Negative electrode sheet, battery and electric device

Abstract

The present disclosure belongs to the field of batteries. Specifically disclosed are a negative electrode sheet, a battery and an electric device, wherein the negative electrode sheet comprises a current collector and a negative electrode active material layer provided on at least one side of the current collector; the negative electrode active material layer comprises first graphite and second graphite; the mean ID / IG ratio of the first graphite is in the range of 0.9-1.4, and the mean ID / IG ratio of the second graphite is in the range of 0.05-0.45; and the tortuosity of the negative electrode active material layer is 2.0%-8.0%. In the present disclosure, by compounding the first graphite and the second graphite to form the negative electrode active material layer, slip between particles is optimized, and the fast-charging performance can be improved without compromising the initial Coulombic efficiency and energy density of a battery. Moreover, by using a suitable particle size gradation to construct a tortuosity that matches the fast-charging capability of the negative electrode material, the fast-charging performance of the negative electrode material can be maximized.

Description

Negative electrode, battery and electrical equipment

[0001] Priority information

[0002] This disclosure claims priority to Chinese Patent Application No. 2025103202446, filed with the China National Intellectual Property Administration on March 17, 2025, entitled “Negative Electrode, Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure pertains to the field of batteries, specifically relating to a negative electrode, a battery, and an electrical device. Background Technology

[0004] Graphite, as a negative electrode material for lithium-ion batteries, has become the mainstream choice for commercial lithium-ion batteries due to its high reversible lithium storage capacity, low lithium intercalation potential, good conductivity and structural stability, and low price. With the increasing demand for ultra-fast charging capabilities in the new energy industry, traditional graphite anodes face problems such as insufficient lithium-ion transport rate, high risk of lithium plating, and excessive electrolyte consumption at high temperatures. In existing technologies, graphite coating can improve interfacial kinetics, but poor coating uniformity leads to localized polarization of the electrode during ultra-fast charging, resulting in the risk of lithium plating. Simultaneously, an unreasonable electrode pore structure can easily lead to uneven electrolyte wetting, affecting fast charging performance. Excessive electrode tortuosity results in poor battery kinetic performance. Therefore, a composite graphite anode design that balances rapid lithium-ion transport, initial efficiency, and energy density is urgently needed. Summary of the Invention

[0005] This disclosure aims to at least partially address one of the technical problems in related technologies. To this end, one object of this disclosure is to provide a negative electrode sheet, a battery, and an electrical device. This disclosure optimizes the slippage between particles by compounding a first graphite (with a defect density ID / IG = 0.9~1.4) and a second graphite (with a defect density ID / IG = 0.05~0.45) to form a negative electrode active material layer, thereby improving fast-charging performance while maintaining initial efficiency and energy density. Simultaneously, by constructing a tortuosity that matches the fast-charging capability of the negative electrode material through appropriate particle pairing, the fast-charging performance of the negative electrode material can be maximized.

[0006] The first aspect of this disclosure provides a negative electrode sheet. According to an embodiment of this disclosure, the negative electrode sheet includes a current collector and a negative electrode active material layer disposed on at least one side of the current collector, the negative electrode active material layer including a first graphite and a second graphite;

[0007] In the Raman peak fitting diagram of graphite, there is a D peak corresponding to the defect site, a G1 peak corresponding to the sp2 in-plane vibration of amorphous carbon, and a G2 peak corresponding to the sp2 in-plane vibration of graphite. The ratio of the peak area of ​​the D peak to the sum of the peak areas of the G1 peak and the G2 peak is ID / IG.

[0008] The average ID / IG value of the first graphite ranges from 0.9 to 1.4;

[0009] The average ID / IG value of the second graphite ranges from 0.05 to 0.45;

[0010] The tortuosity of the negative electrode active material layer is 2.0%~8.0%.

[0011] According to the negative electrode sheet of the above embodiments of this disclosure, by compounding a first graphite (with a defect density ID / IG=0.9~1.4) and a second graphite (with a defect density ID / IG=0.05~0.45) to form a negative electrode active material layer, the slippage between particles is optimized. This design can improve fast charging performance while also considering the first-time efficiency and energy density. This design fully utilizes the characteristics of the two types of graphite and achieves comprehensive optimization of battery performance through synergistic effect. In addition, from the perspective of electrode sheet design, by constructing a tortuosity that matches the fast charging capability of the negative electrode material through appropriate particle matching, the fast charging performance of the negative electrode material can be maximized. This disclosure limits the tortuosity of the negative electrode active material layer to 2.0%~8.0%. By limiting the tortuosity of the negative electrode active material layer within the above range, fast charging performance can be improved while also considering the battery's first-time efficiency and energy density.

[0012] In addition, the negative electrode sheet according to the above embodiments of this disclosure may also have the following additional technical features:

[0013] In some embodiments of this disclosure, at least a portion of the surface of the first graphite is provided with a coating layer, while the surface of the second graphite is not provided with a coating layer.

[0014] In some embodiments of this disclosure, the coating layer includes a carbon coating layer comprising amorphous carbon.

[0015] In some embodiments of this disclosure, the average ID / IG value of the first graphite ranges from 1.05 to 1.25.

[0016] In some embodiments of this disclosure, the average ID / IG value of the second graphite ranges from 0.08 to 0.15.

[0017] In some embodiments of this disclosure, the discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 15% to 35%.

[0018] In some embodiments of this disclosure, the discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 20% to 34%.

[0019] In some embodiments of this disclosure, in the Raman peak fitting plot of the first graphite, the full width at half maximum (FWHM) of peak D is 1000 m / s. D The full width at half maximum (FWHM) of peak G1 is 1000 m. G1 The full width at half maximum (FWHM) of peak G2 is 1000 m / s. G2 FWHM D / (FWHM G1 +FWHM G2 The range is 1.0 to 1.7.

[0020] In some embodiments of this disclosure, the percentage of test points with ID / IG in the range of 0 to 0.45 is less than or equal to 45% of the percentage of test points with ID / IG in the range of 0 to 2.0.

[0021] In some embodiments of this disclosure, the number of test points with ID / IG in the range of 0 to 0.45 accounts for 10% to 25% of the number of test points with ID / IG in the range of 0 to 2.0.

[0022] In some embodiments of this disclosure, the areal density of the negative electrode active material layer on one side of the current collector is 80 g / m². 2 ~150g / m 2 .

[0023] In some embodiments of this disclosure, the compaction density of the negative electrode active material layer on one side of the current collector is 1.45 g / cm³. 3 ~1.8g / cm 3 .

[0024] In some embodiments of this disclosure, the first graphite and the second graphite respectively comprise at least one of artificial graphite and natural graphite.

[0025] A second aspect of this disclosure provides a battery. According to an embodiment of this disclosure, the battery includes the negative electrode sheet of the first aspect. Therefore, the battery of this disclosure has good fast-charging capability and high energy density and initial efficiency.

[0026] A third aspect of this disclosure provides an electrical device. According to an embodiment of this disclosure, the electrical device includes the battery of the second aspect. Therefore, because the electrical device uses the aforementioned battery, the battery of the electrical device has good fast-charging capability and high energy density and initial efficiency. The features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0027] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 shows the Raman spectrum of one of the test points in Example 1 (ID / IG≥0.45).

[0030] Figure 2 is a Raman peak fitting diagram of Figure 1;

[0031] Figure 3 shows the Raman spectrum of another test point in Example 1 (ID / IG < 0.45).

[0032] Figure 4 is the Raman peak fitting diagram of Figure 3. Embodiments of the present invention

[0033] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0035] This disclosure was made by the inventors based on the following questions:

[0036] The inventors discovered that optimizing the design of the battery's negative electrode is necessary to improve its ultra-fast charging capability while maintaining energy density. From a materials perspective, increasing the carbon content coated on the graphite surface can increase the defect density of the graphite surface, thereby increasing lithium intercalation sites and improving the lithium intercalation kinetics of the material. Furthermore, increasing the carbon content coated on the graphite surface can increase the content of inorganic components in the SEI film, improving the SEI's ability to transport Li ions and synergistically enhancing the material's fast charging capability. The inventors also found that reducing the carbon content coated on the graphite surface can reduce the irreversible consumption of active lithium caused by the high defect density of the graphite surface, thus improving the first-stage efficiency and thus the energy density of the cell. Moreover, reducing the carbon content coated on the graphite surface can promote the slippage between graphite powder particles, improving the tortuosity and compaction density of the electrode sheet, thereby increasing the battery's energy density.

[0037] The inventors also discovered that the uniformity of carbon coating on the graphite surface is another key parameter for ultra-fast-charging graphite materials. A uniformly coated carbon layer on the graphite surface promotes the uniform transport of ions and electrons. If the coating is uneven, differences in electronic conductivity and ion diffusion resistance may exist between particles within the negative electrode and in different regions of the same particle, leading to localized polarization, increasing the risk of lithium plating, and affecting battery safety and lifespan. Furthermore, the uniformity of carbon coating on the graphite surface is beneficial for forming a stable and uniform SEI film, and uniform coating at the same fast-charging capability can reduce the amount of coated carbon used, comprehensively reducing side reactions. In addition, the uniformity of carbon distribution on the graphite surface also affects the lithium-ion diffusion path; a uniform coating can reduce ion transport resistance and improve the battery's rate performance.

[0038] The inventors also discovered that, from an electrode design perspective, the tortuosity of the electrode can be controlled by designing and adjusting the material selection to construct a negative electrode that achieves both ultra-fast charging and sufficient energy density. By using a reasonable particle configuration, a suitable range of electrode tortuosity can be achieved to optimize and improve electrolyte diffusion, thus realizing the design of an ultra-fast charging negative electrode. Excessive tortuosity degrades kinetic performance and increases the difficulty of electrolyte wetting.

[0039] Based on the above analysis, this disclosure provides a graphite precision design combined with electrode tortuosity control technology. By designing the defect density of the graphite material surface and interface, and optimizing the electrode tortuosity through particle matching, high liquid phase diffusion of the negative electrode and ion transport at the graphite surface and interface are achieved, realizing the ultimate fast charging of the negative electrode while taking into account energy density.

[0040] In view of the above, the first aspect of this disclosure provides a negative electrode sheet. According to an embodiment of this disclosure, the negative electrode sheet includes a current collector and a negative electrode active material layer disposed on at least one side of the current collector. The negative electrode active material layer includes a first graphite and a second graphite. In the Raman peak fitting diagram of the graphite, there is a D peak corresponding to a defect site, a G1 peak corresponding to the sp2 in-plane vibration of amorphous carbon, and a G2 peak corresponding to the sp2 in-plane vibration of graphite. The ratio of the peak area of ​​the D peak to the sum of the peak areas of the G1 and G2 peaks is ID / IG. The average value of ID / IG of the first graphite ranges from 0.9 to 1.4 (e.g., it can be 0.9, 1.1, or 1.15). The values ​​of the second graphite are 1.2, 1.25, 1.3, 1.35, 1.4, etc.; the average value of the ID / IG of the second graphite is 0.05~0.45 (e.g., 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, etc.); the tortuosity of the negative electrode active material layer is 2.0%~8.0% (e.g., 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, etc.).

[0041] The beneficial effects that the negative electrode sheet proposed in this disclosure can achieve are described in detail below:

[0042] In this disclosure, the average ID / IG value of the first graphite represents the defect density on the surface of the first graphite. By limiting the average ID / IG value of the defect density of the first graphite to the range of 0.9 to 1.4, this disclosure can effectively increase the lithium-ion insertion and extraction sites, thereby improving the lithium insertion kinetics performance of the material; at the same time, it helps the rapid transport of lithium ions and reduces the resistance in the lithium insertion process, thereby achieving a faster charging speed; by controlling the defect density, it is possible to improve the fast charging performance while taking into account the energy density and cycle life of the battery. This range of defect density can provide sufficient lithium-ion insertion sites and avoid side reactions and structural degradation caused by excessive defects.

[0043] Meanwhile, to balance the tortuosity and high-temperature performance of the negative electrode active material layer, the negative electrode active material layer of this disclosure also includes a second graphite. The average ID / IG value of the second graphite represents the defect density on the surface of the second graphite. By limiting the average ID / IG value of the second graphite defect density to the range of 0.05 to 0.45, this disclosure helps to improve the tortuosity of the electrode, reduce the difficulty of electrolyte wetting, and optimize the lithium-ion transport path. Furthermore, it helps to reduce side reactions and improve the thermal and chemical stability of the material. This allows for the improvement of high-temperature performance and tortuosity optimization while simultaneously considering the interfacial stability of the electrode and the battery's initial efficiency and energy density. It should be noted that a lower defect density in the second graphite indicates a relatively more regular surface with fewer defects. Such graphite particles are more likely to slide within the electrode, thereby reducing interparticle friction. The improved particle sliding ability helps to form a more uniform particle distribution during electrode manufacturing, thus optimizing the tortuosity of the electrode. Meanwhile, the lower defect density of the second graphite particles allows for better filling of voids in the electrode during stacking. This optimized stacking method reduces irregular spaces within the electrode, keeping its tortuosity within a reasonable range. Furthermore, the lower defect density of the second graphite implies a more complete structure with fewer defects and pores. Under high-temperature conditions, this structural integrity reduces structural deformation caused by thermal expansion. For example, graphite materials with high defect density are prone to structural damage at high temperatures due to uneven thermal expansion at defects, while the low defect density of the second graphite effectively avoids this, thus improving the electrode's stability at high temperatures.

[0044] This disclosure utilizes a composite of first graphite (with a defect density ID / IG = 0.9~1.4) and second graphite (with a defect density ID / IG = 0.05~0.45) to form the negative electrode active material layer, optimizing the slippage between particles. This improves fast charging performance while also considering the battery's initial efficiency and energy density. This design fully leverages the characteristics of the two types of graphite, achieving comprehensive optimization of battery performance through synergy. Furthermore, from an electrode design perspective, by constructing a tortuosity that matches the fast charging capability of the negative electrode material through appropriate particle combinations, the fast charging performance of the negative electrode material can be maximized. This disclosure limits the tortuosity of the negative electrode active material layer to 2.0%~8.0%. By limiting the tortuosity of the negative electrode active material layer within this range, fast charging performance can be improved while also considering the battery's energy density and cycle stability. This disclosure, through the synergistic design of graphite composite and electrode tortuosity, fully leverages the characteristics of the two types of graphite and optimizes the electrode structure. This design not only improves the battery's fast charging performance but also considers energy density and initial efficiency.

[0045] In the embodiments of this disclosure, during the preparation of the negative electrode sheet, first graphite and second graphite with different ID / IG values ​​can be selected, and the mass ratio of the first graphite and second graphite can be controlled to regulate the ID / IG values ​​of the first graphite and second graphite in the formed negative electrode active material layer and the tortuosity of the negative electrode active material layer.

[0046] According to some preferred embodiments of this disclosure, the average ID / IG value of the first graphite is in the range of 1.05 to 1.25. Thus, by controlling the average defect density ID / IG value of the first graphite, the fast charging performance can be improved while further taking into account the energy density and cycle life of the battery. This range of defect density can provide sufficient lithium-ion insertion sites and avoid side reactions and structural degradation caused by excessive defects.

[0047] According to some preferred embodiments of this disclosure, the average ID / IG value of the second graphite is in the range of 0.08 to 0.15. Thus, by controlling the average ID / IG value of the defect density of the second graphite, it is possible to further improve the tortuosity of the electrode, reduce the difficulty of electrolyte wetting, and optimize the lithium ion transport path. At the same time, it is possible to further reduce side reactions and improve the thermal and chemical stability of the material. It is possible to improve high-temperature performance and tortuosity optimization while taking into account the conductivity of the electrode, interface stability and overall battery performance.

[0048] According to some specific embodiments of this disclosure, at least a portion of the surface of the first graphite is provided with a coating layer. By providing a coating layer on at least a portion of the surface of the first graphite, the defect density at the graphite surface can be effectively increased, the number of lithium intercalation sites on the graphite surface can be increased, and the battery kinetics can be improved. Moreover, the increased defect density can promote the increase of inorganic components in the SEI film, thereby facilitating the transport of lithium ions in the SEI film. Meanwhile, in order to take into account the tortuosity of the negative electrode active material layer, the negative electrode active material layer of this disclosure also includes a second graphite, the surface of which is not provided with a coating layer.

[0049] According to some further embodiments of this disclosure, the coating layer includes a carbon coating layer, wherein the carbon coating layer includes amorphous carbon. Those skilled in the art can use raw materials such as pitch and resin to form an amorphous carbon coating layer on at least a portion of the surface of the first graphite.

[0050] According to some specific embodiments of this disclosure, the discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 15% to 35%. σ represents the standard deviation of the ID / IG ratio at 100–1000 test points within the range of 0.5–2.0. The RSD (Relative Dispersion Tolerance) of the ID / IG ratio of the first graphite within the range of 0.45–2.0 characterizes the uniformity of carbon coating on the surface of the first graphite within the range of 100–1000 test points. By limiting the RSD of the ID / IG ratio of the first graphite within the range of 0.45–2.0 to 15%–35%, the uniformity of carbon coating on the first graphite surface can be ensured. Uniform carbon coating on the graphite surface promotes the formation of a stable and uniform SEI film. Furthermore, uniform coating under the same fast-charging capability can reduce the amount of residual coating material, thus comprehensively reducing side reactions. In addition, the uniformity of carbon distribution on the graphite surface also affects the lithium-ion diffusion path; good uniformity coating can reduce ion transport resistance and improve the battery's rate performance. Preferably, the discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 20% to 34%.

[0051] According to some further embodiments of this disclosure, in the Raman peak fitting plot of the first graphite, the full width at half maximum (FWHM) of the D peak is 0.5 m. D The full width at half maximum (FWHM) of peak G1 is 1000 m. G1 The full width at half maximum (FWHM) of peak G2 is 1000 m / s. G2 FWHM D / (FWHM G1 +FWHM G2 The range is 1.0~1.7, FWHM D / (FWHM G1 +FWHM G2This can characterize the uniformity of the carbon coating itself on the first graphite surface, through FWHM D / (FWHM G1 +FWHM G2 By limiting the value to the range of 1.0 to 1.7, the effects of carbon layer shedding and conductive agent interference can be effectively eliminated.

[0052] According to some specific embodiments of this disclosure, the percentage of test points with ID / IG in the range of 0 to 0.45 is less than or equal to 45% of the percentage of test points with ID / IG in the range of 0 to 2.0 (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.). By limiting the proportion of low defect density test points (i.e., test points with ID / IG in the range of 0 to 0.45), it can be ensured that most test points have a moderate defect density, which can avoid the decline in fast charging performance due to too few defects and reduce side reactions. Preferably, the percentage of test points with ID / IG in the range of 0 to 0.45 is 10% to 25% of the percentage of test points with ID / IG in the range of 0 to 2.0.

[0053] According to some specific embodiments of this disclosure, in the above-mentioned negative electrode active material layer, the mass of the second graphite accounts for less than 45% of the total mass of the first and second graphite (for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.). By limiting the mass ratio of the second graphite, it can be ensured that most of the graphite in the negative electrode active material layer has a moderate defect density, which can avoid the decrease in fast charging performance due to too few defects and reduce side reactions. Preferably, the mass of the second graphite accounts for 10% to 25% of the total mass of the first and second graphite.

[0054] In the embodiments of this disclosure, the ID / IG of the first graphite and the ID / IG of the second graphite can be tested using a forward testing method, and the ID / IG of the first graphite and the ID / IG of the second graphite can be tested using a reverse testing method, as detailed below:

[0055] Forward test: Place the negative electrode under test on a glass plate, and flatten it with another glass plate to form a flat test surface. Before the test begins, use a single-crystal silicon wafer (520nm). -1 Calibration wavenumber error (accuracy < 1 cm) -1 The laser beam was then examined for focusing. The laser wavelength was 532 nm, the attenuation power was 10%, and the scanning range was 100–3000 cm⁻¹. -1Exposure time was 10 seconds, repeated 3 times. The sample was observed under a 100x objective lens, and 100–1000 well-focused test points were selected for testing. Subsequently, intelligent polynomial baseline fitting was used to remove the test substrate. A 1355 cm⁻¹ was observed in the Raman spectrum of graphite. -1 The D peaks on the left and right and 1582 cm -1 The G peaks on the left and right are shown in Figure 1. This peak shape is a superposition of the surface amorphous carbon signal and the internal graphite signal. Through peak fitting, the D peak, G1 peak, and G2 peak can be obtained, as shown in Figure 2. The D peak corresponds to defects and disordered structures in graphite, the G1 peak corresponds to the in-plane vibration of sp2 carbon in amorphous carbon, and the G2 peak corresponds to the in-plane vibration of sp2 carbon in graphite. On each scan curve, the area ratio of the D peak to the (G1+G2) peak can be used as a characteristic index of the graphite defect content ID / IG. The average ID / IG value can be obtained by calculating the average of multiple test results. Furthermore, the half-width at half-maximum (WHM) of the D peak, the half-width at half-maximum (FWHM) of the G1 peak, and the half-width at half-maximum (FWHM) of the G2 peak can be obtained from the scan curve at each test point as characteristic indices. D / (FWHM G1 +FWHM G2 Additionally, a statistical method was used to calculate the percentage of test points with an ID / IG value between 0 and 0.45 compared to those with an ID / IG value between 0 and 2.0. It should be noted that test points with an ID / IG value ≥ 0.45 can be considered as first-grade graphite, while those with an ID / IG value < 0.45 can be considered as second-grade graphite.

[0056] Reverse test: The negative electrode is placed in a 0.5M HCl solution. Stirring or ultrasonic treatment accelerates the dissolution process, removing the Cu foil, SBR and CMC from the coating layer, and the SEI film from the carbon material. The solution and insoluble components are then separated by filtration or centrifugation. The insoluble components are dried and ground into fine particles of a specific size. These particles are then mixed with an appropriate amount of solvent or dispersant and ultrasonically treated in an ultrasonic bath or using an ultrasonic probe to form a homogeneous suspension. During ultrasonic treatment, slight aggregation and dispersion occur due to the different properties of graphite and carbon black particles. After ultrasonication, the sample is centrifuged. Adjusting the centrifugation rate separates the graphite from the carbon black. After drying the graphite powder, a Raman test is performed. Subsequent procedures are the same as for the forward test and will not be repeated here.

[0057] In embodiments of this disclosure, the tortuosity of the negative electrode active material layer can be tested using electrochemical impedance spectroscopy, specifically:

[0058] The formula for calculating tortuosity can be obtained by rearranging the MacMullin equation and Ohm's law: Where A is the cross-sectional area of ​​the negative electrode active material layer, κ is the conductivity of the electrolyte, d is the thickness of the negative electrode active material layer, and ε is the porosity of the negative electrode active material layer (which can be obtained from mercury porosimetry data). Therefore, the ion transport impedance (R) can be used to determine the cross-sectional area of ​​the negative electrode active material layer. ion To calculate R, ion The calculation method is as follows:

[0059] (1) Assemble a symmetrical battery. Take small negative electrode discs of the same size and assemble a symmetrical battery according to the structure of electrode + separator + electrolyte.

[0060] (2) Perform electrochemical impedance spectroscopy test, frequency range: 10 mHz-1 kHz high-frequency impedance (>10 Hz), and perform circuit fitting based on component B2 to obtain R. ion The value was then used to further calculate the tortuosity of the negative electrode active material layer.

[0061] The porosity ε can be tested using the mercury intrusion porosimetry method, including the following steps: ① Load 2g ± 0.1g of negative electrode sample into a sample tube. ② Place the sample tube in a low-pressure station and evacuate (vacuum degree < 5Pa). ③ Inject mercury, ensuring the sample tube is completely filled up to the capillary. ④ Introduce nitrogen gas to pressurize to 30 psia, remove the sample tube from the low-pressure station, and weigh it. ⑤ Place the sample tube in a high-pressure station and maintain a constant pressure of 15 psia. ⑥ Test, with an upper limit of 30,000 psia. In addition to 30 points for each order of magnitude, 30 points are required for the range of 1000~10,000 psia. ⑦ Data processing: calibrate the porosity measured by the mercury intrusion porosimetry. Consider the mercury injection volume at 10 psia as the interstitial volume between the continuous macroscopic surface of the sample and the liquid mercury interface. calibrate the sample pore volume and sample volume measured by the mercury intrusion porosimetry, and calculate the true porosity ε of the negative electrode active material layer using the following formula. V p =V Hg -V Hg,10psia V sam =V Hg / ε sam -V Hg Among them, V p Indicates the sample pore volume; V sam Indicates sample volume; h sam The sample thickness is indicated by a thickness gauge; hc represents the thickness of the negative electrode active material layer (measured by a thickness gauge); V Hg Indicates the upper limit of mercury pressure in the equipment; V Hg,10psia Indicates mercury pressure at 10 psia; ε sam This indicates the porosity of the sample as given by the equipment test.

[0062] According to some specific embodiments of this disclosure, the areal density of the negative electrode active material layer on one side of the current collector is 80 g / m².2 ~150g / m 2 (For example, it can be 80g / m 2 90g / m 2 100g / m 2 110g / m 2 120g / m 2 130g / m 2 140g / m 2 150g / m 2 By limiting the areal density of the negative electrode active material layer on one side of the current collector to the aforementioned range, it is possible to improve fast charging performance, reduce internal resistance, and increase cycle life while simultaneously ensuring battery energy density and safety. Preferably, the areal density of the negative electrode active material layer on one side of the current collector is 85 g / m³. 2 ~125g / m 2 .

[0063] According to some specific embodiments of this disclosure, the compaction density of the negative electrode active material layer on one side of the current collector is 1.45 g / cm³. 3 ~1.8g / cm 3 (For example, it can be 1.45g / cm) 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 By limiting the compaction density of the negative electrode active material layer on one side of the current collector to the aforementioned range, it is possible to improve fast charging performance, reduce internal resistance, and increase cycle life while simultaneously ensuring battery energy density and safety. Preferably, the compaction density of the negative electrode active material layer on one side of the current collector is 1.5 g / cm³. 3 ~1.65g / cm 3 .

[0064] In the embodiments of this disclosure, the method for testing the areal density and compaction density of the negative electrode active material layer on one side of the current collector is as follows:

[0065] Areal density: Cut the negative electrode sheet into small circular pieces of a certain size, measure the weight of the negative electrode coating per unit area of ​​the small circular piece, and calculate the areal density.

[0066] Compacted density: Cut the negative electrode sheet into small circular pieces of a certain size, measure the weight of the negative electrode dressing per unit area of ​​the small circular piece, calculate the areal density, and measure the thickness of the negative electrode dressing. The compacted density is obtained by calculating the negative electrode sheet areal density / (electrode sheet thickness - current collector thickness).

[0067] According to some specific embodiments of this disclosure, the first graphite and the second graphite respectively include at least one of artificial graphite and natural graphite. Natural graphite has low cost and high specific capacity, while artificial graphite has good cycle performance and excellent fast-charging performance. A suitable graphite material can be selected according to the requirements.

[0068] In embodiments of this disclosure, the aforementioned negative electrode active material layer may include a binder in addition to the negative electrode active material (i.e., the first graphite and the second graphite). In some cases, it may also include a conductive agent and other additives. The binder and conductive agent are conventional choices in the battery field. Exemplary binders include, but are not limited to, one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyolefins (such as polypropylene, polyethylene, etc.), carboxymethyl cellulose (CMC), sodium alginate, etc. Conductive agents include, but are not limited to, one or more of carbon nanotubes, carbon black, graphene, carbon fibers, acetylene black, Ketjen black, graphite flakes, etc. Other additives include, but are not limited to, one or more of mesoporous silica, mesoporous alumina, silica microspheres, alumina nanoparticles, etc.

[0069] The aforementioned negative electrode sheet can be obtained by coating a slurry containing negative electrode active material, binder, and optionally conductive agent onto a negative electrode current collector using a normal slurry coating process, followed by drying and rolling. The negative electrode current collector can be single-sided or double-sided coated. In other words, one surface of the negative electrode current collector can have a negative electrode active coating, or both opposite surfaces of the negative electrode current collector can have a negative electrode active material coating. When the negative electrode current collector is double-sided coated, it is sufficient as long as the design of the negative electrode active material layer on either side meets the aforementioned scheme of this disclosure. The current collector carrying the negative electrode active material layer can include, but is not limited to, any of the following: copper foil, composite copper foil, carbon-coated copper foil, aluminum foil, composite aluminum foil, carbon-coated aluminum foil, stainless steel foil, copper alloy foil, copper-plated film, etc.

[0070] A second aspect of this disclosure provides a battery. According to an embodiment of this disclosure, the battery includes the negative electrode sheet of the first aspect. Therefore, the battery of this disclosure has good fast-charging capability and high energy density and initial efficiency.

[0071] The aforementioned battery also includes a positive electrode, a separator, and an electrolyte disposed between the positive and negative electrodes. The specific type of battery is not particularly limited, and includes, but is not limited to, lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries.

[0072] In embodiments of this disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, a binder, and an optional conductive agent. The positive active material for lithium-ion batteries may include, but is not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), and lithium phosphates with an olivine structure (such as lithium iron phosphate (LFP) and lithium manganese iron phosphate (LFMP)).

[0073] The battery further includes a separator, which is disposed between the positive electrode and the negative electrode to isolate the positive and negative electrodes. This disclosure does not limit the type of separator; any separator material from existing batteries can be used. Examples include, but are not limited to, single-layer PP (polypropylene) membranes, single-layer PE (polyethylene) membranes, double-layer PP / PE membranes, double-layer PP / PP membranes, and triple-layer PP / PE / PP membranes.

[0074] In the embodiments of this disclosure, the battery further includes an electrolyte, which includes an electrolyte salt and a solvent. The specific types and components of the electrolyte salt and the organic solvent are not specifically limited and can be selected according to actual needs.

[0075] The batteries disclosed herein may be in the form of individual battery cells, battery modules, and battery packs. In some embodiments, individual battery cells may be assembled into battery modules, and a battery module may contain one or more battery cells, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into battery packs, and a battery pack may contain one or more battery modules, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0076] A third aspect of this disclosure provides an electrical device. According to an embodiment of this disclosure, the electrical device includes the battery of the second aspect. Therefore, because the electrical device uses the aforementioned battery, the battery of the electrical device has good fast-charging capability and high energy density and initial efficiency. The features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0077] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0078] As electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0079] One possible implementation method for the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery for this electrical device, a battery pack or battery module can be used.

[0080] Another implementation method could be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a single battery cell as its power source.

[0081] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0082] The embodiments of this disclosure are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0083] Example 1

[0084] This embodiment provides a method for preparing a lithium secondary battery, including:

[0085] 1) Preparation of positive electrode:

[0086] Lithium iron phosphate, carbon black, and PVDF are mixed in a mass ratio of 96:2:2. The mixed powder is placed in a vacuum mixer, and N-methylpyrrolidone (NMP) is added as solvent. The mixture is stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry is sieved (through a 200-mesh sieve) and coated onto aluminum foil for the positive electrode current collector. After drying in an oven at 120°C, the positive electrode sheet is obtained by rolling and slitting.

[0087] 2) Electrolyte preparation:

[0088] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. 1 wt% of vinylene carbonate (VC) was added to the mixed solvent, and then dry lithium salt LiPF6 was added to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0089] 3) Preparation of negative electrode sheet:

[0090] The negative electrode active material, conductive agent carbon black, thickener CMC and binder SBR are mixed in a solid mass ratio of 100:1:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain a negative electrode slurry. The negative electrode slurry is sieved (through a 200-mesh sieve) and then coated onto the negative electrode current collector aluminum foil. After drying in an oven at 105°C, it is then rolled and slit to obtain the negative electrode sheet.

[0091] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.14, the average ID / IG value of the second graphite is 0.12, and the mass ratio of the first graphite to the second graphite is 80:20.

[0092] 4) Assemble the battery:

[0093] In an argon-filled glove box, the positive electrode, separator (specifically a polyethylene film), and negative electrode are stacked in sequence to obtain a battery cell. The separator must completely isolate the positive and negative electrode. The stacked battery cell is then placed into an aluminum-plastic film soft package and injected with the electrolyte. After vacuum sealing, settling, formation, cutting, and sealing, a 2Ah lithium-ion battery is obtained.

[0094] Example 2

[0095] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0096] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.05, the average ID / IG value of the second graphite is 0.09, and the mass ratio of the first graphite to the second graphite is 90:10.

[0097] Example 3

[0098] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0099] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.12, the average ID / IG value of the second graphite is 0.11, and the mass ratio of the first graphite to the second graphite is 85:15.

[0100] Example 4

[0101] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0102] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.19, the average ID / IG value of the second graphite is 0.14, and the mass ratio of the first graphite to the second graphite is 80:20.

[0103] Example 5

[0104] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0105] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.25, the average ID / IG value of the second graphite is 0.15, and the mass ratio of the first graphite to the second graphite is 75:25.

[0106] Example 6

[0107] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0108] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 0.95, the average ID / IG value of the second graphite is 0.05, and the mass ratio of the first graphite to the second graphite is 95:5.

[0109] Example 7

[0110] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0111] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.03, the average ID / IG value of the second graphite is 0.08, and the mass ratio of the first graphite to the second graphite is 95:5.

[0112] Example 8

[0113] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0114] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.28, the average ID / IG value of the second graphite is 0.22, and the mass ratio of the first graphite to the second graphite is 70:30.

[0115] Example 9

[0116] The preparation method in this embodiment is basically the same as that in Example 1, the difference being in the negative electrode active material:

[0117] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.35, the average ID / IG value of the second graphite is 0.35, and the mass ratio of the first graphite to the second graphite is 65:35.

[0118] Example 10

[0119] The preparation method of this embodiment is basically the same as that of Example 1, except that the areal density and compaction density of the negative electrode sheet are as shown in Table 1 by adjusting the amount of negative electrode slurry coated on the negative electrode current collector aluminum foil and the rolling pressure.

[0120] Example 11

[0121] The preparation method of this embodiment is basically the same as that of Example 1, except that the areal density and compaction density of the negative electrode sheet are as shown in Table 1 by adjusting the amount of negative electrode slurry coated on the negative electrode current collector aluminum foil and the rolling pressure.

[0122] Comparative Example 1

[0123] The preparation method of this comparative example is basically the same as that of Example 1, except for the negative electrode active material:

[0124] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 0.52, the average ID / IG value of the second graphite is 0.01, and the mass ratio of the first graphite to the second graphite is 40:60.

[0125] Comparative Example 2

[0126] The preparation method of this comparative example is basically the same as that of Example 1, except for the negative electrode active material:

[0127] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 0.73, the average ID / IG value of the second graphite is 0.03, and the mass ratio of the first graphite to the second graphite is 35:65.

[0128] Comparative Example 3

[0129] The preparation method of this comparative example is basically the same as that of Example 1, except for the negative electrode active material:

[0130] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.53, the average ID / IG value of the second graphite is 0.01, and the mass ratio of the first graphite to the second graphite is 80:20.

[0131] Comparative Example 4

[0132] The preparation method of this comparative example is basically the same as that of Example 1, except for the negative electrode active material:

[0133] The negative electrode active material includes a first graphite and a second graphite. The surface of the first graphite is provided with an amorphous carbon coating layer, while the surface of the second graphite is not provided with a coating layer. The average ID / IG value of the first graphite is 1.71, the average ID / IG value of the second graphite is 0.03, and the mass ratio of the first graphite to the second graphite is 80:20.

[0134] The ID / IG ratio of the negative electrode sheets of Examples 1-11 and Comparative Examples 1-4 were tested respectively, and the test results are shown in Table 1. The test method is as follows:

[0135] The negative electrode to be tested is placed on a glass plate and flattened with another glass plate to form a flat test surface. Before the test begins, a single-crystal silicon wafer (520nm) is used. -1 Calibration wavenumber error (accuracy < 1 cm) -1 The laser beam was then examined for focusing. The laser wavelength was 532 nm, the attenuation power was 10%, and the scanning range was 100–3000 cm⁻¹. -1 Exposure time was 10 seconds, repeated 3 times. The sample was observed under a 100x objective lens, and 100 well-focused test points were selected for testing. Subsequently, intelligent polynomial baseline fitting was used to remove the test substrate. A 1355 cm⁻¹ diameter was observed in the Raman spectrum of graphite. -1 The D peaks on the left and right and 1582 cm -1 The G peaks on the left and right are shown in Figure 1. This peak shape is a superposition of the surface amorphous carbon signal and the internal graphite signal. Through peak fitting, the D peak, G1 peak, and G2 peak can be obtained, as shown in Figure 2. The D peak corresponds to defects and disordered structures in graphite, the G1 peak corresponds to the in-plane vibration of sp2 carbon in amorphous carbon, and the G2 peak corresponds to the in-plane vibration of sp2 carbon in graphite. On each scan curve, the area ratio of the D peak to the (G1+G2) peak can be used as a characteristic index of the graphite defect content ID / IG. The average ID / IG value can be obtained by calculating the average of multiple test results. Furthermore, the half-width at half-maximum (WHM) of the D peak, the half-width at half-maximum (FWHM) of the G1 peak, and the half-width at half-maximum (FWHM) of the G2 peak can be obtained from the scan curve at each test point as characteristic indices. D / (FWHM G1 +FWHMG2 In addition, statistical methods were used to calculate the percentage of test points with ID / IG in the range of 0 to 0.45 out of the total number of test points with ID / IG in the range of 0 to 2.0.

[0136] The discrete distribution tolerance of ID / IG for the first graphite in the range of 0.45 to 2.0 , where σ is the standard deviation of the test data for 100 test points ID / IG in the range of 0.45 to 2.0.

[0137] Figure 1 shows the Raman spectrum of one test point in Example 1 (ID / IG≥0.45), Figure 2 shows the peak fitting diagram of Figure 1, Figure 3 shows the Raman spectrum of another test point in Example 1 (ID / IG<0.45), and Figure 4 shows the peak fitting diagram of Figure 3.

[0138] The tortuosity of the negative electrode active material layers in Examples 1-11 and Comparative Examples 1-4 was tested, and the test results are shown in Table 1. The test methods are as follows:

[0139] The formula for calculating tortuosity can be obtained by rearranging the MacMullin equation and Ohm's law: Where A is the cross-sectional area of ​​the negative electrode active material layer, κ is the conductivity of the electrolyte, d is the thickness of the negative electrode active material layer, and ε is the porosity of the negative electrode active material layer (which can be obtained from mercury porosimetry data). Therefore, the ion transport impedance (R) can be used to determine the cross-sectional area of ​​the negative electrode active material layer. ion To calculate R, ion The calculation method is as follows:

[0140] (1) Assemble a symmetrical battery. Take small negative electrode discs of the same size and assemble a symmetrical battery according to the structure of electrode + separator + electrolyte.

[0141] (2) Perform electrochemical impedance spectroscopy test, frequency range: 10 mHz-1 kHz high-frequency impedance (>10 Hz), and perform circuit fitting based on component B2 to obtain R. ion The value was then used to further calculate the tortuosity of the negative electrode active material layer.

[0142] The porosity ε can be tested using the mercury intrusion porosimetry method, including the following steps: ① Load 2g ± 0.1g of negative electrode sample into a sample tube. ② Place the sample tube in a low-pressure station and evacuate (vacuum degree < 5Pa). ③ Inject mercury, ensuring the sample tube is completely filled up to the capillary. ④ Introduce nitrogen gas to pressurize to 30 psia, remove the sample tube from the low-pressure station, and weigh it. ⑤ Place the sample tube in a high-pressure station and maintain a constant pressure of 15 psia. ⑥ Test, with an upper limit of 30,000 psia. In addition to 30 points for each order of magnitude, 30 points are required for the range of 1000~10,000 psia. ⑦ Data processing: calibrate the porosity measured by the mercury intrusion porosimetry. Consider the mercury injection volume at 10 psia as the interstitial volume between the continuous macroscopic surface of the sample and the liquid mercury interface. calibrate the sample pore volume and sample volume measured by the mercury intrusion porosimetry, and calculate the true porosity of the negative electrode active material layer using the following formula. Porosity V p =V Hg -V Hg,10psia V sam =V Hg / ε sam -V Hg Among them, V p Indicates the sample pore volume; V sam Indicates sample volume; h sam The sample thickness is indicated by a thickness gauge; hc represents the thickness of the negative electrode active material layer (measured by a thickness gauge); V Hg Indicates the upper limit of mercury pressure in the equipment; V Hg,10psia Indicates mercury pressure at 10 psia; ε sam This indicates the porosity of the sample as given by the equipment test.

[0143] The areal density and compaction density of the negative electrode sheets of Examples 1-11 and Comparative Examples 1-4 were tested respectively, and the test results are shown in Table 1. The test methods are as follows:

[0144] Areal density: Cut the negative electrode sheet into small circular pieces of a certain size, measure the weight of the negative electrode coating per unit area of ​​the small circular piece, and calculate the areal density;

[0145] Compacted density: Cut the negative electrode sheet into small circular pieces of a certain size, measure the weight of the negative electrode dressing per unit area of ​​the small circular piece, calculate the areal density, and measure the thickness of the negative electrode dressing. The compacted density is obtained by calculating the negative electrode sheet areal density / (electrode sheet thickness - current collector thickness).

[0146] Table 1

[0147]

[0148] It should be noted that, in the same embodiment, when the ID / IG of the test point is ≥ 0.45, it can be identified as the first graphite, and when the ID / IG of the test point is < 0.45, it can be identified as the second graphite.

[0149] The initial efficiency, rate charge ratio, and volumetric energy density of the batteries prepared in Examples 1-11 and Comparative Examples 1-4 were tested respectively, and the test results are shown in Table 2. The test methods are as follows:

[0150] First-effect test method:

[0151] After the battery was filled with electrolyte, it was charged to 3.8V at 0.33C, and the charging capacity was recorded as C. 化成容量 Subsequently, at 45 o The sample was aged for 24 hours at a constant temperature of C. After aging, it was discharged to 2.0V at 0.33C, and the discharge capacity was recorded as C. 分容容量 According to the formula, first-effect = C 分容容量 / C 化成容量 The first effect was calculated.

[0152] Method for testing the rate of charge:

[0153] In a constant temperature environment of 25℃, the battery was charged at a constant current of 4C and 0.33C to 3.8V, and then left to rest for 10 minutes; subsequently, it was discharged at 0.33C to 2.0V, and the specific capacity at 4C and 0.33C was recorded. Calculate the 4C charging rate.

[0154] The method for testing volumetric energy density is as follows:

[0155] At 25°C, the volume of a battery composed of a negative electrode, separator, and positive electrode was measured using the water displacement method and recorded as the cell volume. Under the same conditions, each lithium-ion battery was first charged at 1 / 3C and then discharged at 1 / 3C (voltage range 2V-3.8V), and the actual discharge amount was recorded. The product of the actual discharge amount at 1 / 3C and the average voltage during discharge is the battery's energy. The ratio of this energy to the cell volume is the actual energy density of the cell using the negative electrode.

[0156] Table 2

[0157]

[0158] As can be seen from Table 1, compared with Comparative Examples 1-4, Examples 1-11 have better overall performance in terms of first-time efficiency, rate-of-charge ratio, and volumetric energy density. It is evident that only by limiting the average ID / IG value of the first graphite to the range of 0.9-1.4, the average ID / IG value of the second graphite to the range of 0.05-0.45, and the tortuosity of the negative electrode active material layer to the range of 2.0%-8.0%, can the fast-charging performance be improved while taking into account the first-time efficiency and energy density.

[0159] As can be seen from Table 1, compared with Examples 6-9, Examples 1-5 have superior overall performance in terms of first-time efficiency, rate-of-charge ratio, and volumetric energy density. It is evident that when the average ID / IG value of the first graphite is in the range of 1.05-1.25, the average ID / IG value of the second graphite is limited to the range of 0.08-0.15, the RSD of the dispersion distribution of the ID / IG of the first graphite in the range of 0.45-2.0 is in the range of 20%-34%, and the percentage of test points with ID / IG in the range of 0-0.45 to the total number of test points with ID / IG in the range of 0-2.0 is in the range of 10%-25%, it is possible to further improve fast charging performance while also taking into account first-time efficiency and energy density.

[0160] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0161] Although embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A negative electrode, wherein, It includes a current collector and a negative electrode active material layer disposed on at least one side of the current collector, wherein the negative electrode active material layer includes a first graphite and a second graphite; In the Raman peak fitting diagram of graphite, there is a D peak corresponding to the defect site, a G1 peak corresponding to the sp2 in-plane vibration of amorphous carbon, and a G2 peak corresponding to the sp2 in-plane vibration of graphite. The ratio of the peak area of ​​the D peak to the sum of the peak areas of the G1 peak and the G2 peak is ID / IG. The average ID / IG value of the first graphite ranges from 0.9 to 1.4; The average ID / IG value of the second graphite ranges from 0.05 to 0.45; The tortuosity of the negative electrode active material layer is 2.0%~8.0%.

2. The negative electrode sheet according to claim 1, wherein, The first graphite has a coating layer on at least a portion of its surface, while the second graphite does not have a coating layer on its surface.

3. The negative electrode sheet according to claim 2, wherein, The coating layer includes a carbon coating layer, and the carbon coating layer includes amorphous carbon.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein, The average ID / IG value of the first graphite ranges from 1.05 to 1.

25.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein, The average ID / IG value of the second graphite ranges from 0.08 to 0.

15.

6. The negative electrode sheet according to any one of claims 3 to 5, wherein, The discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 15% to 35%.

7. The negative electrode sheet according to claim 6, wherein, The discrete distribution tolerance RSD of the ID / IG of the first graphite in the range of 0.45 to 2.0 is 20% to 34%.

8. The negative electrode sheet according to any one of claims 3 to 7, wherein, In the Raman peak fitting plot of the first graphite, the full width at half maximum (FWHM) of peak D is 1000 m / s. D The full width at half maximum (FWHM) of peak G1 is 1000 m. G1 The full width at half maximum (FWHM) of peak G2 is 1000 m / s. G2 FWHM D / (FWHM G1 +FWHM G2 The range is 1.0 to 1.

7.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein, The percentage of test points with ID / IG in the range of 0 to 0.45 is less than or equal to 45% of the percentage of test points with ID / IG in the range of 0 to 2.

0.

10. The negative electrode according to claim 9, wherein, The percentage of test points with ID / IG in the range of 0 to 0.45 is 10% to 25% of the percentage of test points with ID / IG in the range of 0 to 2.

0.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein, The areal density of the negative electrode active material layer on one side of the current collector is 80 g / m³. 2 ~150g / m 2 .

12. The negative electrode sheet according to any one of claims 1 to 11, wherein, The compaction density of the negative electrode active material layer on one side of the current collector is 1.45 g / cm³. 3 ~1.8g / cm 3 .

13. The negative electrode sheet according to any one of claims 1 to 12, wherein, The first graphite and the second graphite each comprise at least one of artificial graphite and natural graphite.

14. A battery, wherein, The negative electrode sheet includes any one of claims 1 to 13.

15. An electrical appliance, wherein, Includes the battery as described in claim 14.

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