Secondary battery and electrical apparatus

Abstract

The present disclosure provides a secondary battery and an electrical 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 comprises a graphite material, and the tap density of the graphite material is 1.2 g / cm3-1.4 g / cm3; the difference value between the compaction density of the negative electrode film layer and the tap density of the graphite material is not less than 0.15 g / cm3.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This disclosure refers to Chinese patent application No. 202311675944.4, 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 relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] As the requirements for the endurance of electrical devices continue to increase, more stringent requirements are placed on the cycle life of secondary batteries. How to further improve the cycle life of secondary batteries is a technical problem that those skilled in the art urgently need to solve.

[0006] Summary of the Invention

[0007] An object of the present disclosure is to provide a secondary battery and an electric device, which can improve the cycle life of the secondary battery.

[0008] The present disclosure provides a secondary battery, characterized in that it includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector, the negative electrode film includes a graphite material, and the tap density of the graphite material is 1.2 g / cm 3 -1.4g / cm 3 ; and the difference between the compacted density of the negative electrode film layer and the tap density of the graphite material is greater than or equal to 0.15g / cm 3 .

[0009] The applicant discovered that the reason why high-tap-density graphite materials are prone to severe black spots in low-compaction-density pole pieces is that high-tap-density graphite materials tend to form dense packing. Under lower cold-pressing pressure, the pole pieces can achieve the expected low compaction density. The lower cold-pressing pressure makes the pores between the graphite materials too large during the compaction process, and the contact between the graphite materials is poor. During the formation process, the electrochemical reaction between the graphite material and the electrolyte is not timely, and the gas generated in the negative electrode film layer cannot be discharged in time, preventing the graphite material in this area from continuing to embed lithium. After full charge, severe black spots are easily formed on the negative electrode surface. The above-mentioned pole pieces will have uneven local lithium ion concentration distribution when stored at high temperatures or after multiple charge and discharge cycles, causing lithium precipitation to cause capacity decay and a significant deterioration in capacity retention. The disclosed embodiments break the prejudice in the prior art by using a high-tap-density negative electrode film layer in combination with a high-tap-density graphite material. This secondary battery can fully utilize the advantages of the high-tap-density graphite material in terms of good cycle performance, while also reducing the probability of severe black spots forming on the negative electrode after the battery is fully charged, and reducing the probability of the battery's performance "diving" after long-cycle cycling or high-temperature storage, thereby improving the battery's cycle stability and high-temperature storage stability.

[0010] In any embodiment of the present disclosure, the compaction density of the negative electrode film layer is less than or equal to 1.55 g / cm 3 , and greater than or equal to 1.40g / cm 3 .

[0011] A reasonable range of electrode film compaction density can not only reduce the probability of severe black spots forming on the electrode after the battery is fully charged, but also improve the integrity of the graphite material particles during the cold pressing process, maintain the pore structure inside the electrode and lower electrode tortuosity, and take into account the long cycle stability and high dynamic performance of the secondary battery.

[0012] In any embodiment of the present disclosure, the graphite material includes primary particles. In some embodiments, the primary particles in the graphite material account for greater than or equal to 85% of the total number of particles in the graphite material. In some exemplary embodiments, the primary particles in the graphite material account for between 85% and 100% of the total number of particles in the graphite material.

[0013] Compared with secondary particles, primary particles can effectively reduce the grain boundary content, reduce the probability of side reactions between graphite materials and electrolytes, improve the uniformity of electrodes, and improve the cycle stability of secondary batteries through a high proportion of primary particle content.

[0014] In any embodiment of the present disclosure, the Dv1 of the graphite material is 1.5 μm to 3.0 μm. In some embodiments, the Dv1 of the graphite material is 1.6 μm to 2.8 μm.

[0015] Applicants have discovered that the Dv1 particle size of graphite materials has a significant impact on the electrochemical performance of secondary batteries. A graphite material with a Dv1 within an appropriate range not only allows the negative electrode film layer to contain a certain proportion of fine powder, namely, small-particle graphite material, which is beneficial for improving the electrical contact of the negative electrode film layer, improving kinetic performance, and advancing the end of gas production at SOC, reducing the probability of severe black spots during battery preparation and the probability of electrochemical performance "diving" during battery cycling or storage; it also reduces the probability of small-particle graphite material clogging the pores of the negative electrode film layer, maintaining normal electrode pores, allowing for high electrolyte wettability, reducing the risk of lithium plating at the negative electrode, and improving the battery's cycling stability and high-temperature storage stability.

[0016] In any embodiment of the present disclosure, the graphite material has a Dv50 of 12 μm to 16 μm. In some embodiments, the graphite material has a Dv50 of 13 μm to 15 μm.

[0017] The graphite material has a large volume distribution particle size Dv50, which is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, which is conducive to the full infiltration of the electrolyte into the negative electrode plate, reducing the possibility of local polarization of the plate, and reducing the impact of black spots on the negative electrode on the cycle life and storage stability of the battery.

[0018] In any embodiment of the present disclosure, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.2-1.7. In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.35-1.60.

[0019] Graphite materials with a particle size distribution within the above range can reduce the uneven distribution of active ions in the graphite material caused by the large difference in particle size, reduce the side reaction between small-particle graphite materials and the electrolyte, and improve the cycle performance and storage stability of secondary batteries.

[0020] In any embodiment of the present disclosure, the specific surface area of ​​the graphite material is 0.6 m 2 / g-1.5m 2 / g. In some embodiments, the specific surface area of ​​the graphite material is 0.9m 2 / g-1.4m 2 / g.

[0021] Graphite material has a small specific surface area, which can reduce the probability of side reactions between graphite material and electrolyte, and improve the cycle performance and storage stability of the battery.

[0022] In any embodiment of the present disclosure, the oil absorption value of the graphite material does not exceed 45 ml / 100 g. In some embodiments, the oil absorption value of the graphite material is 30 ml / 100 g to 45 ml / 100 g.

[0023] The oil absorption value of the graphite material can, to a certain extent, reflect the dispersibility of the graphite material in the negative electrode slurry. A high oil absorption value of the graphite material means that the graphite material needs to be infiltrated with more dispersants, such as sodium carboxymethyl cellulose, during the dispersion process. The slurry is more likely to settle, resulting in unstable quality during the electrode coating process and uneven electrode thickness after cold pressing. Graphite materials with oil absorption values ​​within the above range can not only have good wettability for the electrolyte, so that the secondary battery has good dynamic performance and cycle stability; they can also maintain good particle dispersion during the stirring process, and are not prone to slurry sedimentation due to excessive adsorption of dispersants by the graphite material, so that the electrode coating has a wide process window and the electrode has good uniformity.

[0024] In any embodiment of the present disclosure, the graphite material has a degree of graphitization of 88% to 93%. In some embodiments, the graphite material has a degree of graphitization of 89% to 92%.

[0025] Controlling the degree of graphitization within the above range can not only take into account the capacity of the graphite material, but also achieve a smaller volume change of the graphite active material during the charging process, which is beneficial to improving the cycle stability.

[0026] In any embodiment of the present disclosure, the surface density of the negative electrode film layer is 7 mg / cm 2 ~14mg / cm 2 In some embodiments, the surface density of the negative electrode film layer is 9 mg / cm 2 ~12mg / cm 2 .

[0027] In any embodiment of the present disclosure, the graphite material includes artificial graphite.

[0028] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] FIG. 1 is a schematic diagram of one embodiment of a secondary battery of the present disclosure.

[0031] FIG. 2 is an exploded schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0032] FIG3 is a schematic diagram of an embodiment of a battery module of the present disclosure.

[0033] FIG. 4 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0034] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0035] FIG6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present disclosure as a power source.

[0036] 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. DETAILED DESCRIPTION

[0037] 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.

[0038] " 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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).

[0044] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0045] 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.

[0046] 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.

[0047] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0048] With the continuous development of the new energy industry, lithium battery energy storage systems have received more and more attention. A lithium battery energy storage system is a device that uses lithium batteries for energy storage. It can store energy generated by renewable energy sources such as solar photovoltaics and wind power, and can also serve as an auxiliary facility for the power grid. Compared with power batteries, energy storage batteries pay more attention to the cycle life of the battery. In order to pursue a long cycle life of the battery, R&D personnel usually choose a negative electrode material with a high tap density and a low electrode film layer compaction density. This is because the negative electrode material with a high tap density is subjected to less pressure during the cold pressing process of the electrode, which is conducive to maintaining the integrity of the particles and low stress inside the particles, reducing the probability of side reactions while maintaining the long-period pore structure of the electrode, ensuring the smooth lithium insertion path, reducing polarization, providing the battery with long cycle dynamic performance, and improving the cycle life of the battery. However, during the research and development process, the applicant discovered that the negative electrode plate is prone to forming black spots on the surface after full charging, which has an adverse effect on the appearance and quality of the plate. In addition, the plate with severe black spots will lead to uneven distribution of local lithium ion concentration after multiple charging and discharging, causing lithium plating and resulting in a "dive" in capacity, which cannot meet the use and storage requirements of long cycle life batteries.

[0049] Based on this, the present disclosure provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector, the negative electrode film comprising a graphite material, the tap density of the graphite material being 1.2 g / cm 3 (g / cm 3 )-1.4g / cm 3 ; and the difference between the compacted density of the negative electrode film layer and the tap density of the graphite material is greater than or equal to 0.15g / cm 3 .

[0050] 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.

[0051] In the present disclosure, the tap density of the graphite material can be tested 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 millimeters (mm), vibration count of 5000 times, and a 25 milliliter (mL) graduated cylinder.

[0052] In some embodiments, the tap density of the graphite material is 1.2 g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3, 1.4g / cm 3 or any range of values ​​between them.

[0053] In the present disclosure, the compaction density of the negative electrode film layer can be tested using methods known in the art. As an example, an electronic balance is used to weigh a negative electrode sheet test sample with an area of ​​S, and the weight is recorded as W1. The thickness of the negative electrode sheet T1 is measured using a caliper. The weighed electrode sheet film layer is then wiped off, the weight of the negative electrode current collector is weighed, recorded as W2, and the thickness of the negative electrode current collector T2 is measured using a caliper. The compaction density of the negative electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0054] In some embodiments, the difference between the compaction density of the negative electrode film layer and the tap density of the graphite material is 0.15 g / cm 3 , 0.16g / cm 3 , 0.17g / cm 3 , 0.18g / cm 3 , 0.19g / cm 3 , 0.2g / cm 3 , 0.21g / cm 3 , 0.22g / cm 3 , 0.23g / cm 3 , 0.24g / cm 3 , 0.25g / cm 3 or any range of values ​​between them.

[0055] The applicant discovered that the reason why high-tap-density graphite materials are prone to severe black spots in low-compaction-density pole pieces is that high-tap-density graphite materials tend to form dense packing. Under lower cold-pressing pressure, the pole pieces can achieve the expected low compaction density. The lower cold-pressing pressure makes the pores between the graphite materials too large during the compaction process, and the contact between the graphite materials is poor. During the formation process, the electrochemical reaction between the graphite material and the electrolyte is not timely, and the gas generated in the negative electrode film layer cannot be discharged in time, preventing the graphite material in this area from continuing to embed lithium. After full charge, severe black spots are easily formed on the negative electrode surface. The above-mentioned pole pieces will have uneven local lithium ion concentration distribution when stored at high temperatures or after multiple charge and discharge cycles, causing lithium precipitation to cause capacity decay and a significant deterioration in capacity retention. The disclosed embodiments break the prejudice in the prior art by using a high-tap-density negative electrode film layer in combination with a high-tap-density graphite material. This secondary battery can fully utilize the advantages of the high-tap-density graphite material in terms of good cycle performance, while also reducing the probability of severe black spots forming on the negative electrode after the battery is fully charged, and reducing the probability of the battery's performance "diving" after long-cycle cycling or high-temperature storage, thereby improving the battery's cycle stability and high-temperature storage stability.

[0056] In some embodiments, the compaction density of the negative electrode film layer is less than or equal to 1.55 g / cm 3 , and greater than or equal to 1.40g / cm 3 .

[0057] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 , 1.43g / cm 3 , 1.46g / cm 3 , 1.49g / cm 3 , 1.52g / cm 3 , 1.55g / cm 3 or any range of values ​​between them.

[0058] A reasonable range of electrode film compaction density can not only reduce the probability of severe black spots forming on the surface of the negative electrode after the battery is fully charged, but also improve the integrity of the graphite material particles during the cold pressing process, maintain the pore structure inside the electrode and the lower electrode tortuosity, and take into account the long cycle stability and high dynamic performance of the secondary battery.

[0059] In some embodiments, the graphite material includes primary particles. In some embodiments, the primary particles in the graphite material account for greater than or equal to 85% of the total number of particles in the graphite material. In some embodiments, the primary particles in the graphite material account for between 85% and 100% of the total number of particles in the graphite material.

[0060] As used herein, the term "primary particles" refers to particles in a non-agglomerated state.

[0061] In the present disclosure, the proportion of primary particles in the graphite material can be tested by methods known in the art. As an example, a test sample is randomly selected in the negative electrode film layer, and multiple test areas are randomly selected in the test sample. Images of the multiple test areas are obtained using a scanning electron microscope. The proportion of the number of graphite material particles with primary particle morphology in each image to the total number of graphite material particles is counted, and the average value of the multiple statistical results is the proportion of primary particles in the graphite material.

[0062] In some embodiments, based on the total number of particles of the graphite material, the number of primary particles in the graphite material accounts for 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% or any range therebetween.

[0063] Compared with secondary particles, primary particles can effectively reduce the grain boundary content, reduce the probability of side reactions between graphite materials and electrolytes, improve the uniformity of the electrodes, and further improve the cycle stability of secondary batteries through a high proportion of primary particle content.

[0064] In some embodiments, the graphite material has a Dv1 of 1.5 micrometers (μm) to 3.0 μm. In some embodiments, the graphite material has a Dv1 of 1.6 μm to 2.8 μm.

[0065] In this article, the terms "Dv1", "Dv50", "Dv90" and "Dv10" refer to the particle sizes corresponding to when the cumulative volume distribution number of the material reaches 1%, 50%, 90% and 10% in the particle size distribution curve, respectively.

[0066] In the present disclosure, the volume distribution particle sizes Dv1, Dv50, Dv90, and Dv10 of the graphite material can be measured using methods known in the art. For example, with reference to GB / T 19077-2016, they can be 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.

[0067] In some embodiments, the Dv1 of the graphite material is 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm or any range therebetween.

[0068] Applicants have discovered that the Dv1 particle size of graphite materials has a significant impact on the electrochemical performance of secondary batteries. A graphite material with a Dv1 within an appropriate range not only allows the negative electrode film layer to contain a certain proportion of fine powder, namely, small-particle graphite material, which is beneficial for improving the electrical contact of the negative electrode film layer, improving kinetic performance, and shortening the gas production cutoff to SOC, reducing the probability of severe black spots during battery preparation and the probability of electrochemical performance "diving" during battery cycling; it also reduces the probability of small-particle graphite material clogging the pores of the negative electrode film layer, maintaining normal electrode pores, allowing for high electrolyte wettability, reducing the risk of lithium plating at the negative electrode, and further improving the battery's cycling stability.

[0069] In some embodiments, the graphite material has a Dv50 of 12 μm to 16 μm. In some embodiments, the graphite material has a Dv50 of 13 μm to 15 μm.

[0070] In some embodiments, the Dv50 of the graphite material is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or any range therebetween.

[0071] The graphite material has a large volume distribution particle size Dv50, which is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, which is conducive to the full infiltration of the electrolyte into the negative electrode plate, reducing the possibility of local polarization of the plate, and reducing the impact of black spots on the negative electrode on the cycle life and storage stability of the battery.

[0072] In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.2-1.7. In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.35-1.60.

[0073] In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, or any range therebetween.

[0074] Graphite materials with a particle size distribution within the above range can reduce the uneven distribution of active ions in the graphite material caused by the large difference in particle size, reduce the side reaction between small-particle graphite materials and the electrolyte, and improve the cycle performance and storage stability of secondary batteries.

[0075] In some embodiments, the specific surface area of ​​the graphite material is 0.6 m 2 / g(m 2 / g)-1.5m 2 / g. In some embodiments, the specific surface area of ​​the graphite material is 0.9m 2 / g-1.4m 2 / g.

[0076] In the present disclosure, the specific surface area of ​​the graphite material can be measured using methods known in the art. For example, the specific surface area of ​​the graphite material can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 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.

[0077] In some embodiments, the specific surface area of ​​the graphite material is 0.6 m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or any range of values ​​between them.

[0078] Graphite material has a small specific surface area, which can reduce the probability of side reactions between graphite material and electrolyte, and improve the cycle performance and storage stability of the battery.

[0079] In some embodiments, the graphite material has an oil absorption value of less than or equal to 45 milliliters (ml) / 100 grams (g). In some embodiments, the graphite material has an oil absorption value of 30 ml / 100 g to 45 ml / 100 g.

[0080] As used herein, the term "oil absorption value" refers to the volume of linseed oil that can be absorbed by 100 g of graphite material. For example, an oil absorption value of 40 ml / 100 g of graphite material means that 100 g of graphite material can absorb 40 ml of linseed oil.

[0081] The oil absorption of graphite materials can be tested using methods and equipment known in the art. For example, the following steps are performed: Test oil and graphite material samples are obtained, and a torque threshold is set for the oil absorption tester. Oil is then added to the sample in the mixing chamber of the oil absorption tester at a constant rate. As the amount of oil absorbed by the sample increases, the viscosity of the sample-oil mixture increases. When the viscosity of the mixture reaches the preset torque threshold, the tester stops and calculates the volume of oil absorbed per unit mass of the sample. This value is the oil absorption value (QI) of the sample. The test oil used is linseed oil (DBP), and the torque threshold is 1 Newton (N).

[0082] In some embodiments, the oil absorption value of the graphite material is 30 ml / 100 g, 31 ml / 100 g, 32 ml / 100 g, 33 ml / 100 g, 34 ml / 100 g, 35 ml / 100 g, 36 ml / 100 g, 37 ml / 100 g, 38 ml / 100 g, 39 ml / 100 g, 40 ml / 100 g, 41 ml / 100 g, 42 ml / 100 g, 43 ml / 100 g, 44 ml / 100 g, 45 ml / 100 g or any range therebetween.

[0083] The oil absorption value of the graphite material can, to a certain extent, reflect the dispersibility of the graphite material in the negative electrode slurry. A high oil absorption value of the graphite material means that the graphite material needs to be infiltrated with more dispersants, such as sodium carboxymethyl cellulose, during the dispersion process. The slurry is more likely to settle, resulting in unstable quality during the electrode coating process and uneven electrode thickness after cold pressing. Graphite materials with oil absorption values ​​within the above range can not only have good wettability for the electrolyte, so that the secondary battery has good dynamic performance and cycle stability; they can also maintain good particle dispersion during the stirring process, and are not prone to slurry sedimentation due to excessive adsorption of dispersants by the graphite material, so that the electrode coating has a wide process window and the electrode has good uniformity.

[0084] In some embodiments, the graphite material has a degree of graphitization of 88% to 93%. In some embodiments, the graphite material has a degree of graphitization of 89% to 92%.

[0085] 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.

[0086] In the present disclosure, the graphitization degree of the graphite material can be tested by methods known in the art. As an example, an X-ray diffractometer (such as Bruker D8 Discover) is used for testing, and the average interlayer spacing d of the (002) crystal plane in the crystal structure of the graphite material is obtained by referring to JIS K0131-1996 and JB / T4220-2011. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. 002 It is the average interlayer spacing of the (002) crystal planes in the crystal structure of graphite material expressed in nanometers (nm).

[0087] In some embodiments, the graphite material has a degree of graphitization of 88%, 89%, 90%, 91%, 92%, 93%, or any range therebetween.

[0088] Controlling the degree of graphitization within the above range can not only take into account the capacity of the graphite material, but also achieve a smaller volume change of the graphite active material during the charging process, which is conducive to further improving the cycle stability.

[0089] In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 (mg / cm 2 )-14mg / cm 2 In some embodiments, the surface density of the negative electrode film layer is 9 mg / cm 2 ~12mg / cm 2 .

[0090] In this disclosure, the areal density of the negative electrode film layer can be measured using methods known in the art. As an example, a cold-pressed negative electrode sheet is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1. The negative electrode film layer of the weighed negative electrode sheet is then wiped off and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1.

[0091] In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 , 14mg / cm 2 or any range of values ​​between them.

[0092] In some embodiments, the graphite material includes synthetic graphite.

[0093] In some embodiments, the preparation method of graphite material includes the following steps: providing raw materials, the raw materials including at least one of petroleum coke, needle coke, and asphalt coke, and based on the total volume of the raw material structure, the volume of the mosaic structure and the regional structure in the raw materials accounts for greater than or equal to 60%; processing the raw materials to obtain an intermediate product; and graphitizing the intermediate product to obtain a graphite material.

[0094] In this article, the term "petroleum coke" refers to the coke formed by high-temperature carbonization of petroleum residue or petroleum asphalt, which is called petroleum coke.

[0095] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which is carbonized in the liquid phase to form an anisotropic mesophase, and then subjected to high-temperature carbonization and other processes to produce coke with a needle-like texture.

[0096] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0097] In some embodiments, the feedstock comprises petroleum coke.

[0098] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low-graphitization and low-expansion graphite materials, which is conducive to the long cycle life of the battery. At the same time, petroleum coke has high compaction density and high gram capacity, which is conducive to improving the energy density of the battery. In addition, the source of petroleum coke is more extensive, which is conducive to industrial production.

[0099] The above-mentioned raw materials generally include at least one of mosaic, regional, and fibrous structures. Generally, based on the morphological characteristics and isochromatic zone size of the char material under a polarizing microscope, isochromatic zones with a size less than 30 μm are classified as mosaic; isochromatic zones with a size greater than 30 μm are classified as regional; and anisotropic banded isochromatic zones are classified as fibrous.

[0100] In the present disclosure, the proportion of mosaic structure and regional structure in the raw material can be tested by 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 0.3mm to 0.5mm and a line spacing of 0.5mm to 0.8mm. Starting from one end of the sample, determine the microstructure category under the intersection of the crosshairs, and divide the number of effective measuring points of the mosaic-type structure and regional-type structure optical tissue by the total number of statistical test points as the volume proportion of the mosaic-type structure and regional-type structure in the raw material.

[0101] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the mosaic structure and the regional structure in the raw material is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% or any numerical range therebetween.

[0102] Precursors with a relatively high volume ratio of mosaic structures and regional structures in the raw materials have higher isotropy, which is conducive to the preparation of graphite materials with a low degree of graphitization, reducing the expansion rate of the lattice during the charge and discharge cycle, and improving the cycle stability of the battery.

[0103] In some embodiments, the power of the graphitization process is 70% to 90% of the rated power of the equipment.

[0104] In some embodiments, the power of the graphitization process is 70%, 75%, 80%, 85%, 90%, or any range therebetween of the rated power of the equipment. It is understood that graphitization processing equipment refers to any device capable of performing graphitization processing, 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 processing equipment produced by different manufacturers may vary, and the rated power can be selected based on actual conditions.

[0105] The graphitization treatment power used in the present disclosure needs to be lower than the rated power of the graphitization treatment equipment to achieve uniformity of the temperature field during the graphitization process, ensure the consistency of the material's gram capacity, and help improve the cycle life of the battery.

[0106] In some embodiments, the maximum power of the graphitization process is 23,000 watts (W) to 25,000 W.

[0107] In some embodiments, the maximum power of the graphitization process is 23,000 W, 23,500 W, 24,000 W, 24,500 W, 25,000 W, or any range therebetween.

[0108] By controlling the maximum power of the graphitization treatment, the graphitization degree of the graphite material during the heat treatment process can be effectively controlled, which is beneficial to improving the cycle life of the battery.

[0109] In some embodiments, the graphitization process is performed at a constant power time of 10 hours (h) to 50 hours at maximum power.

[0110] In some embodiments, the constant power time of the graphitization treatment at maximum power is 10 h, 13 h, 16 h, 19 h, 22 h, 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, or any range therebetween.

[0111] In some embodiments, the graphitization treatment equipment is an internal series furnace, and the graphitization treatment time at maximum power is 10 hours to 30 hours.

[0112] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the graphitization treatment time at maximum power is 30 hours to 50 hours.

[0113] The appropriate graphitization treatment time is 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 the cycle performance; it can also effectively increase the gram capacity of the graphite material, thereby facilitating the simultaneous improvement of the energy density and cycle life of the secondary battery.

[0114] In some embodiments, the processing of raw materials specifically includes the following steps: crushing, shaping and grading the raw materials to obtain secondary raw materials; removing a certain proportion of fine powder in the secondary raw materials, the mass of the removed fine powder is 15%-45% of the total mass of the secondary raw materials, and obtaining a precursor, wherein the Dv50 of the fine powder is 3μm-7μm, and Dv99 is less than or equal to 30μm.

[0115] In some embodiments, during the step of crushing the raw material, a crusher, such as a jaw crusher, can be used to crush the raw material. For example, the raw material can be crushed to a predetermined particle size and then sieved, such as through a 3-20 mesh screen.

[0116] In some embodiments, in the step of shaping the raw material, a shaping machine can be used to shape the crushed raw material. The shaping process can reduce burrs on the surface of the crushed raw material, thereby facilitating the production of rounded graphite materials.

[0117] In some embodiments, during the step of classifying the raw materials, an air classifier can be used to classify the shaped raw materials. In some embodiments, the induced air frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 65 Hz. Classification can reduce the content of large and small particles in the precursor.

[0118] In some embodiments, based on the total mass of the secondary raw material, the proportion of fine powder removed from the secondary raw material is any value of 10%, 15%, 20%, 25%, 30%, 35%, or a range consisting of any two values ​​therein.

[0119] By controlling the proportion of fine powder removal within a suitable range, the volume distribution particle size Dv1 of the graphite material can be controlled within a suitable range, which can not only make the electrode have an excellent liquid absorption rate and the electrolyte can fully infiltrate the negative electrode, but also make the graphite particles have excellent electrical contact, thereby comprehensively improving the cycle performance of the battery.

[0120] In some embodiments, the volume distribution particle size Dv50 of the precursor is 12 μm-18 μm.

[0121] In some embodiments, the volume distribution particle size Dv50 of the precursor is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any range therebetween.

[0122] In some embodiments, the (Dv90-Dv10) / Dv50 of the precursor is 1.3-2.0.

[0123] In some embodiments, (Dv90-Dv10) / Dv50 of the precursor is 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any range therebetween.

[0124] Controlling the volume distribution particle size Dv50 or (Dv90-Dv10) / Dv50 of the precursor within a suitable range is beneficial to controlling the volume distribution particle size Dv50 or (Dv90-Dv10) / Dv50 of the graphite material within a suitable range, which can improve the cycle performance of the battery.

[0125] 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.

[0126] [Negative electrode]

[0127] 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.

[0128] In some embodiments, the negative electrode film layer comprises the graphite material of the first aspect of the embodiment of the present disclosure or the graphite material prepared by the method described in the second aspect of the embodiment of the present disclosure. This enables the secondary battery to have high initial coulombic efficiency, high energy density, good cycle performance and storage stability.

[0129] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned graphite materials. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, 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.

[0130] In some embodiments, the negative electrode film layer further includes a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. As an 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.

[0131] In some embodiments, the negative electrode film layer further includes a negative electrode binder. The present disclosure does not particularly limit the type of the negative electrode binder. As an example, 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).

[0132] In some embodiments, the negative electrode film layer further comprises other additives, for example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0133] 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).

[0134] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, conductive agent, binder, and other additives in a solvent and stirring until uniformly mixed. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0135] 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.

[0136] [Positive electrode]

[0137] 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.

[0138] 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).

[0139] The positive electrode film layer generally comprises a positive electrode active material, a binder and a 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, a conductive agent, a binder and any other components in a solvent and stirring them 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.

[0140] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0141] 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 lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxides 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. Examples of the lithium-containing phosphates 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 manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0142] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having a general formula of Li a Ni b Co c M d O e A f and its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0143] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4. [[ID=四十九]] [[ID=五十]]

[0144] 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.

[0145] [Electrolytes]

[0146] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0147] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0148] 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).

[0149] 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.

[0150] In some embodiments, the electrolyte further includes 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.

[0151] [Isolation film]

[0152] 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.

[0153] 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.

[0154] 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.

[0155] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0156] 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).

[0157] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG1 shows a secondary battery 5 with a square structure as an example.

[0158] In some embodiments, as shown in FIG2 , 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 isolation film 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.

[0159] 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.

[0160] 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.

[0161] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , 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 using fasteners.

[0162] In some embodiments, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 may be received in the receiving space.

[0163] 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.

[0164] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, 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 can be arranged in any manner within the battery box.

[0165] Electrical devices

[0166] 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.

[0167] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0168] Figure 6 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.

[0169] 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.

[0170] Example

[0171] 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.

[0172] Material 1

[0173] The petroleum coke with a mosaic and regional structure accounting for 63.1% is coarsely crushed; the coarsely crushed material is then crushed and sieved, and the sieved material is shaped and graded. During the grading process, a certain amount of fine powder is removed to obtain a precursor, wherein the removed fine powder accounts for 17% of the total mass of the petroleum coke raw material. The obtained precursor has a Dv50 particle size of 15.5μm and a particle size distribution (Dv90-Dv10) / Dv50 of 1.92; fine powder refers to a component with a Dv50 of 3μm-7μm and a Dv99 of less than or equal to 30μm.

[0174] The precursor was graphitized in an Acheson furnace at a temperature of 2800°C and a maximum power of 24000W. After 40 hours of treatment at the maximum power, the surface temperature of the Acheson furnace crucible was cooled to 400°C, the graphite crucible was taken out, and the graphite material was obtained after screening and demagnetization.

[0175] The tap density of graphite material is 1.21g / cm 3 , Dv1 is 1.8μm, Dv50 is 14.6μm, particle size distribution (Dv90-Dv10) / Dv50 is 1.42, and the specific surface area is 1.14m 2 / g, and the degree of graphitization is 91.1%.

[0176] Materials 2-5

[0177] The preparation method of material 2-5 is similar to that of material 1, except that the proportion of fine powder removal and the particle size distribution of the precursor are adjusted.

[0178] The material adjustment parameters and specific material properties are shown in Table 1.

[0179] Table 1

[0180] Example 1

[0181] The above-prepared material 1, conductive agent carbon black (Super P), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent at a weight ratio of 95.4:1.8:1.0:1.8 to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The compacted density of the negative electrode film was 1.50 g / cm 3 , with a surface density of 9.4 mg / cm 2 .

[0182] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder PVDF were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone NMP was added. The mixture was stirred in a vacuum mixer until the system was uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheets were obtained after drying, cold pressing, and slitting. The compacted density of the positive electrode film layer is 2.50g / cm 3 , with a surface density of 20 mg / cm 2 .

[0183] 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.

[0184] Polypropylene film is used as the isolation membrane.

[0185] 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.

[0186] Examples 2-6 and Comparative Examples 1-2

[0187] The preparation method of the secondary battery is similar to that of Example 1, except that different graphite materials are used or the compaction density of the electrode film layer is adjusted, as shown in Table 2 for details.

[0188] Performance Testing

[0189] (1) Formation-End State of Charge (SOC) Test

[0190] At 25° C., the battery after injection prepared in the example and the comparative example was charged at 0.33C, and the gas generated during the formation process was collected. When the total amount of gas did not increase, the corresponding SOC was recorded.

[0191] (2) Dark spot test

[0192] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, disassembled in a drying room, and the surface of the negative electrode plate was observed to see whether there were black spots; the total area of ​​black spots / total area of ​​the negative electrode plate ≤1%, and the area of ​​black spots in a single electrode plate / area of ​​a single electrode plate ≤8% were defined as first-level black spots; 1% <total area of ​​black spots / total area of ​​the negative electrode plate ≤3%, or 8% <area of ​​black spots in a single electrode plate / area of ​​a single electrode plate ≤15% were defined as second-level black spots; the total area of ​​black spots / total area of ​​the negative electrode plate >3%, or the area of ​​black spots in a single electrode plate / area of ​​a single electrode plate >15%, were defined as third-level black spots.

[0193] (3) Cycle performance test of secondary batteries

[0194] 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 of 0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge-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 number of cycles was recorded.

[0195] (4) 120-day storage stability test of secondary batteries

[0196] In a 25°C environment, a charge and discharge test was performed. The battery was charged to 3.65V at a constant current of 0.5C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.5V at a constant current of 0.5C. The discharge capacity at this time was recorded, which was the initial discharge capacity. The battery cell was then fully charged and placed in a 60°C environment for different periods of time. Every 30 days, the remaining capacity was tested at 25°C. This was a storage cycle, and the discharge capacity this time was the discharge capacity after the first storage. Subsequently, the first storage test process was repeated, and the discharge capacity value during the storage process was recorded. The discharge capacity after 120 days / initial discharge capacity was used as the 120-day storage capacity retention rate.

[0197] Test results

[0198] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0199] Table 2

[0200] From the comparison between the embodiment and the comparative example, it can be seen that in the secondary battery, the negative electrode film layer includes a graphite material, and the tap density of the graphite material is 1.2 g / cm 3 -1.4g / cm 3 ; and the difference between the compacted density of the negative electrode film layer and the tap density of the graphite material is greater than or equal to 0.15g / cm 3 , which can give full play to the advantages of high tap density negative electrode materials, improve the battery cycle stability while reducing the severity of negative electrode black spots, thereby improving the battery cycle stability and storage stability.

[0201] As can be seen from Examples 1-4, when the Dv1 of the graphite material is 1.5μm-3.0μm, the battery's formation-end SOC is further reduced and the cycle stability is further improved. Formation is the process of charging the battery for the first time and activating the electrochemical reaction inside the battery. As the formation charge proceeds, lithium ions are deintercalated from the positive electrode material, transported through the diaphragm by the electrolyte to the negative electrode and embedded in the negative electrode material, thereby forming a potential difference between the positive and negative electrodes, converting electrical energy into chemical energy of the battery. When the formation voltage reaches a certain value, an oxidation-reduction reaction occurs at the solid-liquid interface between the negative electrode and the electrolyte, forming a solid electrolyte interface film (SEI film). The higher the formation-end SOC, the higher the amount of electricity charged during the formation process, the more lithium ions consumed to form the SEI film, the greater the severity of black spots generated at the negative electrode of the battery, and the lower the battery's first efficiency. Reducing the battery's formation-end SOC is beneficial to reducing the severity of negative electrode black spots and improving the battery's cycle stability and high-temperature storage stability.

[0202] 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, characterized in that: The invention comprises 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, wherein the negative electrode film layer comprises a graphite material, and the tap density of the graphite material is 1.2 g / cm 3 -1.4g / cm 3 ; and the difference between the compaction density of the negative electrode film layer and the tap density of the graphite material is greater than or equal to 0.15g / cm 3 .

2. The secondary battery according to claim 1, characterized in that: The compaction density of the negative electrode film layer is less than or equal to 1.55 g / cm 3 , and greater than or equal to 1.40g / cm 3 .

3. The secondary battery according to claim 1 or 2, characterized in that: The graphite material includes primary particles; optionally, based on the total number of particles of the graphite material, the number of primary particles in the graphite material accounts for greater than or equal to 85%, and optionally 85%-100%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The Dv1 of the graphite material is 1.5 μm-3.0 μm, and can be optionally 1.6 μm-2.8 μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The Dv50 of the graphite material is 12 μm-16 μm, and can be optionally 13 μm-15 μm.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.2-1.70, and can be optionally 1.35-1.

60.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The specific surface area of ​​the graphite material is 0.6 m 2 / g-1.5m 2 / g, optional 0.9m 2 / g-1.4m 2 / g.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: The oil absorption value of the graphite material is less than or equal to 45 ml / 100 g, and can be optionally 30 ml / 100 g-45 ml / 100 g.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The graphitization degree of the graphite material is 88%-93%, and can be optionally 89%-92%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that: The surface density of the negative electrode film layer is 7 mg / cm 2 ~14mg / cm 2 , optional 9mg / cm 2 ~12mg / cm 2 .

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The graphite material includes artificial graphite.

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

Images