Charging method

Abstract

The invention relates to the technical field of lithium batteries, and provides a charging method. The charging method comprises a first charging section and a second charging section, the voltage of the first charging section is smaller than that of the second charging section, the voltage of the first charging section is increased along with the increase of the charging time, the voltage of the second charging section is unchanged, and the first charging section comprises the following charging processes: charging the lithium ion battery with a first current within a first time; charging the lithium ion battery with a second current within a second time; charging the lithium ion battery with a third current within a third time; and charging the lithium ion battery with a fourth current within a fourth time. The first time is greater than the second time; the third current is not greater than the first current; the third time is greater than the second time; the fourth current is smaller than the third current; the charging method can reduce the gas production rate of the battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a charging method. Background Art

[0002] In recent years, as the application scope of batteries becomes wider and wider, batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. In the application process of lithium batteries, the battery capacity is getting larger and larger, and the electrodes in the battery are getting thicker and thicker; batteries with larger capacity and thicker electrodes are needed. However, as the battery capacity increases, especially the thicker electrodes, the gas generation problem in the battery is more and more serious than before, and the phenomenon of battery explosion-proof valves being flushed open is increasing. After the explosion-proof valve is flushed open, the battery can no longer be used. We expect the battery's explosion-proof valve to be flushed open during abnormal use or extreme environments, rather than during normal use.

[0003] How to further improve battery capacity and rate performance, while reducing the risk of battery scrapping due to unreasonable opening of the explosion-proof valve, has become a problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its object is to provide a large-capacity lithium-ion battery whose explosion-proof valve is not blown open during normal use.

[0005] In order to achieve the above-mentioned object, the present application provides a lithium-ion battery, comprising a shell, a battery cell, and an electrolyte, wherein the battery cell and the electrolyte are arranged inside the shell, the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode collector and a positive electrode active material layer, wherein the positive electrode active material layer is electrically connected to the positive electrode collector, the negative electrode sheet comprises a negative electrode collector and a negative electrode active material layer, wherein the negative electrode active material layer is electrically connected to the negative electrode collector;

[0006] The negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the thickness of the single-side active material layer of the negative electrode sheet is between 50 μm and 95 μm; the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite; the Dv50 of the graphite is in the range of 10 μm to 30 μm, and the graphitization degree of the graphite is greater than or equal to 90%;

[0007] The positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the thickness of the single-side active material layer of the positive electrode sheet is between 60 μm and 105 μm; the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium-containing phosphate and a carbon layer located on the surface of the lithium-containing phosphate;

[0008] The capacity L of the lithium-ion battery is 300Ah<L≤500Ah, and the actual gas storage space v of the lithium-ion battery is >87cm 3 .

[0009] The present application further provides batteries of different capacities, specifically:

[0010] The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.29cm 3 / Ah·L; or,

[0011] The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.33cm 3 / Ah·L;

[0012] The actual gas storage space v of the lithium-ion battery is greater than or equal to the theoretical gas storage space V0 of the lithium-ion battery.

[0013] Further preferred:

[0014] The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.4cm 3 / Ah·L; or,

[0015] The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.47cm 3 / Ah·L;

[0016] The actual gas storage space v of the lithium-ion battery is greater than or equal to the theoretical gas storage space V0 of the lithium-ion battery.

[0017] From the perspective of improving energy density, it is further defined as follows:

[0018] The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.4cm 3 / Ah·L; or,

[0019] The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.47cm 3 / Ah·L;

[0020] The actual gas storage space v of the lithium-ion battery is less than or equal to the theoretical maximum gas storage space V0max of the lithium-ion battery.

[0021] In some embodiments, at least a portion of the surface of the graphite is covered with a carbon layer, Dv90 of the graphite is ≤40 μm, Dv10 of the graphite is ≥3 μm, and Dv99 of the graphite is ≤49 μm.

[0022] In some embodiments, the OI value of the graphite is in the range of 3-30, preferably the OI value of the graphite is in the range of 10-30, and more preferably the OI value of the graphite is in the range of 15-30.

[0023] In some embodiments, the graphitization degree of the graphite is between 90% and 95%, and preferably the graphitization degree of the graphite is between 91% and 95%.

[0024] In some embodiments, the surface density of the single-sided active material layer of the negative electrode sheet is 0.07 mg / mm 2 -0.13mg / mm 2 between.

[0025] In some embodiments, the compaction density of the single-sided active material layer of the negative electrode sheet is between 1.3 g / cc and 1.7 g / cc.

[0026] In some embodiments, the surface density of the single-sided active material layer of the positive electrode sheet is 0.16 mg / mm 2 -0.26mg / mm 2 between.

[0027] In some embodiments, the compaction density of the single-sided active material layer of the positive electrode sheet is between 2.3 g / cc and 2.7 g / cc.

[0028] In some embodiments, the diaphragm includes a base film and a coating, the coating is bonded to the surface of the base film and partially located inside the base film, and the porosity of the diaphragm is between 30% and 50%.

[0029] In some implementations, the thickness of the carbon layer on the graphite surface is between 0.5 μm and 2 μm.

[0030] In some embodiments, the negative electrode active material layer further includes carbon tubes; the carbon tubes include at least one of oligo-walled carbon tubes and single-walled carbon tubes.

[0031] In some embodiments, the negative electrode active material layer further includes silicon, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-10%.

[0032] In some embodiments, in the thickness direction of the negative electrode active material layer, the silicon is distributed on a side of the negative electrode active material layer close to the negative electrode current collector.

[0033] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate is doped with a metal element, and the metal element is selected from at least one of titanium or vanadium.

[0034] In some implementations, the mass ratio of the doped metal element to the mass ratio of the positive electrode active material does not exceed 0.4%.

[0035] In some implementations, the doped metal element includes titanium, and the mass ratio of the titanium to the mass ratio of the positive electrode active material is 0.2%-0.4%.

[0036] In some embodiments, the doped metal element includes titanium and vanadium, the mass of the titanium accounts for 0.1%-0.2% of the mass of the positive electrode active material, and the mass of the vanadium accounts for 0.01%-0.05% of the mass of the positive electrode active material.

[0037] In some embodiments, the positive electrode active material layer includes carbon tubes, and the carbon tubes include at least one of oligo-walled carbon tubes and single-walled carbon tubes.

[0038] In some embodiments, the electrolyte includes a lithium salt and a solvent, the volume molar content of the lithium salt is 0.8 mol / L-1.5 mol / L, and the lithium salt includes lithium hexafluorophosphate.

[0039] In some embodiments, the lithium salt further comprises lithium bis(fluorosulfonyl)imide.

[0040] In some embodiments, the volume molar content of the lithium hexafluorophosphate is higher than the volume molar content of the lithium bis(fluorosulfonyl)imide.

[0041] In some embodiments, the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 1% and 9%.

[0042] In some embodiments, the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 1% and 5%.

[0043] In some embodiments, the solvent includes EC, DMC, EMC, and DEC; the content of the EC is between 30% and 40%, the sum of the masses of the DMC and the EMC is greater than the mass of the EC; the content of the EC is the mass of the EC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0044] In some implementations, the total content of the EMC and the DMC is 50%-60%; the total content of the EMC and the DMC is the total mass of the EMC and the DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0045] In some implementations, the content of DMC is 10%-15%; the content of DMC is the mass of DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0046] In some embodiments, the electrolyte further includes carboxylate, wherein the content of the carboxylate does not exceed 10%; the content of the carboxylate is the mass of the carboxylate / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0047] In some implementations, the negative electrode sheet is a square structure, the width of the negative electrode sheet is between 100 mm and 150 mm, and the porosity of the separator is between 30% and 50%; preferably, the aspect ratio of the battery cell is between 6 and 8.

[0048] In some embodiments, the negative electrode sheet is a square structure, the width of the negative electrode sheet is between 200 mm and 250 mm, and the porosity of the separator is between 35% and 50%. Preferably, the aspect ratio of the battery cell is between 2.8 and 4.

[0049] In some embodiments, the negative electrode sheet further includes a negative electrode tab, which is electrically connected to the negative electrode current collector, and the positive electrode sheet further includes a positive electrode tab, which is electrically connected to the positive electrode current collector;

[0050] The shell includes a positive pole, a negative pole, and an explosion-proof valve. The positive pole is electrically connected to the positive pole tab, and the negative pole is electrically connected to the negative pole tab. The explosion-proof valve is arranged at the first end of the shell. At least one of the positive pole and the negative pole is also arranged at the first end of the shell. The opening pressure of the explosion-proof valve is 0.55Mpa-0.65Mpa. The ratio of the area of ​​the explosion-proof valve to the capacity of the lithium-ion battery is in the range of 0.5mm 2 / Ah-1.5mm 2 / Ah.

[0051] In some embodiments, the positive electrode column is arranged at the first end of the shell, the positive electrode tab is arranged on the short side of the positive electrode collector, and a first upper exhaust channel is formed between the upper end of the positive electrode tab and the shell, and along the airflow direction of the first upper exhaust channel, the projection area of ​​the explosion-proof valve at least partially overlaps with the projection area of ​​the first upper exhaust channel.

[0052] In some embodiments, along the airflow direction of the first upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel exceeds 80%; the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel is: the ratio of the area of ​​the overlapping area between the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel to the area of ​​the projection area of ​​the first upper exhaust channel.

[0053] In some embodiments, the positive electrode tabs are asymmetrically distributed on the short sides of the positive electrode current collector.

[0054] In some embodiments, along the width direction of the battery cell, the vertical distance from the upper end of the positive electrode tab to the upper end of the positive electrode sheet is a first distance, and the vertical distance from the lower end of the positive electrode tab to the lower end of the positive electrode sheet is a second distance, and the first distance is greater than the second distance.

[0055] In some embodiments, the negative electrode column is arranged at the first end of the shell, the negative electrode tab is arranged on the short side of the negative electrode collector, and a second upper exhaust channel is formed between the upper end of the negative electrode tab and the shell, and along the airflow direction of the second upper exhaust channel, the projection area of ​​the explosion-proof valve at least partially overlaps with the projection area of ​​the second upper exhaust channel.

[0056] In some embodiments, along the airflow direction of the second upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel exceeds 80%; the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel is: the ratio of the area of ​​the overlapping area between the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel to the area of ​​the projection area of ​​the second upper exhaust channel.

[0057] In some embodiments, the ratio of the width of the negative electrode tab to the width of the short side of the negative electrode collector is in the range of 0.5-0.8, and optionally in the range of 0.6-0.8.

[0058] In some embodiments, the negative electrode tabs are asymmetrically distributed on the short sides of the negative electrode current collector.

[0059] In some embodiments, along the width direction of the battery cell, the vertical distance from the upper end of the negative electrode tab to the upper end of the negative electrode sheet is a third distance, and the vertical distance from the lower end of the negative electrode tab to the lower end of the negative electrode sheet is a fourth distance, and the third distance is greater than the fourth distance.

[0060] In some implementations, the difference between Dv50 and Dv10 of the graphite is ≤10 μm, and the difference between Dv90 and Dv50 of the graphite is ≤15 μm.

[0061] In some embodiments, the positive electrode current collector is aluminum foil, the thickness of the single-sided active material layer of the positive electrode sheet is ≤95 μm, the thickness of the positive electrode current collector is D1, and the value range of D1 is 11 μm-13.5 μm.

[0062] In some embodiments, the thickness of the active material layer on one side of the positive electrode sheet is greater than 95 μm, the thickness of the positive electrode current collector is D2, and the value range of D2 is 13.5 μm-16 μm.

[0063] In some implementations, the thickness of the active material layer on a single side of the negative electrode sheet is between 50 μm and 70 μm.

[0064] In some implementations, the thickness of the single-sided active material layer of the negative electrode sheet is 70 μm-80 μm, and the mass content of silicon in the negative electrode active material layer is in the range of 1%-8%.

[0065] In some implementations, the thickness of the active material layer on a single side of the negative electrode sheet is between 80 μm and 95 μm, and the mass content of silicon in the negative electrode active material layer is between 1% and 5%.

[0066] In some embodiments, the content of the carboxylic acid ester is between 5% and 10%, and the mass of the lithium bis(fluorosulfonyl)imide accounts for between 1% and 5% of the mass of the electrolyte.

[0067] In some embodiments, the negative electrode active material includes primary particles composed of the graphite and the carbon layer on the surface of the graphite, and the Dv50 of the primary particles is 10 μm-20 μm.

[0068] In some embodiments, the negative electrode active material includes secondary particles, the secondary particles include agglomerates of the primary particles, and the Dv50 of the secondary particles is between 10 μm and 30 μm.

[0069] In some embodiments, the surface of the agglomerates is coated with a carbon layer.

[0070] The present application also discloses a charging method, including a first charging section and a second charging section, wherein the voltage of the first charging section is less than the voltage of the second charging section, the voltage of the first charging section increases with the increase of charging time, and the voltage of the second charging section remains unchanged, and the first charging section includes the following charging process:

[0071] charging the lithium-ion battery with a first current within a first time;

[0072] charging the lithium-ion battery with a second current within a second time;

[0073] charging the lithium-ion battery with a third current within a third time;

[0074] charging the lithium-ion battery with a fourth current within a fourth time;

[0075] The first current is greater than the second current, the first time is greater than the second time, the third current is not greater than the first current, the third time is greater than the second time, the fourth current is less than the third current, and the fourth time is less than the third time.

[0076] The second current is equal to the fourth current.

[0077] The present application further provides a lithium-ion battery system, the system comprising a management module and a lithium-ion battery, the management module comprising a charging program for the lithium-ion battery, and the charging program implements the charging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 This is a schematic diagram of the positive electrode structure of the present application.

[0079] Figure 2 This is a schematic diagram of the structure of a negative electrode sheet of the present application.

[0080] Figure 3 This is a schematic diagram of the structure of a lithium-ion battery in the present application.

[0081] Figure 4 This is a schematic diagram of the gas production process of a lithium-ion battery in the present application.

[0082] Figure 5 This is another schematic diagram of the negative electrode sheet structure of the present application.

[0083] Figure 6 This is another schematic diagram of the positive electrode structure of the present application.

[0084] Figure 7 This is another schematic diagram of the positive electrode structure of the present application.

[0085] Figure 8 This is another schematic diagram of the negative electrode sheet structure of the present application.

[0086] Fig. 9 This is another schematic diagram of the structure of a lithium-ion battery in this application.

[0087] Fig.10 This is another schematic diagram of the gas production process of a lithium-ion battery in the present application.

[0088] Description of reference numerals:

[0089] 10 positive electrode sheet; 11 positive electrode tab; 20 negative electrode sheet; 21 negative electrode tab; 30 battery cell; 40 shell; 41 positive electrode column; 42 negative electrode column; 43 explosion-proof valve; 50 arrow for schematic diagram of air flow direction; 51 first upper exhaust channel; h1 first distance; h2 second distance; h3 third distance; h4 fourth distance; Ld length direction; Hd height direction. DETAILED DESCRIPTION

[0090] The following detailed description with reference to the accompanying drawings specifically discloses the implementation methods of the lithium-ion battery, charging method, and lithium-ion battery system of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure 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 application and are not intended to limit the subject matter described in the claims.

[0091] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0092] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0093] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0094] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0095] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0096] The lithium-ion battery of the present application includes a shell, a battery cell, and an electrolyte. The battery cell and the electrolyte are arranged inside the shell, and the shell is sealed. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a diaphragm, which are as follows:

[0097] Negative plate:

[0098] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the negative electrode active material layer is electrically connected to the negative electrode current collector.

[0099] The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite. The graphite can be natural graphite or artificial graphite, preferably artificial graphite.

[0100] Graphite with different particle sizes has different specific surface areas and different gas production. The smaller the graphite particle size, the easier it is for lithium ions to embed and escape from the graphite interlayer. However, the smaller the graphite particle size, the larger its specific surface area, which causes more SEI to be generated, which will increase the gas production; on the one hand, the increase in SEI leads to low initial efficiency of lithium-ion batteries, and on the other hand, as the charge and discharge cycle of lithium-ion batteries proceeds, SEI is in a process of continuous consumption and regeneration, so it will lead to an increase in gas production throughout the life cycle. At the same time, the particle size of graphite cannot be too large. When the particle size of graphite is too large, lithium dendrites will be generated on the surface of large-particle graphite because lithium ions cannot enter the graphite interlayer in time, and then react with the electrolyte to produce gas, especially at high rates (charging rate above 1C), lithium dendrites and gas production problems will be more serious. For the large-capacity thick-electrode cell of the present application [the large-capacity thick-electrode cell in the present application refers to a lithium-ion battery with a capacity of not less than 200Ah, and a compaction density of a single-sided negative electrode active material layer between 1.3g / cc and 1.7g / cc (this compaction density is measured when the number of charge and discharge times of the lithium-ion battery is less than or equal to 100 times. During the preparation process of lithium-ion batteries, the pole pieces are generally rolled to increase the compaction density of the pole pieces, but the compaction density of the pole pieces in the early stage of the cycle of the finished lithium-ion battery often rebounds and becomes smaller. Therefore, in order to more effectively reflect the compaction density of the finished lithium-ion battery, the applicant selects the compaction density of the single-sided active material layer of the negative electrode piece in the lithium-ion battery with less charge and discharge times), and the surface density of the single-sided negative electrode active material layer is 0.07mg / mm 2 To 0.13mg / mm 2 The surface density is between 10 μm and 30 μm (this surface density is measured when the number of charge and discharge times of the lithium-ion battery is less than or equal to 100 times)], and the graphite particle size calculated by Dv50 is selected to be 10 μm-30 μm.

[0101] At the same time, the applicant further designed that too much large-sized graphite cannot be formed in the negative electrode sheet. This is because in the negative electrode sheet, when the graphite particle size is greater than 50 μm, the position corresponding to the large-sized graphite is very likely to cause some lithium ions to deposit on the graphite surface to form lithium dendrites because the lithium ions gathered at this position do not have time to fully enter the graphite interlayer, and may even pierce the SEI film, causing the electrolyte to be further consumed to form SEI and produce gas. Moreover, as the lithium dendrites continue to grow, in addition to causing the local temperature at this position to rise, the lithium dendrites may even pierce the diaphragm. , causing internal short circuit of lithium-ion batteries, resulting in violent gas production and even explosion and other hidden dangers; further, at the position on the negative electrode sheet that contacts the edge of the positive electrode sheet, the lithium dendrite problem caused by such large-particle graphite is more serious; the more concentrated the large-particle graphite is, the easier it is to form lithium dendrites at the concentrated position, so in the process of preparing the negative electrode sheet, large-particle graphite should be removed as much as possible, and the number of large-particle graphite should be within a controllable range, specifically, the Dv90 value of the graphite can be controlled to be no more than 40μm, and the Dv99 value of the graphite can be further controlled to be no more than 49μm.

[0102] On the other hand, for the large-capacity thick-electrode battery cells of the present application, in addition to controlling the Dv50 range of the graphite particle size, it is also necessary to control the appearance of too many small-particle graphite in the electrode to reduce the continuous gas production problem caused by the specific surface area factor of small-particle graphite. Specifically, the value of Dv10 can be controlled to be no less than 3μm.

[0103] In addition, the inventors have also creatively designed that the difference between Dv50 and Dv10 of graphite is ≤10μm, and the difference between Dv90 and Dv50 of graphite is ≤15μm. The setting of these two differences makes the particle size distribution of graphite more concentrated, so that the current density in various places in the negative electrode sheet is more uniform. The more uniform the current density distribution inside the negative electrode sheet, the less likely it is to produce lithium dendrites, and the SEI destructive effect on the graphite surface is reduced, further reducing the gas production. But on the other hand, in order to increase the compaction density of the electrode sheet, the compaction density is often deliberately increased by mixing large and small particles during the preparation process, thereby further increasing the volume capacity of the battery cell. In batteries with high volume capacity requirements, the design of the difference between Dv50 and Dv10 ≤10μm and the difference between Dv90 and Dv50 ≤15μm may not be adopted.

[0104] Since graphite is a layered structure, during the cycle of lithium-ion batteries, lithium ions in the electrolyte are more likely to be inserted into graphite from between graphite layers to complete lithium insertion, but cannot be inserted in the direction perpendicular to the graphite layer. The corresponding OI value (degree of orientation, C004 / C110) of graphite, the larger the OI value, the easier it is to insert lithium. When graphite is used as the negative electrode active material, the inventor designs the OI value of graphite (or carbon-coated graphite) to be in the range of 3-30; when OI is less than 3, it will be difficult for graphite to insert lithium, and then a large number of lithium dendrites will appear, and in large-capacity batteries above 200Ah, the gas production will be very large; in addition, for lithium-ion batteries above 200Ah, they are generally used as energy storage lithium-ion batteries, and do not require high-rate charging and discharging (but in some implementation methods or usage scenarios, large-capacity energy storage lithium-ion batteries will also be required to have high-rate charging and discharging), so for cost considerations, the OI value does not need to exceed 30, otherwise the cost performance is not high.

[0105] The graphite produced by different processes has different graphitization degrees. The inventors hope to use graphite with higher graphitization degrees. The higher the graphitization degree, the less likely it is for the graphite layers to peel off during the cycle, the more stable the SEI is, and the less gas is produced in the long cycle. However, due to the existing preparation process of artificial graphite and the cost performance, the graphitization degree cannot be unlimitedly high. According to the design of the inventors of this application, in the large-capacity thick-electrode lithium-ion battery of this application, the graphitization degree (including the graphite after carbon coating in this application) should be greater than or equal to 90%. Furthermore, in order to meet the needs of large-capacity lithium-ion batteries above 400Ah, the inventors prefer that the graphitization degree of graphite is between 91% and 95%. If the graphitization degree is less than 91%, the gas production of large-capacity lithium-ion batteries above 400Ah will be large during the long cycle. However, when the graphitization degree exceeds 95%, the inventors believe that, based on the existing graphite price, the cost performance of graphite with a graphitization degree exceeding 95% is no longer advantageous.

[0106] In order to further reduce gas production, the inventors of this application have carbon-coated the graphite surface. After graphite is coated with amorphous carbon, due to the large number of lithium-embedded sites in amorphous carbon, on the one hand, it can alleviate the impact of lithium ions on the graphite layers during fast charging, reduce the peeling problem between graphite layers, and thus better reduce gas production; on the other hand, carbon coating may reduce the capacity of the negative electrode sheet, so the amount of carbon coating cannot be too much; at the same time, the amount of carbon coating cannot be too little, which is not conducive to the formation of a uniform carbon coating layer; the inventors of this application control the carbon coating thickness of graphite between 0.5μm-2μm; in order to verify the carbon coating thickness and carbon coating uniformity, the inventors of this application discharged and disassembled the lithium-ion battery after cycling, scraped the negative electrode sheet obtained by disassembly, and took samples to measure TEM, randomly selected 5 graphite particles in the TEM field of view, and evenly selected 5 points on the outer peripheral surface of each graphite particle to measure the carbon coating thickness, and the average of the 25 measurement results was taken to obtain the carbon coating thickness. Since the thickness of the carbon coating is very small, the effect on the particle size of the aforementioned graphite is very small. The present application ignores the effect of the carbon coating on the graphite particle size (such as Dv50), and also ignores the effect of the carbon coating on the graphitization degree and OI value. In addition, in order to facilitate the analysis of the above-mentioned impact of the graphite particle size from the finished lithium-ion battery end, when testing and analyzing the finished lithium-ion battery, although there are factors such as conductive agents in the negative electrode active material layer that will affect the particle size range of the graphite, due to factors such as the small content, the present application also ignores them. After ignoring such minor factors, the present application considers the graphite particle size range obtained by the finished lithium-ion battery test to be the same as the initial graphite particle size range, and considers the graphitization degree and OI value of the graphite obtained by the finished lithium-ion battery test to be the same as the initial graphite graphitization degree and OI value range.

[0107] Graphite can be a primary particle or a carbon-coated primary particle. In this case, the negative electrode active material includes primary particles composed of graphite and a carbon layer on the surface of graphite. The Dv50 of the primary particles is 10μm-20μm. It can also be an agglomerate formed by the agglomeration of primary particles, that is, a secondary particle. The Dv50 of the secondary particles is 10μm-30μm. However, this agglomerate has an increased specific surface area due to the presence of primary particles. In order to reduce gas production, the preferred structure for this type of secondary particles is: the surface of the primary particles is coated with a carbon layer, and the carbon-coated primary particles agglomerate to form secondary particles; and further optimized, the surface of the secondary particles formed by agglomeration is coated with a carbon layer; the composition of the carbon layer on the surface of the primary particles and the carbon layer coated on the surface of the secondary particles can be different or the same. The present application further discloses a preparation process of such carbon-coated secondary particles: primary particles are dispersed in a solution containing an organic carbon source monomer, and a hydrothermal polymerization reaction is carried out. After the polymerization reaction, a coating layer containing an organic carbon source polymer is formed on the surface of the primary particles, and then carbonized to obtain carbon-coated primary particles; the carbon-coated primary particles are then dispersed in a liquid containing an organic carbon source precursor, and then spray-dried and carbonized. Such carbon-coated secondary particles can better meet the gas production requirements of large-capacity thick-electrode cells of the present application, especially for large-capacity cells above 400Ah.

[0108] In addition to negative electrode active materials (the negative electrode active materials of the present application include graphite, and the surface of the graphite can be coated with carbon), the negative electrode sheet also includes a binder and a conductive agent. The technical solution of the present application is used for a single-sided negative electrode active material layer with a compaction density between 1.3g / cc and 1.7g / cc (this compaction density is measured within the range of less than or equal to 100 times of charge and discharge of the lithium-ion battery. During the preparation process of the lithium-ion battery, the pole piece is generally rolled to increase the compaction density of the pole piece, but the compaction density of the pole piece in the early stage of the cycle of the finished lithium-ion battery often rebounds and becomes smaller. Therefore, in order to more effectively measure the compaction density of the finished lithium-ion battery, the applicant selects a battery cell with less charge and discharge times to measure the compaction density of the single-sided active material layer of the negative electrode sheet). The surface density of the single-sided negative electrode active material layer is 0.07mg / mm 2 -0.13mg / mm 2The thickness of the single-sided negative electrode active material layer is between 50 μm and 95 μm, and the thickness of the negative electrode current collector is 5 μm. When the negative electrode current collector is coated with a negative electrode active material layer on both sides, the thickness of the negative electrode sheet is 105 μm to 195 μm (the thickness of the negative electrode active material layer and the thickness of the negative electrode sheet are measured when the number of charge and discharge of the lithium-ion battery is less than 100 times). Since the thickness of the negative electrode sheet used in the technical solution of the present application is high, In order to maintain good electrical contact at all positions in the negative electrode active material layer, the present application preferably comprises a conductive agent in the negative electrode active material layer including carbon tubes, and preferably single-walled carbon tubes and / or oligo-walled carbon tubes; the single-walled carbon tubes used in the present application have a length of 1 μm-50 μm, and a cross-section of a layer of graphene sheets with a diameter of 0.75 nm-10 nm, and further preferably 1 nm-3 nm; the oligo-walled carbon tubes used in the present application have a cross-section of 2-5 layers of graphene sheets with a diameter of 1 nm-15 nm, and further preferably 2 nm-5 nm. Compared with other conventional conductive agents such as carbon black, on the one hand, single-walled carbon tubes or oligo-walled carbon tubes have better conductivity; on the other hand, in thick electrode sheets, due to the large electrode coating area and the expansion and contraction of graphite during the cycle, especially after silicon is doped into graphite, the thickness difference of expansion and contraction is further enlarged, and the thick electrode sheet may cause difficulty for the upper active material of the thick electrode sheet to obtain electrons during the cycle, and even cause the thick electrode sheet to be delaminated, and the problem of difficulty for the upper active material to obtain electrons is more serious; and single-walled carbon tubes or oligo-walled carbon tubes have a large aspect ratio relative to carbon black, so they can fix the thick electrode sheet, improve the ability of the upper active material to obtain electrons, and prevent delamination.

[0109] The negative active material of the negative electrode sheet of the present application may include silicon in addition to graphite. The addition of silicon is to increase the capacity of the entire lithium-ion battery. However, due to the cyclic expansion problem of silicon, the silicon content in the thick electrode sheet cannot be too much. Especially in the large-capacity thick electrode sheet battery cell of the present application, the expansion problem is more likely to cause the thick electrode sheet to be delaminated, causing the conductive path of the active material to be disconnected. On the other hand, due to the expansion of silicon during the charge and discharge cycle, the SEI is constantly broken and regenerated. This process is accompanied by continuous gas production, and the larger the capacity of the lithium-ion battery, the more serious the gas production problem caused by silicon expansion. Therefore, the present application needs to consider two factors for the mass content range of silicon in the negative electrode active material layer, and the intersection of the two factors is required; the first factor is the influence of the capacity of the lithium ion battery on the silicon content, which is as follows: when the capacity of the lithium ion battery is 200Ah≤L≤500Ah, and further preferably 300Ah<L≤500A, the mass content range of silicon in the negative electrode active material layer is 1%-10%; when the capacity L of the lithium ion battery is 500Ah<L≤700Ah, the mass content range of silicon in the negative electrode active material layer is 1%-8%; when the capacity of the lithium ion battery is 700Ah<L≤1100Ah, the mass content range of silicon in the negative electrode active material layer is 1%-20%. The mass content of silicon in the negative electrode active material layer ranges from 1% to 5%; the second factor is the influence of the thickness of the single-sided active material layer of the negative electrode sheet on the silicon content, which is as follows: when the thickness of the single-sided active material layer of the negative electrode sheet is 50μm-70μm, the mass content of silicon in the negative electrode active material layer ranges from 1% to 10%; when the thickness of the single-sided active material layer of the negative electrode sheet is 70μm-80μm, it is further preferred that the mass content of silicon in the negative electrode active material layer ranges from 1% to 8%; when the thickness of the single-sided active material layer of the negative electrode sheet is 80μm-95μm, it is further preferred that the mass content of silicon in the negative electrode active material layer ranges from 1% to 5%.

[0110] In the thickness direction of the negative electrode active material layer, silicon is mainly or entirely distributed in the lower part of the negative electrode active material layer, that is, on the side close to the negative electrode current collector. Further preferably, the silicon content on the surface of the negative electrode active material layer close to the negative electrode current collector is higher than the silicon content on the surface of the negative electrode active material layer away from the negative electrode current collector, and further preferably, the surface of the negative electrode active material layer away from the negative electrode current collector does not contain silicon.

[0111] The lower part of the negative electrode active material layer described in the present application refers to the part of the negative electrode active layer close to the negative electrode current collector in the thickness direction of the negative electrode active material layer; correspondingly, the negative electrode active layer includes an upper part, which refers to the part of the negative electrode active layer away from the negative electrode current collector. The surface of the negative electrode active material layer away from the negative electrode current collector described in the present application refers to the area from the surface of the negative electrode active material layer away from the negative electrode current collector to a depth of 20 μm along the thickness direction of the negative electrode active material layer; the surface of the negative electrode active material layer close to the negative electrode current collector described in the present application refers to the area from the surface of the negative electrode active material layer close to the negative electrode current collector to a depth of 20 μm along the thickness direction of the negative electrode active material layer. The negative electrode active material layer can be cut open, the cut interface can be observed with a scanning electron microscope (SEM), and an element scan can be performed with an EDS (X-ray energy dispersive spectrometer) to determine the element content of silicon.

[0112] In the thickness direction of the negative electrode active material layer, silicon is mainly or entirely distributed in the lower part of the negative electrode active material layer, so that in the process of silicon expansion and contraction, the upper part of the negative electrode active material layer can be used to press the lower part of the negative electrode active material layer, thereby alleviating the adverse effects of silicon expansion. And the silicon in the negative electrode active material layer in this application refers to silicon element, for example, specifically can include silicon element, or silicon oxide, or silicon nitride, or one or more of silicon element-containing salts (such as silicates).

[0113] Specifically, the structure of the negative electrode active material layer containing silicon in this application has the following forms:

[0114] The first method: Silicon is distributed in both the upper and lower parts of the negative electrode active material layer, but the content of silicon in the upper part of the negative electrode active material layer is less than that in the lower part; specifically, the silicon content near the lower surface of the negative electrode active material layer (close to the surface of the current collector) and the silicon content near the upper surface of the negative electrode active material layer can be measured.

[0115] The second method: Silicon is only distributed in the lower part of the negative electrode active material layer, and the upper part of the negative electrode active material layer does not contain silicon. Specifically, silicon is not contained within a thickness range of 20 μm from the upper surface of the negative electrode active material layer, because after exceeding 20 μm, the upper negative electrode active material layer cannot play the role of pressing the lower diaphragm.

[0116] Negative electrode structure:

[0117] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode current collector can be a copper foil, a carbon-containing fiber current collector, or a porous current collector. The negative electrode active material layer is combined with the negative electrode current collector. During the cycle of the lithium-ion battery, the negative electrode active material layer obtains electrons through the negative electrode current collector.

[0118] The negative electrode sheet also includes a negative electrode tab, which is electrically connected to the negative electrode collector. There are many ways to connect the negative electrode tab to the negative electrode collector, such as welding the negative electrode tab to the negative electrode collector, or the negative electrode tab and the negative electrode collector are an integrated structure (such as the negative electrode collector is copper foil, and the negative electrode tab is formed by cutting the negative electrode collector).

[0119] The negative electrode collector can be of various structures. For example, in the first structure, the negative electrode collector can be rectangular, including long sides and short sides. The long side of the negative electrode collector is the length of the rectangular structure, and the short side of the negative electrode collector is the width of the rectangle. The negative electrode active material layer is arranged on at least part of the upper and lower surfaces of the negative electrode collector, and the negative electrode tab is arranged on the short side of the negative electrode collector. For another example, in the second structure, the negative electrode collector is a rectangular structure, including long sides and short sides. The negative electrode tab is arranged on the long side of the negative electrode collector, and multiple negative electrode tabs are arranged on each long side. The long side of the negative electrode collector of the second structure is longer than the long side of the negative electrode collector of the first structure, so it is necessary to arrange multiple negative electrode tabs on the negative electrode collector of the second structure, which is conducive to reducing the heat generation at the tab position of the thick electrode sheet battery cell. Under the first structure, negative electrode tabs can be arranged on one or more short sides of the negative electrode collector. Since the long side of the negative electrode current collector is relatively long, specifically, the aspect ratio of the negative electrode current collector is greater than 6, the electron supply in the entire negative electrode sheet is related to the width of the negative electrode tab. If the width of the negative electrode tab is not enough, it will cause serious heating at the negative electrode tab position. Therefore, the ratio of the width of the negative electrode tab to the width of the short side of the negative electrode current collector should be no less than 0.5; further optimization, the ratio of the width of the negative electrode tab to the width of the short side of the negative electrode current collector is in the range of 0.5-0.8, and cannot exceed 0.8, because after exceeding 0.8, the negative electrode collector will be very close to the negative electrode. Close to the shell, when the shell is a conductor, a slight impact can easily cause electrical connection between the negative electrode collector and the shell; further, the ratio of the width of the negative electrode tab to the width of the short side of the negative electrode collector is in the range of 0.6-0.8. Because when the charging rate is not less than 3C, the heat generation effect on the negative electrode tab position is further aggravated, so the heat generation effect of the negative electrode tab position can be alleviated by setting the width of the negative electrode tab to the width of the short side of the negative electrode collector to not less than 0.6 (the setting principle of the positive electrode tab position is the same as that of the negative electrode tab).

[0120] Negative electrode preparation process:

[0121] The preparation process of the negative electrode sheet includes the following steps:

[0122] Process 1: Mixing materials including negative electrode active material, conductive agent, binder and other materials to form a negative electrode active material layer. This mixing process includes two methods: Method 1: Mixing negative electrode active material, conductive agent, binder, binder solvent and other materials to form a liquid slurry, coating it on the surface of copper foil as negative electrode current collector, or on the surface of carbon fiber and between carbon fibers as negative electrode current collector, and after coating, drying, rolling and other processes are performed to obtain a negative electrode sheet precursor for preparing a battery cell; Method 2: Mixing negative electrode active material, conductive agent, binder and other materials (may include a small amount of binder and solvent) to form a non-flowable solid or semi-solid mixture, and hot pressing it onto the negative electrode current collector to form a negative electrode sheet precursor.

[0123] Process 2: cutting the negative electrode sheet precursor to obtain negative electrode sheets to be used.

[0124] On the negative electrode sheet precursor formed in process one, there is a thin area in the negative active material layer on the surface of the negative current collector. There are many ways to form the thin area. For example, in the above method one, the sheet where the negative current collector is located is coated by multiple coating dies. During the coating process, the coating amount of some dies is smaller than that of other dies. Then, during the subsequent drying process, the coating area formed by the die with a small coating amount is the thin area. The gaps between the multiple coating dies can also be adjusted so that the coating liquids formed by the multiple coating dies do not contact or partially contact each other on the sheet of the negative current collector. Since the edge thickness of the coating liquid is thin during the coating and drying process, a thin area is formed at the edge of the coating liquid.

[0125] In the second process, the cutting is performed along the thin area, so that the edge of the long side of the obtained negative electrode sheet includes the thin area; that is, the edge thickness of the long side of the negative electrode sheet is less than the middle thickness of the negative electrode sheet.

[0126] The above-mentioned preparation process increases the cost. Therefore, from the perspective of cost, the thin area may not be formed, so that the edge thickness of the long side of the negative electrode sheet obtained after cutting is substantially consistent with the thickness of the negative electrode sheet.

[0127] Positive electrode:

[0128] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer is electrically connected to the positive electrode current collector.

[0129] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be selected from lithium-containing phosphates such as lithium iron phosphate or lithium iron manganese phosphate, or ternary positive electrode materials such as nickel cobalt manganese oxide or nickel cobalt aluminum oxide, or the former two can be doped with elements. Due to the material properties, the ternary positive electrode material is prone to produce gas during the charge and discharge cycle, especially when the nickel content in the ternary positive electrode material is high, which makes the gas production abnormally large during normal circulation under large-capacity batteries, and it is even possible that the gas production during normal circulation can break the explosion-proof valve, causing the lithium-ion battery to fail. Therefore, the preferred positive electrode material in the technical solution of this application is a lithium-containing phosphate. However, the lithium-containing phosphate has poor conductivity, and a carbon layer needs to be coated on the surface of the lithium-containing phosphate. At the same time, considering that the capacity of the lithium-containing phosphate is low compared with the ternary positive electrode material, the present application increases the capacity by doping the lithium-containing phosphate with metal elements, and specifically, one or more of the metal titanium element and the metal vanadium element can be doped, which can increase the capacity of the lithium-containing phosphate, and can improve the conductivity, and can also be beneficial to improve the charge and discharge speed of the large-capacity battery of this application. The present application considers that the mass ratio of the doping element to the mass ratio of the positive electrode active material (including lithium-containing phosphate and carbon layer) does not exceed 0.4%, and the specific range is 0.01%-0.4%; more specifically, 0.2%-0.4% of titanium element can be doped; 0.1%-0.2% of titanium element can also be doped and 0.01%-0.05% of vanadium element can be doped at the same time. However, the content of doping elements is not necessarily the higher the better. The inventor conducted a charge and discharge study on the large-capacity thick-electrode battery cell of the present application. The positive electrode active material uses lithium iron phosphate containing doping elements. When the mass ratio of the doping element to the mass ratio of the positive electrode active material exceeds 0.4%, the lattice structure of the lithium iron phosphate will begin to change significantly, which is not conducive to the performance.

[0130] In addition to the positive electrode active material (the positive electrode active material of the present application includes lithium-containing phosphate, which may be carbon-coated and doped with metal elements), the positive electrode plate also includes a binder and a conductive agent. The compaction density of the single-sided active material layer of the positive electrode plate used in the technical solution of the present application is between 2.3g / cc and 2.7g / cc (this compaction density is measured within the range of less than or equal to 100 times of charge and discharge of the lithium-ion battery. During the preparation of lithium-ion batteries, the pole pieces are generally rolled to increase the compaction density of the pole pieces. However, the compaction density of the pole pieces in the early stage of the cycle of the finished lithium-ion battery often rebounds and becomes smaller. However, the positive pole piece rebounds less than the negative pole piece), and the surface density of the single-sided active material layer of the positive pole piece is 0.16mg / mm 2 -0.26mg / mm 2The thickness of the single-sided active material layer of the positive electrode sheet is between 60μm and 105μm (this surface density is measured when the number of charge and discharge times of the lithium-ion battery is less than or equal to 100 times), and further corresponds to the thickness of the single-sided active material layer of the positive electrode sheet being between 60μm and 105μm. At the position where the positive electrode active material layer is coated on both sides of the positive electrode collector, the thickness of the positive electrode sheet is measured to be in the range of 135μm to 225μm (the thickness of the single-sided active material layer of the positive electrode sheet and the thickness of the positive electrode sheet are measured when the number of charge and discharge times of the lithium-ion battery is less than 100 times) of the thick electrode sheet battery cell. Since the single-sided active material layer of the positive electrode sheet of the present application is relatively thick, the inventor of the present application further arranges that, when the positive electrode current collector is aluminum foil, when the thickness of the single-sided active material layer of the positive electrode sheet is ≤95 μm, the thickness of the positive electrode current collector is measured to be D1, and when the thickness of the single-sided active material layer of the positive electrode sheet is greater than 95 μm, the thickness of the positive electrode current collector is measured to be D2, wherein D2>D1; it is further arranged that the numerical range of D1 is 11 μm-13.5 μm, and further preferably 12 μm-13 μm; the numerical range of D2 is 13.5 μm-16 μm, and further preferably 14 μm-15 μm; because the thicker the thickness of the positive electrode active material layer, the stronger the conductive current capacity of the required current collector, and the correspondingly thicker the required current collector.

[0131] Since the thickness of the positive electrode sheet used in the technical solution of the present application is high, in order to maintain good electrical contact at all positions in the positive electrode active material layer, the present application preferably uses a conductive agent in the positive electrode active material layer including carbon tubes, and preferably single-walled carbon tubes or oligo-walled carbon tubes. Compared with other conventional conductive agents such as carbon black, on the one hand, single-walled carbon tubes or oligo-walled carbon tubes have better conductivity, and on the other hand, thick electrode sheets are likely to make it difficult for the active material on the upper part of the thick electrode sheet to obtain electrons during the cycle, and even cause the thick electrode sheet to delaminate. Single-walled carbon tubes or oligo-walled carbon tubes have a large aspect ratio relative to carbon black, so they can fix the thick electrode sheet, improve the ability of the upper active material to obtain electrons, and prevent delamination.

[0132] Positive electrode structure:

[0133] The positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode current collector can be an aluminum foil, a carbon-containing fiber current collector, or a porous current collector. The positive electrode active material layer is combined with the positive electrode current collector. During the cycle of the lithium-ion battery, the positive electrode active material layer obtains electrons through the positive electrode current collector.

[0134] The positive electrode sheet also includes a positive electrode tab, which is electrically connected to the positive electrode collector. There are many ways to connect the positive electrode tab and the positive electrode collector, such as welding the positive electrode tab to the positive electrode collector, or the positive electrode tab and the positive electrode collector are an integrated structure (such as the positive electrode collector is aluminum foil, and the positive electrode tab is formed by cutting the positive electrode collector).

[0135] The positive electrode collector can be of various structures. For example, in the first structure, the positive electrode collector can be a rectangle, including a long side and a short side. The long side of the positive electrode collector is the length of the rectangular structure, and the short side of the positive electrode collector is the width of the rectangle. The positive electrode active material layer is arranged on at least part of the upper and lower surfaces of the positive electrode collector, and the positive electrode tab is arranged on the short side of the positive electrode collector. For example, in the second structure, the positive electrode collector is a rectangular structure, including a long side and a short side, and the positive electrode tab is arranged on the long side of the positive electrode collector. Multiple positive electrode tabs are arranged on each long side. The long side of the positive electrode collector of the second structure is longer than the long side of the positive electrode collector of the first structure. Therefore, it is necessary to arrange multiple positive electrode tabs on the positive electrode collector of the second structure, which is beneficial to reduce the heat generation of the thick electrode cell at the tab position. In the first structure, a positive electrode tab may be provided on one or more short sides of the positive electrode collector, and the ratio of the width of the positive electrode tab to the width of the short side of the positive electrode collector is in the range of 0.5-0.8, further in the range of 0.6-0.8, and cannot exceed 0.8. The principle of setting the ratio is the same as that of the negative electrode tab, which will not be repeated here.

[0136] In the present application, the structure of the positive electrode sheet, the positive electrode ear and the preparation process of the positive electrode sheet are similar to those of the negative electrode sheet, and the present application will not repeat them here; however, it is still necessary to indicate that in some embodiments of the present application, the positive electrode ear is also unevenly distributed on the positive electrode collector, and the distance from the upper end of the positive electrode ear to the upper end of the positive electrode sheet is a third distance h3, and the distance from the lower end of the positive electrode ear to the lower end of the positive electrode sheet is a fourth distance h4, and h3>h4.

[0137] The specific test method for the thickness of the negative electrode sheet or the thickness of the positive electrode sheet described in the present application is: discharge the lithium-ion battery with a charge and discharge cycle of 1-100 times to a voltage of 2.5V, at which voltage the lithium-ion battery is considered to be fully discharged, then disassemble the lithium-ion battery to obtain the positive electrode sheet and the negative electrode sheet, and wash the positive electrode sheet and the negative electrode sheet with an electrolyte solvent such as EC solution to wash away the lithium salt or other residues on the surface of the positive electrode sheet and the negative electrode sheet, then dry the solvent, and measure the thickness of the positive electrode sheet and the thickness of the negative electrode sheet.

[0138] The test method for the particle size of the active material in the present application is as follows: a lithium-ion battery with a charge-discharge cycle of 1-100 is discharged to a voltage of 2.5V, at which voltage the lithium-ion battery is considered to be fully discharged, and then the lithium-ion battery is disassembled to obtain a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet and the negative electrode sheet are cleaned with an electrolyte solvent such as an EC solution to wash away lithium salts or other residues on the surface of the positive electrode sheet and the negative electrode sheet, and then the solvent is dried, and then the electrode sheet is subjected to a high-temperature treatment (such as 500°C-600°C) under an inert atmosphere to inactivate the binder in the electrode sheet. After the high-temperature treatment, the electrode sheet is pulverized to obtain an active material, and then the pulverized active material is sieved (pressed), and a lower layer of particle samples are taken for particle size testing;

[0139] The cycles mentioned in this application (such as 100 cycles) refer to one charge plus one discharge as one cycle. More specifically, in actual use, it is not necessarily fully charged or fully discharged, but as long as it is charged once and then discharged until the next charge begins, it is counted as one cycle.

[0140] Diaphragm:

[0141] The diaphragm used in the present application includes a base film, the base film includes fibers, the base film material includes PP or PE, a coating is provided on the surface of the base film, the coating includes inorganic substances and inorganic particles, the coating is applied and bonded to the surface of the base film and partially penetrates into the interior of the base film, and the presence of the coating can effectively inhibit the lithium dendrites generated by the negative electrode from penetrating the diaphragm and causing a short circuit in the lithium-ion battery; however, the coating cannot make the diaphragm completely closed, because the electrolyte still needs to pass through, so the porosity of the diaphragm is set to between 30% and 50%.

[0142] Electrolyte:

[0143] The electrolyte includes lithium salt and solvent, and the lithium salt includes lithium hexafluorophosphate (LiPF6). However, lithium hexafluorophosphate has poor thermal stability and begins to decompose into phosphorus pentafluoride (PF5) and lithium fluoride (LiF) at 80°C. Phosphorus pentafluoride (PF5) can further react with water to generate hydrogen fluoride gas, and lithium fluoride (LiF) can further react with solvents such as DMC to generate gas. Therefore, the effect of lithium hexafluorophosphate on the gas production of large-capacity batteries cannot be ignored. And as the capacity of lithium-ion batteries increases, the accumulated temperature inside the battery will also become higher and higher, so the gas production effect of LiPF6 in large-capacity batteries will also become greater and greater.

[0144] Another lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), which has good thermal stability and a decomposition temperature of up to 200°C, which helps reduce the gas production problem caused by increased temperature. Part of the reason is that the cost of lithium bis(fluorosulfonyl)imide (LiFSI) is too high, so the lithium salt of the electrolyte still needs to retain lithium hexafluorophosphate (LiPF6). In addition, LiFSI has a certain corrosive effect on the positive electrode current collector aluminum foil, and LiPF6 can alleviate this corrosion. Taking all factors into consideration, the volume molar content of LiPF6 is higher than the volume molar content of LiFSI.

[0145] Since a large amount of lithium salt is consumed during the cycling process of lithium-ion batteries, especially during the first charge and discharge to form SEI, the solution of the present application monitors the lithium salt content in the finished lithium-ion batteries during cycling more. Specifically, when the number of charge and discharge cycles of the lithium-ion battery is measured between 5 and 100 times and the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), the volume molar content of the lithium salt is between 0.8 mol / L and 1.5 mol / L; considering the reduction of aluminum foil corrosion, the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte is further limited to be between 0.1% and 9%.

[0146] On the other hand, considering that the gas generation intensifies after the capacity of the lithium-ion battery is increased, when the capacity of the lithium-ion battery is greater than 300 Ah, the mass percentage of LiFSI in the electrolyte is not less than 1%.

[0147] According to the capacity and cost considerations of the lithium-ion battery: when the capacity L of the lithium-ion battery satisfies 200 Ah ≤ L ≤ 300 Ah, the mass percentage of LiFSI in the electrolyte is 0.1% - 9%, and for cost considerations, it is preferably 0.1% - 5%; when the capacity L of the lithium-ion battery satisfies 300 Ah < L ≤ 500 Ah, the mass percentage of LiFSI in the electrolyte is 1% - 9%, and for cost considerations, it is preferably 1% - 5%; when the capacity L of the lithium-ion battery satisfies 500 Ah < L ≤ 700 Ah, the mass percentage of LiFSI in the electrolyte is 3% - 9%; when the capacity L of the lithium-ion battery satisfies 700 Ah < L ≤ 1100 Ah, the mass percentage of LiFSI in the electrolyte is 5% - 9%.

[0148] In the electrolyte of the present application, the solvent includes EC, DMC, EMC, and DEC, and the specific corresponding Chinese names are: ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Because EC is a cyclic carbonate, cyclic carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode, but its viscosity is relatively large, which is not conducive to the diffusion of lithium ions, so the content of EC is between 30% and 40%; among them, DMC and EMC are both chain carbonates, and the viscosity of chain carbonates is generally lower than that of cyclic carbonates. For the thick-electrode lithium-ion battery of the present application, it is necessary to control that the sum of the masses of DMC and EMC must be greater than the mass of EC, and further control the total content of EMC and DMC to be 50%-60%. In addition, compared with EMC, DMC has a low boiling point and is easy to produce gas. From the perspective of controlling high-temperature gas production, it is necessary to control the mass of EMC to be higher than DMC. However, the lower viscosity of DMC is conducive to the climbing of the electrolyte on the long electrode and the diaphragm (constant and longitudinal diffusion capacity), which requires the presence of DMC and satisfies the content of DMC at 10%-15%. Among them, the content of EC refers to the mass of EC divided by the difference between the mass of the electrolyte and the mass of the lithium salt, that is, the mass of EC / (the difference between the mass of the electrolyte and the mass of the lithium salt); similarly, the total content of EMC and DMC refers to the total mass of EMC and DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt, that is, the total mass of EMC and DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt); the content of DMC refers to the mass of DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt, that is, the mass of DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0149] In some embodiments, a certain amount of carboxylate is also added to the electrolyte. The content of carboxylate refers to the mass of carboxylate divided by the difference between the mass of the electrolyte and the mass of the lithium salt, that is, the content of carboxylate is the mass of carboxylate / (the difference between the mass of the electrolyte and the mass of the lithium salt). Carboxylate helps to form a film at the negative electrode during the charging and discharging process of the lithium-ion battery, improves ionic conductivity, and reduces gas production at the negative electrode interface. However, excessive carboxylate content will increase gas production, especially in fast charging systems. For some embodiments of the present application, the content of carboxylate does not exceed 10%.

[0150] In some embodiments, the carboxylic acid ester can also be used in combination with LiFSI. The combination of the two can reduce gas generation. The most intuitive effect is that it can reduce the dosage of LiFSI, thereby reducing costs. Specifically, when the content of the carboxylic acid ester is 5%-10%: for a lithium-ion battery with a capacity L of 200 Ah ≤ L ≤ 300 Ah, the mass percentage of LiFSI in the electrolyte is 0.1%-5%; for a lithium-ion battery with a capacity L of 300 Ah < L ≤ 500 Ah, the mass percentage of LiFSI in the electrolyte is 1%-5%; for a lithium-ion battery with a capacity L of 500 Ah < L ≤ 700 Ah, the mass percentage of LiFSI in the electrolyte is 2%-7%; when the capacity L of the lithium-ion battery is 700 Ah < L ≤ 1100 Ah, the mass percentage of LiFSI in the electrolyte is 3%-8%.

[0151] Cell structure:

[0152] The cell structure of this application includes a positive electrode sheet, a negative electrode sheet, and a separator. The cell structure of this application can be a stacked structure or a wound structure. The solution of this application is applicable to large cells, and the capacity of the lithium-ion battery is between 200 Ah and 1100 Ah.

[0153] Regardless of whether it is a stacked structure or a wound structure cell, during use, the cell is often placed vertically. The wider the cell, the longer the distance required for the electrolyte to climb from the lower end of the cell to the upper end. The electrolyte climbs from the lower end of the cell to the upper end mainly through the separator. Specifically, it is related to the porosity of the separator. Especially in the later stage of the lithium-ion battery cycle, the amount of electrolyte inside the housing becomes less. If the electrolyte at the bottom of the housing cannot climb to the upper end of the cell, it will cause the electrode sheets at the upper end of the cell to not be able to contact the electrolyte or have less electrolyte, resulting in uneven deposition of lithium ions on the negative electrode and generating a large amount of lithium dendrites, causing an increase in gas generation. On the other hand, the wider the cell, the more difficult it is for the heat in the middle of the cell to dissipate, resulting in heat concentration in the middle of the cell and an increase in the gas generation of the cell. A high porosity of the separator will also help with heat dissipation to a certain extent. However, the porosity of the separator cannot be too high, otherwise it is easy to cause an increase in lithium dendrites on the negative electrode due to uneven current density during charging, resulting in an increase in gas generation, especially during high-rate charging. Under the electrolyte composition of this application, when the width of the negative electrode sheet is between 100 mm and 150 mm, the porosity of the separator can be 30%-50%; when the width of the negative electrode sheet is between 200 mm and 250 mm, the porosity of the separator should be between 35%-50%. According to the capacity requirements of the aforementioned cell, when the width of the negative electrode sheet is between 100 mm and 150 mm, the aspect ratio of the cell is preferably between 6 and 8; when the width of the negative electrode sheet is between 200 mm and 250 mm, the aspect ratio of the cell is preferably between 2.8 and 4.

[0154] Lithium-ion battery:

[0155] The lithium-ion battery in the present application includes a shell, a battery cell, and an electrolyte, wherein the electrolyte and the battery cell are arranged inside the shell. The shell is sealed, and the shell includes a positive electrode column, a negative electrode column, and an explosion-proof valve. The positive electrode column is electrically connected to the positive electrode tab, and the negative electrode column is electrically connected to the negative electrode tab; the positive electrode column and the negative electrode column can be arranged at both ends of the shell respectively or at the same end of the shell.

[0156] The explosion-proof valve is arranged at the first end of the shell, and at least one of the positive pole and the negative pole is also arranged at the first end of the shell.

[0157] Preferably, the explosion-proof valve is arranged at the edge of one end of the shell where the positive electrode column is located, that is, the explosion-proof valve is arranged at the first end of the shell, and the positive electrode column is also arranged at the first end of the shell. A first upper exhaust channel is formed between the upper end of the positive electrode ear and the shell, and along the airflow direction of the first upper exhaust channel, the projection area of ​​the explosion-proof valve partially overlaps with the projection area of ​​the first upper exhaust channel. Furthermore, along the airflow direction of the first upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel exceeds 80%.

[0158] Or the explosion-proof valve is arranged at the edge of one end of the shell where the negative electrode column is located, that is, the explosion-proof valve is arranged at the first end of the shell, and the negative electrode column is also arranged at the first end of the shell. A second upper exhaust channel is formed between the upper end of the negative electrode ear and the shell, and along the airflow direction of the second upper exhaust channel, the projection area of ​​the explosion-proof valve partially overlaps with the projection area of ​​the second upper exhaust channel, and further, along the airflow direction of the second upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel exceeds 80%.

[0159] The overlap degree between the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel refers to the ratio of the area of ​​the overlap between the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel along the airflow direction of the first upper exhaust channel to the area of ​​the projection area of ​​the first upper exhaust channel. Similarly, the overlap degree between the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel refers to the ratio of the area of ​​the overlap between the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel along the airflow direction of the second upper exhaust channel to the area of ​​the projection area of ​​the second upper exhaust channel.

[0160] The explosion-proof valve and the first upper exhaust channel or the second upper exhaust channel have a partial overlap in the projected area of ​​the airflow so that in abnormal circumstances, when the internal air pressure of the lithium-ion battery is too high, the explosion-proof valve can be quickly opened to prevent the air pressure from accumulating inside the shell and causing an explosion. The reason why the degree of overlap between the explosion-proof valve and the first upper exhaust channel or the second upper exhaust channel exceeds 80% is because the large-capacity battery cells of the present application (the capacity of the lithium-ion battery is greater than or equal to 200Ah) produce a huge amount of gas under abnormal circumstances. According to the applicant's experiments and simulations, the overlap is lower than 80%, and some lithium-ion batteries will explode. In order to further prevent the explosion of lithium-ion batteries, for the large-capacity battery cells of the present application (the capacity of the lithium-ion battery is greater than or equal to 200Ah), the applicant has further optimized the ratio of the area of ​​the explosion-proof valve to the capacity of the lithium-ion battery to be in the range of 0.5mm 2 / Ah-1.5mm 2 / Ah; and further stipulates that when the capacity of the lithium-ion battery is less than 600Ah, the ratio of the area of ​​the explosion-proof valve to the capacity of the lithium-ion battery is less than or equal to 1mm 2 / Ah; When the capacity of the lithium-ion battery is greater than or equal to 600Ah and less than 1200Ah, the ratio of the area of ​​the explosion-proof valve to the capacity of the lithium-ion battery is less than or equal to 1.5mm 2 / Ah. In order to further prevent the explosion of lithium-ion batteries, for the large-capacity battery cells of this application (the capacity of the lithium-ion battery is greater than or equal to 200Ah), the applicant has further optimized that when the aspect ratio of the battery cell is greater than 2.8, there are multiple explosion-proof valves, and the multiple explosion-proof valves are all located in the upper half of the lithium-ion battery. Here, the upper half of the lithium-ion battery is relative to the placement position in the actual use scenario of the lithium-ion battery. Because when the lithium-ion battery is actually used, in the early stage of the lithium-ion battery cycle, there is still a large amount of free electrolyte in the lithium-ion battery. If an abnormal use occurs at this time and causes the explosion-proof valve to be opened, the applicant does not want the electrolyte to also follow the generated gas to spray out from the explosion-proof valve, because the sprayed electrolyte will further cause other external short circuits, so the explosion-proof valve should be set in the upper half of the lithium-ion battery. Even if there are multiple explosion-proof valves, each explosion-proof valve should be set in the upper half of the lithium-ion battery.

[0161] The explosion-proof valve can be located on the short sides of the lithium-ion battery (as in the present application) Figure 3 As shown), it can also be located on the long side of the lithium-ion battery. In this case, there are many ways to set it up, such as in this application Fig. 9 One method is shown below.

[0162] It can also be arranged as follows: the explosion-proof valve is located on the long side of the shell, the positive electrode ear is located on the short side of the positive electrode collector, the negative electrode ear is located on the short side of the negative electrode collector, the positive electrode ear and the negative electrode ear are respectively located at both ends of the battery cell, and the positive electrode ear and / or the negative electrode ear are symmetrically arranged relative to the pole piece (at least one reason for the asymmetrical arrangement in other arrangements is to leave space for the explosion-proof valve or other devices (such as the injection channel), and at the same time, in order to take into account the current flow capacity of the ear, the ear needs to have a certain width, so the ear is often arranged relative to the upper end of the pole piece. However, the tab moves downward, but there is a risk of contacting the shell when it moves downward, so it is often necessary to control the distance between the lower edge of the tab and the shell), and the explosion-proof valve is located on the long side of the shell, and the tab is located on the short side of the collector (the pole is also located on the short side of the shell), there is no need to worry too much about the lower edge of the tab being too close to the shell and causing a short circuit, because the explosion-proof valve is set on the long side at this time, the tab can be symmetrically set relative to the short side of the collector, and the ratio of the tab width to the short side of the collector is increased accordingly. This ratio can be set to 0.7-0.8, thereby increasing the current flow capacity of the tab.

[0163] The present application does not limit the specific structure of the explosion-proof valve. As long as the part of the shell that can be broken open under abnormal circumstances can play the role of an explosion-proof valve, for example, when the shell is formed of an aluminum-plastic film, the weak area encapsulated by the aluminum-plastic film can play the role of an explosion-proof valve. In this case, the weak area may be a linear structure. The area of ​​the explosion-proof valve is calculated by taking the length of the weak area as the area of ​​a square corresponding to the perimeter.

[0164] There are multiple explosion-proof valves. There are multiple design options. For example, if there are two explosion-proof valves, the two explosion-proof valves are located on two opposite short sides of the lithium-ion battery. In this case, the two explosion-proof valves need to be symmetrically arranged, otherwise one explosion-proof valve will not be activated after the other explosion-proof valve is activated. Another example is that if there are two explosion-proof valves, both explosion-proof valves are located on the long side of the upper end of the lithium-ion battery. In this case, the two explosion-proof valves need to be symmetrically distributed relative to the long side of the lithium-ion battery. Symmetrical distribution here means that the distance from each explosion-proof valve to the midpoint of the long side of the lithium-ion battery is equal, because for long batteries, if an abnormal situation (such as collision) occurs near the middle of the battery, the battery will be damaged. For example, if the battery is not arranged in a predetermined manner, a large amount of gas may be rapidly generated at the collision position, resulting in the inability to quickly transmit to the explosion-proof valves at both ends of the battery cell, which may cause the lithium ion battery to explode. For another example, there may be three explosion-proof valves, two of which are symmetrically arranged on two opposite short sides of the lithium ion battery, and the third explosion-proof valve is arranged on the long side of the lithium ion battery, and is preferably arranged in the middle of the long side, because for a long battery cell, if an abnormal situation (such as a collision) occurs near the middle of the battery cell, a large amount of gas may be rapidly generated at the collision position, resulting in the inability to quickly transmit to the explosion-proof valves at both ends of the battery cell, which may cause the lithium ion battery to explode.

[0165] When the battery cell is a laminated battery cell, the positive electrode column and the negative electrode column are respectively arranged at both ends of the shell or at the same end of the shell; when the battery cell is a wound battery cell, the positive electrode column and the negative electrode column are preferably arranged at the same end of the shell.

[0166] Gas production analysis:

[0167] In the preparation process of lithium-ion batteries, the first charge and discharge will form an SEI layer on the surface of the active material of the negative electrode sheet. A large amount of gas is generated in this process. A vacuum procedure is required to discharge this part of the gas out of the lithium-ion battery, and then the shell is sealed and shipped as a finished lithium-ion battery. The use of finished lithium-ion batteries includes normal charge and discharge cycles, as well as abnormal use environments, such as high temperature and collision. Under normal use conditions, as the charge and discharge cycles proceed, lithium is continuously deintercalated between the graphite layers in the negative electrode, which will cause the graphite volume to expand and may also cause graphite interlayer peeling. These factors will cause the SEI on the surface of the negative electrode active material to be destroyed and regenerated, and the process of regenerating SEI will produce gas. In addition, as the graphite is intercalated with lithium, especially for thick electrodes, some lithium ions do not have time to be embedded in the graphite layers, thereby precipitating lithium dendrites on the surface of the negative electrode active material. The precipitated metal lithium dendrites will react with the electrolyte, generating SEI while consuming the electrolyte and generating gas. The positive electrode sheet also produces gas during the charging and discharging process. When the ternary material is used as the positive electrode active material, more gas is produced. However, the technical solution of this application adopts lithium-containing phosphate, so the positive electrode produces less gas. When the lithium-ion battery is used abnormally, such as at high temperature, the specific reaction part in the lithium-ion battery is as follows:

[0168] When the temperature of lithium-ion batteries exceeds 80°C, the organic lithium in the SEI film will decompose and produce gas, and lithium hexafluorophosphate will decompose and react with the solvent to produce gas;

[0169] When the temperature of lithium-ion batteries exceeds 120°C, the SEI film on the surface of the negative electrode has been mostly decomposed, causing the lithium and other substances in the negative electrode to react with the organic solvent to produce gas;

[0170] When the temperature of lithium-ion batteries is between 110°C and 300°C, lithium hexafluorophosphate decomposes in large quantities, and the electrolyte also reacts to produce gas in large quantities;

[0171] When the temperature of lithium-ion batteries exceeds 300°C, lithium-containing phosphates decompose and produce gas, and further induce the decomposition and gas production of the electrolyte;

[0172] In addition, when the temperature of the lithium-ion battery exceeds 235°C, the PVDF binder used in the positive and negative electrodes also begins to decompose.

[0173] The gas production in the early stage of thermal runaway is relatively mild. At this time, if the charging and discharging of the lithium-ion battery is stopped and the temperature is cooled as soon as possible, the further occurrence of thermal runaway will be prevented, and the SEI film can be re-formed at the negative electrode of the lithium-ion battery, and the lithium-ion battery can continue to be used. However, if the thermal runaway is not prevented in time, then in the middle and late stages of thermal runaway, with the accumulation of heat, a large amount of gas will be produced, causing the gas pressure in the lithium-ion battery to increase significantly and break open the explosion-proof valve. Although the explosion-proof valve prevents the explosion reaction of the lithium-ion battery, the lithium-ion battery can no longer be used after the explosion-proof valve is opened.

[0174] Therefore, the technical solution of the present application continuously optimizes the features of the positive electrode sheet, negative electrode sheet, diaphragm, electrolyte, cell structure, etc. in the lithium-ion battery, so that the gas production under normal use is reduced as much as possible, so as to first ensure that the gas produced during the normal use life cycle of the lithium-ion battery (such as 3000 charge and discharge cycles) is not enough to flush the explosion-proof valve; and further ensure that as much space as possible can be left for the gas produced by thermal runaway, so that the lithium-ion battery does not flush the explosion-proof valve in the early stage of thermal runaway. Specifically, if the gas production during the normal cycle is small, the gas produced in the early stage of thermal runaway is still not enough to reach the opening pressure of the explosion-proof valve, and the explosion-proof valve will not be flushed. At this time, if the thermal runaway is prevented from occurring further, the lithium-ion battery can continue to be used. More specifically, the opening pressure of the explosion-proof valve is generally between 0.6Mpa and 1Mpa. For the safety of lithium-ion batteries, the present application designs the opening pressure of the explosion-proof valve to be 0.55Mpa-0.65Mpa. In order to leave gas space for thermal runaway, the present application designs the internal pressure of the lithium-ion battery to not exceed 0.35Mpa after 3000 charge and discharge cycles at 40°C.

[0175] In addition to the battery cells and electrolyte, there is also theoretical gas storage space inside the shell. The theoretical gas storage space usually indicates the maximum gas storage capacity reserved for the battery during design. The theoretical gas storage space is formed on the one hand by the space between the battery cells and the shell that is not filled with electrolyte added during the preparation of the lithium-ion battery, and on the other hand, the electrolyte is continuously consumed during the cycle of the lithium-ion battery, which frees up space for the consumed electrolyte. These two factors together form the theoretical gas storage space inside the lithium-ion battery. Especially in the later stages of the lithium-ion battery cycle, since a large amount of electrolyte is consumed, most of the remaining electrolyte is located in the pores of the diaphragm, leaving very little electrolyte between the battery cells and the shell. Therefore, when designing the theoretical gas storage space in this application, on the one hand, the space between the battery cell and the shell in the thickness direction of the battery cell is ignored, because in the preparation process of lithium-ion batteries, the thickness of the battery cell and the thickness of the shell in the thickness direction of the battery cell are almost the same, and the reserved space is very small. The battery cell expands after the cycle and the electrolyte fills the battery cell, so the battery cell and the shell in the thickness direction are almost in contact with the shell, so the space between the battery cell and the shell in the thickness direction of the battery cell can be ignored; on the other hand, as the cycle proceeds, especially in the later stage of the battery cycle, the electrolyte is consumed in large quantities, and most of the remaining electrolyte is located in the pores of the diaphragm, so there is very little electrolyte between the battery cell and the shell. Therefore, the space between the battery cell and the shell in the width direction of the battery cell and the space between the battery cell and the shell in the length direction of the battery cell can be calculated, and the sum of the two constitutes the actual gas storage space.

[0176] Specifically, when designing the battery cell, the present application first presets the capacity, and based on the relationship between volume and capacity, the required theoretical gas storage space V0 can be calculated; for a finished lithium-ion battery, the capacity of the lithium-ion battery is the capacity at a charge and discharge rate of 0.33C.

[0177] The solution of the present application is applicable to various lithium-ion battery structures, which are described as follows in conjunction with the accompanying drawings:

[0178] like Figure 1 , Figure 2 , Figure 3 , Figure 4 The square laminated lithium-ion battery shown in the figure has an aspect ratio of 6.5. The lithium-ion battery includes a housing 40, and a battery cell 30 and an electrolyte (not shown in the figure) located inside the housing 40. Figure 1 Zhong Zheng electrode 10 and Figure 2 The negative electrode sheet 20 and the separator (not shown) are stacked to form the battery cell 30 . The housing 40 further includes a positive electrode column 41 , a negative electrode column 42 , and an explosion-proof valve 43 .

[0179] Both the positive electrode sheet 10 and the negative electrode sheet 20 are square structures. The square structure here refers to the overall shape of the tabs being ignored. The positive electrode sheet 10 includes a positive tab 11, a positive current collector, and a positive active material layer. The positive current collector is a rectangular structure. The positive tab 11 is arranged on a short side of the positive current collector. The positive tab 11 is asymmetrically distributed on the short side of the positive current collector. Along the width direction of the battery cell, that is, along the short side direction of the positive current collector, the vertical distance from the upper end of the positive tab 11 to the upper end of the positive electrode sheet 10 is a first distance h1, and the vertical distance from the lower end of the positive tab 11 to the lower end of the positive electrode sheet 10 is a second distance h2, wherein h1 is greater than h2, and the ratio of the width of the positive tab 11 to the short side width of the positive current collector is 0.75. The negative electrode sheet 20 includes a negative electrode tab 21, a negative electrode current collector, and a negative electrode active material layer. The negative electrode current collector is a rectangular structure. The negative electrode tab 21 is arranged on a short side of the negative electrode current collector, and the negative electrode tab 21 is asymmetrically distributed on the short side of the negative electrode current collector. Along the width direction of the battery cell, that is, along the short side direction of the negative electrode current collector, the vertical distance from the upper end of the negative electrode tab 21 to the upper end of the negative electrode sheet 20 is a third distance h3, and the vertical distance from the lower end of the negative electrode tab 21 to the lower end of the negative electrode sheet 20 is a fourth distance h4, wherein h3 is greater than h4, and the ratio of the width of the negative electrode tab 21 to the short side width of the negative electrode current collector is 0.75.

[0180] The battery cell 30 is formed by stacking multiple positive electrode sheets 10, multiple negative electrode sheets 20 and a separator. A positive electrode tab 11 is provided on a short side of each positive electrode sheet 10, and a negative electrode tab 21 is provided on a short side of each negative electrode sheet 20. The positive electrode tab 11 and the negative electrode tab 21 are respectively located at both ends of the battery cell 30.

[0181] The positive pole column 41 is electrically connected to the positive pole tab 11, and the negative pole column 42 is electrically connected to the negative pole tab 21. The positive pole column 41 and the negative pole column 42 are arranged at both ends of the housing 40, and the explosion-proof valve 43 is arranged at the edge of one end of the housing 40 where the positive pole column 41 is located. Figure 3 and Figure 4 As shown, a first upper exhaust channel 51 is formed between the upper end of the positive electrode tab 11 and the shell 40, and the end of the shell 40 connected to the positive electrode tab 11 includes an explosion-proof valve 43. Figure 4 In the horizontal direction (which is also the length direction Ld of the battery cell), the explosion-proof valve 43 partially overlaps with the first upper exhaust channel 51. Specifically, along the airflow direction of the first upper exhaust channel 51, the overlap degree of the explosion-proof valve 43 and the first upper exhaust channel 51 is 85%, that is, Figure 4 In the vertical direction (also the height direction Hd, which is also the width direction of the lithium-ion battery), the ratio of the width of the explosion-proof valve 43 to the width of the first upper exhaust passage 51 is 85%. Figure 4As shown, the flow direction of the gas inside the lithium-ion battery is illustrated. The gas generated inside the battery cell 30 is mostly discharged from the battery cell 30 along the edge of the electrode through the pores between the electrode pieces or the diaphragm. In a normal cycle, since the gas is continuously and relatively slowly generated, due to the fluidity, the generated gas is relatively evenly dispersed inside the shell 40, including part of the gas concentrated at the position of the first upper exhaust channel 51; in an abnormal situation, the gas is rapidly generated, resulting in an increase in the air pressure inside the shell 40, which causes the air pressure at the position of the first upper exhaust channel 51 to increase, thereby opening the explosion-proof valve 43.

[0182] like Figure 3 As shown, in the thickness direction of the electrode sheet, which is also the thickness direction of the battery cell 30 (in the figure, the thickness direction is the direction perpendicular to the plane of the view, that is, perpendicular to the direction of Hd and Ld), the gap between the battery cell 30 and the shell 40 is small, and as the battery cell 30 expands during the cycle, and the expansion mainly occurs in the thickness direction of the battery cell 30, the gap between the battery cell 30 and the shell 40 after the cycle is further reduced. When calculating the actual gas storage space, the thickness direction can be ignored, and only the length direction of the battery cell 30 and the height direction (also the width direction) of the battery cell 30 are calculated. The space between the battery cell 30 and the shell 40, that is, Figure 3 The space where the middle numbers ①②③④ are located.

[0183] Figures 1 to 4 It is just for illustration, the explosion-proof valve 43 can also be arranged at the edge of one end of the housing 40 of the negative pole 42, that is, at Figure 3 or Figure 4 In the embodiment, the explosion-proof valve 43 is arranged on the short side of the right side of the lithium-ion battery.

[0184] like Figure 5 , Figure 6 , Fig. 9 , Fig.10 Another lithium-ion battery structure of the present application has an aspect ratio of 3. The lithium-ion battery also includes a housing 40, and a battery cell 30 and an electrolyte (not shown in the figure) located inside the housing 40. Figure 5 Middle negative electrode sheet 20 and Figure 6The positive electrode sheet 10 and the diaphragm (not shown in the figure) are stacked to form the battery cell 30, and the shell 40 also includes a positive electrode column 41, a negative electrode column 42, and an explosion-proof valve 43. The positive electrode sheet 10 and the negative electrode sheet 20 are both square structures, and the square structure here refers to the overall shape of the pole ear being ignored. The positive electrode sheet includes a positive pole ear 11, a positive current collector, and a positive active material layer. The positive current collector is a rectangular structure, and the positive pole ear 11 is arranged on one long side of the positive current collector. The negative electrode sheet 20 includes a negative pole ear 21, a negative current collector, and a negative active material layer. The negative current collector is a rectangular structure, and the negative pole ear 21 is arranged on one long side of the negative current collector. The battery cell 30 is formed by stacking a plurality of positive electrode sheets 10, a plurality of negative electrode sheets 20 and a separator, a positive electrode tab 11 is provided on one long side of each positive electrode sheet 10, a negative electrode tab 21 is provided on one long side of each negative electrode sheet 20, and the positive electrode tab 11 and the negative electrode tab 21 are both located at the upper end of the battery cell 30. The positive electrode column 41 is electrically connected to the positive electrode tab 11, the negative electrode column 42 is electrically connected to the negative electrode tab 21, the positive electrode column 41 and the negative electrode column 42 are arranged at the upper end of the housing 40, and the explosion-proof valve 43 is arranged between the positive electrode column 41 and the negative electrode column 42. Fig.10 A schematic diagram of the airflow direction is also given. Fig. 9 As shown, in the thickness direction of the electrode sheet, which is also the thickness direction of the battery cell 30 (in the figure, the thickness direction is the direction perpendicular to the plane of the view, that is, perpendicular to the direction of Hd and Ld), the gap between the battery cell 30 and the shell 40 is small, and as the battery cell 30 expands during the cycle, and the expansion mainly occurs in the thickness direction of the battery cell 30, the gap between the battery cell 30 and the shell 40 after the cycle is further reduced. Therefore, when calculating the actual gas storage space, the thickness direction can be ignored, and only the space volume between the battery cell 30 and the shell 40 in the length direction of the battery cell 30 and the height direction of the battery cell 30 is calculated, that is Fig. 9 The space at the location of the number ①②③④. A more specific calculation method is: the spatial volume in the length direction of the battery cell 30 (that is, the sum of the spatial volumes of number ① and number ②): the difference between the inner cavity length of the shell 40 and the length of the battery cell 30 multiplied by the inner cavity width of the shell 40 multiplied by the inner cavity thickness of the shell 40; the spatial volume in the height direction of the battery cell 30 (that is, the spatial volume in the width direction, that is, the sum of the spatial volumes of number ③ and number ④): the difference between the inner cavity width of the shell 40 and the width of the battery cell 30 multiplied by the length of the battery cell 30 multiplied by the inner cavity thickness of the shell 40. The actual gas storage space is the sum of the spatial volume in the length direction of the battery cell 30 and the spatial volume in the width direction of the battery cell 30.

[0185] The inner cavity thickness of the shell 40 of the present application is also referred to as the inner thickness of the shell 40 (i.e., the distance between the inner wall of one side of the shell 40 and the inner wall of the other side of the shell 40 in the thickness direction), the inner cavity width of the shell 40 is also referred to as the inner width of the shell 40 (i.e., the distance between the inner wall of one side of the shell 40 and the inner wall of the other side of the shell 40 in the width direction), and the inner cavity length of the shell 40 is also referred to as the inner length of the shell 40 (i.e., the distance between the inner wall of one side of the shell 40 and the inner wall of the other side of the shell 40 in the length direction). In addition, the width of the negative electrode current collector (excluding the tabs) is used instead of the width of the battery cell 30; the length of the negative electrode current collector (excluding the tabs) is used instead of the length of the battery cell 30; although the tabs will also occupy a certain space, the space volume occupied by the tabs is ignored in the present application.

[0186] When calculating the actual gas storage space, the thickness direction can be ignored, and only the space between the battery cell 30 and the shell 40 in the length direction and the height direction is calculated. The space at the positions marked ①②③④ does not include other components between the shell 40 and the battery cell 30, such as supporting structures, etc. These components also occupy volume. The actual gas storage space is subtracted from the volume of other components.

[0187] like Figure 7 , Figure 8 , Fig. 9 , Fig.10 Another lithium-ion battery structure of the present application has an aspect ratio of 3. The lithium-ion battery also includes a housing 40, and a battery cell 30 and an electrolyte (not shown in the figure) located inside the housing 40. Figure 7 Zhong Zheng electrode 10 and Figure 8 The negative electrode sheet 20 and the separator (not shown in the figure) are wound to form the battery cell 30, and the shell 40 also includes a positive electrode column 41, a negative electrode column 42, and an explosion-proof valve 43. Both the positive electrode sheet 10 and the negative electrode sheet 20 are square structures, and the square structure here refers to the overall shape of the pole ear being ignored. The positive electrode sheet includes a positive pole ear 11, a positive electrode collector, and a positive electrode active material layer. The positive electrode collector is a rectangular structure. The positive pole ear 11 is arranged on a long side of the positive electrode collector, and a plurality of positive pole ears 11 are evenly arranged on a positive electrode collector. The negative electrode sheet 20 includes a negative pole ear 21, a negative electrode collector, and a negative electrode active material layer. The negative electrode collector is a rectangular structure. The negative pole ear 21 is arranged on a long side of the negative electrode collector, and a plurality of negative pole ears 21 are evenly arranged on a negative electrode collector. The battery cell 30 is formed by winding a positive electrode sheet 10, a negative electrode sheet 20 and a diaphragm, and the positive electrode tab 11 and the negative electrode tab 21 are both located at the upper end of the battery cell 30; the positive electrode column 41 is electrically connected to the positive electrode tab 11, and the negative electrode column 42 is electrically connected to the negative electrode tab 21. The positive electrode column 41 and the negative electrode column 42 are arranged at the upper end of the shell 40, and the explosion-proof valve 43 is arranged between the positive electrode column 41 and the negative electrode column 42. Fig.10 A schematic diagram of the airflow direction is also given. Fig. 9As shown, in the thickness direction of the pole piece, which is also the thickness direction of the battery cell 30 (in the figure, the thickness direction is the direction perpendicular to the plane of the view, that is, perpendicular to the direction of Hd and Ld), the gap between the battery cell 30 and the shell 40 is small, and as the battery cell 30 expands during the cycle, and the expansion mainly occurs in the thickness direction of the battery cell 30, the gap between the battery cell 30 and the shell 40 after the cycle is further reduced. When calculating the actual gas storage space, the thickness direction can be ignored, and only the space between the battery cell 30 and the shell 40 in the length direction and the height direction is calculated, that is, Fig. 9 The space where the middle numbers ①②③④ are located.

[0188] In order to further study the actual gas storage space required by different lithium-ion battery systems and different materials, the applicant designed a series of experiments based on his design experience in small-capacity lithium-ion batteries and previous explorations. The experimental groups are as follows:

[0189] [First basic group]

[0190] The applicant first set up a total of 100 lithium-ion batteries of the first basic group. The purpose of the design of the first basic group is to obtain the ratio of capacity to gas production of large-capacity batteries. The original materials added to the first basic group of lithium-ion batteries and the structure of lithium-ion batteries are as follows: the negative electrode active material uses carbon-coated graphite, the OI value of the graphite is 10, the degree of graphitization is 92%, the Dv50 of the graphite is 15μm, the Dv10 is 6μm, the Dv90 is 26μm, the Dv99 is 42μm, the graphite is a non-agglomerated single particle, and the surface density of the single-sided active material layer of the negative electrode sheet is 0.11mg / mm 2 The compaction density of the single-sided active material layer of the negative electrode sheet is 1.4g / cc, the single-sided thickness of the negative electrode active material layer is 79μm, the negative electrode collector is copper foil with a thickness of 6μm, and negative electrode active material layers are arranged on both sides of the negative electrode collector. The negative electrode ear is arranged at one end of the length direction of the negative electrode sheet, that is, it is arranged on the short side, and the negative electrode ear and the negative electrode sheet are an integrated structure. The width of the negative electrode sheet is 120mm, the width of the negative electrode ear is 75mm, and along the width direction of the negative electrode sheet, the distance h3 from the upper end of the negative electrode ear to the upper end of the negative electrode sheet is 28mm, and the distance h4 from the lower end of the negative electrode ear to the lower end of the negative electrode sheet is 17mm; there are multiple negative electrode sheets, and multiple negative electrode sheets are provided with negative electrode ears, and multiple negative electrode ears are electrically connected to the negative electrode column on the second end of the shell, and the first end of the shell is provided with an explosion-proof valve.

[0191] The positive electrode active material is carbon-coated lithium iron phosphate (LFP). The compaction density of the single-sided active material layer of the positive electrode sheet is 2.6g / cc, and the surface density of the single-sided active material layer of the positive electrode sheet is 0.24mg / mm 2The thickness of the single-sided active material layer of the positive electrode sheet is 92 μm, the positive electrode ear is arranged at one end of the length direction of the positive electrode sheet, that is, arranged on the short side, and the positive electrode ear and the positive electrode sheet are an integrated structure, the width of the positive electrode sheet is 116 mm, the width of the positive electrode ear is 75 mm, the distance h1 from the upper end of the positive electrode ear to the upper end of the positive electrode sheet is 26 mm, and the distance h2 from the lower end of the positive electrode ear to the lower end of the positive electrode sheet is 15 mm. There are multiple positive electrode sheets, and the multiple positive electrode sheets are all provided with positive electrode ears, and the multiple positive electrode ears are electrically connected to the positive electrode column on the second end of the shell; a first upper exhaust channel is formed between the upper end of the positive electrode ear and the shell; An explosion-proof valve is provided at the first end of the shell, and the explosion-proof valve is arranged above the positive electrode column. Along the airflow direction of the first upper exhaust channel, the overlap degree between the explosion-proof valve and the first upper exhaust channel is 85%; (the average particle size of the primary particles of the positive electrode active material LFP is 0.1μm-5μm. Since the LFP particles themselves are very easy to agglomerate, their average particle size cannot be accurately measured. However, since the gas production of LFP is very small relative to the ternary positive electrode material, and after LFP and graphite form a lithium-ion battery, the gas production at the negative electrode graphite position is much greater than the gas production at the positive electrode LFP position, so this application does not limit the particle size of LFP as a positive electrode material).

[0192] The diaphragm comprises a PE base film, an aluminum oxide coating is arranged on the base film, and the porosity of the diaphragm is 40%.

[0193] The lithium salt of the electrolyte is LiPF6, which accounts for 16% by mass of the electrolyte. The solvents of the electrolyte include EC, DMC, EMC, and DEC, which account for 30%, 13%, 38%, and 8% by mass, respectively.

[0194] The cell structure is a stacked structure. The capacity of the lithium-ion battery is designed to be 300Ah. The gas storage space of the first basic group of lithium-ion batteries is 1500cm 3 The gas storage space of the lithium-ion battery in the first basic group is designed to be much larger than the required space. There are multiple considerations as follows: on the one hand, it is to ensure that each basic group can circulate 3,000 times without the explosion-proof valve being activated during testing, so as to calculate the relationship between the capacity and gas production of the lithium-ion batteries in different basic groups; on the other hand, the gas storage space of the lithium-ion battery in this first basic group is large, which is convenient for setting a gas pressure sensor inside the shell.

[0195] After the lithium-ion battery is filled, it will go through the formation and gas extraction process;

[0196] The bursting pressure of the explosion-proof valve is 0.6Mpa.

[0197] The shell of the lithium-ion battery is made of aluminum alloy, and a gas pressure sensor is arranged inside the shell.

[0198] For the 100 lithium-ion battery charge and discharge cycles of the first basic group, the external environment temperature of the lithium-ion battery is 40°C, the charge and discharge cut-off voltage is 2.5V-3.65V, and the charging process includes a constant current section and a constant voltage section. In the constant current section: the lithium-ion battery is first charged with a constant current of 1C times to the cut-off voltage (3.65V), and in the constant voltage section: constant voltage charging; the discharge process is to discharge the lithium-ion battery at a rate of 1C to the discharge cut-off voltage (2.5V). After 50 cycles of charge and discharge of the basic group, 5 lithium-ion batteries were taken out and analyzed for changes in the components of the lithium-ion batteries, and the remaining 95 lithium-ion batteries continued to cycle for 3000 cycles. Analysis of the five lithium-ion batteries removed found that most of the positive and negative electrode materials and positive and negative electrode sheets did not change much, except for the compaction density and thickness of the negative electrode sheet. The compaction density of the single-sided active material layer of the negative electrode sheet was measured to be 1.35g / cc, and the thickness of the single-sided active material layer of the negative electrode sheet was measured to be 85μm; the compaction density and thickness of the single-sided active material layer of the positive electrode sheet changed relatively little. After measurement, the compaction density of the single-sided active material layer of the positive electrode sheet became 2.59g / cc, and the thickness of the single-sided active material layer of the positive electrode sheet became 93μm.

[0199] The remaining 95 lithium-ion batteries had no explosion-proof valves opened after 3000 cycles. After the lithium-ion batteries were cycled for 3000 cycles, the gas pressure P of the gas pressure sensor in each lithium-ion battery was recorded (the gas pressure P of different lithium-ion batteries may be different), and according to PV=NRT, T was taken as 40℃, R was 8.314, and V was 1500cm 3 , the air pressure P is taken in MPa, and the gas production N corresponding to each lithium-ion battery is obtained. 95 data are summarized and it is calculated that when the capacity L of the lithium-ion battery is 300Ah, the ratio of the gas production N of the lithium-ion battery to the capacity of the lithium-ion battery N / L is between 0.02554mmol / Ah (millimolar ampere-hour) and 0.03495mmol / Ah.

[0200] According to Pv=NRT, when the fixed pressure P is 0.35Mpa, the ratio of the gas storage space v to the capacity L of the lithium-ion battery is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, N / L is 0.02554mmol / Ah (millimoles per ampere hour)-0.03495mmol / Ah, thus obtaining 0.19cm 3 / Ah≤v / L≤0.26cm 3 / Ah, that is, 0.19L≤v≤0.26L, v is in cubic centimeters (cm 3 ).

[0201] [First Adjustment Group]

[0202] On the basis of the first basic group, a first adjustment group is set up. The design idea of ​​the first adjustment group is to design a series of lithium-ion batteries with graphite of different OI values ​​on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0203] After this series of lithium-ion batteries were cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained, and it was found that the graphite OI value was 3, and the corresponding average value of the ratio of gas production to capacity of several first adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah); when the graphite OI value was lower than 3, the corresponding average value of the ratio of gas production to capacity of several first adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); it was found that when the graphite OI value was higher than 3 and less than or equal to 30 (for cost considerations, this application did not verify the case where the OI value was higher than 30, but according to the inventor's speculation, the higher the graphite OI value, the better the fast charging performance and the less gas production), the corresponding average values ​​of the ratio of gas production to capacity of several first adjustment groups of lithium-ion batteries were lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0204] [First and Second Adjustment Group]

[0205] On the basis of the first adjustment group, a first secondary adjustment group is further provided. The first secondary adjustment group is different from the first adjustment group only in that the charging rate is changed to 2C.

[0206] It was found that the average value of the ratio of gas production to capacity of several first and second adjustment groups of lithium-ion batteries corresponding to the graphite OI value of 10 was close to the upper limit of the first basic group (0.03495mmol / Ah); when the graphite OI value was lower than 10, the average value of the ratio of gas production to capacity of several first and second adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); it was found that when the graphite OI value was higher than 10 and less than or equal to 30, the corresponding average values ​​of the ratio of gas production to capacity of several first and second adjustment groups of lithium-ion batteries were all lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0207] [The first and third adjustment groups]

[0208] On the basis of the first adjustment group, first and third adjustment groups are further set. The first and third adjustment groups are different from the first adjustment group only in that the charging rate is changed to 3C.

[0209] It was found that the average value of the ratio of gas production to capacity of several first and third adjustment groups of lithium-ion batteries corresponding to the graphite OI value of 15 was close to the upper limit of the first basic group (0.03495mmol / Ah); when the graphite OI value was lower than 15, the average value of the ratio of gas production to capacity of several first and third adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); it was found that when the graphite OI value was higher than 15 and less than or equal to 30, the corresponding average values ​​of the ratio of gas production to capacity of several first and third adjustment groups of lithium-ion batteries were all lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0210] Therefore, based on the results of the first basic group, the first adjustment group, the first secondary adjustment group and the first tertiary adjustment group, it can be concluded that when the battery cell is required to have high-rate charging capability, such as when the rate is above 2C, the graphite OI value range can be designed to be 10-30, such as when the rate is above 3C, the graphite OI value range can be designed to be 15-30.

[0211] [Second adjustment group]

[0212] On the basis of the first basic group, a second adjustment group is set up. The design idea of ​​the second adjustment group is to design a series of lithium-ion batteries with graphites of different graphitization degrees on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0213] After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that the average value of the ratio of gas production to capacity of several second adjustment groups of lithium-ion batteries corresponding to a graphitization degree of 90% was close to the upper limit of the first basic group (0.03495mmol / Ah), and when the graphitization degree was lower than 90%, the average value of the ratio of gas production to capacity of several second adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); when the graphitization degree was higher than 90 and less than or equal to 95 (due to cost considerations, this application did not verify the case where the graphitization degree was higher than 95, but according to the inventor's speculation, the higher the graphitization degree of graphite, the better the fast charging performance and the less gas production), the corresponding average value of the ratio of gas production to capacity of several second adjustment groups of lithium-ion batteries was lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0214] [Secondary Adjustment Group]

[0215] On the basis of the second adjustment group, a second secondary adjustment group is set. The design idea of ​​the second secondary adjustment group is that, on the basis of the second adjustment group, the charging rate is set to 2C, and other characteristics are controlled to be the same as the second adjustment group.

[0216] After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that the average value of the ratio of gas production to capacity of several second secondary adjustment groups of lithium-ion batteries corresponding to a graphitization degree of 91% was close to the upper limit of the first basic group (0.03495mmol / Ah), and when the graphitization degree was lower than 91%, the average value of the ratio of gas production to capacity of several second secondary adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah).

[0217] [Third Adjustment Group]

[0218] On the basis of the first basic group, a third adjustment group is set up. The design idea of ​​the third adjustment group is to design a series of lithium-ion batteries with different Dv50 graphites on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0219] After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the graphite Dv50 was 10μm, the average value of the ratio of gas production to capacity of several third-adjustment group lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah). When the graphite Dv50 was lower than 10μm, the average value of the ratio of gas production to capacity of several third-adjustment group lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah). It was found that when the graphite Dv50 was 30μm, the average value of the ratio of gas production to capacity of several third-adjustment group lithium-ion batteries was The average value of the value is close to the upper limit of the first basic group (0.03495mmol / Ah). When the graphite Dv50 is higher than 30μm, the corresponding average value of the ratio of gas production to capacity of several third adjustment groups of lithium-ion batteries exceeds the upper limit of the first basic group (0.03495mmol / Ah); when the graphite Dv50 is between 10μm and 30μm, the corresponding average value of the ratio of gas production to capacity of several third adjustment groups of lithium-ion batteries is lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0220] [Third and Secondary Adjustment Group]

[0221] On the basis of the third adjustment group, a third secondary adjustment group is further set up, which differs from the third adjustment group only in that the charging rate is changed to 2C.

[0222] It was found that when the graphite Dv50 was 20μm, the corresponding average value of the ratio of gas production to capacity of several third-secondary adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah); when the graphite Dv50 exceeded 20μm, the corresponding average value of the ratio of gas production to capacity of several third-secondary adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); when the graphite Dv50 was between 10μm and 20μm, the corresponding average value of the ratio of gas production to capacity of several third-secondary adjustment groups of lithium-ion batteries was lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0223] [33rd Adjustment Group]

[0224] On the basis of the third adjustment group, a third and third adjustment group is further set up. The difference from the third adjustment group is that the graphite used is carbon-coated graphite secondary particles.

[0225] It was found that the Dv50 of the carbon-coated graphite secondary particles was 30μm, and the corresponding average value of the ratio of gas production to capacity of several third and third adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah). When the Dv50 of the carbon-coated graphite secondary particles exceeded 30μm, the corresponding average value of the ratio of gas production to capacity of several third and third adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); when the Dv50 of the carbon-coated graphite secondary particles was between 10μm and 30μm, the corresponding average value of the ratio of gas production to capacity of several third and third adjustment groups of lithium-ion batteries was lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0226] [Third and fourth adjustment groups]

[0227] On the basis of the first basic group, the third and fourth adjustment groups are set up. The design idea of ​​the third and fourth adjustment groups is to design a series of Dv10 lithium-ion batteries with different graphites based on the first basic group, and control other characteristics to be the same as the first basic group.

[0228] After this series of lithium-ion batteries were cycled 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the graphite Dv10 was 3μm, the average value of the ratio of gas production to capacity of several corresponding third and fourth adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah). When the graphite Dv10 was lower than 3μm, the average value of the ratio of gas production to capacity of several corresponding third and fourth adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah).

[0229] [The 35th Adjustment Group]

[0230] On the basis of the first basic group, the third and fifth adjustment groups are set up. The design idea of ​​the third and fifth adjustment groups is to design a series of Dv90 lithium-ion batteries with different graphites based on the first basic group, and control other characteristics to be the same as the first basic group.

[0231] After this series of lithium-ion batteries were cycled 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the graphite Dv90 was 40μm, the average value of the ratio of gas production to capacity of several lithium-ion batteries in the third and fifth adjustment groups was close to the upper limit of the first basic group (0.03495mmol / Ah). When the graphite Dv90 was higher than 40μm, the average value of the ratio of gas production to capacity of several lithium-ion batteries in the third and fifth adjustment groups exceeded the upper limit of the first basic group (0.03495mmol / Ah).

[0232] [The 36th Adjustment Group]

[0233] On the basis of the first basic group, the third and sixth adjustment groups are set up. The design idea of ​​the third and sixth adjustment groups is to design a series of Dv99 lithium-ion batteries with different graphites based on the first basic group, and control other characteristics to be the same as the first basic group.

[0234] After this series of lithium-ion batteries were cycled 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the graphite Dv99 was 49μm, the average value of the ratio of gas production to capacity of several corresponding third-sixth adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah). When the graphite Dv99 was higher than 49μm, the average value of the ratio of gas production to capacity of several corresponding third-sixth adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah).

[0235] [Fourth Adjustment Group]

[0236] On the basis of the first basic group, a fourth adjustment group is set up. The design idea of ​​the fourth adjustment group is to design a series of lithium-ion batteries with negative electrode sheets with different surface densities on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0237] After 3000 cycles, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained, and it was found that the surface density of the single-sided active material layer of the negative electrode sheet was 0.13 mg / mm 2When the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the fourth adjustment group is close to the upper limit of the first basic group (0.03495mmol / Ah), the surface density of the single-sided active material layer of the negative electrode sheet exceeds 0.13mg / mm 2 When the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the fourth adjustment group exceeds the upper limit (0.03495mmol / Ah) of the first basic group; when the surface density of the single-sided active material layer of the negative electrode sheet is 0.07mg / mm 2 -0.13mg / mm 2 When the average value of the ratio of gas production to capacity of the corresponding fourth adjustment group of lithium-ion batteries is lower than the upper limit (0.03495mmol / Ah) of the first basic group; in addition, when the surface density of the single-sided active material layer of the negative electrode sheet is lower than 0.07mg / mm 2 For the entire negative electrode sheet, due to the presence of the negative electrode current collector, the active material on the negative electrode sheet is relatively small. Especially for large-capacity batteries exceeding 200Ah, more negative electrode sheets are required to achieve large capacity, so for large-capacity batteries, the volume proportion of the current collector will increase. Therefore, according to the previous practice of the inventor, some embodiments of this application stipulate that the surface density of the single-sided active material layer of the negative electrode sheet is not less than 0.07mg / mm 2 .

[0238] [Fifth Adjustment Group]

[0239] On the basis of the first basic group, a fifth adjustment group is set up. The design idea of ​​the fifth adjustment group is to design a lithium-ion battery composed of negative electrode sheets with different compaction densities after a series of rolling processes on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0240] After this series of lithium-ion batteries were cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the compaction density of the single-sided active material layer of the negative electrode sheet after rolling was 1.74g / cc, the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the fifth adjustment group was close to the upper limit of the first basic group (0.03495mmol / Ah). When the compaction density of the single-sided active material layer of the negative electrode sheet after rolling exceeded 1.74g / cc, the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the fifth adjustment group exceeded the upper limit of the first basic group (0.03495mmol / Ah). When the compaction density of the single-sided active material layer of the negative electrode sheet after rolling was 1.32 When the density of the single-sided active material layer of the negative electrode sheet is lower than 1.32 g / cc after rolling, the setting principle is similar to the surface density. For the entire negative electrode sheet, the mass proportion of the negative electrode collector is relatively high. Especially for large-capacity batteries exceeding 200 Ah, more negative electrode sheets are required to achieve large capacity, so that for large-capacity batteries, the mass proportion of the current collector will increase. Therefore, according to the previous practice of the inventor, this application stipulates that the compaction density of the single-sided active material layer of the negative electrode sheet shall not be lower than 1.32 g / cc. In the fifth adjustment group, several lithium-ion batteries with a compaction density of 1.74 g / cc on a single side of the negative electrode sheet after rolling were disassembled after 50 cycles, and it was found that the compaction density of the active material layer on a single side of the negative electrode sheet was 1.7 g / cc; several lithium-ion batteries with a compaction density of 1.32 g / cc on a single side of the negative electrode sheet after rolling were disassembled after 50 cycles, and it was found that the compaction density of the active material layer on a single side of the negative electrode sheet was 1.3 g / cc.

[0241] [Sixth Adjustment Group]

[0242] On the basis of the first basic group, a sixth adjustment group is set up. The design idea of ​​the sixth adjustment group is to design a lithium-ion battery composed of positive electrode sheets with different densities after a series of rolling processes based on the first basic group, and control other characteristics to be the same as the first basic group.

[0243] After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that the surface density of the single-sided active material layer of the positive electrode sheet after rolling was 0.26 mg / mm 2 When the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the sixth adjustment group is close to the upper limit of the first basic group (0.03495mmol / Ah), the surface density of the single-sided active material layer of the positive electrode sheet after rolling exceeds 0.26mg / mm 2When the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the sixth adjustment group exceeds the upper limit (0.03495mmol / Ah) of the first basic group; the surface density of the single-sided active material layer of the positive electrode sheet after rolling is 0.16mg / mm 2 -0.26mg / mm 2 When the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the sixth adjustment group is lower than the upper limit (0.03495mmol / Ah) of the first basic group, when the surface density of the single-sided active material layer of the positive electrode sheet is lower than 0.16mg / mm 2 For the entire positive electrode sheet, due to the presence of the positive electrode current collector, the active material on the positive electrode sheet is relatively small. Especially for large-capacity batteries exceeding 200Ah, more positive electrode sheets are required to achieve large capacity, so for large-capacity batteries, the volume proportion of the current collector will increase. Therefore, according to the inventor's previous practice, this application stipulates that the surface density of the single-sided active material layer of the positive electrode sheet is not less than 0.16mg / mm 2 .

[0244] [Seventh Adjustment Group]

[0245] On the basis of the first basic group, a seventh adjustment group is set up. The design idea of ​​the seventh adjustment group is to design a lithium-ion battery composed of positive electrode sheets with different compaction densities after a series of rolling processes on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0246] After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the compaction density of the single-sided active material layer of the positive electrode sheet after rolling was 2.71g / cc, the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the seventh adjustment group was close to the upper limit of the first basic group (0.03495mmol / Ah). When the compaction density of the single-sided active material layer of the positive electrode sheet after rolling exceeded 2.71g / cc, the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the seventh adjustment group exceeded the upper limit of the first basic group (0.03495mmol / Ah). When the compaction density of the single-sided active material layer of the positive electrode sheet after rolling was 2. 3g / cc-2.71g / cc, the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the seventh adjustment group is lower than the upper limit of the first basic group (0.03495mmol / Ah); in addition, when the compaction density of the single-sided active material layer of the positive electrode sheet after rolling is lower than 2.3g / cc, the setting principle is similar to the surface density. For the entire positive electrode sheet, the mass proportion of the positive electrode collector is relatively high, especially for large-capacity batteries exceeding 200Ah, more positive electrode sheets are required to achieve large capacity, so that for large-capacity batteries, the mass proportion of the current collector will increase. Therefore, according to the previous practice of the inventor, this application stipulates that the compaction density of the single-sided active material layer of the positive electrode sheet shall not be less than 2.3g / cc. In the seventh adjustment group, several lithium-ion batteries with a compaction density of 2.71 g / cc on the single-sided active material layer of the positive electrode after rolling were disassembled after 50 cycles, and it was found that the compaction density of the single-sided active material layer of the negative electrode was 2.7 g / cc; several lithium-ion batteries with a compaction density of 1.3 g / cc on the single-sided active material layer of the positive electrode after rolling were disassembled after 50 cycles, and it was found that the compaction density of the single-sided active material layer of the positive electrode was 1.3 g / cc. When the compaction density is low, the compression of the positive electrode sheet hardly changes.

[0247] [Eighth Adjustment Group]

[0248] On the basis of the first basic group, an eighth adjustment group is set up. The design idea of ​​the eighth adjustment group is to design a series of lithium-ion batteries composed of diaphragms with different diaphragm porosities on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0249] After this series of lithium-ion batteries were cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the diaphragm porosity was 50%, the average value of the ratio of gas production to capacity of several corresponding eighth adjustment groups of lithium-ion batteries was close to the upper limit of the first basic group (0.03495mmol / Ah). It was found that when the diaphragm porosity exceeded 50%, the average value of the ratio of gas production to capacity of several corresponding eighth adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah); and it was found that when the diaphragm porosity was 30%, the corresponding The average value of the ratio of gas production to capacity of several lithium-ion batteries in the eighth adjustment group is close to the upper limit of the first basic group (0.03495mmol / Ah), and the diaphragm porosity is lower than 30%, and the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the eighth adjustment group exceeds the upper limit of the first basic group (0.03495mmol / Ah); it is found that the diaphragm porosity is between 30% and 50%, and the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the eighth adjustment group is lower than the upper limit of the first basic group (0.03495mmol / Ah). On the basis of the basic group, an eighth secondary adjustment group is further set. The difference between the eighth secondary adjustment group and the first basic group is that the width of the negative electrode sheet is different (the corresponding battery cell width, positive electrode sheet width, negative electrode ear width, and positive electrode ear width are all different). A series of lithium-ion batteries composed of negative electrode sheets with different widths are designed. After this series of lithium-ion batteries are cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries is obtained. It is found that when the width of the negative electrode sheet is 250mm, the average value of the ratio of gas production to capacity of several corresponding eighth secondary adjustment groups of lithium-ion batteries is close to the upper limit of the first basic group. (0.03495mmol / Ah), after exceeding 250mm, the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the eighth secondary adjustment group exceeds the upper limit of the first basic group (0.03495mmol / Ah); after the negative electrode sheet width is 100mm-250mm (for the conventional design of large-capacity batteries, the negative electrode sheet width is greater than 100mm, so this application does not verify the case of less than 100mm), the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the eighth secondary adjustment group is lower than the upper limit of the first basic group (0.03495mmol / Ah); on the basis of the first basic group, an eighth third adjustment group is further set up. The difference between the eighth third adjustment group and the first basic group is that the width of the negative electrode sheet is 200mm (the corresponding width of the battery cell, the width of the positive electrode sheet, the width of the negative electrode tab, and the width of the positive electrode tab are all different). A series of lithium-ion batteries composed of diaphragms with different porosities are designed. After 3000 cycles of this series of lithium-ion batteries, the ratio of gas production to capacity of this series of lithium-ion batteries is obtained. It is found that when the porosity of the diaphragm is 35%, the corresponding eighth third adjustment group The average value of the ratio of gas production to capacity of the lithium-ion batteries in the eighth third adjustment group is close to the upper limit of the first basic group (0.03495mmol / Ah). When the diaphragm porosity is lower than 35%, the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the eighth third adjustment group exceeds the upper limit of the first basic group (0.03495mmol / Ah). When the diaphragm porosity is between 35% and 50%, the average value of the ratio of gas production to capacity of the corresponding lithium-ion batteries in the eighth third adjustment group is lower than the upper limit of the first basic group (0.03495mm ol / Ah); on the basis of the first basic group, an eighth fourth adjustment group is further set up. The difference between the eighth fourth adjustment group and the first basic group is that the width of the negative electrode sheet is 150mm (the corresponding width of the battery cell, the width of the positive electrode sheet, the width of the negative electrode tab, and the width of the positive electrode tab are all different). A series of lithium-ion batteries composed of diaphragms with different porosities are designed. After this series of lithium-ion batteries are cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries is obtained. It is found that when the porosity of the diaphragm is 30%, the corresponding number of lithium-ion batteries in the eighth fourth adjustment group The average value of the ratio of gas production to capacity is close to the upper limit of the first basic group (0.03495mmol / Ah). When the membrane porosity is lower than 30%, the average value of the ratio of gas production to capacity of several corresponding eighth and fourth adjustment groups of lithium-ion batteries exceeds the upper limit of the first basic group (0.03495mmol / Ah); when the membrane porosity is between 30% and 50%, the average value of the ratio of gas production to capacity of several corresponding eighth and fourth adjustment groups of lithium-ion batteries is lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0250] [9th Adjustment Group]

[0251] On the basis of the first basic group, a ninth adjustment group is set. The design idea of ​​the ninth adjustment group is to design a series of lithium-ion batteries composed of electrolytes with different DMC contents on the basis of the first basic group. DMC content refers to the mass of DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt. Changes in DMC content will bring about changes in the proportions of electrolyte solvents such as EC, DMC, EMC, and DEC, but according to the experience and experimental exploration of the inventors, it is necessary to make the EC content between 30% and 40%, and the sum of the masses of EMC and DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt between 50% and 60% (at this content, since there will be other additives in the electrolyte, in some cases, the sum of the masses of EC, EMC, and DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt will be less than 100%). Since a high DMC content will reduce the viscosity of the electrolyte, it is beneficial to reduce gas production and fast charging, but DMC produces a large amount of gas during the charging and discharging process of the lithium-ion battery, so for the lithium-ion battery of this application, DMC requires a range.

[0252] After this series of lithium-ion batteries were cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the DMC content was 10%, the average value of the ratio of gas production to capacity of several lithium-ion batteries in the ninth adjustment group was close to the upper limit of the first basic group (0.03495mmol / Ah). When the DMC content was lower than 10%, the average value of the ratio of gas production to capacity of several lithium-ion batteries in the ninth adjustment group exceeded the upper limit of the first basic group (0.03495mmol / Ah). It was found that when the DMC content was 15%, the corresponding The average value of the ratio of gas production to capacity of several lithium-ion batteries in the ninth adjustment group is close to the upper limit of the first basic group (0.03495mmol / Ah). When the DMC content is higher than 15%, the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the ninth adjustment group exceeds the upper limit of the first basic group (0.03495mmol / Ah); when the DMC content is between 10% and 15%, the corresponding average value of the ratio of gas production to capacity of several lithium-ion batteries in the ninth adjustment group is lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0253] [Tenth Adjustment Group]

[0254] On the basis of the first basic group, the tenth adjustment group is set up. The design idea of ​​the tenth adjustment group is to design a series of lithium-ion batteries composed of electrolytes with different carboxylate contents on the basis of the first basic group. The carboxylate content refers to the mass of the carboxylate divided by the difference between the mass of the electrolyte and the mass of the lithium salt. Carboxylates help to form a film at the negative electrode during the charging and discharging process of lithium-ion batteries, improve ionic conductivity, help fast charging, and reduce gas production at the negative electrode interface. However, excessive carboxylate content will cause an increase in gas production, especially in the fast charging system. The content of carboxylate needs to be within a certain range.

[0255] After this series of lithium-ion batteries were cycled for 3000 times, the ratio of gas production to capacity of this series of lithium-ion batteries was obtained. It was found that when the carboxylate content was lower than 10%, the corresponding average values ​​of the ratio of gas production to capacity of several tenth adjustment groups of lithium-ion batteries were lower than the upper limit of the first basic group (0.03495mmol / Ah). It was found that when the carboxylate content was 10%, the corresponding average values ​​of the ratio of gas production to capacity of several tenth adjustment groups of lithium-ion batteries were close to the upper limit of the first basic group (0.03495mmol / Ah). It was found that when the carboxylate content was higher than 10%, the corresponding average values ​​of the ratio of gas production to capacity of several tenth adjustment groups of lithium-ion batteries exceeded the upper limit of the first basic group (0.03495mmol / Ah).

[0256] [11th Adjustment Group]

[0257] On the basis of the first basic group, the eleventh adjustment group is set up. The eleventh adjustment group only needs 10 lithium-ion batteries. The difference from the first basic group is that the charging method is different. In the constant current section, it is no longer charged with a fixed constant current, but charged with high and low currents alternatingly. The specific method is: 1C rate charging for 2 minutes, followed by 0.2C charging for 0.5 minutes, and then 1C charging for 2 minutes again, alternating until the charging cut-off voltage is reached, and constant voltage charging is started.

[0258] Using the high and low current staggered distribution charging method of this group, after 3000 cycles, the gas production of each lithium-ion battery in the eleventh adjustment group is less than that of the corresponding lithium-ion battery in the corresponding first basic group, and other conditions are the same as those of the first basic group.

[0259] [Twelfth Adjustment Group]

[0260] On the basis of the first basic group, a twelfth adjustment group is set up. The twelfth adjustment group only needs 10 lithium-ion batteries. The difference from the first basic group is that the charging method is different. In the constant current section, it is no longer charged with a fixed constant current, but charged with high and low currents alternately. The specific method is: charging at a rate of 1C for 2 minutes, followed by charging at 0.2C for 0.5 minutes, then charging at 0.8C for 2 minutes again, and then charging at 0.2C for 0.5 minutes. In this way, the current value of the high current is gradually reduced until the charging cut-off voltage is reached, and constant voltage charging is started.

[0261] Using the high and low current staggered distribution charging method of this group, after 3000 cycles, the gas production of each lithium-ion battery in the twelfth adjustment group is less than that of the corresponding lithium-ion battery in the corresponding first basic group, and other conditions are the same as those of the first basic group.

[0262] [Thirteenth Adjustment Group]

[0263] On the basis of the first basic group, a thirteenth adjustment group is set up. The thirteenth adjustment group only needs 10 lithium-ion batteries. The difference from the first basic group is that the charging method is different. In the constant current section, it is no longer charged with a fixed constant current, but charged with high and low currents alternatingly. The specific method is: charge at a rate of 1C for 2 minutes, then stop charging for 0.1 minutes, and then charge at 1C again for 2 minutes, and so on and so forth until the charging cut-off voltage is reached, and then start constant voltage charging.

[0264] The inventors were pleasantly surprised to find that, using the high and low current staggered distribution charging method of this group, after 3000 cycles, the gas production of each lithium-ion battery in the thirteenth adjustment group was less than that of the corresponding lithium-ion battery in the first basic group, and other conditions were the same as those of the first basic group.

[0265] Based on the eleventh adjustment group, the twelfth adjustment group, and the thirteenth adjustment group, the inventors further summarized a charging method for reducing gas production, including a constant current charging section and a constant voltage charging section. In the constant current charging section, the following charging process is included: first charging with a first current for a first time, then charging with a second current for a second time, again charging with a third current for a third time, and again charging with a fourth current for a fourth time, the first current is greater than the second current, the first time is greater than the second time, the third current is not greater than the first current, the third time is greater than the second time, the fourth current is less than the third current, and the fourth time is less than the third time; wherein the second current can be 0; and it is further preferred that the second current is equal to the fourth current.

[0266] [Second basic group to twelfth basic group]

[0267] On the basis of the first basic group, a second basic group is set up. The difference from the first basic group is that by reducing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 100Ah. Other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production N to the capacity L of the lithium-ion battery is between 0.01479mmol / Ah (millimoles per ampere hour) and 0.02285mmol / Ah. According to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, and air pressure P as 0.35Mpa, N / L is 0.01479mmol / Ah (millimoles per ampere hour)-0.02285mmol / Ah, thus obtaining 0.11cm 3 / Ah≤v / L≤0.17cm 3 / Ah, that is, 0.11L≤v≤0.17L, v is in cubic centimeters (cm 3 ).

[0268] On the basis of the first basic group, a third basic group is set, which is different from the first basic group in that: by reducing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 200Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.01882mmol / Ah (millimoles per ampere-hour) and 0.02689mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, the air pressure P as 0.35Mpa, N / L is 0.01882mmol / Ah (millimoles per ampere-hour)-0.02689mmol / Ah, and thus 0.14cm 3 / Ah≤v / L≤0.2cm 3 / Ah, that is, 0.14L≤v≤0.2L, v is in cubic centimeters (cm 3 ).

[0269] On the basis of the first basic group, a fourth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 400Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.03226mmol / Ah (millimoles per ampere-hour) and 0.04571mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.03226mmol / Ah (millimoles per ampere-hour)-0.04571mmol / Ah, thus obtaining 0.24cm 3 / Ah≤v / L≤0.34cm 3 / Ah, that is, 0.24L≤v≤0.34L, v is in cubic centimeters (cm 3 ).

[0270] On the basis of the first basic group, a fifth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 500Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.03899mmol / Ah (millimoles per ampere-hour) and 0.05377mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.03899mmol / Ah (millimoles per ampere-hour)-0.05377mmol / Ah, and thus 0.29cm 3 / Ah≤v / L≤0.4cm 3 / Ah, that is, 0.29L≤v≤0.4L, v is in cubic centimeters (cm 3 ).

[0271] On the basis of the first basic group, a sixth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 600Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.04436mmol / Ah (millimoles per ampere hour) and 0.06318mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.04436mmol / Ah (millimoles per ampere hour)-0.06318mmol / Ah, thus obtaining 0.33cm 3 / Ah≤v / L≤0.47cm 3 / Ah, that is, 0.33L≤v≤0.47L, v is in cubic centimeters (cm 3 ).

[0272] On the basis of the first basic group, a seventh basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 700Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.05109mmol / Ah (millimoles per ampere-hour) and 0.07259mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.05109mmol / Ah (millimoles per ampere-hour)-0.07259mmol / Ah, and thus 0.38cm 3 / Ah≤v / L≤0.54cm 3 / Ah, that is, 0.38L≤v≤0.54L, v is in cubic centimeters (cm 3 ).

[0273] On the basis of the first basic group, an eighth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 800Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.05915mmol / Ah (millimoles per ampere-hour) and 0.08738mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.05915mmol / Ah (millimoles per ampere-hour)-0.08738mmol / Ah, thus obtaining 0.44cm 3 / Ah≤v / L≤0.65cm 3 / Ah, that is, 0.44L≤v≤0.65L, v is in cubic centimeters (cm 3 ).

[0274] On the basis of the first basic group, a ninth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 900Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.06856mmol / Ah (millimoles per ampere hour) and 0.09545mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.06856mmol / Ah (millimoles per ampere hour)-0.09545mmol / Ah, thus obtaining 0.51cm 3 / Ah≤v / L≤0.71cm 3 / Ah, that is, 0.51L≤v≤0.71L, v is in cubic centimeters (cm 3 ).

[0275] On the basis of the first basic group, a tenth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 1000Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.07932mmol / Ah (millimoles per ampere-hour) and 0.10486mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.07932mmol / Ah (millimoles per ampere-hour)-0.10486mmol / Ah, thus obtaining 0.59cm 3 / Ah≤v / L≤0.78cm 3 / Ah, that is, 0.59L≤v≤0.78L, v is in cubic centimeters (cm 3 ).

[0276] On the basis of the first basic group, an eleventh basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 1100Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.09141mmol / Ah (millimoles per ampere-hour) and 0.11696mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.09141mmol / Ah (millimoles per ampere-hour)-0.11696mmol / Ah, and 0.68cm 3 / Ah≤v / L≤0.87cm 3 / Ah, that is, 0.68L≤v≤0.87L, v is in cubic centimeters (cm 3 ).

[0277] On the basis of the first basic group, a twelfth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative electrodes, the capacity of the lithium-ion battery is adjusted to 1200Ah, and other conditions are the same. Finally, after 3000 cycles, the ratio of the gas production to the capacity of the lithium-ion battery is between 0.1062mmol / Ah (millimoles per ampere hour) and 0.13174mmol / Ah; according to Pv=NRT, the ratio of the gas storage space v to the capacity L is obtained: v / L=NRT / PL; taking T as 40°C, R as 8.314, air pressure P as 0.35Mpa, N / L is 0.1062mmol / Ah (millimoles per ampere hour)-0.13174mmol / Ah, and thus 0.79cm 3 / Ah≤v / L≤0.98cm 3 / Ah, that is, 0.79L≤v≤0.98L, v is in cubic centimeters (cm 3 ).

[0278] Combining the above adjustment group and basic group, the inventor further analyzed and believed that the ratio of gas production to capacity of lithium-ion batteries increases with the increase of capacity; in order to provide design guidance for lithium-ion batteries of different capacities on theoretical gas storage space, from the perspective of maximum safety, the inventor provides different design standards for lithium-ion batteries with different capacities L. For lithium-ion batteries with a capacity below 200Ah, there is no need to pay attention to the problem of theoretical gas storage space, because during the assembly of the battery cell, since the pole ear needs to be welded to the pole column and the width of the pole ear is shorter than the width of the pole piece, there must be a certain space around the pole ear due to the assembly of the battery cell, and the inevitable space is generally 35cm 3 About, while for the second basic group the maximum gas production is 17cm 3 The maximum gas production of the third basic group is 40cm 3 Therefore, for lithium-ion batteries below 200Ah, the assembly space around the tabs is basically sufficient for gas accumulation. Therefore, this application focuses more on lithium-ion batteries of 200Ah and above. For lithium-ion batteries of 200Ah and above, their theoretical gas storage space is more meaningful.

[0279] For cells 200Ah and above:

[0280] For greater safety and to improve the tolerance of abnormal high temperatures, the gas storage space standard needs to be enlarged. Specifically, for lithium-ion batteries with a capacity of 200Ah≤L≤300Ah, the actual gas storage space should not be less than the lower limit of the ratio of the gas storage space v to the capacity L of the fourth basic group of lithium-ion batteries, which is 0.24cm 3 / Ah, specifically, the lower limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fourth basic group is 0.24cm 3 / Ah is used to calculate the theoretical gas storage space;

[0281] In order to further reduce the problems caused by gas generation, it is further preferred that the actual gas storage space is not less than the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fourth basic group 0.34 cm 3 / Ah, the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery using the fourth basic group is 0.34cm 3 / Ah is used to calculate the theoretical gas storage space;

[0282] In order to take into account the energy density of lithium-ion batteries, the lower limit of the ratio of the gas storage space v to the capacity L of the lithium-ion batteries of the fourth basic group is 0.24 cm 3 / Ah is used to calculate the theoretical gas storage space, and further preferably the actual gas storage space is not greater than the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fourth basic group 0.34cm 3 / Ah, the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery using the fourth basic group is 0.34cm 3 / Ah is used to calculate the theoretical maximum gas storage space.

[0283] Similarly, for lithium-ion batteries with a capacity of 300Ah<L≤400Ah:

[0284] The actual gas storage space should not be less than the lower limit of the ratio of the gas storage space v to the capacity L of the fifth basic group of lithium-ion batteries, which is 0.29 cm 3 / Ah, specifically, the lower limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fifth basic group is 0.29cm 3 / Ah is used to calculate the theoretical gas storage space;

[0285] It is further preferred that the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fifth basic group is not less than the upper limit of 0.4 cm 3 / Ah, the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery using the fifth basic group is 0.4cm 3 / Ah is used to calculate the theoretical gas storage space;

[0286] In order to take into account the energy density of lithium-ion batteries, the lower limit of the ratio of the gas storage space v to the capacity L of the lithium-ion batteries of the fifth basic group is 0.29 cm 3 / Ah is used to calculate the theoretical gas storage space, and further preferably the actual gas storage space is not greater than the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery of the fifth basic group 0.4cm 3 / Ah, the upper limit of the ratio of the gas storage space v to the capacity L of the lithium-ion battery using the fifth basic group is 0.4cm 3 / Ah is used to calculate the theoretical maximum gas storage space.

[0287] Similar designs are made for other capacity ranges.

[0288] Specifically:

[0289] 1) When the capacity L of the lithium-ion battery satisfies L ≥ 200Ah, preferably 200Ah ≤ L ≤ 300Ah, the corresponding theoretical gas storage space V0 = 0.24cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.24cm 3 / Ah·L, if the capacity L of a lithium-ion battery is 200Ah, then the theoretical gas storage space is 0.24cm 3 / Ah·200Ah=48cm 3 For lithium-ion battery with a capacity of L ≥ 200Ah, preferably 200Ah ≤ L ≤ 300Ah, the actual gas storage space v ≥ 48cm 3 .

[0290] In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0 = 0.34 cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.34cm 3 / Ah·L, if the capacity L of a lithium-ion battery is 200Ah, then the theoretical gas storage space is 0.34cm 3 / Ah · 200Ah = 68cm 3 .

[0291] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.34cm 3 / Ah·L, unit is cm 3 Then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.24 cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.34cm 3 / Ah·L, if the capacity of lithium-ion battery L is 200Ah, then the theoretical maximum gas storage space is 68cm 3 .

[0292] 2) When the capacity L of the lithium-ion battery satisfies 300Ah<L≤400Ah, the corresponding theoretical gas storage space V0=0.29cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.29cm3 / Ah·L. Considering L>300Ah, the theoretical gas storage space V0>0.29cm 3 / Ah·300Ah=87cm 3 That is, when the capacity L of the lithium-ion battery satisfies 300Ah<L≤400Ah, the actual gas storage space v>87cm 3 .

[0293] In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0 = 0.4 cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.4cm 3 / Ah·L.

[0294] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.4cm 3 / Ah·L, unit is cm 3 Then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.29 cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.4cm 3 / Ah·L.

[0295] 3) When the capacity L of the lithium-ion battery satisfies 400Ah<L≤500Ah, the corresponding theoretical gas storage space V0=0.33cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.33cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.47cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.47cm 3 / Ah·L.

[0296] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.47cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.33cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.47cm 3 / Ah·L.

[0297] It can be understood that, in combination with the above 2) and 3), when the capacity L of the lithium-ion battery satisfies 300Ah<L≤500Ah, the actual gas storage space v>87cm 3 .

[0298] 4) When the capacity L of the lithium-ion battery satisfies 500Ah<L≤600Ah, the corresponding theoretical gas storage space V0=0.38cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.38cm 3 / Ah·L. Considering L>500Ah, the theoretical gas storage space V0>0.38cm 3 / Ah 500Ah = 190cm 3 That is, when the capacity L of the lithium-ion battery satisfies 500Ah<L≤600Ah, the actual gas storage space v>190cm 3 .

[0299] In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0 = 0.54 cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.54cm 3 / Ah·L.

[0300] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.54cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.38cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.54cm 3 / Ah·L.

[0301] 5) When the capacity L of the lithium-ion battery satisfies 600Ah<L≤700Ah, the corresponding theoretical gas storage space V0=0.44cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.44cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.65cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.65cm 3 / Ah·L.

[0302] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.65cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.44cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.65cm 3 / Ah·L.

[0303] It can be understood that, in combination with the above 4) and 5), when the capacity L of the lithium-ion battery satisfies 500Ah<L≤700Ah, the actual gas storage space v>190cm 3 .

[0304] 6) When the capacity L of the lithium-ion battery satisfies 700Ah<L≤800Ah, the corresponding theoretical gas storage space V0=0.51cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.51cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.71cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.71cm 3 / Ah·L.

[0305] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.71cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.51cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.71cm 3 / Ah·L.

[0306] 7) When the capacity L of the lithium-ion battery satisfies 800Ah<L≤900Ah, the corresponding theoretical gas storage space V0=0.59cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.59 cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.78cm 3 / Ah·L, unit is cm 3, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.78cm 3 / Ah·L.

[0307] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.78cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.59 cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.78cm 3 / Ah·L.

[0308] 8) When the capacity L of the lithium-ion battery satisfies 900Ah<L≤1000Ah, the corresponding theoretical gas storage space V0=0.68cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.68cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.87cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.87cm 3 / Ah·L.

[0309] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.87cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.68cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.87cm 3 / Ah·L.

[0310] 9) When the capacity L of the lithium-ion battery satisfies 1000Ah<L≤1100Ah, the corresponding theoretical gas storage space V0=0.79cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.79cm 3 / Ah·L; In order to further reduce the problems caused by gas production, the corresponding theoretical gas storage space V0=0.98cm 3 / Ah·L, unit is cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.98cm 3 / Ah·L.

[0311] In order to take into account the energy density of lithium-ion batteries, the theoretical maximum gas storage space V0max = 0.98cm 3 / Ah·L, unit is cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.79 cm 3 / Ah·L, at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.98cm 3 / Ah·L.

[0312] When actually designing a lithium-ion battery, the theoretical gas storage space V0 and the theoretical maximum gas storage space V0max can be calculated according to the preset capacity L of the lithium-ion battery. Then, the actual gas storage space v actually reserved in the battery shell should be greater than or equal to the theoretical gas storage space V0. In order to take into account the energy density, it is preferred that the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max.

[0313] The actual gas storage space does not include other components between the shell and the battery cell, such as supporting structures, which also occupy volume.

[0314] The above basic groups and adjustment groups are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application.

[0315] Example 1, the difference from the first basic group is that the gas storage space of the lithium-ion battery is equal to the theoretical gas storage space of 72cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0316] Example 2, the difference from the third basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 48cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0317] Example 3, the difference from the eleventh basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 869cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0318] Example 4, the difference from the fourth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 116cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0319] Example 5, the difference from the fifth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 165cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0320] Example 6, the difference from the sixth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 228cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0321] Example 7, the difference from the seventh basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 308cm 3, and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0322] Example 8, the difference from the eighth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 408cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0323] Example 9, the difference from the ninth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 531cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0324] Example 10, the difference from the tenth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 680cm 3 , and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is up to 3000 times.

[0325] Comparative Example 1, the difference from the first basic group is that the lithium ion battery gas storage space is equal to 54cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.18cm 3 / Ah, less than the lower limit of the first basic group 0.19cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0326] Comparative Example 2, the difference from the third basic group is that the lithium ion battery gas storage space is equal to 26cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.13cm 3 / Ah, less than the lower limit of the third basic group 0.14cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0327] Comparative Example 3, the difference from the eleventh basic group is that the lithium ion battery gas storage space is equal to 737cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.67cm 3 / Ah, less than the lower limit of 0.68cm of the eleventh basic group 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0328] Comparative Example 4, the difference from the fourth basic group is that the lithium ion battery gas storage space is equal to 92cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.23cm 3 / Ah, less than the lower limit of the fourth basic group 0.24cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0329] Comparative Example 5, the difference from the fifth basic group is that the lithium ion battery gas storage space is equal to 140cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.28cm 3 / Ah, less than the lower limit of the fifth basic group 0.29cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0330] Comparative Example 6, the difference from the sixth basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 192cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.32cm 3 / Ah, less than the lower limit of the sixth basic group 0.33cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0331] Comparative Example 7, the difference from the seventh basic group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 259cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.37cm3 / Ah, less than the lower limit of the seventh basic group 0.38cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is cycled for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped); In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, a 3-minute 90°C cycle is added during the charging process at 40 degrees Celsius. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued to 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, charging and discharging are stopped).

[0332] Comparative Example 8, the difference from the eighth basic group is that the lithium ion battery gas storage space is equal to 344cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.43cm 3 / Ah, less than the lower limit of the eighth basic group 0.44cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0333] Comparative Example 9, the difference from the ninth basic group is that the lithium ion battery gas storage space is equal to 450cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.50cm 3 / Ah, less than the lower limit of the ninth basic group 0.51cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0334] Comparative Example 10, the difference from the tenth basic group is that the lithium ion battery gas storage space is equal to 580cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.58cm 3 / Ah, less than the lower limit of the tenth basic group 0.59cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0335] Comparative Example 11, the difference from the first basic group is that the lithium ion battery gas storage space is equal to 66cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.22cm 3 / Ah, less than the upper limit of the first basic group 0.26cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0336] Comparative Example 12, the difference from the third basic group is that the lithium ion battery gas storage space is equal to 36cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.18cm 3 / Ah, less than the upper limit of the third basic group 0.2cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0337] Comparative Example 13, the difference from the eleventh basic group is that the lithium ion battery gas storage space is equal to 836cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.76cm 3 / Ah, less than the upper limit of 0.87cm of the eleventh basic group 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0338] Comparative Example 14, the difference from the fourth basic group is that the lithium ion battery gas storage space is equal to 114cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.28cm 3 / Ah, less than the upper limit of the fourth basic group 0.34cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0339] Comparative Example 15, the difference from the fifth basic group is that the lithium ion battery gas storage space is equal to 155cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.31cm 3 / Ah, less than the upper limit of the fifth basic group 0.4cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0340] Comparative Example 16, the difference from the sixth basic group is that the lithium ion battery gas storage space is equal to 216cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.36cm 3 / Ah, less than the upper limit of the sixth basic group 0.47cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0341] Comparative Example 17, the difference from the seventh basic group is that the lithium ion battery gas storage space is equal to 294cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.42cm 3 / Ah, less than the upper limit of the seventh basic group 0.54cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0342] Comparative Example 18, the difference from the eighth basic group is that the lithium ion battery gas storage space is equal to 392cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.49 cm 3 / Ah, less than the upper limit of the eighth basic group 0.65cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0343] Comparative Example 19, the difference from the ninth basic group is that the lithium ion battery gas storage space is equal to 513cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.57cm 3 / Ah, less than the upper limit of 0.71cm of the ninth basic group 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0344] Comparative Example 20, the difference from the tenth basic group is that the lithium ion battery gas storage space is equal to 660cm 3 (The corresponding relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.66cm 3 / Ah, less than the upper limit of the tenth basic group 0.78cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the 50 lithium-ion batteries in the first part of this embodiment are cycled for 3000 times at 40 degrees Celsius, and the 50 lithium-ion batteries in the second part of this embodiment are cycled for 1500 times at 40 degrees Celsius. Each subsequent charging process is as follows: before charging to the cut-off voltage, during the charging process at 40 degrees Celsius, a 3-minute 90°C cycle is added. The other conditions are the same as the 50 lithium-ion batteries in the first part, and the cycle is continued for 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, the charging and discharging is stopped).

[0345] The difference between Comparative Example 21 and the first basic group is that the positive electrode active material adopts lithium nickel cobalt manganese oxide in which the atomic ratio of nickel content to the three metal contents of nickel, cobalt and manganese is 0.8, and the charge and discharge cut-off voltage, as well as the positive electrode film thickness and compaction density are adjusted accordingly. Other conditions are similar to those of the first basic group.

[0346] In Examples 1-10, the explosion-proof valves of the lithium-ion batteries were not opened after 3000 cycles;

[0347] In Comparative Examples 1-10, none of the first part of lithium-ion batteries in each comparative example was opened, and 15-25 lithium-ion batteries in the second part of lithium-ion batteries in each comparative example were opened;

[0348] In Comparative Examples 11-20, none of the first part of lithium-ion batteries in each comparative example was opened, while 1-10 lithium-ion batteries in the second part of lithium-ion batteries in each comparative example were opened;

[0349] In Comparative Example 21, 70 lithium-ion batteries were opened;

[0350] Comparison between Comparative Example 21 and Example 1 shows that the selection of the material system, especially the selection of the positive electrode material, has a great influence on whether the explosion-proof valve is opened. From the perspective of gas production, lithium phosphate materials are preferred;

[0351] Comparison between Examples 1-10 and Comparative Examples 1-10 and Comparative Examples 11-20 shows that when the actual gas storage space is not less than the theoretical gas storage space, not only will the normally circulated lithium-ion battery not be opened, but it will also have the ability to resist high temperature anomalies, thereby making the lithium-ion battery safer; Comparative Examples 1-10 and Comparative Examples 11-20 show that although the actual gas storage space is smaller than the theoretical gas storage space, the closer it is to the theoretical gas storage space, the higher the ability to resist high temperature anomalies.

[0352] This application considers multiple factors, from positive electrode active materials and negative electrode active materials, to positive electrode sheets and negative electrode sheets, to diaphragms and electrolytes, to minimize gas production, thereby reducing unnecessary internal space, so that more active materials can be installed and the capacity of lithium-ion batteries can be increased. At the same time, on the basis of the aforementioned measures to reduce gas production, the gas storage space is also optimized, so that the explosion-proof valve of the lithium-ion battery of this application will not be opened under normal use conditions, and it has the ability to resist high temperature abnormalities, thereby reducing the risk of lithium-ion batteries being scrapped due to the explosion-proof valve being opened.

[0353] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A charging method, characterized in that: The device comprises a first charging section and a second charging section, wherein the voltage of the first charging section is less than the voltage of the second charging section, the voltage of the first charging section increases as the charging time increases, and the voltage of the second charging section remains unchanged, and the first charging section comprises the following charging process: charging the lithium-ion battery with a first current within a first time; charging the lithium-ion battery with a second current within a second time; charging the lithium-ion battery with a third current within a third time; charging the lithium-ion battery with a fourth current within a fourth time; The first current is greater than the second current, the first time is greater than the second time, the third current is not greater than the first current, the third time is greater than the second time, the fourth current is less than the third current, and the fourth time is less than the third time.

2. The charging method according to claim 1, characterized in that: The second current is equal to the fourth current.

3. The charging method according to claim 2, characterized in that: The lithium-ion battery comprises a shell, a battery cell, and an electrolyte. The battery cell and the electrolyte are arranged inside the shell. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is electrically connected to the positive electrode current collector. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is electrically connected to the negative electrode current collector. The negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the thickness of the single-side active material layer of the negative electrode sheet is between 50 μm and 95 μm; the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite; the Dv50 of the graphite is in the range of 10 μm to 30 μm, and the graphitization degree of the graphite is greater than or equal to 90%; The positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the thickness of the single-side active material layer of the positive electrode sheet is between 60 μm and 105 μm; the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium-containing phosphate and a carbon layer located on the surface of the lithium-containing phosphate; The capacity of the lithium-ion battery L≥200Ah, and the actual gas storage space v of the lithium-ion battery ≥48cm 3 .

4. The charging method according to claim 3, characterized in that: The capacity L of the lithium-ion battery is 200Ah≤L≤300Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.24cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.29cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.33cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 500Ah<L≤600Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.38cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 600Ah<L≤700Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.44cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 700Ah<L≤800Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.51cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 800Ah<L≤900Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.59cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 900Ah<L≤1000Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.68cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 1000Ah<L≤1100Ah, and the theoretical gas storage space of the lithium ion battery is V0, V0=0.79cm 3 / Ah·L; The actual gas storage space v of the lithium-ion battery is greater than or equal to the theoretical gas storage space V0 of the lithium-ion battery.

5. The charging method according to claim 3, characterized in that: The capacity L of the lithium ion battery is 200Ah≤L≤300Ah, and the theoretical gas storage space of the lithium ion battery is V0, V0=0.34cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.4cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.47cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 500Ah<L≤600Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.54cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 600Ah<L≤700Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.65cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 700Ah<L≤800Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.71cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 800Ah<L≤900Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.78cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 900Ah<L≤1000Ah, and the theoretical gas storage space of the lithium-ion battery is V0, V0=0.87cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 1000Ah<L≤1100Ah, and the theoretical gas storage space of the lithium ion battery is V0, V0=0.98cm 3 / Ah·L; The actual gas storage space v of the lithium-ion battery is greater than or equal to the theoretical gas storage space V0 of the lithium-ion battery.

6. The charging method according to claim 4, characterized in that: The capacity L of the lithium-ion battery is 200Ah≤L≤300Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.34cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 300Ah<L≤400Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.4cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 400Ah<L≤500Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.47cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 500Ah<L≤600Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.54cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 600Ah<L≤700Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.65cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 700Ah<L≤800Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.71cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 800Ah<L≤900Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.78cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 900Ah<L≤1000Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.87cm 3 / Ah·L; or, The capacity L of the lithium-ion battery is 1000Ah<L≤1100Ah, and the theoretical maximum gas storage space V0max of the lithium-ion battery is V0max=0.98cm 3 / Ah·L; The actual gas storage space v of the lithium-ion battery is less than or equal to the theoretical maximum gas storage space V0max of the lithium-ion battery.

7. The charging method according to any one of claims 3 to 6, characterized in that: The graphite is at least partially covered with a carbon layer, the graphite has a Dv90 of ≤40 μm, the graphite has a Dv10 of ≥3 μm, and the graphite has a Dv99 of ≤49 μm; and / or, The OI value of the graphite is in the range of 3-30; and / or, The graphitization degree of the graphite is between 90% and 95%.

8. The charging method according to claim 7, characterized in that: The OI value of the graphite is in the range of 10-30; and / or, The OI value of the graphite is in the range of 15-30; and / or, The graphitization degree of the graphite is between 91% and 95%.

9. The charging method according to any one of claims 3 to 6, characterized in that: The surface density of the single-sided active material layer of the negative electrode sheet is 0.07 mg / mm 2 -0.13mg / mm 2 between; and / or, The compaction density of the single-sided active material layer of the negative electrode sheet is between 1.3 g / cc and 1.7 g / cc; and / or, The surface density of the single-sided active material layer of the positive electrode sheet is 0.16 mg / mm 2 -0.26mg / mm 2 between; and / or, The compaction density of the single-sided active material layer of the positive electrode sheet is between 2.3 g / cc and 2.7 g / cc.

10. The charging method according to any one of claims 3 to 6, characterized in that: The diaphragm comprises a base film and a coating, wherein the coating is bonded to the surface of the base film and partially located inside the base film, and the porosity of the diaphragm is between 30% and 50%.

11. The charging method according to claim 7, characterized in that: The thickness of the carbon layer on the graphite surface is between 0.5 μm and 2 μm.

12. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode active material layer further includes carbon tubes, and the carbon tubes include at least one of oligo-walled carbon tubes and single-walled carbon tubes.

13. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode active material layer further includes silicon; The capacity L of the lithium-ion battery is 200Ah≤L≤500Ah, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-10%; or, The capacity L of the lithium-ion battery is 500Ah<L≤700Ah, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-8%; or, The capacity L of the lithium-ion battery is within the range of 700Ah<L≤1100Ah, and the mass content of the silicon in the negative electrode active material layer is within the range of 1%-5%.

14. The charging method according to claim 13, characterized in that: In the thickness direction of the negative electrode active material layer, the silicon is distributed on a side of the negative electrode active material layer close to the negative electrode current collector.

15. The charging method according to any one of claims 3 to 6, characterized in that: The lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate is doped with a metal element, and the metal element is selected from at least one of titanium and vanadium.

16. The charging method according to claim 15, characterized in that: The mass ratio of the doped metal element to the mass ratio of the positive electrode active material does not exceed 0.4%.

17. The charging method according to claim 16, characterized in that: The doped metal element includes titanium, and the mass ratio of the titanium to the mass ratio of the positive electrode active material is 0.2%-0.4%.

18. The charging method according to claim 16, characterized in that: The doped metal elements include titanium and vanadium, the mass ratio of the titanium to the mass ratio of the positive electrode active material is 0.1%-0.2%, and the mass ratio of the vanadium to the mass ratio of the positive electrode active material is 0.01%-0.05%.

19. The charging method according to any one of claims 3 to 6, characterized in that: The positive electrode active material layer includes carbon tubes, and the carbon tubes include at least one of oligo-walled carbon tubes and single-walled carbon tubes.

20. The charging method according to any one of claims 3 to 6, characterized in that: The electrolyte includes a lithium salt and a solvent, the volume molar content of the lithium salt is 0.8 mol / L-1.5 mol / L, and the lithium salt includes lithium hexafluorophosphate.

21. The charging method according to claim 20, characterized in that: The lithium salt also includes lithium bis(fluorosulfonyl)imide.

22. The charging method according to claim 21, characterized in that: The volume molar content of the lithium hexafluorophosphate is higher than the volume molar content of the lithium bis(fluorosulfonyl)imide.

23. The charging method according to claim 22, characterized in that: The capacity L of the lithium-ion battery is 200Ah≤L≤300Ah, and the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 0.1% and 9%; or, The capacity L of the lithium-ion battery is 300Ah<L≤500Ah, and the mass percentage of the bis(fluorosulfonyl)imide lithium to the mass percentage of the electrolyte is between 1% and 9%; or, The capacity L of the lithium-ion battery is 500Ah<L≤700Ah, and the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 3% and 9%; or, The capacity L of the lithium ion battery is 700Ah<L≤1100Ah, and the mass percentage of the bis(fluorosulfonyl)imide lithium to the mass percentage of the electrolyte is between 5% and 9%.

24. The charging method according to claim 23, characterized in that: The mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 0.1% and 5%; or, The capacity L of the lithium ion battery is 300Ah<L≤500Ah, and the mass percentage of the bis(fluorosulfonyl)imide lithium to the mass percentage of the electrolyte is between 1% and 5%.

25. The charging method according to claim 21, characterized in that: The solvent includes EC, DMC, EMC, and DEC; the content of the EC is between 30% and 40%, the sum of the masses of the DMC and the EMC is greater than the mass of the EC; the content of the EC is the mass of the EC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

26. The charging method according to claim 25, characterized in that: The total content of the EMC and the DMC is 50%-60%; the total content of the EMC and the DMC is the total mass of the EMC and the DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

27. The charging method according to claim 26, characterized in that: The content of the DMC is between 10% and 15%; the content of the DMC is the mass of the DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

28. The charging method according to claim 21, characterized in that: The electrolyte also includes carboxylate, and the content of the carboxylate does not exceed 10%; the content of the carboxylate is the mass of the carboxylate / (the difference between the mass of the electrolyte and the mass of the lithium salt).

29. The charging method according to claim 28, characterized in that: The content of the carboxylic acid ester is 5%-10%; The capacity L of the lithium-ion battery is 200Ah≤L≤300Ah, and the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 0.1% and 5%; or, The capacity L of the lithium-ion battery is 300Ah<L≤500Ah, and the mass percentage of the bis(fluorosulfonyl)imide lithium to the mass percentage of the electrolyte is between 1% and 5%; or, The capacity L of the lithium-ion battery is 500Ah<L≤700Ah, and the mass percentage of the lithium bis(fluorosulfonyl)imide to the mass percentage of the electrolyte is between 2% and 7%; or, The capacity L of the lithium ion battery is 700Ah<L≤1100Ah, and the mass percentage of the bis(fluorosulfonyl)imide lithium to the mass percentage of the electrolyte is between 3% and 8%.

30. The charging method according to any one of claims 21 to 29, characterized in that: The negative electrode sheet is a square structure, the width of the negative electrode sheet is between 100 mm and 150 mm, and the porosity of the diaphragm is between 30% and 50%.

31. The charging method according to any one of claims 21 to 29, characterized in that: The negative electrode sheet is a square structure, the width of the negative electrode sheet is between 200 mm and 250 mm, and the porosity of the diaphragm is between 35% and 50%.

32. The charging method according to claim 30, characterized in that: The aspect ratio of the battery cell is between 6 and 8.

33. The charging method according to claim 31, characterized in that The aspect ratio of the battery cell is between 2.8 and 4.

34. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode sheet further includes a negative electrode tab, which is electrically connected to the negative electrode current collector, and the positive electrode sheet further includes a positive electrode tab, which is electrically connected to the positive electrode current collector; The shell includes a positive pole, a negative pole, and an explosion-proof valve. The positive pole is electrically connected to the positive pole tab, and the negative pole is electrically connected to the negative pole tab. The explosion-proof valve is arranged at the first end of the shell. At least one of the positive pole and the negative pole is also arranged at the first end of the shell. The opening pressure of the explosion-proof valve is 0.55Mpa-0.65Mpa. The ratio of the area of ​​the explosion-proof valve to the capacity of the lithium-ion battery is in the range of 0.5mm 2 / Ah-1.5mm 2 / Ah.

35. The charging method according to claim 34, characterized in that: The positive electrode column is arranged at the first end of the shell, the positive electrode tab is arranged on the short side of the positive electrode collector, and a first upper exhaust channel is formed between the upper end of the positive electrode tab and the shell, and along the airflow direction of the first upper exhaust channel, the projection area of ​​the explosion-proof valve at least partially overlaps with the projection area of ​​the first upper exhaust channel.

36. The charging method according to claim 35, characterized in that: Along the airflow direction of the first upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel exceeds 80%; the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel is: the ratio of the area of ​​the overlap area between the projection area of ​​the explosion-proof valve and the projection area of ​​the first upper exhaust channel to the area of ​​the projection area of ​​the first upper exhaust channel.

37. The charging method according to claim 35 or 36, characterized in that: The positive electrode tabs are asymmetrically distributed on the short sides of the positive electrode current collector.

38. The charging method according to claim 37, characterized in that: Along the width direction of the battery cell, the vertical distance from the upper end of the positive electrode tab to the upper end of the positive electrode sheet is a first distance, and the vertical distance from the lower end of the positive electrode tab to the lower end of the positive electrode sheet is a second distance, and the first distance is greater than the second distance.

39. The charging method according to claim 34, characterized in that: The negative electrode column is arranged at the first end of the shell, the negative electrode tab is arranged on the short side of the negative electrode collector, and a second upper exhaust channel is formed between the upper end of the negative electrode tab and the shell, and along the airflow direction of the second upper exhaust channel, the projection area of ​​the explosion-proof valve at least partially overlaps with the projection area of ​​the second upper exhaust channel.

40. The charging method according to claim 39, characterized in that: Along the airflow direction of the second upper exhaust channel, the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel exceeds 80%; the overlap degree of the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel is: the ratio of the area of ​​the overlap area between the projection area of ​​the explosion-proof valve and the projection area of ​​the second upper exhaust channel to the area of ​​the projection area of ​​the second upper exhaust channel.

41. The charging method according to claim 39 or 40, characterized in that: The ratio of the width of the negative electrode tab to the width of the short side of the negative electrode collector is in the range of 0.5-0.

8.

42. The charging method according to claim 41, characterized in that: The ratio of the width of the negative electrode tab to the width of the short side of the negative electrode collector is in the range of 0.6-0.

8.

43. The charging method according to claim 39 or 40, characterized in that: The negative electrode tabs are asymmetrically distributed on the short sides of the negative electrode current collector.

44. The charging method according to claim 43, characterized in that: Along the width direction of the battery cell, the vertical distance from the upper end of the negative electrode tab to the upper end of the negative electrode sheet is a third distance, and the vertical distance from the lower end of the negative electrode tab to the lower end of the negative electrode sheet is a fourth distance, and the third distance is greater than the fourth distance.

45. The charging method according to any one of claims 3 to 6, characterized in that: The difference between Dv50 and Dv10 of the graphite is ≤10 μm, and the difference between Dv90 and Dv50 of the graphite is ≤15 μm.

46. ​​The charging method according to any one of claims 3 to 6, characterized in that: The positive electrode current collector is aluminum foil, the thickness of the single-sided active material layer of the positive electrode sheet is ≤95 μm, the thickness of the positive electrode current collector is D1, and the value range of D1 is 11 μm-13.5 μm.

47. The charging method according to any one of claims 3 to 6, characterized in that: The thickness of the single-sided active material layer of the positive electrode sheet is greater than 95 μm, and the thickness of the positive electrode current collector is D2, and the value range of D2 is 13.5 μm-16 μm.

48. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode active material layer also includes silicon; the thickness of the single-sided active material layer of the negative electrode sheet is 50 μm-70 μm, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-10%.

49. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode active material layer also includes silicon; the thickness of the single-sided active material layer of the negative electrode sheet is 70 μm-80 μm, and the mass content of silicon in the negative electrode active material layer is in the range of 1%-8%.

50. The charging method according to any one of claims 3 to 6, characterized in that: The negative electrode active material layer also includes silicon; the thickness of the single-sided active material layer of the negative electrode sheet is 80 μm-95 μm, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-5%.

51. The charging method according to claim 7, characterized in that: The negative electrode active material includes primary particles composed of the graphite and the carbon layer on the surface of the graphite, and the Dv50 of the primary particles is between 10 μm and 20 μm.

52. The charging method according to claim 51, characterized in that: The negative electrode active material includes secondary particles, the secondary particles include agglomerates of the primary particles, and the Dv50 of the secondary particles is between 10 μm and 30 μm.

53. The charging method according to claim 52, characterized in that: The surface of the agglomerates includes a carbon layer.

Images