Secondary battery and electric apparatus

Abstract

The present disclosure provides a secondary battery and an electric apparatus. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface. The thickness of the negative electrode film layer is denoted as H, the region from the second surface of the negative electrode film layer to the thickness range of 0.3 H is denoted as a first region of the negative electrode film layer, and the region from the first surface of the negative electrode film layer to the thickness range of 0.3 H is denoted as a second region of the negative electrode film layer. ID / IG of an active material in the second region is greater than ID / IG of an active material in the first region. ID / IG is the ratio of the D peak intensity and the G peak intensity obtained by Raman mapping. ID represents the D peak intensity of a Raman spectrum at 1350±100 cm-1, and IG represents the G peak intensity of the Raman spectrum at 1580±100 cm-1.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] The present disclosure claims priority to Chinese Patent Application No. 202311679328.6, filed on December 7, 2023, entitled “Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure belongs to the field of battery technology, and particularly relates to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As the scope of secondary battery applications expands, people are facing severe challenges in their performance. For example, they are required to balance various performance requirements such as energy density, dynamic performance, and service life. However, the existing technology faces the following problems: when improving the dynamic performance of secondary batteries, it is often difficult to take into account the cycle life of secondary batteries; when improving the energy density of secondary batteries, it is often at the expense of the dynamic performance and service life of secondary batteries.

[0005] Summary of the Invention

[0006] The present disclosure is developed in view of the above technical problems, and its object is to provide a secondary battery with both long cycle life and high energy density.

[0007] According to a first aspect of the present disclosure, a secondary battery is provided, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface disposed opposite to the first surface, the thickness of the negative electrode film layer being denoted as H, the region within a thickness range from the second surface of the negative electrode film layer to 0.3H being denoted as the first region of the negative electrode film layer, the region within a thickness range from the first surface of the negative electrode film layer to 0.3H being denoted as the second region of the negative electrode film layer, and the I of the active material in the second region being 1. D / I G Greater than the I of the active material in the first region D / I G , I D / I G is the ratio of the D peak intensity to the G peak intensity of the Raman spectrum, I D Indicates that the Raman spectrum is at 1350±100cm -1The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

[0008] Raman spectroscopy I D / I G It can be used to characterize the disorder degree of the surface of the active material. It can be understood that the first region and the second region each include at least one active material. D / I G Greater than the I of the active material in the first region D / I G This does not mean that the I of each active material in the second region D / I G The I of any active material in the first region must be greater than D / I G The I of the active material in the negative electrode sheet located in the second region away from the current collector D / I G Greater than the I of the active material in the first region D / I G , which means that the active material in the second region outside the electrode has a higher average disorder degree than the active material in the first region. In materials with high disorder, active ions are more easily embedded in and extracted from the active material, which can effectively reduce the volume expansion during the ion extraction process and improve the battery's cycle performance. At the same time, the electrolyte is also more likely to penetrate the active material, thereby improving the battery's kinetic performance. The I of the active material in the first region near the current collector in the negative electrode is D / I G The active material has a higher capacity and is easy to be compacted during the cold pressing process, which improves the compaction of the pole piece and achieves a high energy density of the secondary battery. D / I G The single-layer electrode sheet, made from a mixture of active materials, utilizes a double-layer design to achieve the same battery energy density with a lower negative electrode film thickness, further overcoming the issues of excessively long transmission paths and reduced battery dynamics associated with thicker negative electrode films. As a result, this secondary battery achieves improved cycling stability and kinetic performance while maintaining a balanced energy density.

[0009] In any embodiment of the present disclosure, the active material in the second region has an I D / I G I of the active material in the first region D / I G The difference ΔK satisfies: 0<ΔK≤0.4, and can be selected as 0.1≤ΔK≤0.25.

[0010] I of the active material in the second region D / I G I of the active material in the first region D / I G The secondary battery with the difference ΔK within the above range can more effectively take into account the cycle stability, dynamic performance and battery capacity of the battery.

[0011] In any embodiment of the present disclosure, the active material in the first region has an I D / I G Less than or equal to 0.14, optionally 0.05-0.1; and / or, the I of the active material in the second region D / I G Greater than or equal to 0.1, optional range is 0.2-0.35.

[0012] I of the active material in the first region D / I G I of the active material in the second region D / I G In the appropriate range, secondary batteries can better improve the cycle stability and kinetic performance of the battery.

[0013] In any embodiment of the present disclosure, the particle size distribution (Dv90-Dv10) / Dv50 of the active material in the second region is greater than the particle size distribution (Dv90-Dv10) / Dv50 of the active material in the first region.

[0014] The active material in the second region of the negative electrode sheet away from the current collector has a larger particle size distribution, which is beneficial to the infiltration of the electrolyte in the negative electrode sheet and improves the kinetic performance; while the active material in the first region close to the current collector side has a smaller particle size distribution, which is beneficial to obtain tightly packed negative electrode active materials and improve the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the active material during the cold pressing process, further improving the integrity of the active material during the processing process, and improving the cycle stability of the battery.

[0015] In any embodiment of the present disclosure, the degree of graphitization of the active material in the second region is less than the degree of graphitization of the active material in the first region.

[0016] Active materials with low graphitization often have larger interlayer spacing, which facilitates the deintercalation of active ions. Active materials with low graphitization in the second region of the negative electrode, away from the current collector, can improve battery kinetics while minimizing the volume expansion of the electrode caused by the deintercalation of active ions, ultimately improving the battery's cycling stability.

[0017] In any embodiment of the present disclosure, the number ratio of primary particles of the active material in the second region is higher than the number ratio of primary particles of the active material in the first region.

[0018] Having a higher primary particle content in the second region of the negative electrode plate away from the current collector side is beneficial to improving the particle integrity of the plate during the cold pressing process, reducing the generation of new interfaces, reducing the consumption of active lithium during the cycle, and further improving the cycle stability of the secondary battery.

[0019] In any embodiment of the present disclosure, the active material in the first region includes a first graphite material, the first particle body of the first graphite material includes an internal region and a surface region that at least partially surrounds the internal region, the surface region refers to a region extending 30 nm from the surface of the first particle body of the first graphite material to the interior of the particle, and the surface region includes a disordered layer.

[0020] In any embodiment of the present disclosure, the thickness of the disordered layer is 1 nm-20 nm.

[0021] Different from the active material with disordered layer coated on the surface of graphite particle, the disordered layer of the first graphite material is part of the graphite particle body, that is, the disordered layer structure in the surface region of the first graphite material and the other parts of the first graphite material are derived from the same precursor, which makes the disordered layer of the first graphite material have high uniformity and extremely thin thickness. The first graphite material has a disordered layer on the surface and has a low I D / I G .

[0022] The disordered layer mainly includes amorphous carbon. The carbon atoms in the amorphous carbon structure have no regular arrangement, which makes the interaction between its molecules more complex, resulting in it having higher strength and hardness than the graphite crystals in the internal area. The probability of surface damage of the graphite particles due to friction between particles and between particles and the mixing tank during the preparation of the slurry is reduced, and the risk of cracking of the negative electrode active material particles and exposing new interfaces during the cold pressing of the pole piece is reduced, so that the graphite material maintains a higher degree of integrity during the manufacturing process. Graphite materials with high particle integrity have fewer surface defects and have a good interface with the electrolyte. They can effectively reduce the side reactions between the negative electrode and the electrolyte, reduce the loss of active lithium, and improve the cycle stability of the battery. At the same time, the first graphite material will not sacrifice the capacity of the graphite material and the energy density of the battery because of the excessive disorder of its surface layer. It can improve the cycle stability of the battery while taking into account the energy density of the battery.

[0023] In any embodiment of the present disclosure, the active material in the second region includes a second graphite material, the second graphite material includes a second particle body and a coating layer at least partially coating a surface of the second particle body, and the coating layer includes amorphous carbon.

[0024] The coating layer on the surface of the second graphite material can greatly increase the surface disorder of the active material in the second region. The highly disordered surface of the second graphite material makes it easier for active ions to be deintercalated, reduces the volume expansion during the deintercalation process of active ions, and further improves the dynamic performance of the battery.

[0025] In any embodiment of the present disclosure, the powder compaction density of the second graphite material under a pressure of 49000N is 1.60g / cm 3 -1.80g / cm 3 .

[0026] Graphite materials with high surface disorder often have high surface strength and hardness, making them difficult to compact under pressure and resulting in a low powder compaction density. This second graphite material, while maintaining a high powder compaction density while possessing high surface disorder, helps to increase the ultimate compaction density of the electrode, thereby further improving the energy density of the battery.

[0027] In any embodiment of the present disclosure, the specific surface area of ​​the first graphite material is 1.0 m 2 / g-1.8m 2 / g, optional 1.1m 2 / g-1.7m 2 / g.

[0028] The low specific surface area of ​​the first graphite material helps to further reduce the degree of side reactions of the active material and improve the cycle life of the secondary battery.

[0029] In any embodiment of the present disclosure, the volume distribution particle size Dv50 of the first graphite material is 7.0 μm-14.0 μm, and optionally 8.0 μm-12.0 μm.

[0030] In any embodiment of the present disclosure, the particle size distribution of the first graphite material (Dv90-Dv10) / Dv50 is 1.0-1.4, and can be optionally 1.1-1.3.

[0031] Controlling the particle size distribution of the first graphite material within the above range is conducive to obtaining tightly packed negative electrode active materials and improving the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the active material during the cold pressing process, and further improving the integrity of the active material during the processing process; and the small stress inside the first graphite material particles is conducive to maintaining the long-period pore structure of the electrode sheet during the cycle, and can maintain the original pore structure of the electrode sheet during the cycle, so that the lithium ion insertion path remains unobstructed, while reducing the re-filming of the negative electrode active material during the charging process, improving the dynamic performance and cycle life. Furthermore, the particle size distribution within the above range can also improve the uniformity of lithium insertion between particles, reduce polarization, avoid lithium precipitation caused by uneven current density, and is conducive to achieving long-term cycle stability. In addition, the particle size distribution within the above range also helps to improve the processing performance of the electrode sheet, and will not affect the uniformity of slurry stirring due to excessive small-sized particles in the first graphite material, which is conducive to improving the uniformity and stability of the electrode sheet quality and helping to achieve long-term cycle stability.

[0032] In any embodiment of the present disclosure, the gram capacity of the first graphite material is 345 mAh / g-355 mAh / g, and can be optionally 347 mAh / g-353 mAh / g.

[0033] The first graphite material with a gram capacity within the above range will not undergo significant lattice expansion during the charge and discharge process due to its excessively high graphitization; nor will it be difficult to compact the material due to its low graphitization. In order to achieve the same electrode compaction density, a higher cold pressing pressure is required, which will cause cracks during the cold pressing process and generate new interfaces during the cycle process, consuming too much active lithium. The above two aspects can comprehensively improve the cycle life of the secondary battery.

[0034] In any embodiment of the present disclosure, the powder compaction density of the first graphite material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , optional 1.78g / cm 3 -1.85g / cm 3 .

[0035] The first graphite material has a high powder compaction density, which helps to increase the compaction density of the pole piece and improve the energy density of the secondary battery.

[0036] In any embodiment of the present disclosure, the volume distribution particle size Dv50 of the graphite material is recorded as A, and the volume distribution particle size Dv50 of the graphite material after cold pressing under a pressure of 20000N is recorded as B, then the graphite material satisfies: B / A≥85%, which can be optionally 85%-98%.

[0037] In any embodiment of the present disclosure, the amount of primary particles in the first graphite material accounts for 40% to 60%, and can be optionally 50% to 60%.

[0038] In any embodiment of the present disclosure, the degree of graphitization of the first graphite material is 88%-95%.

[0039] In any embodiment of the present disclosure, the volume distribution particle size Dv50 of the second graphite material is less than or equal to 15.0 μm, and can be optionally 9.0 μm-14.0 μm.

[0040] The second graphite material has a small volume distribution particle size Dv50, and the path for active ion embedding and extraction is short, which can improve the transmission performance of active ions and electrons and improve the kinetic performance of the battery.

[0041] In any embodiment of the present disclosure, the tap density of the second graphite material is 1.0 g / cm 3 -1.3g / cm 3 .

[0042] The second graphite material having a tap density within the above range can further enhance electron conduction between particles and improve the kinetic performance of the battery.

[0043] In any embodiment of the present disclosure, the specific surface area of ​​the second graphite material is 0.75 m 2 / g-1.75m 2 / g.

[0044] The second graphite material with a specific surface area within a suitable range has suitable adsorption sites, which can promote the adsorption of active ions, thereby further improving the kinetic performance of the secondary battery, while reducing the probability of side reactions with the electrolyte, taking into account both the cycle performance and kinetic performance of the battery.

[0045] In any embodiment of the present disclosure, the number of primary particles in the second graphite material accounts for greater than or equal to 80%.

[0046] The primary particles have excellent structural stability, which helps to reduce the breakage of graphite material particles caused by expansion and contraction of the second graphite material during the cycle, improve the stability of the second graphite material, reduce the irreversible consumption of active ions, and achieve improved cycle performance of the secondary battery.

[0047] In any embodiment of the present disclosure, the degree of graphitization of the second graphite material is 85%-90%.

[0048] The second graphite material with a graphitization degree within the above range can take into account the material's cycle stability, gram capacity and active ion transport performance, which is conducive to obtaining a battery with high energy density, long cycle and high kinetic performance.

[0049] In any embodiment of the present disclosure, the particle size distribution of the second graphite material (Dv90-Dv10) / Dv50 is 1.20-1.70.

[0050] The second graphite material with a volume particle size distribution within a suitable range is beneficial for making the negative electrode film layer have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the dynamic performance of the secondary battery; in addition, the second graphite material can also have good stacking properties, which is beneficial for improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0051] In any embodiment of the present disclosure, the gram capacity of the second graphite material is 325 mAh / g-340 mAh / g.

[0052] The second graphite material with a gram capacity within the above range has a relatively small lattice expansion rate and high crystal structure stability, which can reduce the cycle expansion and full charge expansion of the battery and further improve the cycle stability of the secondary battery.

[0053] A second aspect of the present disclosure provides an electrical device including the secondary battery according to the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0055] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet disclosed herein.

[0056] FIG2 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0057] FIG3 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0058] FIG. 4 is a schematic diagram of a cross-sectional image of a particle of the first graphite material of the present disclosure.

[0059] FIG5 is a schematic diagram of one embodiment of a secondary battery of the present disclosure.

[0060] FIG6 is an exploded schematic diagram of one embodiment of a secondary battery according to the present disclosure.

[0061] FIG. 7 is a schematic diagram of an embodiment of a battery module according to the present disclosure.

[0062] FIG8 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0063] FIG. 9 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 8 .

[0064] FIG. 10 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present disclosure as a power source.

[0065] FIG11 is a Raman surface scan diagram of the first region of an embodiment of a pole piece disclosed herein.

[0066] FIG12 is a Raman surface scan diagram of the second region of an embodiment of a pole piece disclosed herein.

[0067] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 10 negative electrode sheet, 101 negative electrode current collector, 102 negative electrode film layer, 102a first surface, 102b second surface, 1021 first region, 1022 second region, 1023 intermediate region, 200 first graphite material, 201 surface region, 202 internal region. DETAILED DESCRIPTION

[0068] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0069] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0071] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0072] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0073] Unless otherwise specified, the terms "include" and "comprising" mentioned in this disclosure may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0074] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0076] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0077] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0078] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0079] The capacity and electrochemical performance of negative electrode active materials are often related to their surface disorder. Negative electrode active materials with low surface disorder usually have higher capacity and compactness, which makes the battery have high energy density; but due to its low surface disorder, the crystal interlayer spacing is small, the lattice expansion rate of the negative electrode active material is large during the cycle, the battery cycle life is reduced, and the active ions in the electrolyte are not easy to insert, resulting in poor secondary battery kinetic performance.

[0080] Based on this, the present disclosure provides a secondary battery including a negative electrode sheet. Figures 1 to 3 are schematic diagrams of embodiments of the negative electrode sheet of the present disclosure. As shown in Figures 1 to 3, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b disposed opposite the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H. The region within the thickness range from the second surface 102b of the negative electrode film layer to 0.3H is denoted as the first region 1021 of the negative electrode film layer. The region within the thickness range from the first surface 102a of the negative electrode film layer to 0.3H is denoted as the second region 1022 of the negative electrode film layer. The active material I in the second region 1022 is denoted as H. D / I G Greater than the I of the active material in the first region 1021 D / I G , I D / IG is the ratio of the D peak intensity to the G peak intensity of the Raman spectrum, I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer located on one side of the negative electrode current collector.

[0081] I in Raman spectra of different regions D / I G The test can be performed using any method known in the art. In the present invention, reference is made to GB / T 40219-2021, and a LabRAM HR Evolution laser micro-Raman spectrometer is used for the test. A solid laser with a wavelength of 523 nm is used as the light source, a beam diameter of 1.2 μm, a power of 1 mW, 100 points are sampled in an area of ​​100 μm × 100 μm, and the relative position of each point at 1350 ± 100 cm is calculated. -1 The peak intensity I D and 1580±100cm -1 The peak intensity I G I D / I G The ratio of 100 points D / I G The median value is taken as the I D / I G FIG11 is a Raman surface scan of the first region of an embodiment of the electrode of the present disclosure; FIG12 is a Raman surface scan of the second region of an embodiment of the electrode of the present disclosure. As can be seen from the figure, in some embodiments, the active material in the second region has a higher I D / I G And the distribution range is wider.

[0082] In some embodiments, the I of the active material in the second region D / I G Greater than the I of the active material in the first region D / I G In the present disclosure, the thickness of the negative electrode film layer can be tested using methods known in the art. As an example, a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm) is used for measurement.

[0083] Raman spectroscopy I D / I G It can be used to characterize the disorder degree of the active material surface. It can be understood that the first region and the second region each include at least one active material.D / I G Greater than the I of the active material in the first region 1021 D / I G This does not mean that the active material in the second region 1022 D / I G is greater than the I of any active material in the first region 1021 D / I G The I of the active material in the second region 1022 of the negative electrode sheet located away from the current collector D / I G Greater than the I of the active material in the first region 1021 D / I G , which means that the active material in the second region outside the electrode has a higher average disorder degree than the active material in the first region. In materials with high disorder, active ions are more easily embedded in and extracted from the active material, which can effectively reduce the volume expansion during the ion embedding and extraction process and improve the battery's cycle performance. At the same time, the electrolyte is also more likely to penetrate the active material, thereby improving the battery's dynamic performance. The I of the active material in the first region 1021 of the negative electrode near the current collector D / I G The lower the active material, the higher the capacity and the easier it is to be compacted during the cold pressing process, thus improving the compaction of the pole piece and achieving a high energy density of the secondary battery. D / I G The single-layer electrode sheet, made from a mixture of active materials, utilizes a double-layer design to achieve the same battery energy density with a lower negative electrode film thickness, further overcoming the issues of excessively long transmission paths and reduced battery dynamics associated with thicker negative electrode films. As a result, this secondary battery achieves improved cycling stability and kinetic performance while maintaining a balanced energy density.

[0084] In some embodiments, the active material in the second region has an I D / I G I of the active material in the first region D / I G The difference ΔK satisfies: 0<ΔK≤0.4, and can be optionally 0.1≤ΔK≤0.25.

[0085] In some embodiments, the active material in the second region has an I D / I G I of the active material in the first region D / I GThe difference ΔK is 0.01, 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.20, 0.23, 0.25, 0.30, 0.35, 0.40 or any range therebetween.

[0086] I of the active material in the second region D / I G I of the active material in the first region D / I G The secondary battery with the difference ΔK within the above range can more effectively take into account the cycle stability, dynamic performance and battery capacity of the battery.

[0087] In some embodiments, the active material in the first region has an I D / I G Less than or equal to 0.14, optionally 0.05-0.1; and / or, the I of the active material in the second region D / I G Greater than or equal to 0.1, optional range is 0.2-0.35.

[0088] In some embodiments, the active material in the first region has an I D / I G The values ​​can be selected as 0.01, 0.03, 0.06, 0.09, 0.1, 0.14 or any range therebetween.

[0089] In some embodiments, the active material in the second region has an I D / I G The optional values ​​are 0.1, 0.13, 0.16, 0.19, 0.22, 0.25, 0.35 or any range therebetween.

[0090] I of the active material in the first region D / I G I of the active material in the second region D / I G In the appropriate range, secondary batteries can better improve the cycle stability and kinetic performance of the battery.

[0091] In some embodiments, the particle size distribution of the active material in the second region (Dv90-Dv10) / Dv50 is greater than the particle size distribution of the active material in the first region (Dv90-Dv10) / Dv50.

[0092] In this article, the terms "Dv90" and "Dv10" refer to the particle sizes corresponding to when the cumulative volume distribution number of particles reaches 90% and 10% in the particle size distribution curve, respectively.

[0093] In the present disclosure, the volume distribution particle size Dv90 and Dv10 of the material can be measured using methods known in the art. As an example, referring to GB / T 19077-2016, they are measured using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0094] The active material in the second region 1022 of the negative electrode sheet, which is located away from the current collector, has a larger particle size distribution, which is beneficial to the infiltration of the electrolyte in the negative electrode sheet and improves the kinetic performance; while the active material in the first region 1021 close to the current collector side has a smaller particle size distribution, which is beneficial to obtaining tightly packed negative electrode active materials and improving the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the active material during the cold pressing process, further improving the integrity of the active material during the processing process, and improving the cycle stability of the battery.

[0095] In some embodiments, the degree of graphitization of the active material in the second region is less than the degree of graphitization of the active material in the first region.

[0096] As used herein, the term "degree of graphitization" refers to an indicator measuring the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure.

[0097] In the present disclosure, the degree of graphitization of the active material can be tested using methods known in the art. For example, an X-ray diffractometer (e.g., a Bruker D8 Discover) is used for testing, with reference to JIS K0131-1996 and JB / T4220-2011, to determine the average interlayer spacing d002 of the (002) plane in the crystal structure of the graphite material. The degree of graphitization is then calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the (002) plane in the crystal structure of the graphite material expressed in nanometers (nm).

[0098] Active materials with low graphitization often have larger interlayer spacing, which facilitates the deintercalation of active ions. Active materials with low graphitization in the second region of the negative electrode, away from the current collector, can improve battery kinetics while minimizing the volume expansion of the electrode caused by the deintercalation of active ions, ultimately improving the battery's cycling stability.

[0099] In some embodiments, the ratio of the number of primary particles of the active material in the second region is higher than the ratio of the number of primary particles of the active material in the first region.

[0100] In this document, the term "primary particles" refers to the initial particles formed during the processing of graphite raw materials, and the primary particles are non-agglomerated particles.

[0101] In the present disclosure, the proportion of primary particles in the active material can be tested by methods known in the art. As an example, a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL of Japan) can be used to prepare the cross-section of the negative electrode sheet; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope from ZEISS of Germany) is used to scan the cross-section of the negative electrode sheet. Multiple test areas are randomly selected in the test sample, and images of the multiple test areas are obtained using a scanning electron microscope. The ratio of the number of active materials with primary particle morphology in each image to the total number of active material particles is counted, and the average value of the multiple statistical results is the proportion of the number of primary particles in the active material.

[0102] Having a higher primary particle content in the second region of the negative electrode plate away from the current collector side is beneficial to improving the particle integrity of the plate during the cold pressing process, reducing the generation of new interfaces, reducing the consumption of active lithium during the cycle, and further improving the cycle stability of the secondary battery.

[0103] In some embodiments, the active material in the first region includes a first graphite material, and the first particle body of the first graphite material includes an internal region and a surface region that at least partially surrounds the internal region, wherein the surface region refers to a region extending 30 nm from the surface of the first particle body of the first graphite material to the interior of the particle, and the surface region includes a disordered layer.

[0104] Figure 4 is a schematic diagram of a cross-sectional image of a particle of the first graphite material 200 of the present disclosure. As shown in Figure 4, the region extending 30 nm inward from the surface of the first particle of the first graphite material 200 is the surface region 201, and the region inside the surface region 201 is the interior region 202. Surface region 201 includes a disordered layer.

[0105] The carbon material in the disordered layer can be characterized using transmission electron microscopy (TEM). Using a focused ion beam (FIB) to slice approximately 100 nm thick slices from the center of the graphite particles, TEM analysis reveals a surface region with long-range disorder and short-range order in the lattice fringes. The electron diffraction pattern in the disordered layer appears halo-like.

[0106] In some embodiments, the disordered layer has a thickness of 1 nm to 20 nm.

[0107] In the present disclosure, the thickness of the disordered layer can be tested using methods known in the art. As an example, it can be obtained by transmission electron microscopy (TEM) testing. A thin slice of about 100 nm in thickness is cut from the middle of the graphite material particle body using a focused ion beam (FIB), and then the slice is subjected to TEM testing to obtain a TEM test original image, which is saved in the original image format (xx.dm3). The original image obtained by the above TEM test is opened in Digital Micrograph software, and the disordered layer is identified by lattice spacing, angle information, and diffraction pattern.

[0108] In some embodiments, the thickness of the disordered layer is 1 nm, 4 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 16 nm, 20 nm, or any range therebetween.

[0109] Different from the active material with disordered layer coated on the surface of graphite particle, the disordered layer of the first graphite material is part of the graphite particle body, that is, the disordered layer structure in the surface region of the first graphite material and the other parts of the first graphite material are derived from the same precursor, which makes the disordered layer of the first graphite material have high uniformity and extremely thin thickness. The first graphite material has a disordered layer on the surface and has a low I D / I G .

[0110] The disordered layer mainly includes amorphous carbon. The carbon atoms in the amorphous carbon structure have no regular arrangement, which makes the interaction between its molecules more complex, resulting in it having higher strength and hardness than the graphite crystals in the internal area. This reduces the probability of surface damage of the graphite particles due to friction between particles and between particles and the mixing tank during slurry preparation, and reduces the risk of cracking of negative electrode active material particles and exposure of new interfaces during the cold pressing of the electrode, so that the graphite material maintains a higher degree of integrity during the manufacturing process. Graphite materials with high particle integrity have fewer surface defects and have a good interface with the electrolyte, which can effectively reduce side reactions between the negative electrode and the electrolyte, reduce the loss of active lithium, and improve the cycle stability of the battery. At the same time, the first graphite material will not sacrifice the capacity of the graphite material and the energy density of the battery due to the excessive disorder of its surface layer. It can improve the cycle stability of the battery while taking into account the energy density of the battery.

[0111] In some embodiments, the active material in the second region includes a second graphite material, the second graphite material includes a second particle body and a coating layer at least partially coating a surface of the second particle body, and the coating layer includes amorphous carbon.

[0112] In this article, the term "amorphous carbon" refers to a non-crystalline structure composed of carbon elements, whose hybridization sp3 With sp 2 The hybrid mixed structure makes it different from the crystalline carbon of the crystalline system, and has a structure and properties similar to amorphous objects (such as glass).

[0113] The amorphous carbon herein can be formed by carbonizing an organic carbon source. The organic carbon source can be any carbonaceous material known in the art suitable for coating, such as coal tar, petroleum tar, phenolic resin, coconut shell, or the like.

[0114] In the present disclosure, the morphology of the second graphite material can be characterized by transmission electron microscopy.

[0115] The coating layer on the surface of the second graphite material can greatly increase the surface disorder of the active material in the second region. The highly disordered surface of the second graphite material makes it easier for active ions to be deintercalated, reduces the volume expansion during the deintercalation process of active ions, and further improves the dynamic performance of the battery.

[0116] In some embodiments, the powder compaction density of the second graphite material under a pressure of 49000N is 1.60g / cm 3 -1.80g / cm 3 .

[0117] In some embodiments, the second graphite material has a powder compaction density of 1.60 g / cm3 at a pressure of 49,000 N. 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 , 1.80g / cm 3 or any range of values ​​between them.

[0118] In this article, the term "powder compaction density" refers to the density of the powder under a preset pressure. A higher powder compaction density indicates a higher mass per unit volume. For graphite materials, a higher powder compaction density increases the compaction density of the negative electrode film, which improves the energy density of the secondary battery.

[0119] The method for measuring the compacted density of powder can be any method known in the art. For example, referring to GB / T24533-2009, 1g of graphite material powder is weighed and added to a bottom area of ​​1.327cm 2 The mold is pressurized to a specific pressure, such as 49000N, and the pressure is maintained for 30s, then the pressure is released and maintained for 10s. The powder compaction density of the graphite material under the selected pressure is measured by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0120] Graphite materials with high surface disorder often have high surface strength and hardness, making them difficult to compact under pressure and resulting in a low powder compaction density. This second graphite material, while maintaining a high powder compaction density while possessing high surface disorder, helps to increase the ultimate compaction density of the electrode, thereby further improving the energy density of the battery.

[0121] In some embodiments, the specific surface area of ​​the first graphite material is 1.0 m 2 / g-1.8m 2 / g, optional 1.1m 2 / g-1.7m 2 / g.

[0122] In the present disclosure, the specific surface area of ​​the active material can be measured using methods known in the art. For example, referring to GB / T 19587-2017, the specific surface area of ​​the active material can be measured using nitrogen adsorption specific surface area analysis and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0123] In some embodiments, the specific surface area of ​​the first graphite material is 1.0 m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g or any range of values ​​between them.

[0124] The low specific surface area of ​​the first graphite material helps to further reduce the degree of side reactions of the active material and improve the cycle life of the secondary battery.

[0125] In some embodiments, the volume distribution particle size Dv50 of the first graphite material is 7.0 μm-14.0 μm, and optionally 8.0 μm-12.0 μm.

[0126] In some embodiments, the volume distribution particle size Dv50 of the first graphite material is 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, or any range therebetween.

[0127] In some embodiments, the particle size distribution of the first graphite material (Dv90-Dv10) / Dv50 is 1.0-1.4, and can be optionally 1.1-1.3.

[0128] In some embodiments, the particle size distribution of the first graphite material (Dv90-Dv10) / Dv50 is 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or any range therebetween.

[0129] Controlling the particle size distribution of the first graphite material within the above range is conducive to obtaining tightly packed negative electrode active materials and improving the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the active material during the cold pressing process, and further improving the integrity of the active material during the processing process; and the small stress inside the first graphite material particles is conducive to maintaining the long-period pore structure of the electrode sheet during the cycle, and can maintain the original pore structure of the electrode sheet during the cycle, so that the lithium ion insertion path remains unobstructed, while reducing the re-filming of the negative electrode active material during the charging process, improving the dynamic performance and cycle life. Furthermore, the particle size distribution within the above range can also improve the uniformity of lithium insertion between particles, reduce polarization, avoid lithium precipitation caused by uneven current density, and is conducive to achieving long-term cycle stability. In addition, the particle size distribution within the above range also helps to improve the processing performance of the electrode sheet, and will not affect the uniformity of slurry stirring due to excessive small-sized particles in the first graphite material, which is conducive to improving the uniformity and stability of the electrode sheet quality and helping to achieve long-term cycle stability.

[0130] In some embodiments, the gram capacity of the first graphite material is 345 mAh / g-355 mAh / g, and optionally 347 mAh / g-353 mAh / g.

[0131] As used herein, the term "gram capacity" refers to the ratio of the amount of electricity that an active material can release to the mass of the active material.

[0132] In the present disclosure, the gram capacity of the graphite material can be tested using methods known in the art. As an example, a graphite material sample is thoroughly stirred and mixed with a conductive agent, carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent NMP to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil and dried and cold pressed; then a metal lithium sheet is used as a counter electrode, a polypropylene (PP) film is used as a separator, and an electrolyte is injected. The electrolyte formula used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the charge capacity was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite sample is the gram capacity of the graphite material.

[0133] In some embodiments, the first graphite material has a specific capacity of 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 353 mAh / g, 354 mAh / g, 355 mAh / g, or any range therebetween.

[0134] The first graphite material with a gram capacity within the above range will not undergo significant lattice expansion during the charge and discharge process due to its excessively high graphitization; nor will it be difficult to compact the material due to its low graphitization. In order to achieve the same electrode compaction density, a higher cold pressing pressure is required, which will cause cracks during the cold pressing process and generate new interfaces during the cycle process, consuming too much active lithium. The above two aspects can comprehensively improve the cycle life of the secondary battery.

[0135] In some embodiments, the powder compaction density of the first graphite material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , optional 1.78g / cm 3 -1.85g / cm 3 .

[0136] The first graphite material has a high powder compaction density, which helps to increase the compaction density of the pole piece and improve the energy density of the secondary battery.

[0137] In some embodiments, the volume distribution particle size Dv50 of the graphite material is recorded as A, and the volume distribution particle size Dv50 of the graphite material after cold pressing under a pressure of 20,000 N is recorded as B. Then the graphite material satisfies: B / A ≥ 85%, which can be optionally 85%-98%.

[0138] In this article, "cold pressing" refers to a pressure processing method performed at room temperature. The Dv50 ratio of the powder before and after cold pressing can be calculated by comparing the Dv50 of the powder to the Dv50 measured by scraping the powder after cold pressing.

[0139] In some embodiments, A / B can be selected as 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% or any range of values ​​therebetween.

[0140] In some embodiments, the primary particles in the first graphite material account for 40% to 60%; optionally 50% to 60%.

[0141] In some embodiments, the amount of primary particles in the first graphite material accounts for 40%, 45%, 50%, 55%, 60%, or any range therebetween.

[0142] In some embodiments, the first graphite material has a degree of graphitization of 88% to 95%.

[0143] In some embodiments, the degree of graphitization of the first graphite material is 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any range therebetween.

[0144] In some embodiments, the first graphite material I D / I G is 0.05-0.1, where I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

[0145] In some embodiments, the first graphite material I D / I G It is 0.05, 0.06, 0.09, 0.1 or any numerical range therebetween.

[0146] In some embodiments, the volume distribution particle size Dv50 of the second graphite material is less than or equal to 15.0 μm, and can be optionally 9.0 μm-14.0 μm.

[0147] In some embodiments, the volume distribution particle size Dv50 of the second graphite material is 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, or any range therebetween.

[0148] The second graphite material has a small volume distribution particle size Dv50, and the path for active ion embedding and extraction is short, which can improve the transmission performance of active ions and electrons and improve the kinetic performance of the battery.

[0149] In some embodiments, the tap density of the second graphite material is 1.0 g / cm 3 -1.3g / cm 3 .

[0150] As used herein, the term "tap density" refers to the mass per unit volume of powder in a container measured after being tapped under specified conditions.

[0151] In the present disclosure, the tap density of the active material can be measured using methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. The test instrument can be a Dandong Better BT-301, with the following test parameters: vibration frequency of 250 ± 15 times / minute, amplitude of 3 ± 0.2 mm, number of vibrations of 5000 times, and a 25 mL graduated cylinder.

[0152] In some embodiments, the tap density of the second graphite material is 1.0 g / cm 3 , 1.05g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 or any range of values ​​between them.

[0153] The second graphite material having a tap density within the above range can further enhance electron conduction between particles and improve the kinetic performance of the battery.

[0154] In some embodiments, the specific surface area of ​​the second graphite material is 0.75 m 2 / g-1.75m 2 / g.

[0155] In some embodiments, the specific surface area of ​​the second graphite material is 0.75 m 2 / g, 0.85m 2 / g, 0.95m 2 / g, 1.05m 2 / g, 1.15m2 / g, 1.25m 2 / g, 1.35m 2 / g, 1.45m 2 / g, 1.55m 2 / g, 1.65m 2 / g, 1.75m 2 / g or any range of values ​​between them.

[0156] The second graphite material with a specific surface area within a suitable range has suitable adsorption sites, which can promote the adsorption of active ions, thereby further improving the kinetic performance of the secondary battery, while reducing the probability of side reactions with the electrolyte, taking into account both the cycle performance and kinetic performance of the battery.

[0157] In some embodiments, the primary particles in the second graphite material account for greater than or equal to 80%.

[0158] In some embodiments, the amount of primary particles in the second graphite material accounts for 80%, 84%, 88%, 92%, 96%, 100%, or any range therebetween.

[0159] The primary particles have excellent structural stability, which helps to reduce the breakage of graphite material particles caused by expansion and contraction of the second graphite material during the cycle, improve the stability of the second graphite material, reduce the irreversible consumption of active ions, and achieve improved cycle performance of the secondary battery.

[0160] In some embodiments, the second graphite material has a degree of graphitization of 85% to 90%.

[0161] In some embodiments, the degree of graphitization of the second graphite material is 85%, 86%, 87%, 88%, 89%, 90%, or any range therebetween.

[0162] The second graphite material with a graphitization degree within the above range can take into account the material's cycle stability, gram capacity and active ion transport performance, which is conducive to obtaining a battery with high energy density, long cycle and high kinetic performance.

[0163] In some embodiments, the particle size distribution of the second graphite material (Dv90-Dv10) / Dv50 is 1.20-1.70.

[0164] In some embodiments, the particle size distribution of the second graphite material (Dv90-Dv10) / Dv50 is 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, or any range therebetween.

[0165] The second graphite material with a volume particle size distribution within a suitable range is beneficial for making the negative electrode film layer have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the dynamic performance of the secondary battery; in addition, the second graphite material can also have good stacking properties, which is beneficial for improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0166] In some embodiments, the second graphite material I D / I G is 0.1-0.35, where I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

[0167] In some embodiments, the second graphite material I D / I G 0.1, 0.12, 0.15, 0.18, 0.21, 0.23, 0.25, 0.30, 0.35 or any range therebetween.

[0168] In some embodiments, the second graphite material has a gram capacity of 325 mAh / g to 340 mAh / g.

[0169] The second graphite material with a gram capacity within the above range has a relatively small lattice expansion rate and high crystal structure stability, which can reduce the cycle expansion and full charge expansion of the battery and further improve the cycle stability of the secondary battery.

[0170] In some embodiments, the first graphite material is prepared by the following method: providing a first raw material; processing the first raw material to obtain a first intermediate product; and performing a first graphitization treatment on the first intermediate product to obtain the first graphite material.

[0171] In this article, the term "graphitization treatment" refers to the heat treatment process of carbon materials. Under the action of high temperature, the carbon material transforms from a two-dimensional carbon network structure to a three-dimensional ordered structure through "microcrystal" growth.

[0172] In some embodiments, the maximum power of the first graphitization process is 70% to 90% of the rated power of the first graphitization process equipment.

[0173] In some embodiments, the power of the first graphitization process may be 70%, 75%, 80%, 85%, 90% of the rated power of the first graphitization process equipment, or any range of values ​​therebetween.

[0174] It is understood that graphitization equipment refers to any device capable of graphitization, including but not limited to Acheson furnaces, box furnaces, internal furnaces, continuous graphitization furnaces, electric calcining furnaces, medium frequency furnaces, and tubular furnaces. The rated power of graphitization equipment produced by different manufacturers may vary, so you can select the right one based on your actual needs.

[0175] The power of the first graphitization treatment used in the present disclosure needs to be lower than the rated power of the first graphitization treatment equipment to achieve uniformity of the temperature field during the graphitization treatment process, ensure the consistency of the material's gram capacity, and help improve the cycle life of the battery.

[0176] In some embodiments, the first graphitization treatment equipment is an inner string furnace, and the rated power of the inner string furnace is 25,000-32,000W.

[0177] In some embodiments, the first graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000-30,000W.

[0178] In some embodiments, the maximum power of the first graphitization process is 22,000W-25,000W.

[0179] In some embodiments, the maximum power of the first graphitization process may be 22,000 W, 22,500 W, 23,000 W, 23,500 W, 24,000 W, 25,000 W, or any range therebetween.

[0180] By controlling the maximum power of the first graphitization treatment, the degree of graphitization of the graphite material during the heat treatment process can be effectively controlled. While the internal region of the particles of the first graphite material is highly graphitized, a uniform disordered layer is formed in the surface region, which is beneficial to improving the cycle stability of the secondary battery.

[0181] In some embodiments, the constant power time of the first graphitization treatment at maximum power is 10 hours to 50 hours.

[0182] In some embodiments, the constant power time of the first graphitization treatment at maximum power is 10 h, 13 h, 16 h, 19 h, 22 h, 25 h, 28 h, 31 h, 33 h, 36 h, 39 h, 42 h, 45 h, 48 h, 50 h, or any range therebetween.

[0183] In some embodiments, the temperature of the first graphitization treatment is 2600°C to 3000°C.

[0184] In some embodiments, the temperature of the first graphitization treatment is 2600° C., 2700° C., 2800° C., 2900° C., 3000° C., or any range therebetween.

[0185] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite material after graphitization and deterioration of high-temperature performance; and can effectively improve the graphitization degree of the first graphite material, thereby facilitating an increase in the cycle life of the secondary battery.

[0186] In some embodiments, the first raw material includes at least one of petroleum coke, needle coke, and pitch coke, and needle coke can be selected.

[0187] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0188] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which, after undergoing liquid phase carbonization to generate an anisotropic mesophase, can produce coke with a needle-like texture through processes such as high-temperature carbonization.

[0189] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0190] Needle coke has a range of advantages, including low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high electrical conductivity, and easy graphitization. The graphite material after graphitization can achieve a high ultimate compaction density and a low cyclic expansion rate.

[0191] In some embodiments, based on the total volume of the first raw material structure, the volume proportion of the fiber-type structure in the first raw material is greater than or equal to 55%, and can be optionally 58%-70%.

[0192] In this article, "fibrous structure" is also called streamlined structure, which refers to the structure of the raw material with obvious fibrous texture observed under a microscope.

[0193] Based on the morphological characteristics and isochromatic zone size under a polarizing microscope, the microstructure of the char material can be divided into mosaic, regional, and fibrous types. Generally, isochromatic zones with a size less than 30 μm are classified as mosaic, those with a size greater than 30 μm are classified as regional, and anisotropic banded isochromatic zones are classified as fibrous.

[0194] In the present disclosure, the volume percentage of the fiber structure in the raw material can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw material is crushed to 1mm and mixed, and 40g to 50g is separated. A square hole sieve is used to take 4g to 5g of a 0.07mm to 1.0mm grade sample for film making; according to the provisions of MT 116.1-86, powder coke and block coke optical films are prepared. The diameter of the powder coke optical film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3; the sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of the first-order red; determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3 to 0.5mm and a line spacing of 0.5 to 0.8mm. Starting from one end of the sample, determine the microstructure category at the intersection of the crosshairs, and divide the number of effective measurement points of the fiber-type optical structure by the total number of test points as the volume proportion of the fiber-type structure in the raw material.

[0195] In some embodiments, based on the total volume of the first raw material structure, the volume proportion of the fibrous structure in the first raw material can be selected as 55%, 58%, 60%, 65%, 70% or any numerical range therebetween.

[0196] Raw materials with a high volume fraction of fiber-type structures help increase the compaction density and specific capacity of the first graphite material, allowing the first graphite material to retain high integrity during the compaction process, resulting in a battery with both a long cycle life and good energy density. However, an excessively high percentage of fiber-type structures increases the cost and expansion rate of the graphite material, and deteriorates its dynamic performance. A first raw material with a volume fraction of fiber-type structures within the above range offers both low cost and good specific capacity for the graphite, ensuring a full lifecycle kinetic window for the battery cell, thereby comprehensively improving the battery's long-term cycle life and electrochemical performance.

[0197] In some embodiments, the first feedstock can achieve a maximum gram capacity that is greater than the gram capacity of the graphite material.

[0198] By using high-grade raw materials and controlling the degree of graphitization, the maximum specific capacity that can be achieved by the first raw material will not be fully utilized, and a graphite material including a disordered layer in the surface area is obtained, thereby achieving a balance between battery cycle life and kinetic performance.

[0199] In some embodiments, the processing of raw materials specifically includes: crushing, shaping and grading the raw materials to obtain a first precursor; granulating the first precursor to obtain a first precursor superfinished product; and low-temperature carbonizing a mixture of the first precursor and the first precursor superfinished product to obtain the first intermediate product.

[0200] Crushing is the process of reducing the particle size of raw materials. The raw materials can be crushed by any mechanical device such as crusher, mechanical mill, etc.

[0201] Shaping and grading are the processes of adjusting the particle size distribution of the raw materials to obtain a first precursor that meets the particle size requirements. The particle size and particle size distribution of the first precursor can be controlled by adjusting the grading frequency and air volume.

[0202] It can be understood that low-temperature carbonization of the first precursor and the first precursor over-product to obtain the intermediate product includes both low-temperature carbonization of a mixture of the first precursor and the first precursor over-product to obtain the intermediate product; and also includes low-temperature carbonization of the first precursor and the first precursor over-product to obtain the first intermediate product and the second intermediate product, respectively.

[0203] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm to 10.0 μm.

[0204] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, or any range therebetween.

[0205] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05-1.75.

[0206] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75, or any range therebetween.

[0207] In some embodiments, the tap density of the first precursor is 0.5 g / cm 3 ~0.7g / cm 3 .

[0208] In some embodiments, the tap density of the first precursor is 0.5 g / cm 3 , 0.55g / cm 3 , 0.6g / cm 3 , 0.65g / cm 3 , 0.7g / cm 3 or any range of values ​​between them.

[0209] In some embodiments, the Dv50 particle size of the first precursor product is 11.0 μm to 15.0 μm.

[0210] In some embodiments, the Dv50 particle size of the first precursor product is 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, or any range therebetween.

[0211] The first precursor superfinished product is obtained by granulating the first precursor. Therefore, the first precursor superfinished product primarily forms secondary particles in the graphite material. Controlling the particle size of the first precursor and the first precursor superfinished product helps regulate the particle size and particle size distribution of the graphite material, improving the battery's cycling stability.

[0212] In some embodiments, the crushing, shaping and grading of the raw materials to obtain the first precursor includes: crushing, shaping and grading the raw materials to obtain secondary raw materials; removing 10%-35% of the fine powder in the secondary raw materials by mass to obtain the first precursor; the Dv50 of the fine powder is 3μm-7μm and Dv99 is less than or equal to 30μm, and the particle size distribution of the fine powder (Dv90-Dv10) / Dv50 is greater than 1.6.

[0213] In some embodiments, the second graphite material is prepared by the following method: providing a second raw material; processing the second raw material to obtain a second precursor; performing a second graphitization treatment on the second precursor to obtain a second graphitized product; and performing a surface treatment on the second graphitized product to obtain a second graphite material.

[0214] In some embodiments, surface treating the second graphitized product to obtain the second graphite material includes performing a fusion treatment on the second graphitized product to obtain a second intermediate, and mixing the second intermediate with asphalt to perform a second carbonization treatment to obtain the second graphite material.

[0215] The existing technology directly uses asphalt to coat the second graphitized product in order to increase the disorder of the graphite material surface, thereby improving the dynamic performance of the material. However, after the second graphitized product is directly coated, it will seriously affect the powder compaction density of the graphite material, reduce the compaction density of the negative electrode film layer, and thus affect the energy density of the secondary battery. The present disclosure performs a fusion treatment on the second graphitized product before the asphalt coating treatment. The fusion treatment can achieve the purpose of spheroidization and de-edgeing. On the one hand, the second intermediate obtained by fusion spheroidization has a relatively regular structure, which can improve the powder compaction density of the second graphite material. On the other hand, the small particles of graphite produced by de-edgeing can be filled in the voids of the second intermediate, further improving the powder compaction density of the second intermediate. The fusion treatment can effectively compensate for the adverse effects of the asphalt coating treatment on the powder compaction density of the graphite material, which is conducive to obtaining a negative electrode film layer with a high compaction density, thereby maintaining the high energy density of the battery.

[0216] In some embodiments, the frequency of the fusion process may be 20 Hz, 25 Hz, 30 Hz, 35 Hz, or 40 Hz, or a range between any two of the above values.

[0217] In some embodiments, the fusion treatment time is 5-15 minutes. In some embodiments, the fusion treatment time can be selected from 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, or a range between any two of the above values.

[0218] The frequency and time of the fusion treatment affect the powder compaction density and specific surface area of ​​the second graphite material. A high fusion treatment frequency can increase the powder compaction density of the second graphite material, while also reducing the damage to the processing equipment caused by an excessively high fusion treatment frequency. In addition, a high fusion treatment frequency can also increase the specific surface area of ​​the second graphite material and improve the material's dynamic properties. The time of the fusion treatment affects the powder compaction density, specific surface area, and Id / Ig of the second graphite material. A long fusion treatment time can increase the powder compaction density, specific surface area, and Id / Ig of the second graphite material, obtain a negative electrode film layer with a high compaction density, and improve the energy density and dynamic performance of the battery.

[0219] In some embodiments, the second carbonization treatment is performed at a temperature of 950-1350°C.

[0220] In some embodiments, the treatment temperature of the second carbonization treatment may be 950° C., 1000° C., 1100° C., 1200° C., 1300° C., or 1350° C., or a range between any two of the above values.

[0221] The treatment temperature of the second carbonization treatment affects the I D / I G If the treatment temperature of the second carbonization treatment is too high, the asphalt coating degree is high, the coating layer integrity of the second graphite material is high, and the I D / I G If the temperature of the second carbonization treatment is too low, the functional groups on the asphalt surface may not be completely removed, which may lead to side reactions during the cycle and affect the battery's cycle performance.

[0222] In some embodiments, the second feedstock comprises one or more of petroleum coke, needle coke, and pitch coke.

[0223] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0224] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which, after undergoing liquid phase carbonization to generate an anisotropic mesophase, can produce coke with a needle-like texture through processes such as high-temperature carbonization.

[0225] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0226] In some embodiments, the second raw material is petroleum coke. Petroleum coke has excellent graphitization performance and low thermal expansion coefficient, which is conducive to obtaining a second graphite material with excellent dynamic performance and cyclic stability, and the raw material cost is low, saving costs.

[0227] In some embodiments, based on the total volume of the second raw material structure, the volume of the mosaic structure and the domain structure accounts for greater than or equal to 50%.

[0228] In some embodiments, the volume proportion of the mosaic structure and the regional structure can be selected to be 50%, 60%, 70%, 80%, 90% or 100%, or a range between any two of the above values.

[0229] In some embodiments, processing the second raw material specifically includes the following steps: crushing the second raw material, shaping it, grading it, removing the crushed fine powder, and obtaining a second precursor, wherein the volume distribution particle size Dv50 of the second precursor is 8.0-16.0 μm, and / or the (Dv90-Dv10) / Dv50 of the second precursor is 1.40-1.70.

[0230] In some embodiments, the volume distribution particle size Dv50 of the second precursor can be selected as 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm or 16.0 μm, or a range between any two of the above values.

[0231] In some embodiments, (Dv90-Dv10) / Dv50 of the second precursor may be 1.40, 1.50, 1.60, or 1.70, or a range between any two of the above values.

[0232] In some embodiments, the maximum power of the second graphitization process is 70% to 90% of the rated power of the second graphitization process equipment.

[0233] In some embodiments, the maximum power of the second graphitization process may be 70%, 75%, 80%, 85%, 90% of the rated power of the second graphitization process equipment, or any range of values ​​therebetween.

[0234] In some embodiments, the maximum power of the equipment in the second graphitization process is 21500 W to 24000 W. In some embodiments, the maximum power of the equipment in the second graphitization process can be 21500 W, 23000 W, 23500 W, 24000 W, or any range therebetween.

[0235] In some embodiments, the constant power time of the second graphitization treatment at the maximum power of the device is 5.5 hours to 7.5 hours. In some embodiments, the constant power time of the second graphitization treatment at the maximum power of the device can be selected from 5.5 hours, 6.0 hours, 6.5 hours, 7 hours, 7.5 hours, or any range therebetween.

[0236] The present disclosure has no particular restrictions on the types of secondary batteries. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present disclosure has no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes can also include an isolation membrane, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0237] [Negative electrode]

[0238] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0239] As shown in FIG. 1 to FIG. 3 , the negative electrode film layer 102 further includes a middle region 1023 located between the first region 1021 and the second region 1022 of the negative electrode film layer and having a thickness of 0.4H (H represents the thickness of the negative electrode film layer 102 ).

[0240] In some embodiments, the intermediate region includes the first graphite material and / or the second graphite material. For example, as shown in FIG2 , the intermediate region 1023 may be compositionally identical to the first region 1021, whereby the active material in the first region is distributed over a thickness range from the second surface 102b of the negative electrode film layer to a thickness of 0.7H in the thickness direction of the negative electrode film layer 102; or, as shown in FIG3 , the intermediate region 1023 may be compositionally identical to the second region 1022, whereby the active material in the second region is distributed over a thickness range from the first surface 102a of the negative electrode film layer to a thickness of 0.7H in the thickness direction of the negative electrode film layer 102; or, as shown in FIG1 , the intermediate region 1023 includes both the active material in the first region and the active material in the second region. In this case, the intermediate region 1023 includes both a layer structure comprising the active material in the first region and a layer structure comprising the active material in the second region, and the two layer structures may further have a layer interface.

[0241] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned active materials. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, other artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0242] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0243] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present disclosure does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0244] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0245] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0246] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present disclosure further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present disclosure further includes a protective layer covering the surface of the negative electrode film layer.

[0247] [Positive electrode]

[0248] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0249] The positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0250] The positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0251] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0252] When the secondary battery of the present disclosure is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of a lithium-containing transition metal oxide, a lithium-containing phosphate, and their respective modified compounds. Examples of the lithium transition metal oxide may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0253] In some embodiments, the positive electrode active material includes a lithium-containing phosphate. Examples of the lithium-containing phosphate may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof.

[0254] In the present disclosure, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification on the positive electrode active materials.

[0255] [Electrolytes]

[0256] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0257] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0258] When the secondary battery of the present disclosure is a lithium ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0259] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, for example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). One or more.

[0260] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0261] [Isolation film]

[0262] The present disclosure has no particular limitation on the type of the isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0263] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0264] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.

[0265] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0266] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0267] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG5 shows a secondary battery 5 with a square structure as an example.

[0268] In some embodiments, as shown in FIG6 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0269] The preparation method of the secondary battery disclosed herein is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped to obtain the secondary battery.

[0270] In some embodiments of the present disclosure, the secondary batteries according to the present disclosure may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0271] Figure 7 is a schematic diagram of an exemplary battery module 4. As shown in Figure 7 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0272] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0273] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0274] Figures 8 and 9 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 8 and 9, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0275] Electrical devices

[0276] The present disclosure also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack of the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0277] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0278] Figure 10 is a schematic diagram of an exemplary electric device. This 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 this device, a battery pack or battery module may be used.

[0279] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0280] Example

[0281] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0282] In the following examples and comparative examples, the first carbon-based material can be prepared by the following method disclosed in the present invention.

[0283] Preparation Example

[0284] Preparation of the first graphite-A

[0285] The needle coke with a fiber structure of 68% was crushed; the crushed material was shaped to remove fine powder to obtain the first precursor, and the first precursor removed 21% of the mass of fine powder relative to the total mass of fine powder. Fine powder refers to the component with a maximum particle size of less than 5μm. Among them, the Dv50 particle size of the first precursor is 9.0μm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.35, and the tap density of the first precursor is 0.65g / cm 3 .

[0286] A portion of the first precursor is granulated and shaped in a reactor to obtain a second precursor process product with a particle size Dv50 of 14.3 μm;

[0287] The first precursor and the second precursor process products were placed in a kiln for carbonization at a temperature of 1100°C and a carbonization time of 24 hours to obtain a first intermediate product and a second intermediate product. The tap density of the first intermediate product was 0.98 g / cm 3 The tap density of the second intermediate product is 0.91g / cm 3 ;

[0288] The first intermediate product and the second intermediate product were respectively placed in an inner series furnace for graphitization treatment at a temperature of 2800°C. The rated power of the inner series furnace is 28000W, the maximum power of the graphitization treatment is 22400W, and the constant power time of the maximum power is maintained for 24 hours to obtain primary particles and secondary particles respectively.

[0289] The primary particles and secondary particles are mixed evenly in a mass ratio of 1:1 and sieved to obtain the final graphite material.

[0290] The thickness of the disordered layer of the graphite material is 11.2 nm, and the coefficient of variation of the disordered layer thickness is 34.1%. D / I G The interlayer spacing d1 of the disordered layer is 0.3368 nm, the interlayer spacing d2 of the inner region is 0.3361 nm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.28, the B / A value is 93.4%, and the specific surface area is 1.65 m 2 / g, the volume distribution particle size Dv50 is 10.2μm, and the powder compaction density under a pressure of 49000N is 1.81g / cm 3 , the gram capacity is 350.8mAh / g.

[0291] Preparation of the first graphite-B

[0292] The preparation method of the first graphite-B is basically the same as that of the first graphite-A, except that the graphitization temperature is 2850°C, the thickness of the disordered layer of the graphite material is 10.5nm, and the graphite material is 10.5nm thick. D / I G It is 0.067.

[0293] Preparation of the first graphite-C

[0294] The preparation method of the first graphite-C is basically the same as the preparation method of the first graphite-A, except that the maximum power is the rated power of the equipment and the constant power time at the maximum power is 36 hours. The surface area of ​​the prepared graphite material body particles has no disordered layer. D / I G It is 0.041.

[0295] Preparation of Second Graphite-A

[0296] A petroleum coke raw material containing 68.0% mosaic and regional structures by volume was coarsely crushed, and the coarsely crushed material was crushed and sieved. The sieved material was shaped and classified, and a certain amount of fine powder was removed during the classification process to obtain precursor particles with a volume distribution particle size Dv50 of 12.0 μm and a particle size distribution (Dv90-Dv10) / Dv50 of 1.61;

[0297] The precursor was placed in a kiln for pre-carbonization at a temperature of 1000°C and a high temperature zone time of 24 hours. The pre-carbonized material was obtained, and its tap density was 0.99 g / cm 3 ;

[0298] The pre-carbonized material was graphitized at a temperature of 2850°C. The graphitization treatment equipment was an internal series furnace with a rated power of 27000W. The maximum power of the graphitization treatment was 23000W. The maximum power was maintained constant for 10.0 hours to obtain a graphitized product.

[0299] The graphitized product is fused in a high-speed fusion machine to obtain an intermediate. The fusion frequency is 30 Hz and the fusion time is 15 minutes. The intermediate is mixed with asphalt. The mass ratio of the intermediate to the asphalt is 98%:2%. After mixing, the intermediate is carbonized at 1150°C for 2 hours. After the finished product is demagnetized and mixed, the second graphite-A is obtained.

[0300] Preparation of Second Graphite-B to Second Graphite-D

[0301] The preparation method of the second graphite-B to the second graphite-D is basically the same as the preparation method of the second graphite-A. The difference is that the I of the graphite material is adjusted by adjusting the type of raw materials, the maximum power of the graphitization treatment, the length of the graphitization treatment or the fusion frequency and fusion time of the fusion treatment. D / I G , please see Table 1 for details.

[0302] Table 1

[0303] The performance parameters of graphite materials are shown in Table 2.

[0304] Table 2

[0305] Example 1

[0306] The first graphite-A, the conductive agent carbon black (Super P), the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96:1:1.8:1.2 to form a first slurry.

[0307] The second graphite-A, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 96:1:1.8:1.2 to form a second slurry.

[0308] The first and second slurries are extruded simultaneously through a dual-chamber coating machine. The first slurry is applied to the negative electrode current collector copper foil, and the second slurry is applied over the first slurry. After drying and cold pressing, the negative electrode sheet is obtained. The coating weight ratio of the second slurry to the first slurry is 4:6 or 5:5.

[0309] LiFePO4 was mixed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 97:1:2. An appropriate amount of NMP solvent was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained.

[0310] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Vinylene carbonate (VC) was then added, and the VC content was 2% of the total mass of the electrolyte.

[0311] Polypropylene film is used as the isolation film.

[0312] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0313] The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface. The thickness of the negative electrode film layer H is 140 μm. The area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer.

[0314] Examples 2-7

[0315] The preparation method is basically the same as that of Example 1, except that the graphite material combination of the upper and lower layers is changed, as shown in Table 3.

[0316] Comparative Example 1

[0317] The preparation method is basically the same as that of Example 1, except that the graphite material combination of the upper and lower layers is changed, as shown in Table 3.

[0318] Table 3

[0319] Performance Testing

[0320] Cycle performance test of secondary batteries

[0321] At 60°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 3.65V. They were then charged at a constant voltage of 3.65V to a current ≤ 0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the discharge capacity (C1) of the first cycle was recorded. This charge and discharge cycle was repeated until the battery capacity decayed to 80% of the initial capacity (C1). The test was then stopped, and the number of test cycles was recorded.

[0322] (2) Charging time test

[0323] At 25°C, the secondary battery was charged to 3.65V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.50V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0324] Then the secondary battery is charged with a constant current of 1.0 C0, 1.3 C0, 1.5 C0, 1.8 C0, 2.0 C0, 2.3 C0, 2.5 C0, 3.0 C0, to a negative electrode cutoff potential of 3.5V or 0V (whichever is reached first). After each charging is completed, it is discharged to 2.5V with 1 C0. The negative electrode potential corresponding to charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge) at different charging rates is recorded, and the charging rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charging rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, C90% SOC, ...110% SOC, C120% SOC, C130% SOC, C140% SOC, C150% SOC, C160% SOC, C170% SOC, C180% SOC, C190% SOC, C20% SOC, C210% SOC, C220% SOC, C230% SOC, C240% SOC, C250% SOC, C260% SOC, C270% SOC, C300% SOC, C310% SOC, C320% SOC, C330% S At 80% SOC, the charging time T (in minutes) required for the secondary battery to charge from 10% SOC to 80% SOC (assuming lithium deposition does not occur in the secondary battery) is calculated using the formula (60 / C10% SOC + 60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0325] (3) Secondary battery cycle expansion test

[0326] At 45°C, charge the battery to 3.65V at a constant current of 1.0C (the current value that completely discharges the theoretical capacity within 1 hour), let it rest for 10 minutes, and then discharge it to 2.5V at a constant current of 1.0C. This constitutes one charge and discharge process; cycle 300 times under this condition. At 25°C, charge the secondary battery after 300 cycles at a constant current of 1.0C to 3.65V, and continue constant voltage charging to a current of 0.05C. Disassemble the secondary battery and record the thickness L1 of the electrode at this time. The initial thickness of the electrode before winding is L0, and (L1 / L0-1)*100% is used as the cyclic expansion rate of the electrode after the 300th cycle.

[0327] Test results

[0328] The test results are shown in Table 4 and Table 5. As can be seen from the table, the I D / I G Greater than the I of the active material in the first region D / I G It helps to improve the cycle stability and kinetic performance of the battery. D / I GA value of 0.2-0.35 helps to further improve the kinetic performance of the battery while maintaining a high cycle life.

[0329] Table 4

[0330] It can be seen from Table 5 that the I of the active material in the first region D / I G It is 0.05-0.1, which is beneficial to further reduce the cycle expansion of the battery and improve the cycle stability of the battery in the later stage.

[0331] Table 5

[0332] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, wherein: The invention comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, and the I of the active material in the second area is D / I G Greater than the I of the active material in the first region D / I G , I D / I G is the ratio of the D peak intensity to the G peak intensity of the Raman spectrum, I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

2. The secondary battery according to claim 1, wherein The I of the active material in the second region D / I G I of the active material in the first region D / I G The difference ΔK satisfies: 0<ΔK≤0.4, and can be selected as 0.1≤ΔK≤0.

25.

3. The secondary battery according to claim 1 or 2, wherein: The I of the active material in the first region D / I G Less than or equal to 0.14, optionally 0.05-0.1; and / or, I of the active material in the second region D / I G Greater than or equal to 0.1, optional range is 0.2-0.

35.

4. The secondary battery according to any one of claims 1 to 3, wherein: The particle size distribution (Dv90-Dv10) / Dv50 of the active material in the second region is greater than the particle size distribution (Dv90-Dv10) / Dv50 of the active material in the first region.

5. The secondary battery according to any one of claims 1 to 4, wherein: The degree of graphitization of the active material in the second region is lower than the degree of graphitization of the active material in the first region.

6. The secondary battery according to any one of claims 1 to 5, wherein: The number ratio of primary particles of the active material in the second region is higher than the number ratio of primary particles of the active material in the first region.

7. The secondary battery according to any one of claims 1 to 6, wherein: The active material in the first region includes a first graphite material, and the first particle body of the first graphite material includes an internal region and a surface region at least partially surrounding the internal region, wherein the surface region refers to a region extending 30 nm from the surface of the first particle body of the first graphite material to the interior of the particle, and the surface region includes a disordered layer.

8. The secondary battery according to claim 7, wherein The thickness of the disordered layer is 1 nm-20 nm.

9. The secondary battery according to any one of claims 1 to 8, wherein: The active material in the second region includes a second graphite material, the second graphite material includes a second particle body and a coating layer at least partially coating the surface of the second particle body, and the coating layer includes amorphous carbon.

10. The secondary battery according to claim 9, wherein The powder compaction density of the second graphite material under a pressure of 49000N is 1.60g / cm 3 -1.80g / cm 3 .

11. The secondary battery according to any one of claims 7 to 10, wherein: The first graphite material satisfies at least one of the following conditions: (1) The specific surface area of ​​the first graphite material is 1.0 m 2 / g-1.8m 2 / g, optional 1.1m 2 / g-1.7m 2 / g; (2) The volume distribution particle size Dv50 of the first graphite material is 7.0 μm-14.0 μm, and can be optionally 8.0 μm-12.0 μm; (3) The particle size distribution (Dv90-Dv10) / Dv50 of the first graphite material is 1.0-1.4, and can be 1.1-1.3; (4) The gram capacity of the first graphite material is 345 mAh / g-355 mAh / g, and can be optionally 347 mAh / g-353 mAh / g; (5) The powder compaction density of the first graphite material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , optional 1.78g / cm 3 -1.85g / cm 3 ; (6) The volume distribution particle size Dv50 of the graphite material is recorded as A, and the volume distribution particle size Dv50 of the graphite material after cold pressing under a pressure of 20000N is recorded as B. Then the graphite material satisfies: B / A ≥ 85%, which can be 85%-98%; (7) The amount of primary particles in the first graphite material accounts for 40% to 60%; optionally 50% to 60%; (8) The graphitization degree of the first graphite material is 88%-95%.

12. The secondary battery according to any one of claims 9 to 10, wherein: The second graphite material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the second graphite material is less than or equal to 15.0 μm, and can be selected from 9.0 μm to 14.0 μm; (2) The tap density of the second graphite material is 1.0 g / cm 3 -1.3g / cm 3 ; (3) The specific surface area of ​​the second graphite material is 0.75 m 2 / g-1.75m 2 / g; (4) The number of primary particles in the second graphite material accounts for greater than or equal to 80%; (5) The degree of graphitization of the second graphite material is 85%-90%; (6) the particle size distribution of the second graphite material (Dv90-Dv10) / Dv50 is 1.20-1.70; (7) The gram capacity of the second graphite material is 325 mAh / g-340 mAh / g.

13. An electrical device comprising the secondary battery according to any one of claims 1 to 11.

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