at least one of the following conditions:

[0012] (1) In the differential specific surface area curve of the negative electrode material, the dA / dlog(W) corresponding to the first pore structure is ≤0.005m 2 / g;

[0013] (2) S1, S2, and S3 are obtained by normalizing the cumulative pore surface area of ​​the negative electrode material based on the cumulative specific surface area curve, with the cumulative pore surface area corresponding to the pore size less than or equal to 2nm as 0.

[0014] (3) 0.095 m 2 / g≤S1≤0.115 m 2 / g;

[0015] (4) S2≤0.005 m 2 / g;

[0016] (5) S3≥0.09m 2 / g.

[0017] The negative electrode material described above, wherein the coating layer comprises a metallic element, and the metallic element comprises at least one of titanium, aluminum, magnesium, zirconium, and lithium.

[0018] The negative electrode material described above satisfies at least one of the following conditions:

[0019] (1) Based on the total mass of the negative electrode material, the content of the metal element is 80 ppm - 360 ppm;

[0020] (2) The metal element exists in the form of a metal compound, which includes at least one of titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium nitride, aluminum fluoride, aluminum phosphate, lithium phosphate, lithium titanate, and lithium aluminate.

[0021] The negative electrode material described above has a weight loss rate of ≤0.5% under an inert atmosphere at 100℃-500℃.

[0022] The negative electrode material described above satisfies at least one of the following conditions:

[0023] (1) The particle size D50 of the graphite substrate is 8μm-15μm;

[0024] (2) The specific surface area S in the micropores and gaps of the graphite substrate. prem Satisfy: 0.25 m 2 / g≤S prem ≤0.40 m 2 / g;

[0025] (3) In the graphite substrate, the external specific surface area S of the particles ext Satisfy: 0.52m 2 / g≤S ext ≤0.62 m 2 / g

[0026] (4) The specific surface area of ​​the negative electrode material is S' ext The specific surface area of ​​the negative electrode material after removing the coating layer is S. ext S grow ≤0.30 m 2 / g, where S grow =S' ext -S ext .

[0027] The negative electrode material described above satisfies at least one of the following conditions:

[0028] (1) The specific surface area of ​​the negative electrode material is 0.50 m². 2 / g -0.85m 2 / g;

[0029] (2) The tap density of the negative electrode material is 1 g / cm³. 3 -1.3g / cm 3 ;

[0030] (3) The 5T compaction density of the negative electrode material is 1.73 g / cm³. 3 -1.82 g / cm 3 .

[0031] This application also provides a negative electrode sheet, including a current collector and a negative electrode active layer located on at least a portion of the surface of the current collector, wherein the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes the aforementioned negative electrode material.

[0032] This application also provides a battery, including the above-described negative electrode material or the above-described negative electrode sheet.

[0033] The modified graphite anode material provided in this application can balance interface stability and active ion migration performance by effectively controlling the pore distribution and interface reaction environment, thereby reducing the risk of interface polarization and side reactions, and improving the first-efficiency, fast-charging performance and cycle performance. Attached Figure Description

[0034] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0035] Figure 1 A schematic diagram illustrating the principle of a battery during charging, as provided in this application;

[0036] Figure 2 A schematic diagram illustrating the principle of a battery during discharge provided in this application;

[0037] Figure 3 The images show the TEM morphology and elemental distribution of the negative electrode materials in Examples 1 and 5. In Example 1, A is the TEM morphology of the negative electrode material; B is the Ti elemental distribution of the negative electrode material in Example 1; C is the TEM morphology of the negative electrode material in Example 5; and D is the Ti elemental distribution of the negative electrode material in Example 5.

[0038] Figure 4 The graphs show the differential specific surface area distribution curves and cumulative specific surface area distribution curves for Example 1 and Comparative Example 4. Specifically, A is the cumulative specific surface area distribution curve in the 2nm-100nm range for Example 1 and Comparative Example 4, B is the differential-to-cumulative specific surface area distribution curve in the 2nm-10nm range for Example 1 and Comparative Example 4, C is the differential specific surface area distribution curve in the 2nm-100nm range for Example 1 and Comparative Example 4, and D is the differential specific surface area distribution curve in the 2nm-10nm range for Example 1 and Comparative Example 4.

[0039] Figure 5 A schematic diagram illustrating the principle of calculating specific surface area S;

[0040] Figure 6 The deBoer t-plot linear fit diagram is shown for the graphite substrate obtained after the negative electrode material in Example 1 has undergone acid etching to remove the coating layer in step a. Detailed Implementation

[0041] To enable those skilled in the art to better understand the solutions of this invention, the following provides a further detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the scope of protection of this invention.

[0042] Graphite anode materials are mainly used in power batteries for new energy vehicles, energy storage systems, and consumer electronics batteries. In these applications, graphite anode materials not only need to handle high reversible lithium intercalation capacity, but also need to maintain stable interfacial reactions and low polarization levels under fast charging and long-cycle conditions. With the increasing demand for fast charging in vehicles and wide-temperature operation in energy storage, the surface state, pore structure distribution, and compatibility with electrolytes of graphite anodes have become important factors affecting the overall performance of batteries.

[0043] To address the problem that existing graphite anodes cannot simultaneously achieve optimal first-efficiency, rate performance, and cycle performance, this application provides an anode material comprising a graphite substrate and a coating layer disposed on at least a portion of the surface of the graphite substrate. The anode material includes a first pore structure and a second pore structure. The pore size D1 of the first pore structure satisfies: 2nm ≤ D1 ≤ 5nm, and the pore size D2 of the second pore structure satisfies: 5nm < D2 ≤ 100nm. In the N2 adsorption slit-pore DFT fitting curve of the anode material, the cumulative pore surface area corresponding to pores with a pore size ≥ 2nm is S1, the cumulative pore surface area corresponding to the first pore structure is S2, and the cumulative pore surface area corresponding to the second pore structure is S3.

[0044] Among them, 0≤S2 / S1×100%≤5%, S3 / S1×100%≥75%.

[0045] In this application, S1, S2, and S3 are obtained through N2 adsorption slit-pore DFT fitting. Specifically, the negative electrode material is degassed under vacuum at an appropriate temperature to remove adsorbed water and organic residues, followed by nitrogen adsorption-desorption testing. The cumulative pore volume distribution (and differential specific surface area distribution) for different pore size ranges is calculated based on the slit-pore DFT pore size distribution model. This method can simulate the adsorption behavior of gases within the pores at the molecular level, resulting in more accurate analysis.

[0046] The negative electrode material provided in this application improves the interface stability problem through the coating layer. At the same time, it has fewer micropores or small defect pores (i.e., the first pore structure) that are easy to adsorb and retain electrolyte, while the second pore structure that is conducive to electrolyte wetting and lithium ion diffusion is maintained at a high level. Thus, it can take into account both interface stability and ion diffusion, and thus take into account the first efficiency, fast charging performance and cycle performance.

[0047] Specifically, in the anode material, the first pore structure, with its narrow internal space and significant contribution to specific surface area, is more prone to exacerbating side reactions due to local electric field and concentration effects. Therefore, maintaining a low specific surface area in this part of the pore structure can significantly reduce the ineffective contact area between graphite and electrolyte, thereby improving the initial coulombic efficiency and reducing the tendency of interfacial film remodeling during long-term cycling. The second pore structure facilitates the passage of active ions and electrolyte wetting. Controlling this to a higher level can reduce ion diffusion resistance, especially under high-current charging conditions, which helps to reduce interfacial polarization and improve charge acceptance. Therefore, the modified graphite anode material provided in this application, with fewer first pore structures and more second pore structures, can balance interfacial stability and ion transport performance, and thus balance initial efficiency, fast charging performance, and cycle performance.

[0048] In this application, S2 / S1×100% can be a range of 0, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these. S3 / S1×100% can be a range of 75%, 80%, 85%, 90%, 95%, 100%, or any two of these.

[0049] In some embodiments, S3 / S1×100%≥90%.

[0050] Studies have shown that when S3 / S1×100%≥90%, it indicates that there are more second-hole structures, which is more conducive to balancing first-time efficiency, fast charging performance and cycle performance.

[0051] In some embodiments, in the differential specific surface area curve of the negative electrode material, the dA / dlog(W) corresponding to the first pore structure is ≤0.005 m 2 / g. Specifically, the dA / dlog(W) corresponding to the first pore structure can be 0 or 0.001m. 2 / g, 0.002m 2 / g, 0.003m 2 / g, 0.004m 2 / g, 0.005m 2 / g or a range consisting of any two of them.

[0052] The differential surface area curve is a graph that clearly shows the contribution of pores of different sizes within a material to the total specific surface area. The horizontal axis represents the pore size, and the vertical axis represents the differential surface area (dA / dlog(W)). It is obtained by measuring the amount of gas adsorbed by the material at pressures from 0.01 times P0 to 1 times P0 (where P0 is the saturated vapor pressure of nitrogen at 77.3 K, specifically 760 mmHg) using a gas adsorption instrument (such as a nitrogen adsorption instrument). The isotherm data is then inverted and plotted using a slit-pore density functional theory (DFT) model. dA represents a small increment in the specific surface area, i.e., the specific surface area contributed by a pore of a certain size; dlog(W) represents a small change in the logarithmic scale of the pore size (W); dA / dlog(W) represents the contribution of a pore of a certain size to the total specific surface area.

[0053] In this application, the dA / dlog(W) corresponding to the first hole structure is ≤0.005 m 2 The / g indicates that the pore specific surface area of ​​the first pore structure in the negative electrode material is small, which can effectively reduce the ineffective contact area between graphite and electrolyte, thereby improving the initial coulombic efficiency and reducing the tendency of interfacial film reconstruction during long-term cycling.

[0054] In this application, S1, S2, and S3 are obtained by normalizing the cumulative pore surface area of ​​the negative electrode material based on the cumulative specific surface area curve, with the cumulative pore surface area corresponding to the pore size range of less than or equal to 2 nm as 0.

[0055] When using N2 adsorption slit-pore DFT to fit and obtain the cumulative pore surface area, pores with a diameter of less than 2 nm cannot be accurately measured. Normalizing the cumulative pore surface area of ​​pores with a diameter of less than or equal to 2 nm as 0 can increase the reliability of the detection results.

[0056] Normalization is performed by setting the cumulative pore surface area corresponding to pores with a diameter less than or equal to 2nm to 0. That is, the cumulative pore surface area corresponding to pores with a diameter less than or equal to 2nm is defined as 0. The increment corresponding to pores with other diameters is calculated, which is the cumulative pore surface area corresponding to pores with diameters in that range.

[0057] In some embodiments, 0.095 m 2 / g≤S1≤0.115 m 2 / g. Specifically, S1 is 0.095 m 2 / g, 0.1m 2 / g, 0.105 m 2 / g, 0.11 m 2 / g, 0.115 m 2 / g or a range consisting of any two of them.

[0058] In some embodiments, S2 ≤ 0.005 m 2 / g. Specifically, S2 is 0.005 m 2 / g, 0.004 m 2 / g, 0.003m 2 / g, 0.002 m 2 / g, 0.001 m 2 / g, 0, or a range consisting of any two of them.

[0059] In some embodiments, S3 ≥ 0.09m 2 / g. Specifically, S3 is 0.09 m 2 / g, 0.01m 2 / g, 0.02m 2 / g, 0.03 m 2 / g or a range consisting of any two of them.

[0060] That is, in the above embodiments, the cumulative pore surface area corresponding to pores with a diameter ≥ 2 nm is 0.095 m². 2 / g-0.115 m 2 / g, the cumulative pore surface area corresponding to the first pore structure is less than or equal to 0.005 m². 2 / g, the cumulative pore surface area corresponding to the second pore structure is greater than or equal to 0.09m². 2 / g, with fewer primary pore structures and more secondary pore structures, can better balance interfacial stability and ion transport performance.

[0061] In some embodiments, the cladding layer includes a metallic element, which includes at least one selected from titanium, aluminum, magnesium, zirconium, and lithium.

[0062] The aforementioned metal elements can preferentially undergo limited interfacial reactions with the active components in the electrolyte, thereby stably forming a more uniform interfacial film and inhibiting subsequent repeated reconstruction.

[0063] In some embodiments, the content of the metal element is 80 ppm to 360 ppm based on the total mass of the negative electrode material. Specifically, the content of the metal element can be a range of 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 330 ppm, 360 ppm, or any combination thereof.

[0064] A metal content of ≥80 ppm ensures complete coating, effectively filling the pores in the graphite substrate. A metal content of ≤360 ppm prevents excessive coating, avoiding the formation of too many islands on the graphite substrate surface, which would create new pores. It also prevents an excessively thick coating from reducing the material's conductivity. In summary, by controlling the metal content within the extremely low range of 80 ppm-360 ppm, good filling of 2nm-5nm micropores or small defect pores can be ensured, while maintaining a significant number of 5nm-100nm pores, satisfying 0≤S2 / S1×100%≤5% and S3 / S1×100%≥75%. Simultaneously, it preserves the intrinsic conductive network of graphite, improving electron transport performance and further enhancing rate performance.

[0065] In some embodiments, the metal element exists in the form of a metal compound, which includes at least one of titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium nitride, aluminum fluoride, aluminum phosphate, lithium phosphate, lithium titanate, and lithium aluminate.

[0066] The coating material preferably uses the aforementioned highly stable or ion-compatible metal compounds, which can construct a thin and dense interfacial barrier on the graphite particle surface, reducing the probability of electrolyte decomposition at defect sites and stabilizing the formation process of the solid electrolyte interfacial film. Specifically, titanium oxide, aluminum oxide, magnesium oxide, and zirconium oxide have high chemical stability and can reduce the direct erosion of graphite by the electrolyte without significantly increasing the coating burden; titanium nitride can also provide a certain interfacial transport capacity; aluminum fluoride, aluminum phosphate, and lithium phosphate can improve interfacial corrosion resistance; lithium titanate and lithium aluminate help improve local ion migration channels, so that the coating layer can suppress side reactions without excessively hindering lithium ion penetration.

[0067] In some embodiments, the weight loss rate of the negative electrode material in an inert atmosphere at 100°C-500°C is ≤0.5%. Specifically, the weight loss rate of the negative electrode material in an inert atmosphere at 100°C-500°C is within the range of 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any combination thereof.

[0068] Anode materials that meet this condition have high purity and are relatively stable, which is beneficial for improving the electrochemical performance of the battery.

[0069] In some embodiments, the particle size D50 of the graphite substrate is 8 μm-15 μm. Specifically, the particle size D50 of the graphite substrate is a range of 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or any combination thereof.

[0070] The graphite substrate can be one or more of natural graphite, artificial graphite, or spherical graphite. Its particle size D50 refers to the median particle size corresponding to 50% of the cumulative particle size distribution, determined using a laser particle size analyzer. It is the median cumulative percentage of the volume distribution, i.e., Dv50. Controlling D50 within the range of 8μm-15μm allows the graphite particles to have both a moderate specific surface area exposure and high compaction and good slurry dispersibility, thus providing a stable foundation for the uniform growth of the subsequent coating layer on the particle surface and in defect areas.

[0071] In some embodiments, the internal specific surface area S of the negative electrode material after removing the coating layer prem Satisfy: 0.25 m 2 / g≤S prem ≤0.40 m 2 / g. Specifically, the internal specific surface area S of the negative electrode material after removing the coating layer. prem It is 0.25m 2 / g, 0.27m 2 / g, 0.29 m 2 / g, 0.31m 2 / g, 0.33 m 2 / g, 0.35m 2 / g, 0.38 m 2 / g, 0.40m 2 / g or a range consisting of any two of them.

[0072] In this embodiment, it is advantageous to better achieve 0≤S2 / S1×100%≤5% and S3 / S1×100%≥75%.

[0073] In some embodiments, the external specific surface area S of the negative electrode material after removing the coating layer ext Satisfy: 0.52m 2 / g≤S ext ≤0.62m 2 / g. Specifically, the external specific surface area S of the negative electrode material after removing the coating layer. ext It is 0.52m 2 / g, 0.54m 2 / g, 0.56m 2 / g, 0.58m 2 / g, 0.60 m 2 / g, 0.62m 2 / g or a range consisting of any two of them.

[0074] Having the external specific surface area of ​​the graphite substrate within the above range is beneficial in two ways: firstly, it helps to better achieve 0≤S2 / S1×100%≤5% and S3 / S1×100%≥75%; secondly, it helps to control the particle size of the negative electrode material within a suitable range, thus facilitating the consideration of properties such as compaction density.

[0075] In some embodiments, the external specific surface area of ​​the negative electrode material is S' ext The specific surface area of ​​the negative electrode material after removing the coating layer is S. ext S grow ≤0.30 m 2 / g, where S grow =S' ext -S ext . Specifically, S grow 0.30m 2 / g, 0.20m 2 / g, 0.10 m 2 / g, 0, or a range consisting of any two of them.

[0076] like Figure 5 As shown, the specific surface area S of the negative electrode material consists of three parts: , among which, S ext S is the external specific surface area of ​​the particle. prem S represents the specific surface area within the micropores and gaps of the particles, also known as the internal specific surface area. grow This refers to the additional external specific surface area generated by the accumulation of the coating material itself. In this embodiment, S grow ≤0.30 m 2 / g indicates that the coating thickness on the surface of the negative electrode material is relatively uniform, and there are no many coating protrusions or other structures. This avoids the local coating thickness increase caused by the accumulation of local coating material, which would affect the ion transport performance and other properties. It is also beneficial to achieve 0≤S2 / S1×100%≤5% and S3 / S1×100%≥75%.

[0077] In some embodiments, the specific surface area of ​​the negative electrode material is 0.50 m². 2 / g -0.85m 2 / g. Specifically, the specific surface area of ​​the negative electrode material is 0.50 m² / g. 2 / g, 0.55m 2 / g, 0.60 m 2 / g, 0.65m 2 / g, 0.70m 2 / g, 0.75m 2 / g, 0.80m 2 / g, 0.85m 2 / g or a range consisting of any two of them.

[0078] Specific surface area reflects the effective interface size between graphite particles and the electrolyte. It is limited to 0.50 m². 2 / g-0.85m 2 / g can reduce the active interface of side reactions, maintain appropriate surface wettability and ion exchange capacity, thereby further improving the initial coulombic efficiency and slowing down the cycle decay.

[0079] It should be noted that the specific surface area here includes both the specific surface area generated by pores of different sizes and the external specific surface area of ​​the negative electrode material particles.

[0080] In some embodiments, the tap density of the negative electrode material is 1 g / cm³. 3 -1.3g / cm 3 Specifically, the tap density of the negative electrode material is 1 g / cm³. 3 2g / cm 3 3g / cm 3 or a range consisting of any two of them.

[0081] In some embodiments, the 5T compaction density of the negative electrode material is 1.73 g / cm³. 3 -1.82 g / cm 3 Specifically, the 5T compaction density of the negative electrode material is 1.73 g / cm³. 3 1.75g / cm 3 1.80g / cm 3 1.82g / cm 3 or a range consisting of any two of them.

[0082] Tap density characterizes the natural packing ability of powder under slight mechanical disturbance, while 5T compaction density characterizes the densification potential of the material during electrode forming. By controlling both within the aforementioned range, particles can possess both good process flow and coating compatibility, and can form a structure with high volumetric energy density after electrode compaction, without significantly increasing transmission impedance.

[0083] The graphite anode material in this application can be prepared by the following method, specifically including the following steps:

[0084] The graphite substrate raw material is ground and graded to obtain a graphite substrate with a sphericity greater than or equal to 0.65.

[0085] Atomic layer deposition (ALD) technology was used to perform 3-12 cycles of coating on the pretreated graphite substrate to obtain the anode material.

[0086] In some embodiments, the graphite substrate may be natural graphite, artificial graphite, or a combination thereof, preferably medium-sized graphite after sieving, to balance compaction density and ion diffusion channels. Grinding and grading can be performed using one or more combinations of air jet milling, mechanical shaping, or roll forming, and excessively fine powder is removed through grading to reduce the high specific surface area and irregular edge exposure caused by fine particles. By smoothing the surface edges and spikes of graphite particles and controlling their sphericity within a good range, localized high-reaction sites during subsequent coating can be reduced, resulting in a more uniform surface energy distribution before atomic layer deposition. This facilitates the formation of a continuous, thin coating layer that grows along the graphite surface morphology (i.e., ensuring that the thickness difference between any two points in the coating layer is less than or equal to 10 nm).

[0087] In this application, the sphericity of the graphite substrate can be a range of 0.65, 0.70, 0.75, 0.80, 0.90, 1, or any two of these.

[0088] The number of times the pretreated graphite substrate is cyclically coated using atomic layer deposition technology can be 3, 5, 6, 8, 10, 12, or any combination thereof.

[0089] The particle size D50 of the graphite substrate raw material can be selected as needed. For example, the particle size D50 of the graphite substrate raw material can be 8μm-15μm. After grinding and classification, it is beneficial to stabilize the specific surface area of ​​the negative electrode material at 0.50m². 2 / g-0.85m 2 Within a suitable range of / g, it helps to obtain a tap density of 1g / cm³. 3 -1.3g / cm 3 The compacted density of 5T is 1.73 g / cm³. 3 -1.82g / cm 3 The material. More specifically, the particle size D50 of the graphite substrate material can be a range of 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or any combination thereof.

[0090] In some embodiments, atomic layer deposition coating can be performed using an alternating pulsed gas inlet method. The coating material includes at least one of titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium nitride, aluminum fluoride, aluminum phosphate, lithium phosphate, lithium titanate, and lithium aluminate. The precursor and reactant gas can be matched according to the selected coating material, for example, using a cyclic pulsed method with metal halides, organometallic compounds, oxidants, or ammonia sources, so that a self-limiting surface reaction occurs on the graphite surface in each cycle, thereby obtaining a thin film with controllable thickness and uniform coverage. By controlling the number of cycles, the metal element content in the coating material based on the total mass of the modified graphite anode material is preferably 80ppm-360ppm. This content range can ensure that the coating layer forms a uniform and dense coverage on the graphite surface and defect areas, with 0≤S2 / S1×100%≤5% and S3 / S1×100%≥75%, avoiding an increase in lithium-ion migration resistance due to excessive coating thickness.

[0091] For example, the conditions for atomic layer deposition technology can be as follows: temperature 110℃-150℃, carrier gas is nitrogen, flow rate is 10sccm-50sccm, pulse process is the first precursor introduced for 2s-10s, held for 30s-60s, then purged for 2min-10min, and then the same pulse process is used to switch the other precursors (such as the second precursor, the third precursor, etc.).

[0092] Specifically, the temperature can be within the range of 110℃, 120℃, 130℃, 140℃, 150℃, or any combination thereof, and the flow rate can be within the range of 10 sccm, 20 sccm, 30 sccm, 40 sccm, 50 sccm, or any combination thereof. In the pulse process, the time for introducing the first precursor can be within the range of 2s, 4s, 6s, 8s, 10s, or any combination thereof, the residence time can be within the range of 30s, 40s, 50s, 60s, or any combination thereof, and the re-purging time can be within the range of 2min, 4min, 6min, 8min, 10min, or any combination thereof.

[0093] Understandably, the first, second, and third precursors can be selected adaptively based on the coating material. For example, when the coating material is titanium oxide, the first precursor can be titanium source tetraisopropyl titanate (TTIP), and the second precursor can be oxygen source H2O; when the coating material is aluminum oxide, the first precursor can be aluminum source trimethylaluminum (TMA), and the second precursor can be oxygen source H2O; when the coating material is magnesium oxide, the first precursor can be magnesium source bis(ethylcyclopentadienyl)magnesium (Mg(EtCp)2), and the second precursor can be oxygen source H2O; when the coating material is zirconium oxide, the first precursor can be zirconium source tetra(ethylmethylamino)zirconia (TEMAZ), and the second precursor can be oxygen source H2O; when the coating material is titanium nitride, the first precursor can be titanium tetrachloride (TiCl4), and the second precursor can be nitrogen source ammonia (NH3); when the coating material is aluminum fluoride, the first precursor can be aluminum source trimethylaluminum (TMA ... oxide, the first precursor can be titanium tetrachloride (TiCl4), and the second precursor can be nitrogen source ammonia (NH3); when the coating material is aluminum fluoride, the first precursor can be aluminum source trimethylaluminum (TMA), and the second precursor can be oxygen source H2O; when the coating material is titanium oxide, the first precursor can be titanium tetrachloride (TiCl4), and the second precursor can be nitrogen source ammonia (NH3); when the coating material is aluminum fluoride, the first precursor can be aluminum source trimethylaluminum (TMA), and the second precursor can be oxygen source H2O; when the coating material is titanium oxide, the first precursor can be titanium tetrachloride (TiCl4), and the second precursor can be titanium tetrachloride (TiCl The first precursor can be a fluorine-based pyridine adduct of hydrogen fluoride (HF·pyridine); when the coating material is aluminum phosphate, the first precursor can be aluminum-based trimethylaluminum (TMA), the second precursor can be phosphorus-based trimethyl phosphate (TMP), and the third precursor can be oxygen-based H2O; when the coating material is lithium phosphate, the first precursor can be lithium-based tert-butoxide (LiOtBu), and the second precursor can be phosphorus-based trimethyl phosphate (TMP); when the coating material is lithium titanate, the first precursor shell can be lithium-based tert-butoxide (LiOtBu), the second precursor can be titanium-based tetraisopropyl titanate (TTIP), and the third precursor can be oxygen-based H2O; when the coating material is lithium aluminate, the first precursor can be lithium-based tert-butoxide (LiOtBu), the second precursor can be aluminum-based trimethylaluminum (TMA), and the third precursor can be oxygen-based H2O.

[0094] Because atomic layer deposition (ALD) exhibits self-limiting growth characteristics, when the coating amount is low, some micropores and active sites are preferentially filled, leading to an initial decrease in the apparent specific surface area. As the number of cycles increases further, the coating layer begins to expand in discontinuous areas and local depressions on the surface, resulting in a certain degree of morphological reconstruction and pore stabilization. This manifests as a rebound in specific surface area with increasing content. Therefore, during the coating process, the specific surface area of ​​the graphite substrate (specifically, the intermediate formed during the coating process) and the coating material content exhibit a non-linear relationship of initial decrease followed by increase. This non-linear relationship reflects the evolution of the coating layer on the graphite surface from point-like coverage to continuous film formation, and also provides a technological basis for adjusting the pore size distribution.

[0095] Furthermore, atomic layer deposition achieves atomic or nanoscale layer-by-layer deposition of the coating layer through surface self-limiting reactions. This allows the coating layer to preferentially cover the outer surface, edges, and defect sites of graphite, reducing the direct contact area between graphite and the electrolyte, and partially passivating the active surface within the original micropores / crevices. Simultaneously, the coating layer introduces new specific surface area S during its growth process. growHowever, since the newly added surface is controlled by extremely low coating amount and dense film morphology, it will not evolve into micron-sized aggregates, thus avoiding an excessive increase in lithium-ion migration resistance.

[0096] In some embodiments, the external specific surface area S of the pretreated graphite substrate ext It is 0.52m 2 / g-0.62m 2 / g, Specific surface area S of micropores and gaps on the particle surface prem It is 0.25 m 2 / g -0.40 m 2 / g. Specifically, the external specific surface area S of the pretreated graphite substrate. ext It is 0.52m 2 / g, 0.54m 2 / g, 0.56 m 2 / g, 0.58m 2 / g, 0.60 m 2 / g, 0.62m 2 / g or a range consisting of any two of them; the specific surface area (i.e., internal specific surface area) of the micropores and gaps on the particle surface S prem It is 0.25m 2 / g, 0.27m 2 / g, 0.29 m 2 / g, 0.31m 2 / g, 0.33 m 2 / g, 0.35m 2 / g, 0.38 m 2 / g, 0.40m 2 / g or a range consisting of any two of them.

[0097] Using this type of pretreated graphite substrate can ensure that the specific surface area of ​​the coated material remains stable at 0.50 m². 2 / g-0.85m 2 Within the suitable range of / g and 0≤S2 / S1×100%≤5%, S3 / S1×100%≥75%.

[0098] In some embodiments, the step of performing 3-12 cycles of cyclic coating on a pretreated graphite substrate using atomic layer deposition technology includes: first activating the pretreated graphite substrate with ozone, and then performing cyclic coating.

[0099] Ozone, as a strong oxidizing gas, first acts on the edge sites, defect sites, and micropore entrance regions of the graphite substrate surface, causing mild oxidation of local carbon atoms and forming oxygen-containing groups such as carbonyl, hydroxyl, and epoxy groups, thereby increasing the surface energy and chemical affinity of graphite. After this step, the originally relatively inert graphite surface can provide more adsorption sites for atomic layer deposition precursors, reducing the nucleation energy barrier, enabling subsequent coating layers to achieve continuous coverage with a lower number of cycles, and reducing the occurrence of island deposition, local agglomeration, and exposed areas.

[0100] Furthermore, the ozone concentration is 12wt%-18wt%, the activation temperature is 110℃-150℃, and the activation time is 5min-10min. Specifically, the ozone concentration can be a range of 12wt%, 14wt%, 16wt%, 18wt%, or any two of these, and the activation time can be a range of 5min, 6min, 7min, 8min, 9min, 10min, or any two of these.

[0101] Controlling the above conditions can achieve an optimal balance between activation efficiency and structural protection: too low a concentration or too short a time will result in insufficient surface activation, affecting the uniformity of coating; too high a concentration or too long a time may cause excessive oxidation, increase surface defects and side reaction activity, and even weaken the integrity of the graphite conductive framework.

[0102] In some embodiments, the step of performing 3-12 cycles of cyclic coating on the pretreated graphite substrate using atomic layer deposition technology includes: first performing 1-6 cycles of low-flow coating with a gas flow rate of 10 sccm-20 sccm, and then performing high-flow coating with a gas flow rate of 20 sccm-50 sccm.

[0103] Specifically, the gas flow rate during low-flow coating of 1-5 times can be a range of 10 sccm, 12 sccm, 15 sccm, 18 sccm, 20 sccm or any two of these; the gas flow rate during high-flow coating can be a range of 20 sccm, 30 sccm, 40 sccm, 50 sccm or any two of these.

[0104] By controlling the number of cycles to 3-12, setting the low-flow coating to 1-5 cycles, and switching to high flow in the later stage, it is possible to balance coating coverage, continuity, and process efficiency, while maintaining the metal element content based on the total mass of the modified graphite anode material within a suitable range of 80ppm-360ppm. It should be understood that the above example is for illustrative purposes only and is not limiting. The number of switching cycles between low and high flow, the flow values ​​at each stage, and the corresponding pulse times can be adjusted equivalently according to equipment specifications, precursor volatility, and the pore structure of the graphite surface.

[0105] In some embodiments, the method further includes a step of heat-treating the coated graphite material. The heat-treating conditions are as follows: under an inert gas atmosphere, the temperature is raised to 600℃-1150℃ at a heating rate of 15℃ / min-30℃ / min and held for 20min-40min. Specifically, the heating rate can be a range of 15℃ / min, 20℃ / min, 25℃ / min, 30℃ / min, or any two of these; the heating temperature can be a range of 600℃, 800℃, 1000℃, 1100℃, 1150℃, or any two of these; and the holding time can be a range of 20min, 30min, 40min.

[0106] After atomic layer deposition (ALD) cycling, the coated material is further processed in a tube furnace, box furnace, or other controllable heat treatment equipment. Before heat treatment, the sample is uniformly spread on a quartz boat, ceramic boat, or metal support, and the furnace cavity is continuously purged with inert gases such as argon or nitrogen to remove oxygen and moisture, typically maintaining a stable low-oxygen environment. This heat treatment step removes residual precursors, adsorbed water, and organic groups from the coating process, thereby reducing the risk of side reactions caused by interfacial impurities. After this heat treatment, the weight loss of the anode material is ≤0.5% under an inert atmosphere at 100℃-500℃.

[0107] It should be understood that the above-mentioned temperature, heating rate and holding time settings can be adjusted according to the type of coating material, but should still aim to achieve the removal of residues, densification of the coating and stabilization of the interface. The above examples are for demonstration purposes only and are not limited.

[0108] This application also provides a negative electrode sheet, including a current collector and a negative electrode active layer located on at least a portion of the surface of the current collector. The negative electrode active layer includes a negative electrode active material, which is the negative electrode material provided above. For the same reasons mentioned above, this negative electrode sheet can still maintain good lithium insertion / extraction kinetics under fast charging conditions, thereby improving the initial coulombic efficiency, cycle stability, and rate performance. Therefore, it is more suitable for applications with high requirements for long lifespan and wide temperature range performance, such as new energy vehicles, energy storage systems, and consumer electronics batteries.

[0109] This application also provides a battery comprising the aforementioned negative electrode material or the aforementioned negative electrode sheet. For the same reasons described above, this battery exhibits lower polarization and more complete capacity release under fast charging and long-cycle conditions, thereby improving initial coulombic efficiency, cycle life, and charging efficiency.

[0110] Specifically, the battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located inside the casing.

[0111] The outer casing can be a packaging bag encapsulated with a film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0112] Please see Figure 1 and Figure 2 The electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. For charging, please refer to [reference needed]. Figure 1 Active ions (such as lithium ions) are extracted from the lattice of the positive electrode material (such as a lithium-ion intercalation compound) in the positive electrode 101, pass through the electrolyte and the separator 103, reach the negative electrode 102, and insert into the lattice of the negative electrode material. For discharge procedures, please refer to [link to relevant documentation]. Figure 2 Active ions (such as lithium ions) are deintercalated from the lattice of the negative electrode material of the negative electrode 102, pass through the electrolyte through the separator 103, reach the positive electrode 101 and are embedded in the lattice of the positive electrode material (such as lithium intercalation compound), generating electrons that travel from the negative electrode 102 to the positive electrode 101 through the external circuit. The reverse movement of electrons forms an electric current, which can be used by electrical appliances.

[0113] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding the positive electrode 101, the separator 103, and the negative electrode 102.

[0114] The positive electrode 101 includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material active layer includes a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0115] The positive electrode material active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0116] The positive electrode active layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative, such as poly(p-phenylenevinylene), poly(p-phenyleneacetylene), or poly(p-phenylenedimethylene).

[0117] The separator 103 includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator 103 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0118] The electrolyte serves to conduct ions between the positive electrode 101 and the negative electrode 102. The electrolyte can be in one or more states, including gel, solid, and liquid. In some embodiments, the electrolyte is a liquid electrolyte solution. The liquid electrolyte solution serves to conduct active ions between the positive electrode 101 and the negative electrode 102. In some embodiments, the liquid electrolyte solution includes a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyllithium (LiC(SO2CF3)3), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is selected as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, other organic solvents, or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0119] In battery manufacturing, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to obtain battery cells. The battery cells are then encapsulated in pre-stamped aluminum-plastic films. After the encapsulated batteries are dried, electrolyte is injected into the dried batteries. The batteries are then left to stand, undergo formation, and are resealed to complete the battery manufacturing process.

[0120] The technical solution of this application will be further explained below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, all reagents used are commercially available or obtained through public channels.

[0121] Example 1

[0122] This embodiment provides a negative electrode material, which is prepared by the following method:

[0123] Step 1: Grind 5.0g of artificial graphite (BTR New Energy Materials Co., Ltd., model: EA-1) continuously at 600rpm for 30min in a shaping and classifying machine. Then turn on the classifying equipment and collect the material from the receiving port to obtain a pretreated graphite substrate. The pretreated graphite substrate has a particle size D50 of 11μm and a sphericity of 0.72.

[0124] Step 2: The pretreated graphite substrate is loaded into the sample chamber of the powder atomic layer deposition (PALD) equipment. Nitrogen gas is introduced to agitate the powder to a slightly bubbling fluidized state, while the temperature is raised to 120°C. Then, an ozone-nitrogen mixture with an ozone mass ratio of 15wt% is introduced for 5 minutes, and then pure nitrogen gas is purged for 30 minutes to remove ozone residue. Finally, the first precursor tetraisopropyl titanate (TTIP) and the second precursor pure water vapor were introduced sequentially, with nitrogen as the carrier gas. The pulse process was as follows: first, the first precursor tetraisopropyl titanate (TTIP, temperature 90±2℃) was introduced for 5 seconds, held for 30 seconds, and then purged with N2 for 10 minutes. Then, the second precursor pure water vapor (temperature 95±2℃) was introduced for 5 seconds, held for 30 seconds, and then purged with N2 for 10 minutes to complete the first cycle. Pure nitrogen was then used to purge for 30 minutes to remove any residues that had not reacted with the graphite substrate. The pulse process was repeated for 3 cycles according to the first cycle to end the deposition and coating. After cooling, the material was removed to obtain the coated graphite material. The nitrogen flow rate was 15 sccm in the first two cycles and 30 sccm in the last cycle.

[0125] Step 3: The graphite material coated in Step 2 is heated to 600℃ at a heating rate of 20℃ / min and held for 30min. After cooling, it is taken out, demagnetized, and passed through a 325-mesh sieve to obtain the negative electrode material. The coating layer contains titanium dioxide.

[0126] Example 2

[0127] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 2, after removing residual ozone, the first precursor lithium source lithium tert-butoxide (Li(OtBu) , temperature 120±2℃), the second precursor titanium source tetraisopropyl titanate (TTIP, temperature 90±2℃), and the third precursor oxygen source pure water vapor are sequentially introduced, and the coating layer contains lithium titanate.

[0128] Example 3

[0129] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 2, the deposition coating is completed after 8 cycles. The nitrogen flow rate is 15 sccm in the first 4 cycles and 30 sccm in the remaining cycles.

[0130] Example 4

[0131] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 2, the deposition coating is completed after 12 cycles. The nitrogen flow rate is 15 sccm for the first 6 cycles and 30 sccm for the remaining cycles.

[0132] Example 5

[0133] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 800°C at a heating rate of 20°C / min and held at that temperature for 30min.

[0134] Example 6

[0135] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 1150°C at a heating rate of 20°C / min and held at that temperature for 30min.

[0136] Example 7

[0137] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that it does not undergo the heat treatment in step 3.

[0138] Example 8

[0139] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 900°C at a heating rate of 20°C / min and held at that temperature for 30min.

[0140] Example 9

[0141] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 1000°C at a heating rate of 20°C / min and held at that temperature for 30min.

[0142] Example 10

[0143] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 1150°C at a heating rate of 20°C / min and held at that temperature for 60 minutes.

[0144] Example 11

[0145] This embodiment provides a negative electrode material, which differs from Embodiment 1 in that, in step 3, the coated graphite material is heated to 1150°C at a heating rate of 5°C / min and held at that temperature for 60 minutes.

[0146] Comparative Example 1

[0147] This comparative example provides a negative electrode material, which differs from Example 1 in that the raw material does not undergo the pretreatment in step 1.

[0148] Comparative Example 2

[0149] This comparative example provides a negative electrode material, which differs from Example 1 in that, in step 2, the deposition coating is completed after one cycle, and the nitrogen flow rate during the cycle is 15 sccm.

[0150] Comparative Example 3

[0151] This comparative example provides a negative electrode material, which differs from Example 1 in that, in step 2, the deposition coating is completed after 20 cycles. The nitrogen flow rate is 15 sccm for the first 10 cycles and 30 sccm for the remaining cycles.

[0152] Comparative Example 4

[0153] This comparative example provides a modified graphite anode material, which is prepared by a conventional liquid-phase coating process, the specific steps of which are as follows:

[0154] 19g of tetraisopropyl titanate (TTIP) was dissolved in 8kg of water, and then 5kg of graphite was added. The mixture was stirred at 1000rpm for 1h, and then the dispersion was dried. The temperature was then increased to 600℃ at a rate of 20℃ / min and held for 30min. After cooling, the mixture was removed, demagnetized, and passed through a 325-mesh sieve to obtain titanium dioxide-coated graphite prepared by the liquid phase coating method.

[0155] Experimental Example 1

[0156] The negative electrode materials in the above embodiments and comparative examples were subjected to the following tests and analyses:

[0157] (1)Morphology analysis: Appropriate amounts of the negative electrode material sample powder to be tested and ethanol were added to a mortar and manually ground for 5 minutes, followed by ultrasonic oscillation for 20 minutes. An appropriate amount of the powder-ethanol mixture was taken, and 2 to 3 drops of this mixture were dropped onto a microgrid (a copper mesh coated with an ultra-thin carbon film). The thickness of the sample coating layer was observed using a Talos F200S transmission electron microscope (TEM), and the acceleration voltage during testing was 200 kV. Under the bright-field image of the TEM, morphology images at magnifications of 2000 - 4000 were collected. Subsequently, using the energy-dispersive X-ray spectrometer equipped with the TEM, the elements to be tested were selected for area scanning, and then a metal element distribution map was generated through signal processing.

[0158] Among them, Figure 3 FIG. 5 shows the TEM morphology and element distribution maps of the negative electrode materials in Example 1 and Example 5. Among them, A is the TEM morphology map of the negative electrode material in Example 1, B is the Ti element distribution map of the negative electrode material in Example 1, C is the TEM morphology map of the negative electrode material in Example 5, and D is the Ti element distribution map of the negative electrode material in Example 5.

[0159] It can be seen from Figure 3 that the element distribution in the coating layer is uniform, and there are no visible agglomerations or uncoated areas.

[0160] (2)Measurement of cumulative pore surface area and specific surface area:

[0161] A specific surface area and pore size analyzer (Micromeritics, TriStar3000&3020, USA) was used to test the specific surface area / pore size distribution of the material in accordance with GB / T 19587-2017 Determination of Specific Surface Area and Pore Volume of Solid Materials by Gas Adsorption - BET Method. Specifically, a dry specific surface area tube was taken, and a material with a volume of 1 / 2 - 2 / 3 of the bulb of the specific surface area tube was weighed; before testing, degassing treatment (removing water vapor or impurities) was required, and vacuum heating or nitrogen purging could be used for degassing (Vacuum heating method: Set the degassing temperature at 300 °C, the degassing time at 1 h. After degassing, it needs to be placed in a cooling tank or on the external specific surface area tube rack for cooling for 20 min, and then backfill the gas for 5 - 10 s. The backfill time depends on the situation to avoid the sample spraying out and sticking to the side wall of the sample tube. Then, the sample tube was disassembled, and the sample tube was quickly plugged with a rubber stopper and then subsequent testing was carried out; Nitrogen purging method: Set the degassing temperature at 300 °C, the degassing time at 1 h. After purging, it needs to be placed in a cooling tank or on the external specific surface area tube rack for cooling for 20 min before the rubber stopper can be quickly pulled out and the degassing needle can be pulled out, and then the rubber stopper was quickly plugged to prevent air from entering); The measurement was carried out in accordance with the instructions of the specific surface area / pore size analyzer to obtain the specific surface area S.

[0162] The adsorption isotherm was fitted using a slit-pore DFT model to obtain the differential and cumulative specific surface area distribution curves. Specifically, the pore size (nm) and its corresponding differential pore volume distribution dA / dlog(W) (m²) on the logarithmic scale were directly obtained using the software's built-in DFT fitting function. 2 The relationship curve between pore size (nm) and cumulative pore surface area S (m²) (i.e., differential specific surface area curve), and the relationship between pore size (nm) and cumulative pore surface area S (m²) 2 The relationship curve between / g) (i.e., the cumulative specific surface area curve). The results are as follows: Figure 4 And as shown in Table 1 below:

[0163] The results of Example 1 and Comparative Example 4 are as follows: Figure 4 As shown in the figure, A is the cumulative specific surface area distribution curve in the 2nm-100nm range of Example 1 and Comparative Example 4, B is the differential cumulative specific surface area distribution curve in the 2nm-10nm range of Example 1 and Comparative Example 4, C is the differential specific surface area distribution curve in the 2nm-100nm range of Example 1 and Comparative Example 4, and D is the differential specific surface area distribution curve in the 2nm-10nm range of Example 1 and Comparative Example 4.

[0164] Table 1

[0165]

[0166] (3) ICP test: Inductively coupled plasma atomic emission spectrometry (ICP-Agilent, OPTIMA 8000 / 5800) was used for the test. Specifically, 1g of negative electrode material was added to a sealable container, followed by 2mL of nitric acid. After sealing the container, microwave-assisted heating was used to digest the material at 120℃ for 6h. After cooling, the material was filtered and then diluted to 100mL with ultrapure water for ICP testing to determine the concentration of metal elements (Ti, Li) in the negative electrode material.

[0167] (4) Hole surface area test: such as Figure 5 As shown, the specific surface area S consists of three components: , among which, S ext S is the external specific surface area of ​​the particle. prem S represents the specific surface area within the micropores / gaps of the particles. grow This refers to the additional specific surface area resulting from the self-accumulation and growth of the coating material. The SL of the pretreated graphite substrate was determined using an "acid treatment-recovery and t-plot separation" method. ext S prem and the S' of the negative electrode material ext S' prem S grow The specific steps are as follows:

[0168] a. Acid etching to remove the coating layer: The prepared negative electrode material is placed in an acid solution (specifically dilute hydrofluoric acid or hot concentrated hydrochloric acid; in this application, dilute hydrofluoric acid is used) and stirred at 300 rpm for 60 minutes under ultrasonic cleaning conditions. Then, the precipitate is filtered out, and after washing 5 times, ICP is tested. If there are obvious coating element values ​​in the precipitate, the above steps are repeated until no coating element residue can be detected, that is, the negative electrode material is restored to the "bare graphite" state, which is the graphite substrate.

[0169] b. Perform standard nitrogen adsorption-desorption experiments: Weigh 0.5g of graphite substrate and place it in a sample tube. Place the tube in the degassing station and degas for 4 hours at 80℃ and a vacuum degree ≤10Pa. After degassing, cool to room temperature. After calibrating the instrument using standard materials, quickly connect the degassed sample tube to the BET adsorption analyzer (American Microtech, TriStar3000 & 3020). Completely immerse the bottom of the sample tube in liquid nitrogen. Start the instrument and automatically record the nitrogen adsorption amount corresponding to each pressure.

[0170] c. Internal and External Surface Area Separation Method (t-plot method): Adsorption data is processed using the de Boer t-plot method, with the statistical thickness of the adsorption layer t (P / P0) as the abscissa and the adsorption amount V as the ordinate. Separation principle: In the high-pressure region of the t-plot, adsorption mainly occurs on the outer surface, and the curve exhibits a good linear relationship. The slope of this linear portion directly corresponds to the external specific surface area S. ext The positive intercept of the extended linear portion on the vertical axis corresponds to the filling volume, which, after conversion, is S. prem For graphite substrates, S grow It is 0.

[0171] d. Using the same method as above, perform steps b and c on the prepared negative electrode material to obtain S'. prem Using formula S grow= S' ext -S ext =S -S' prem -S ext Get S grow Where S is the total specific surface area obtained in the specific surface area test in (4), S ext The specific surface area S of "bare graphite" ext .

[0172] Figure 6 This is a de Boer t-plot linear fit diagram of the graphite substrate obtained after the negative electrode material in Example 1 of the present invention has undergone acid etching to remove the coating layer in step a.

[0173] (5) Weight loss rate: Thermogravimetric analysis (TGA) was used to determine the weight loss rate using a Mettler TGA / DSC system. Approximately 5-10 mg of the negative electrode material to be tested was placed in an alumina crucible. High-purity nitrogen gas was introduced into the thermogravimetric analyzer as a protective gas (flow rate approximately 20-50 mL / min), and the temperature was increased from room temperature to above 500℃ at a rate of 10℃ / min. The sample mass m at 100℃ was used as the weight loss rate. 100 Using this temperature as a baseline (this temperature can remove interference from surface physically adsorbed water, so that subsequent weight loss mainly reflects the removal of residual precursors, organic groups, and bound water), record the sample mass m at 500℃. 500 According to the weight loss rate = (m 100 − m 500 ) / m 100 Calculate the weight loss rate in the range of 100 to 500℃ by multiplying by 100%, and take the average of 2 to 3 parallel measurements.

[0174] (6) Tapped density: The tapped density was determined using a tapped density meter according to the general method of GB / T 5162. The equipment model was a Canta tapped density meter (DAT-6-220-50). Specifically: a certain mass m of the powder to be tested (usually 50 to 100 g, 60 g in this application, recorded to 0.01 g) was weighed and placed into a graduated cylinder through a funnel. The graduated cylinder was fixed on the tapped density meter and vibrated at a frequency of about 300 times / min until the volume no longer changed (generally set to 2000 vibrations). The volume V of the powder after tapping was read and calculated according to tapped density = m / V, with the unit being g / cm³. 3 The measurements were performed in three parallel trials, and the average value was taken.

[0175] (7) 5T compaction density: The compaction density was determined using an electric powder compaction density tester, specifically the FTYS-50KN fully automatic powder compaction density testing system. Specifically: A certain mass m of the powder to be tested (1.0 g in this application, recorded to 0.001 g) was weighed and uniformly loaded into a cylindrical mold with an inner diameter of 2 cm. The pressure was applied at a constant rate to 5 tons (i.e., 5T, held for 30 s to densify the material). The thickness h of the compressed material was read by a displacement sensor. The volume of the material was V = A × h. The compaction density was calculated using the formula 5T compaction density = m / V, with units of g / cm³. 3 The measurements were performed in three parallel trials, and the average value was taken.

[0176] Table 2

[0177]

[0178] Experimental Example 2

[0179] The negative electrode materials from the above embodiments and comparative examples were used to prepare coin cells, and the following performance tests were performed. The methods for preparing the coin cells are as follows, and the test results are shown in Table 3 below:

[0180] Button cell fabrication: The negative electrode material, conductive carbon black, and polyvinylidene fluoride were mixed evenly in N-methylpyrrolidone at a mass ratio of 92:5:3, and coated onto a copper foil current collector. The mixture was then vacuum dried at 120°C to obtain the electrode sheet. The electrode sheet was then assembled into a button cell CR2016 in a glove box for testing. The counter electrode was made of lithium metal, the separator was Celgard C2400, and the electrolyte was a 1.3 mol / L LiPF6 solution of EC (ethylene carbonate), PC (propylene carbonate), and DEC (diethyl carbonate) (volume ratio of 3:1:6).

[0181] (1) First-time efficiency test: The battery was charged and discharged at 25°C using a battery charge-discharge tester. The charge-discharge regime was as follows: 0.1C (C=372mAh / g, i.e., charging current = 0.1×372mA / g×mass of electrode active material) constant current charging to the upper voltage limit of 1.5V (vs Li / Li⁺), then switched to constant voltage charging until the current dropped to 0.01C, charging was stopped, the first charge capacity was recorded, and the battery was left to stand for 10 minutes. Then, constant current discharge was performed at 0.1C to the lower voltage limit of 0.01V (vs Li / Li⁺), and the first discharge capacity was recorded. The first-time efficiency (i.e., the first coulombic efficiency) was calculated according to the following formula:

[0182] Initial coulombic efficiency (η) = (initial discharge capacity / initial charge capacity) × 100%.

[0183] (2) Rate test: The battery was charged and discharged at 25°C using a battery charge and discharge tester. The charge and discharge regime was as follows: constant current charging at 0.1C to 1.5V, then constant voltage charging at 1.5V until the current decreased to 0.01C, left to stand for 5 minutes, and then constant current discharging at 0.2C to 0.01V. The discharge capacity Q was recorded. 0.2c After resting for 5 minutes, charge with a constant current of 0.1C to 1.5V, then switch to a constant voltage of 1.5V and charge until the current decreases to 1.5V. After resting for 5 minutes, discharge with a constant current of 2C to 0.01V and record the discharge capacity Q. 2c The capacity retention rate at 2C / 0.2C discharge rate can be calculated using the following formula:

[0184] 2C / 0.2C discharge rate capacity retention rate = Q 2c / Q 0.2c ×100%.

[0185] (3) Cyclic performance test: The battery was charged and discharged at 25°C using a battery charge and discharge tester. The charge and discharge regime was as follows: constant current charging at 1C to the upper voltage limit of 1.5V (vs Li / Li⁺), then constant voltage charging until the current dropped to 0.01C, charging was stopped, the initial charge capacity was recorded, and the battery was left to stand for 10 minutes. Then constant current discharge at 1C was performed to the lower voltage limit of 0.01V (vs Li / Li⁺), and this charge and discharge cycle was repeated 100 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 100th cycle were measured. 100 The capacity retention rate Q after 100 cycles is calculated using the following formula:

[0186] Capacity retention rate Q = Q 100 / Q1×100%.

[0187] Table 3

[0188]

[0189] As can be seen from the above results, the batteries prepared by the negative electrode materials in Examples 1-11 have better first-time efficiency, 2C / 0.2C discharge rate, and 100-cycle retention rate than those in Comparative Examples 1-4, indicating that the negative electrode material provided by the present invention is beneficial to improving the first-time efficiency, rate performance and cycle performance of the battery.

[0190] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A negative electrode material, characterized in that, It includes a graphite substrate and a coating layer disposed on at least a portion of the surface of the graphite substrate; The negative electrode material includes a first pore structure and a second pore structure. The pore size D1 of the first pore structure satisfies: 2nm≤D1≤5nm, and the pore size D2 of the second pore structure satisfies: 5nm<D2≤100nm. In the N2 adsorption slit-pore DFT fitting curve of the negative electrode material, the cumulative pore surface area corresponding to the pore with a pore size ≥2nm is S1, the cumulative pore surface area corresponding to the first pore structure is S2, and the cumulative pore surface area corresponding to the second pore structure is S3. Among them, 0≤S2 / S1×100%≤5%, S3 / S1×100%≥75%.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) S3 / S1×100%≥90%; (2) The S2 / S1×100% is a range consisting of 0, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any two of them; (3) The S3 / S1×100% is a range of 75%, 80%, 85%, 90%, 95%, 100% or any two of them.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) In the differential specific surface area curve of the negative electrode material, the dA / dlog(W) corresponding to the first pore structure is ≤0.005m 2 / g; (2) In the differential specific surface area curve of the negative electrode material, the dA / dlog(W) corresponding to the first pore structure is 0 and 0.001m. 2 / g, 0.002m 2 / g, 0.003m 2 / g, 0.004m 2 / g, 0.005m 2 / g or a range consisting of any two of them; (3) S1, S2, and S3 are obtained by normalizing the cumulative pore surface area of ​​the negative electrode material based on the cumulative specific surface area curve, with the cumulative pore surface area corresponding to the pore size less than or equal to 2nm as 0. (4)0.095 m 2 / g≤S1≤0.115 m 2 / g; (5) The S1 is 0.095 m 2 / g, 0.1 m 2 / g, 0.105 m 2 / g, 0.11 m 2 / g, 0.115 m 2 / g or a range consisting of any two of them; (6)S2≤0.005 m 2 / g; (7) The S2 is 0.005 m 2 / g, 0.004 m 2 / g, 0.003 m 2 / g, 0.002 m 2 / g, 0.001 m 2 A range consisting of / g, 0, or any two of them; (8)S3≥0.09m 2 / g; (9) The S3 is 0.09 m 2 / g, 0.01m 2 / g, 0.02m 2 / g, 0.03 m 2 / g or a range consisting of any two of them.

4. The negative electrode material according to any one of claims 1-3, characterized in that, The coating layer includes a metallic element, which includes at least one of titanium, aluminum, magnesium, zirconium, and lithium.

5. The negative electrode material according to claim 4, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) Based on the total mass of the negative electrode material, the content of the metal element is 80 ppm - 360 ppm; (2) Based on the total mass of the negative electrode material, the content of the metal element is in the range of 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 330 ppm, 360 ppm or any two of these. (3) The metal element exists in the form of a metal compound, which includes at least one of titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium nitride, aluminum fluoride, aluminum phosphate, lithium phosphate, lithium titanate, and lithium aluminate.

6. The negative electrode material according to any one of claims 1-3, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The weight loss rate of the negative electrode material is ≤0.5% under an inert atmosphere at 100℃-500℃; (2) The weight loss rate of the negative electrode material under an inert atmosphere at 100℃-500℃ is 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any two of them.

7. The negative electrode material according to any one of claims 1-3, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The particle size D50 of the graphite substrate is 8μm-15μm; (2) The particle size D50 of the graphite substrate is a range of 8 μm, 10 μm, 12 μm, 14 μm, 15 μm or any two of these; (3) The internal specific surface area S of the negative electrode material after removing the coating layer prem Satisfy: 0.25 m 2 / g≤S prem ≤0.40 m 2 / g; (4) The internal specific surface area S of the negative electrode material after removing the coating layer prem It is 0.25m 2 / g, 0.27m 2 / g, 0.29 m 2 / g, 0.31m 2 / g, 0.33 m 2 / g, 0.35m 2 / g, 0.38 m 2 / g, 0.40m 2 / g or a range consisting of any two of them; (5) The specific surface area S of the negative electrode material after removing the coating layer ext Satisfy: 0.52m 2 / g≤S ext ≤0.62 m 2 / g; (6) The specific surface area S of the negative electrode material after removing the coating layer ext It is 0.52m 2 / g, 0.54m 2 / g, 0.56 m 2 / g, 0.58m 2 / g, 0.60 m 2 / g, 0.62m 2 / g or a range consisting of any two of them; (7) The specific surface area of ​​the negative electrode material is S' ext The specific surface area of ​​the negative electrode material after removing the coating layer is S. ext S grow ≤0.30 m 2 / g, where S grow =S' ext -S ext ; (8) The specific surface area of ​​the negative electrode material is S' ext The specific surface area of ​​the negative electrode material after removing the coating layer is S. ext S grow ≤0.30 m 2 / g, where S grow =S' ext -S ext S grow 0.30m 2 / g, 0.20m 2 / g, 0.10 m 2 / g, 0, or a range consisting of any two of them.

8. The negative electrode material according to any one of claims 1-3, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The specific surface area of ​​the negative electrode material is 0.50 m². 2 / g -0.85m 2 / g; (2) The specific surface area of ​​the negative electrode material is 0.50 m². 2 / g, 0.55m 2 / g, 0.60 m 2 / g, 0.65m 2 / g, 0.70m 2 / g, 0.75m 2 / g, 0.80m 2 / g, 0.85m 2 / g or a range consisting of any two of them; (3) The tap density of the negative electrode material is 1 g / cm³. 3 -1.3g / cm 3 ; (4) The tap density of the negative electrode material is 1 g / cm³. 3 2g / cm 3 3g / cm 3 or a range consisting of any two of them; (5) The 5T compaction density of the negative electrode material is 1.73 g / cm³. 3 -1.82 g / cm 3 ; (6) The 5T compaction density of the negative electrode material is 1.73 g / cm³. 3 1.75g / cm 3 1.80g / cm 3 1.82g / cm 3 or a range consisting of any two of them.

9. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode active layer located on at least a portion of the surface of the current collector, the negative electrode active layer including a negative electrode active material, the negative electrode active material including the negative electrode material according to any one of claims 1-8.

10. A battery, characterized in that, Includes the negative electrode material according to any one of claims 1-8 or the negative electrode sheet according to claim 9.

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