Lithium-ion battery, charging method, and lithium-ion battery system

Abstract

A lithium-ion battery, a charging method, and a lithium-ion battery system. The lithium-ion battery comprises a housing (40), a battery cell (30), and an electrolyte. The battery cell (30) comprises a positive electrode sheet (10), a negative electrode sheet (20), and a separator; a negative electrode active material comprises graphite; a positive electrode active material comprises a lithium-containing phosphate and a carbon layer located on the surface of the lithium-containing phosphate; the thickness of a single-sided active material layer of the negative electrode sheet is 50-95 μm, the thickness of a single-sided active material layer of the positive electrode sheet is 60-105 μm, the Dv50 of the negative electrode active material is 10-30 μm, and the graphitization degree of the negative electrode active material is greater than or equal to 90%; and the capacity L of the lithium-ion battery is greater than or equal to 200 Ah, and the actual gas storage space of the lithium-ion battery is greater than or equal to 48 cm3. Under normal use conditions, an explosion-proof valve (43) of the lithium-ion battery will not be forced open, and the lithium-ion battery has the ability to withstand abnormal high temperatures, thereby reducing the risk of battery scrap caused by the forced opening of the explosion-proof valve (43).

Description

Lithium ion battery, charging method, lithium ion battery system

[0001] The present application claims priority to the Chinese patent application No. 202411346279.9, filed on September 26, 2024 in the China Patent Office, and entitled "Lithium ion battery, charging method, lithium ion battery system", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a lithium ion battery, a charging method and a lithium ion battery system. BACKGROUND

[0003] In recent years, with the application range of batteries becoming more and more extensive, batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. In the application process of lithium batteries, the battery capacity is getting larger and larger, and the electrode sheet in the battery is getting thicker and thicker; a battery with larger capacity and thicker electrode sheet is needed. However, as the battery capacity becomes larger, especially the thick electrode sheet, the gas production problem in the battery is more and more serious than before, and the phenomenon of the explosion-proof valve being blown off is more and more common. After the explosion-proof valve is blown off, the battery cannot be used any more. We expect the explosion-proof valve of the battery to be blown off in abnormal use or extreme environment, rather than in normal use.

[0004] How to further improve the battery capacity and rate performance, while reducing the risk of the explosion-proof valve being blown off unreasonably and causing the battery to be scrapped, has become a problem to be solved at present. TECHNICAL PROBLEM

[0005] One of the purposes of the embodiments of the present application is to provide a lithium ion battery, a charging method and a lithium ion battery system. TECHNICAL SOLUTION

[0006] In order to achieve the above-mentioned purpose, the present application provides a lithium ion battery, which comprises a shell, an electric core and an electrolyte, the electric core and the electrolyte are arranged in the interior of the shell, the electric core 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 with 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 with the negative electrode current collector;

[0007] The negative electrode current collector is provided with the negative electrode active material layer on at least one side, the thickness of the single-sided active material layer of the negative electrode sheet is between 50 μm and 95 μm; the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises 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%;

[0008] The positive electrode current collector is provided with the positive electrode active material layer on at least one side, the thickness of the single-sided 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, the positive electrode active material comprises a lithium-containing phosphate and a carbon layer on the surface of the lithium-containing phosphate;

[0009] The capacity L of the lithium ion battery is greater than or equal to 200 Ah, and the actual gas storage space v of the lithium ion battery is greater than or equal to 48 cm 3 .

[0010] The present application further provides batteries with different capacities, in particular:

[0011] The capacity L of the lithium ion battery is greater than or equal to 200 Ah and less than or equal to 300 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.24 cm 3 / Ah·L; or,

[0012] The capacity L of the lithium ion battery is greater than 300 Ah and less than or equal to 400 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.29 cm 3 / Ah·L; or,

[0013] The capacity L of the lithium ion battery is greater than 400 Ah and less than or equal to 500 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.33 cm 3 / Ah·L; or,

[0014] The capacity L of the lithium ion battery is greater than 500 Ah and less than or equal to 600 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.38 cm 3 / Ah·L; or,

[0015] The capacity L of the lithium ion battery is greater than 600 Ah and less than or equal to 700 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.44 cm 3 / Ah·L; or,

[0016] The capacity L of the lithium ion battery is greater than 700 Ah and less than or equal to 800 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0 = 0.51 cm 3 / Ah·L; or,

[0017] The capacity L of the lithium ion battery is 800 Ah < L ≤ 900 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.59 cm 3 / Ah·L; or,

[0018] The capacity L of the lithium ion battery is 900 Ah < L ≤ 1000 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.68 cm 3 / Ah·L; or,

[0019] The capacity L of the lithium ion battery is 1000 Ah < L ≤ 1100 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.79 cm 3 / Ah·L;

[0020] 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.

[0021] Further preferably:

[0022] The capacity L of the lithium ion battery is 200 Ah ≤ L ≤ 300 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.34 cm 3 / Ah·L; or,

[0023] The capacity L of the lithium ion battery is 300 Ah < L ≤ 400 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.4 cm 3 / Ah·L; or,

[0024] The capacity L of the lithium ion battery is 400 Ah < L ≤ 500 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.47 cm 3 / Ah·L; or,

[0025] The capacity L of the lithium ion battery is 500 Ah < L ≤ 600 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.54 cm 3 / Ah·L; or,

[0026] The capacity L of the lithium ion battery is 600 Ah < L ≤ 700 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.65 cm 3 / Ah·L; or,

[0027] The capacity L of the lithium ion battery is 700 Ah < L ≤ 800 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.71 cm 3 / Ah·L; or,

[0028] The capacity L of the lithium ion battery is 800 Ah < L ≤ 900 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.78 cm 3 / Ah·L; or,

[0029] The capacity L of the lithium ion battery is 900 Ah < L ≤ 1000 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.87 cm 3 / Ah·L; or,

[0030] The capacity L of the lithium ion battery is 1000 Ah < L ≤ 1100 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.98 cm 3 / Ah·L;

[0031] 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.

[0032] From the perspective of improving energy density, it is further limited that:

[0033] The capacity L of the lithium ion battery is 200 Ah ≤ L ≤ 300 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.34 cm 3 / Ah·L; or,

[0034] The capacity L of the lithium ion battery is 300 Ah < L ≤ 400 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.4 cm 3 / Ah·L; or,

[0035] The capacity L of the lithium ion battery is 400 Ah < L ≤ 500 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.47 cm 3 / Ah·L; or,

[0036] The capacity L of the lithium ion battery is 500 Ah < L ≤ 600 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.54 cm 3 / Ah·L; or,

[0037] The capacity L of the lithium ion battery is 600 Ah < L ≤ 700 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.65 cm 3 / Ah·L; or,

[0038] The capacity L of the lithium ion battery is in the range of 700 Ah < L < 800 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.71 cm3 / Ah·L; or, 3

[0039] The capacity L of the lithium ion battery is in the range of 800 Ah < L < 900 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.78 cm3 / Ah·L; or, 3

[0040] The capacity L of the lithium ion battery is in the range of 900 Ah < L < 1000 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.87 cm3 / Ah·L; or, 3

[0041] The capacity L of the lithium ion battery is in the range of 1000 Ah < L < 1100 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.98 cm3 / Ah·L; or, 3

[0042] 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.

[0043] In some embodiments, at least part of the surface of the graphite is coated with a carbon layer, the Dv90 of the graphite is < 40 μm, the Dv10 of the graphite is > 3 μm, and the Dv99 of the graphite is < 49 μm.

[0044] 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.

[0045] In some embodiments, the graphitization degree of the graphite is in the range of 90%-95%, and preferably the graphitization degree of the graphite is in the range of 91%-95%.

[0046] In some embodiments, the areal density of the single-sided active material layer of the negative electrode sheet is in the range of 0.07 mg / mm 2 - 0.13 mg / mm 2 .

[0047] In some embodiments, the compaction density of the single-sided active material layer of the negative electrode sheet is in the range of 1.3 g / cc-1.7 g / cc.

[0048] In some embodiments, the areal density of the single-sided active material layer of the positive electrode sheet is in the range of 0.16 mg / mm 2 - 0.26 mg / mm 2 ​​​​between 2.3 g / cc and 2.7 g / cc.

[0049] In some embodiments, the single-sided active material layer of the positive electrode sheet has a compaction density between 2.3 g / cc and 2.7 g / cc.

[0050] In some embodiments, the separator includes a base film and a coating layer, the coating layer is bonded to the surface of the base film and partially inside the base film, and the porosity of the separator is between 30% and 50%.

[0051] In some embodiments, the thickness of the carbon layer on the surface of the graphite is between 0.5 μm and 2 μm.

[0052] In some embodiments, the negative electrode active material layer further includes carbon tubes; the carbon tubes include at least one of oligomeric wall carbon tubes and single wall carbon tubes.

[0053] In some embodiments, the negative electrode active material layer further includes silicon, and when the capacity L of the lithium ion battery is 200 Ah≤L≤500 Ah, the mass content of the silicon in the negative electrode active material layer ranges from 1% to 10%.

[0054] In some embodiments, in the thickness direction of the negative electrode active material layer, the silicon is distributed on the side of the negative electrode active material layer close to the negative current collector.

[0055] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate is doped with a metal element selected from at least one of titanium or vanadium.

[0056] In some embodiments, the mass of the doped metal element accounts for no more than 0.4% of the mass of the positive electrode active material.

[0057] In some embodiments, the doped metal element includes titanium, and the mass of the titanium accounts for 0.2% to 0.4% of the mass of the positive electrode active material.

[0058] In some embodiments, the doped metal element includes titanium and vanadium, and the mass of the titanium accounts for 0.1% to 0.2% of the mass of the positive electrode active material, and the mass of the vanadium accounts for 0.01% to 0.05% of the mass of the positive electrode active material.

[0059] In some embodiments, the positive electrode active material layer includes carbon tubes, and the carbon tubes include at least one of oligomeric wall carbon tubes and single wall carbon tubes.

[0060] 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 to 1.5 mol / L, and the lithium salt includes lithium hexafluorophosphate.

[0061] In some embodiments, the lithium salt further comprises lithium bisfluorosulfonylimide.

[0062] In some embodiments, the volume molar content of the lithium hexafluorophosphate is higher than the volume molar content of the lithium bisfluorosulfonylimide.

[0063] In some embodiments, the capacity L of the lithium ion battery is in the range of 200 Ah≤L≤300 Ah, and the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is in the range of 0.1%-9%.

[0064] In some embodiments, the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is in the range of 0.1%-5%.

[0065] In some embodiments, the capacity L of the lithium ion battery is in the range of 300 Ah

[0066] In some embodiments, the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is in the range of 1%-5%.

[0067] In some embodiments, the solvent comprises EC, DMC, EMC, DEC; the content of the EC is in the range of 30%-40%, the total mass 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 divided by the difference between the mass of the electrolyte and the mass of the lithium salt.

[0068] In some embodiments, the total content of the EMC and the DMC is in the range of 50%-60%; the total content of the EMC and the DMC is the total mass of the EMC and the DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt.

[0069] In some embodiments, the content of the DMC is in the range of 10%-15%; the content of the DMC is the mass of the DMC divided by the difference between the mass of the electrolyte and the mass of the lithium salt.

[0070] In some embodiments, the electrolyte further comprises a carboxylic acid ester, the content of the carboxylic acid ester is not more than 10%; the content of the carboxylic acid ester is the mass of the carboxylic acid ester divided by the difference between the mass of the electrolyte and the mass of the lithium salt.

[0071] In some embodiments, the negative electrode sheet is in a square structure, the width of the negative electrode sheet is in the range of 100mm-150mm, and the porosity of the separator is in the range of 30%-50%; preferably, the aspect ratio of the battery cell is in the range of 6-8.

[0072] In some embodiments, the negative electrode sheet has a square structure, the width of the negative electrode sheet is between 200mm and 250mm, 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.

[0073] In some embodiments, the negative electrode sheet further comprises a negative electrode tab, the negative electrode tab being electrically connected to the negative electrode current collector, and the positive electrode sheet further comprises a positive electrode tab, the positive electrode tab being electrically connected to the positive electrode current collector.

[0074] The shell comprises a positive electrode post, a negative electrode post, and an explosion-proof valve, the positive electrode post being electrically connected to the positive electrode tab, the negative electrode post being electrically connected to the negative electrode tab, the explosion-proof valve being arranged at the first end of the shell, at least one of the positive electrode post and the negative electrode post also being arranged at the first end of the shell, the opening air pressure of the explosion-proof valve being between 0.55Mpa and 0.65Mpa, and the ratio of the area of the explosion-proof valve to the capacity of the lithium ion battery being in the range of 0.5mm 2 / Ah-1.5mm 2 / Ah.

[0075] In some embodiments, the positive electrode post is arranged at the first end of the shell, the positive electrode tab is arranged on the short side of the positive electrode current collector, a first upper exhaust passage is formed between the upper end of the positive electrode tab and the shell, and the projection area of the explosion-proof valve at least partially overlaps the projection area of the first upper exhaust passage in the airflow direction of the first upper exhaust passage.

[0076] In some embodiments, the overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage is more than 80% in the airflow direction of the first upper exhaust passage; and the overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage is the ratio of the area of the overlapping area of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage to the area of the projection area of the first upper exhaust passage.

[0077] In some embodiments, the positive electrode tabs are asymmetrically distributed on the short side of the positive electrode current collector.

[0078] In some embodiments, in 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, the first distance being greater than the second distance.

[0079] In some embodiments, the negative post is disposed at the first end of the shell, the negative tab is disposed on the short side of the negative current collector, a second upper exhaust passage is formed between the upper end of the negative tab and the shell, and the projection area of the explosion-proof valve overlaps at least partially with the projection area of the second upper exhaust passage along the airflow direction of the second upper exhaust passage.

[0080] In some embodiments, the overlap of the projection area of the explosion-proof valve with the projection area of the second upper exhaust passage along the airflow direction of the second upper exhaust passage is more than 80%, and the overlap of the projection area of the explosion-proof valve with the projection area of the second upper exhaust passage is the ratio of the area of the overlapping region of the projection area of the explosion-proof valve with the projection area of the second upper exhaust passage to the area of the projection area of the second upper exhaust passage.

[0081] In some embodiments, the ratio of the width of the negative tab to the width of the short side of the negative current collector is in the range of 0.5-0.8.

[0082] In some embodiments, the ratio of the width of the negative tab to the width of the short side of the negative current collector is in the range of 0.6-0.8.

[0083] In some embodiments, the negative tab is asymmetrically distributed on the short side of the negative current collector.

[0084] In some embodiments, along the width direction of the battery cell, the vertical distance from the upper end of the negative tab to the upper end of the negative tab is a third distance, and the vertical distance from the lower end of the negative tab to the lower end of the negative tab is a fourth distance, and the third distance is greater than the fourth distance.

[0085] In some embodiments, 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.

[0086] In some embodiments, the positive current collector is an aluminum foil, the thickness of the single-sided active material layer of the positive tab is ≤95 μm, and the thickness of the positive current collector is D1, and the numerical range of D1 is 11 μm-13.5 μm.

[0087] In some embodiments, the thickness of the single-sided active material layer of the positive tab is >95 μm, the thickness of the positive current collector is D2, and the numerical range of D2 is 13.5 μm-16 μm.

[0088] In some embodiments, the negative active material layer further comprises silicon, the thickness of the single-sided active material layer of the negative tab is in the range of 50 μm-70 μm, and the mass content of the silicon in the negative active material layer is in the range of 1%-10%.

[0089] In some embodiments, the negative active material layer further comprises silicon; the thickness of the single-sided active material layer of the negative electrode sheet is 70-80 μm, and the mass content of the silicon in the negative active material layer is 1-8%.

[0090] In some embodiments, the negative active material layer further comprises silicon; the thickness of the single-sided active material layer of the negative electrode sheet is 80-95 μm, and the mass content of the silicon in the negative active material layer is 1-5%.

[0091] In some embodiments, the capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, the content of the carboxylic acid ester is 5-10%, and the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is 0.1-5%.

[0092] In some embodiments, the capacity L of the lithium ion battery is 300 Ah

[0093] In some embodiments, the negative active material comprises primary particles composed of the graphite and the carbon layer on the surface of the graphite, and the Dv50 of the primary particles is 10-20 μm.

[0094] In some embodiments, the negative active material comprises secondary particles, and the secondary particles comprise agglomerates of the primary particles, and the Dv50 of the secondary particles is 10-30 μm.

[0095] In some embodiments, the surface of the agglomerates comprises a carbon layer.

[0096] The application also discloses a charging method for charging a lithium ion battery, which comprises a first charging stage and a second charging stage, the voltage of the first charging stage is less than that of the second charging stage, the voltage of the first charging stage increases with the increase of the charging time, the voltage of the second charging stage is constant, and the first charging stage comprises the following charging processes:

[0097] charging the lithium ion battery with a first current for a first time;

[0098] charging the lithium ion battery with a second current for a second time;

[0099] charging the lithium ion battery with a third current for a third time;

[0100] charging the lithium ion battery with a fourth current for a fourth time;

[0101] 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.

[0102] The second current is equal to the fourth current.

[0103] The application further provides a lithium ion battery 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 DRAWINGS

[0104] Fig. 1 is a schematic diagram of a positive electrode sheet structure according to the application.

[0105] Fig. 2 is a schematic diagram of a negative electrode sheet structure according to the application.

[0106] Fig. 3 is a schematic diagram of a lithium ion battery structure according to the application.

[0107] Fig. 4 is a schematic diagram of a lithium ion battery gas production process according to the application.

[0108] Fig. 5 is a schematic diagram of another negative electrode sheet structure according to the application.

[0109] Fig. 6 is a schematic diagram of another positive electrode sheet structure according to the application.

[0110] Fig. 7 is a schematic diagram of another positive electrode sheet structure according to the application.

[0111] Fig. 8 is a schematic diagram of another negative electrode sheet structure according to the application.

[0112] Fig. 9 is a schematic diagram of another lithium ion battery structure according to the application.

[0113] Fig. 10 is a schematic diagram of another lithium ion battery gas production process according to the application.

[0114] BRIEF DESCRIPTION OF DRAWINGS

[0115] 10 positive electrode sheet; 11 positive electrode tab; 20 negative electrode sheet; 21 negative electrode tab; 30 cell; 40 shell; 41 positive electrode column; 42 negative electrode column; 43 explosion-proof valve; 50 gas flow direction schematic arrow; 51 first upper exhaust passage; h1 first distance; h2 second distance; h3 third distance; h4 fourth distance; Ld length direction; Hd height direction. EMBODIMENTS OF THE INVENTION

[0116] The embodiments of the lithium ion battery, the charging method, the lithium ion battery system according to the present application are specifically disclosed in the following with reference to the drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters known to those skilled in the art, repeated explanations of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. Furthermore, the drawings and the following explanations are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0117] The ranges disclosed herein are defined by their lower and upper limits. Ranges that include both the upper and lower limits are inclusive of the endpoints. Ranges that include either the upper or lower limit are not inclusive of the excluded limit. The ranges are also inclusive of any and all sub-ranges subsumed therein. For example, a range of "60% to 85%" is inclusive of "62% to 84%" and "63% to 83%", but excludes 60% and 85%. Other understood ranges are "from 60% to 85%" and "60% to less than 85%". It is specifically intended that the scope of the patent include all such sub-ranges. Furthermore, statements regarding the scope of the application as encompassed by the claims are intended to include any and all structural, functional, and positional equivalents of a claimed element by those skilled in the art, and not merely the recited literal examples. For example, if a claim recites a "first element", it is specifically intended that the scope of the claim include a "second element" or a "third element" or a "first element" (where the name of the element is not to limit the type of element). Likewise, although the term "comprising" is used herein, it is specifically intended that the scope of the claims include the term "consisting of" and the term "consisting essentially of".

[0118] If not specifically explained, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0119] If not specifically explained, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0120] If not specifically explained, the "including" and "comprising" mentioned in the present application represent open-ended and closed-ended. For example, the "including" and "comprising" can represent that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0121] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0122] The lithium ion battery of the present application comprises a shell, an electrode core, an electrolyte, the electrode core and the electrolyte are arranged inside the shell, and the shell is sealingly arranged; wherein the electrode core comprises a positive electrode sheet, a negative electrode sheet, and a separator, which are respectively as follows:

[0123] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, at least one side of the negative electrode current collector is provided with the negative electrode active material layer, and the negative electrode active material layer is electrically connected with the negative electrode current collector.

[0124] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, at least one side of the negative electrode current collector is provided with the negative electrode active material layer, and the negative electrode active material layer is electrically connected with the negative electrode current collector.

[0125] The negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite, which can be natural graphite or artificial graphite, and is preferably artificial graphite.

[0126] The specific surface area of graphite with different particle sizes is different, and the gas production is different. The smaller the particle size of the graphite, the easier it is for lithium ions to be inserted into and extracted from the graphite interlayer. However, the smaller the particle size of the graphite, the larger the specific surface area, thereby causing more SEI to be generated, which will increase the gas production; on the one hand, the low first efficiency of the lithium ion battery is caused, and on the other hand, the SEI is in a process of continuous consumption and regeneration as the lithium ion battery charging and discharging cycle proceeds, so the gas production in the entire life cycle is increased. At the same time, the particle size of the graphite cannot be too large, when the particle size of the graphite is too large, lithium dendrites will be generated on the surface of the large particle graphite due to the fact that lithium ions cannot enter the graphite interlayer in time, and further, the lithium dendrites can react with the electrolyte to produce gas, especially under high rate (when the charging rate is above 1C), the problem of lithium dendrites and gas production will be more serious. For the large-capacity thick electrode sheet electrode core of the present application [in the present application, the large-capacity thick electrode sheet electrode core refers to a lithium ion battery with a capacity of not less than 200 Ah, and a single-sided negative electrode active material layer with a compactness density of between 1.3 g / cc and 1.7 g / cc (this compactness density is measured in a lithium ion battery with a charging and discharging number of less than or equal to 100. During the preparation process of the lithium ion battery, the electrode sheet is generally subjected to a rolling operation to increase the compactness density of the electrode sheet, but the compactness density of the electrode sheet often rebounds and becomes smaller in the early stage of the cycle of the finished lithium ion battery, so in order to more effectively reflect the compactness density of the finished lithium ion battery, the applicant selects the compactness density of the single-sided active material layer of the negative electrode sheet in a lithium ion battery with a small number of charging and discharging times), and a single-sided negative electrode active material layer with an area density of 0.07 mg / mm 2 to 0.13 mg / mm 2between 10 μm and 30 μm (the particle size of the graphite is calculated by Dv50, and the surface density is measured when the number of charge-discharge cycles of the lithium ion battery is less than or equal to 100).

[0127] Meanwhile, the applicant further designs that too much graphite with large particle size cannot be formed in the negative electrode sheet, because when the particle size of the graphite is greater than 50 μm, the lithium ions gathered at the position corresponding to the large particle size graphite cannot enter the interlayer of the graphite in time, and part of the lithium ions are deposited on the surface of the graphite to form lithium dendrites, which may even pierce the SEI film, causing further consumption of the electrolyte to form SEI and produce gas. As the lithium dendrites continue to grow, in addition to causing local temperature rise at the position, the lithium dendrites may even pierce the separator, causing internal short circuit of the lithium ion battery, resulting in severe gas production and even explosion. Furthermore, the problem of lithium dendrites caused by such large particle size graphite is more serious at the position where the negative electrode sheet contacts the edge of the positive electrode sheet. The more concentrated the large particle size graphite is, the more likely it is to form lithium dendrites at the concentrated position. Therefore, during the preparation of the negative electrode sheet, large particle size graphite should be removed as much as possible, and the number of large particle size graphite should be controlled within a controllable range. Specifically, the value of Dv90 of the graphite can be controlled to be not greater than 40 μm, and the value of Dv99 of the graphite can be further controlled to be not greater than 49 μm.

[0128] On the other hand, in the large-capacity thick electrode sheet battery of the present application, in addition to controlling the range of the particle size of the graphite within the range of Dv50, too much small particle size graphite should also be controlled in the electrode sheet to reduce the problem of continuous gas production caused by the specific surface area of small particle size graphite. Specifically, the value of Dv10 can be controlled to be not less than 3 μm.

[0129] In addition, the inventor has creatively designed 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. The setting of these two differences makes the particle size distribution of the graphite more concentrated, so that the current density in the negative electrode sheet is more uniform, and the more uniform the current density distribution in the negative electrode sheet is, the less likely it is to produce lithium dendrites, and the damage to the SEI on the surface of the graphite is reduced, further reducing the amount of gas production. On the other hand, in order to improve the compaction density of the electrode sheet, the compaction density is often intentionally improved by mixing large and small particles during the preparation process, thereby further improving the volume capacity of the battery. In the battery with high demand for volume capacity, the design of the difference between Dv50 and Dv10 being ≤10 μm and the difference between Dv90 and Dv50 being ≤15 μm can not be used.

[0130] Since graphite is a layered structure, during the lithium ion battery cycle process, lithium ions in the electrolyte are more likely to insert into graphite from between the graphite layers to complete lithium intercalation, and cannot intercalate lithium in the direction perpendicular to the graphite layer. The OI value (orientation, C004 / C110) of graphite is greater, the easier it is to intercalate lithium. When graphite is used as a negative active material, the inventors design the OI value of graphite (which can also be graphite after carbon coating) to be in the range of 3-30; when the OI is less than 3, it is difficult for graphite to intercalate lithium, and then a large number of lithium dendrites appear, and in large-capacity cells above 200 Ah, the gas production will be very large; in addition, for lithium ion batteries above 200 Ah, generally used for energy storage lithium ion batteries, do not need large rate charging and discharging (but in some embodiments or use scenarios, large rate charging and discharging requirements will also be put forward for large-capacity energy storage lithium ion batteries), so from the cost consideration, it is also not necessary for the OI value to exceed 30, otherwise the cost performance will not be high.

[0131] The graphitization degree of graphite produced by different processes is different, and the inventors expect to use graphite with higher graphitization degree, the higher the graphitization degree, the less likely the graphite interlayer is to peel off during the cycle process, the more stable the SEI, and the less gas is produced during long cycle, but limited by the preparation process of existing artificial graphite and the cost performance, the graphitization degree cannot be too high; according to the design of the inventors, in the large-capacity thick electrode sheet lithium ion battery of the present application, the graphitization degree (also including the graphite after carbon coating in the present application) is greater than or equal to 90%; further, in order to meet the large-capacity lithium ion battery above 400 Ah, the inventors prefer the graphitization degree of graphite to be between 91% and 95%. When the graphitization degree is less than 91%, the gas production of the large-capacity lithium ion battery above 400 Ah will be larger during the long cycle process, but when the graphitization degree exceeds 95%, the inventors believe that according to the current price of graphite, the cost performance of graphite with a graphitization degree exceeding 95% is no longer advantageous.

[0132] In order to further reduce gas production, the present inventors coated the surface of graphite with carbon. After graphite is coated with amorphous carbon, the multiple lithium insertion sites of amorphous carbon can alleviate the impact of lithium ions on the interlayer of graphite during fast charging, reducing the problem of interlayer peeling of graphite, thereby better reducing 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 small, too small is not conducive to the formation of a uniform carbon coating layer. The present inventors control the carbon coating thickness of graphite to be between 0.5 μm and 2 μm. In order to verify the carbon coating thickness and the uniformity of carbon coating, the present inventors discharged the lithium ion battery after cycling and disassembled it, scraped the powder of the disassembled negative electrode sheet, and then sampled and measured TEM. In the TEM field of view, 5 graphite particles were randomly selected, and 5 points were uniformly selected on the outer surface of each graphite particle to measure the carbon coating thickness. The average of the 25 measurement results obtained is the carbon coating thickness. Since the carbon coating thickness is very small, it has little effect on the particle size of the aforementioned graphite. The present application ignores the effect of carbon coating on the particle size (such as Dv50) of graphite, and also ignores the effect of carbon coating on the graphitization degree and OI value. In addition, in order to facilitate the analysis of the above-mentioned graphite particle size from the end of the finished lithium ion battery, when testing and analyzing the finished lithium ion battery, although there are conductive agents and other factors in the negative active material layer that will affect the particle size range of graphite, due to the small content and other factors, the present application also ignores it. After ignoring such secondary factors, the present application considers that the graphite particle size range obtained by testing the finished lithium ion battery is the same as the original graphite particle size range, and the graphitization degree and OI value of the graphite obtained by testing the finished lithium ion battery are considered to be the same as the original graphite graphitization degree and OI value range.

[0133] The graphite can be primary particles or primary particles after carbon coating. In this case, the negative active material includes primary particles composed of graphite and a carbon layer on the surface of the graphite, and the Dv50 of the primary particles is 10-20 μm. The graphite can also be secondary particles formed by agglomeration of primary particles, i.e., secondary particles. The Dv50 of the secondary particles is 10-30 μm. However, the specific surface area of the agglomerates increases due to the presence of primary particles. In order to reduce gas production, the secondary particles preferably have the following structure: the surface of the primary particles is coated with a carbon layer, the carbon-coated primary particles are agglomerated to form secondary particles, and the surface of the agglomerated secondary particles is further coated with a carbon layer. The carbon layer on the surface of the primary particles and the carbon layer on the surface of the secondary particles can be different or the same. The application further discloses a preparation process for such carbon-coated secondary particles: dispersing primary particles in a solution containing organic carbon source monomers and performing a hydrothermal polymerization reaction, forming a coating layer containing organic carbon source polymers on the surface of the primary particles after the polymerization reaction, and then carbonizing to obtain carbon-coated primary particles; and then dispersing the carbon-coated primary particles in a liquid containing an organic carbon source precursor, and performing spray drying and carbonization. Such carbon-coated secondary particles can better meet the gas production requirements of the large-capacity thick electrode sheets of the application, especially for large-capacity electrode sheets of more than 400 Ah.

[0134] The negative electrode sheet includes a negative active material (the negative active material of the application includes graphite, and the surface of the graphite can be coated with carbon) and a binder and a conductive agent. The technical solution of the application is used for a single-sided negative active material layer with a compaction density of 1.3-1.7 g / cc (this compaction density is measured within 100 times of charging and discharging of the lithium ion battery. During the preparation of the lithium ion battery, the electrode sheet is generally subjected to a rolling operation to increase the compaction density of the electrode sheet, but the compaction density of the electrode sheet often rebounds and becomes smaller in the early stage of the cycle of the finished lithium ion battery. Therefore, in order to more effectively determine the compaction density of the finished lithium ion battery, the applicant selects a battery with a small number of charging and discharging times to determine the compaction density of the single-sided negative active material layer of the negative electrode sheet), and the area density of the single-sided negative active material layer is 0.07-0.13 mg / mm 2 -0.13mg / mm 2between 50 μm and 95 μm, the thickness of the negative electrode current collector is 5 μm, and when the negative electrode current collector is coated with the negative electrode active material layer on both sides, the thickness of the negative electrode sheet is 105 μm-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 cycles 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 each position in the negative electrode active material layer, the conductive agent in the negative electrode active material layer of the present application preferably includes carbon tubes, and preferably single-walled carbon tubes and / or few-walled carbon tubes; the single-walled carbon tubes used in the present application have a length of 1 μm-50 μm, a cross-section of one graphene sheet, a diameter of 0.75 nm-10 nm, and further preferably 1 nm-3 nm; the few-walled carbon tubes used in the present application have a cross-section of 2-5 graphene sheets, 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 few-walled carbon tubes have better electrical conductivity; on the other hand, in a thick electrode sheet, due to the large coating area of the electrode sheet, and due to the expansion and contraction of graphite during the cycle process, especially after doping silicon in the graphite, the thickness difference of expansion and contraction is further enlarged, so that the upper active material of the thick electrode sheet may become difficult to obtain electrons during the cycle process, and even cause the thick electrode sheet to delaminate, and the problem of the upper active material being difficult to obtain electrons is more serious; while single-walled carbon tubes or few-walled carbon tubes have a large aspect ratio compared with carbon black, thereby being able to fix the thick electrode sheet, improve the ability of the upper active material to obtain electrons, and prevent delamination from occurring.

[0135] The negative electrode active material of the negative electrode sheet of the present application can also contain silicon in addition to graphite. The addition of silicon is to increase the capacity of the entire lithium ion battery. However, the problem of the cycle expansion of silicon makes the content of silicon in the thick electrode sheet not too much, especially in the large-capacity thick electrode sheet cell of the present application, the expansion problem is more likely to cause the delamination of the thick electrode sheet, causing the problem of the disconnection of the conductive path of the active material. On the other hand, due to the continuous rupture and regeneration of SEI caused by the expansion of silicon during the charging and discharging cycle, this process is accompanied by the continuous production of gas, and the larger the capacity of the lithium ion battery, the more serious the problem of gas production caused by the expansion of silicon. Therefore, the mass content range of silicon in the negative electrode active material layer of the present application needs to consider two factors, and the intersection of the two factors; the first factor is the influence of the capacity of the lithium ion battery on the content of silicon, which is as follows: when the capacity of the lithium ion battery is 200 Ah≤L≤500 Ah, further preferably 300 Ah

[0136] 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, the side close to the negative electrode current collector. Further preferably, the content of silicon on the surface of the negative electrode active material layer close to the negative electrode current collector is higher than the content of silicon 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.

[0137] The lower part of the negative electrode active material layer refers to the part of the negative electrode active material layer close to the negative electrode current collector in the thickness direction of the negative electrode active material layer. Correspondingly, the upper part of the negative electrode active material layer refers to the part of the negative electrode active material layer away from the negative electrode current collector. The surface of the negative electrode active material layer away from the negative electrode current collector refers to the region 20 μm deep from the surface of the negative electrode active material layer away from the negative electrode current collector in 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 refers to the region 20 μm deep from the surface of the negative electrode active material layer close to the negative electrode current collector in 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 by a scanning electron microscope (SEM), and element scanning can be performed by an EDS (X-ray energy spectrometer) to determine the element content of silicon.

[0138] 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 expansion and contraction of silicon, 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. In the present application, the silicon in the negative electrode active material layer refers to the element silicon, which can specifically include one or more of elemental silicon, oxides of silicon, nitrides of silicon, or salts containing silicon elements (such as silicates).

[0139] Specifically, the negative electrode active material layer structure containing silicon in the present application has the following several ways:

[0140] The first way: silicon is distributed in both the upper part and the lower part 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. The content of silicon close to the lower surface of the negative electrode active material layer (the surface close to the current collector) can be measured, and the content of silicon close to the upper surface of the negative electrode active material layer can be measured.

[0141] The second way: 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, the thickness range of 20 μm away from the upper surface of the negative electrode active material layer does not contain silicon, because the upper part of the negative electrode active material layer cannot press the lower film after more than 20 μm.

[0142] Negative electrode sheet structure:

[0143] The negative electrode sheet of the present application comprises a negative electrode current collector and a negative electrode active material layer. 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, and the negative electrode active material layer obtains electrons through the negative electrode current collector during the cycle of the lithium ion battery.

[0144] The negative electrode sheet also includes a negative electrode tab, which is electrically connected to the negative electrode current collector. The negative electrode tab can be connected to the negative electrode current collector in various ways, such as being welded to the negative electrode current collector or being an integral structure with the negative electrode current collector (e.g., the negative electrode current collector is a copper foil, and the negative electrode tab is formed by cutting the negative electrode current collector).

[0145] The negative electrode current collector can have various structures. For example, in a first structure, the negative electrode current collector is rectangular, including long sides and short sides. The long sides of the negative electrode current collector are the length of the rectangular structure, and the short sides of the negative electrode current collector are the width of the rectangular structure. The negative electrode active material layer is arranged on at least part of the upper and lower surfaces of the negative electrode current collector, and the negative electrode tab is arranged on the short side of the negative electrode current collector. For another example, in a second structure, the negative electrode current collector is rectangular, including long sides and short sides. The negative electrode tab is arranged on the long side of the negative electrode current collector, and multiple negative electrode tabs are arranged on each long side. The long side of the negative electrode current collector in the second structure is longer than the long side of the negative electrode current collector in the first structure, so multiple negative electrode tabs need to be arranged on the negative electrode current collector in the second structure, which is beneficial to reducing heat generation at the tab position of the thick electrode sheet cell. In the first structure, the negative electrode tab can be arranged on one or more short sides of the negative electrode current 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 supply of electrons 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 heat generation 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 is that 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. If the ratio exceeds 0.8, the negative electrode current collector will be very close to the shell. In the case of a conductive shell, a slight impact can easily cause an electrical connection between the negative electrode current 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 current collector is in the range of 0.6-0.8. When the charge rate is not less than 3C, the heat generation at the negative electrode tab position is further intensified. Therefore, by setting the ratio of the width of the negative electrode tab to the width of the short side of the negative electrode current collector to be no less than 0.6, the heat generation at the negative electrode tab position can be alleviated. The same principle applies to the arrangement of the positive electrode tab.

[0146] The negative electrode sheet preparation process includes the following processes:

[0147] The negative electrode sheet preparation process includes the following processes:

[0148] Process one, mixing the negative electrode active material, conductive agent, binder and other materials to form the negative electrode active material layer. This mixing process includes two methods, method one: mixing the negative electrode active material, conductive agent, binder, solvent of the binder and other materials to form a liquid slurry, which is coated on the surface of the copper foil as the negative electrode current collector, or coated on the surface of the carbon fiber as the negative electrode current collector and between the carbon fibers, and then subjected to drying, rolling and other processes to obtain the negative electrode sheet precursor for preparing the battery cell; method two: mixing the negative electrode active material, conductive agent, binder and other materials (which can include a small amount of binder and solvent) to form a non-flowing solid or semi-solid mixture, and hot-pressing it onto the negative electrode current collector to form the negative electrode sheet precursor.

[0149] Process two, slitting the negative electrode sheet precursor to obtain the negative electrode sheet to be used.

[0150] The negative electrode active material layer on the surface of the negative electrode current collector of the negative electrode sheet precursor formed in process one has a thin area. The thin area can be formed in various ways. For example, in the above-mentioned method one, the coating amount of some of the coating dies is less than that of the other coating dies during the coating process, and then during the drying process, the coating area formed by the coating dies with a small coating amount is the thin area. The gap between the multiple coating dies can also be adjusted so that the coating liquid formed by the multiple coating dies does not contact or partially contacts each other on the sheet of the negative electrode 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.

[0151] In process two, the slitting is performed along the thin area, so that the edge of the long side of the 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 thickness of the middle part of the negative electrode sheet.

[0152] The above preparation process increases the cost, so from the cost point of view, the thin area can also not be formed, so that the edge thickness of the long side of the negative electrode sheet obtained after slitting is basically the same as the thickness of the negative electrode sheet.

[0153] Positive electrode sheet:

[0154] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is arranged 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.

[0155] The positive electrode active material layer includes a positive electrode active material, which can be selected from lithium-containing phosphates such as lithium iron phosphate or lithium iron manganese phosphate, or ternary positive electrode materials such as lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, or elements doped in the former two. Due to material properties, the ternary positive electrode material is prone to produce gas during the charging and discharging cycle, especially when the nickel content in the ternary positive electrode material is high, which makes the gas production abnormally large during normal cycling of the large-capacity battery, and even the gas production during normal cycling can burst the explosion-proof valve, causing the lithium ion battery to fail. Therefore, the preferred positive electrode material in the technical solution of the present application is a lithium-containing phosphate. However, lithium-containing phosphates have poor electrical conductivity and need to be coated with a carbon layer on the surface. At the same time, considering that the capacity of lithium-containing phosphates is lower than that of ternary positive electrode materials, the present application improves the capacity by doping metal elements into the lithium-containing phosphates. Specifically, one or more of titanium elements and vanadium elements can be doped to improve the capacity of lithium-containing phosphates and improve the electrical conductivity, which can also help to improve the charging and discharging speed of the large-capacity battery of the present application. The present application considers that the mass ratio of the doping element to the mass of the positive electrode active material (including lithium-containing phosphate and carbon layer) is not more than 0.4%, specifically in the range of 0.01%-0.4%; more specifically, 0.2%-0.4% of titanium element can be doped; or 0.1%-0.2% of titanium element and 0.01%-0.05% of vanadium element can be doped. However, the content of the doping element is not the more the better. The inventors have studied the charging and discharging of the large-capacity thick electrode sheet battery of the present application, and the positive electrode active material uses lithium iron phosphate containing doping elements. When the mass ratio of the doping element to the mass of the positive electrode active material exceeds 0.4%, the crystal structure of the lithium iron phosphate begins to change greatly, which is not conducive to performance.

[0156] In addition to the positive electrode active material (the positive electrode active material of the present application includes lithium-containing phosphate, which can be coated with carbon and doped with metal elements), the positive electrode sheet also includes a binder and a conductive agent. The technical solution of the present application is used for the compaction density of the single-sided active material layer of the positive electrode sheet, which is between 2.3 g / cc and 2.7 g / cc (this compaction density is measured within 100 times of charging and discharging of the lithium ion battery. During the preparation process of the lithium ion battery, the electrode sheet is usually subjected to rolling operation to improve the compaction density of the electrode sheet, but the compaction density of the electrode sheet often rebounds and becomes smaller before the cycle of the finished lithium ion battery. However, the positive electrode sheet rebounds less than the negative electrode sheet), and the areal density of the single-sided active material layer of the positive electrode sheet is between 0.16 mg / mm 2 -0.26 mg / mm 2further, the thickness of the single-side active material layer of the positive electrode sheet is between 60 μm and 105 μm, and the thickness of the positive electrode sheet is between 135 μm and 225 μm at the position where the double-side positive active material layer is coated on the positive current collector (the thickness of the single-side active material layer of the positive electrode sheet and the thickness of the positive electrode sheet are measured when the number of charge-discharge cycles of the lithium ion battery is less than 100 times). Since the single-side active material layer of the positive electrode sheet is relatively thick, the inventors of the present application further provide that when the positive current collector is an aluminum foil, the thickness of the positive current collector is D1 when the thickness of the single-side active material layer of the positive electrode sheet is less than or equal to 95 μm, and the thickness of the positive current collector is D2 when the thickness of the single-side active material layer of the positive electrode sheet is greater than 95 μm, wherein D2 > D1; further, the numerical range of D1 is between 11 μm and 13.5 μm, and further preferably between 12 μm and 13 μm; and the numerical range of D2 is between 13.5 μm and 16 μm, and further preferably between 14 μm and 15 μm; because the thicker the positive active material layer, the stronger the current-carrying capacity of the required current collector, and the thicker the required current collector.

[0157] 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 each position in the positive active material layer, the conductive agent in the positive active material layer preferably includes carbon tubes, and more preferably single-walled carbon tubes or few-walled carbon tubes. Compared with other conventional conductive agents such as carbon black, on the one hand, single-walled carbon tubes or few-walled carbon tubes have better conductivity, and on the other hand, during the cycling process, the upper active material of the thick electrode sheet may become difficult to obtain electrons, and even cause delamination of the thick electrode sheet. However, single-walled carbon tubes or few-walled carbon tubes have a large aspect ratio compared with carbon black, thereby being able to fix the thick electrode sheet, improve the ability of the upper active material to obtain electrons, and prevent delamination from occurring.

[0158] Positive electrode sheet structure:

[0159] The positive electrode sheet of the present application includes a positive current collector and a positive active material layer, wherein the positive current collector can be an aluminum foil, a carbon-containing fiber current collector, or a porous current collector, and the positive active material layer is combined with the positive current collector, and the positive active material layer obtains electrons through the positive current collector during the cycling process of the lithium ion battery.

[0160] The positive electrode sheet further includes a positive electrode tab, and the positive electrode tab is electrically connected to the positive current collector. The connection mode of the positive electrode tab and the positive current collector can be various, such as welding the positive electrode tab on the positive current collector, or the positive electrode tab and the positive current collector belong to an integrated structure (for example, the positive current collector is an aluminum foil, and the positive electrode tab is cut from the positive current collector).

[0161] The positive electrode current collector can be various structures, such as a first structure, the positive electrode current collector can be a rectangle, including a long side and a short side, the long side of the positive electrode current collector is the length of the rectangular structure, and the short side of the positive electrode current 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 current collector, and the positive electrode tab is arranged on the short side of the positive electrode current collector; for example, the second structure, the positive electrode current collector is a rectangular structure, including a long side and a short side, the positive electrode tab is arranged on the long side of the positive electrode current collector, and a plurality of positive electrode tabs are arranged on each long side. The long side of the positive electrode current collector of the second structure is longer than the long side of the positive electrode current collector of the first structure, so a plurality of positive electrode tabs need to be arranged on the positive electrode current collector of the second structure, which is beneficial to reduce the heat generation of the thick tab cell at the tab position. In the first structure, the positive electrode tab can be arranged on one or more short sides of the positive electrode current collector, and the ratio of the width of the positive electrode tab to the width of the short side of the positive electrode current 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 setting principle is the same as that of the negative electrode tab, which will not be repeated here.

[0162] In this application, the positive tab structure, the positive tab and the preparation process of the positive tab are similar to the negative tab, which will not be repeated here. However, it should be pointed out that in some embodiments of the application, the positive tabs are also unevenly distributed on the positive current collector, the distance from the upper end of the positive tab to the upper end of the positive tab is a third distance h3, and the distance from the lower end of the positive tab to the lower end of the positive tab is a fourth distance h4, h3>h4.

[0163] In this application, the thickness of the negative tab or the thickness of the positive tab is tested as follows: the lithium ion battery after 1-100 cycles of charge and discharge is discharged to 2.5V voltage, which is considered as the completion of discharge of the lithium ion battery, then the positive tab and the negative tab are obtained by disassembling the lithium ion battery, the positive tab and the negative tab are cleaned with a solvent of electrolyte such as EC solution to wash off the lithium salt or other residues on the surface of the positive tab and the negative tab, then the solvent is dried, and the thickness of the positive tab and the thickness of the negative tab are measured.

[0164] In this application, the particle size of the active material is tested as follows: the lithium ion battery after 1-100 cycles of charge and discharge is discharged to 2.5V voltage, which is considered as the completion of discharge of the lithium ion battery, then the positive tab and the negative tab are obtained by disassembling the lithium ion battery, the positive tab and the negative tab are cleaned with a solvent of electrolyte such as EC solution to wash off the lithium salt or other residues on the surface of the positive tab and the negative tab, then the solvent is dried, and the positive tab and the negative tab are subjected to high temperature treatment (such as 500-600℃) in an inert atmosphere to deactivate the binder in the tab, after high temperature treatment, the tab is pulverized to obtain the active material, then the active material after pulverization is sieved (pressed) to obtain the lower particle sample for particle size test.

[0165] The cycle (such as 100 cycles) described in the present application refers to one charging plus one discharging as one cycle, more specifically, in actual use, it is not necessarily full charging or full discharging, but as long as it is charged once and then discharged until the next charging begins, it is recorded as one cycle.

[0166] The diaphragm:

[0167] The diaphragm used in the scheme of the present application includes a base film, the base film includes fibers, the base film material includes PP or PE, the surface of the base film is provided with a coating layer, the coating layer includes inorganic substances and inorganic particles, the coating layer is coated and bonded on the surface of the base film and partially penetrates into the inside of the base film, the presence of the coating layer can well inhibit the lithium dendrites generated by the negative plate from penetrating the diaphragm to cause internal short circuit of the lithium ion battery; but the coating layer cannot make the diaphragm completely closed, because the electrolyte still needs to pass through, so the porosity of the diaphragm is set to be between 30%-50%.

[0168] The electrolyte:

[0169] The electrolyte includes lithium salt and solvent, the lithium salt includes lithium hexafluorophosphate (LiPF6). But lithium hexafluorophosphate has poor thermal stability, starts to decompose phosphorus pentafluoride (PF5) and lithium fluoride (LiF) at 80℃, and 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, so the gas production of lithium hexafluorophosphate on large-capacity cells cannot be ignored. And with the increase of the capacity of lithium ion batteries, the internal temperature of the cell will also be higher and higher, so the gas production of LiPF6 in large-capacity cells will also be more and more.

[0170] Another lithium salt is lithium bisfluorosulfonylimide (LiFSI), which has good thermal stability and a decomposition temperature as high as 200℃, which is beneficial to reduce the gas production problem caused by temperature rise. Partly because lithium bisfluorosulfonylimide (LiFSI) is too high in cost, so the lithium salt of the electrolyte still needs to retain lithium hexafluorophosphate (LiPF6), in addition, LiFSI has a certain corrosion effect on the positive current collector aluminum foil, while LiPF6 can alleviate this corrosion effect. After comprehensive consideration, the volume molar content of LiPF6 should be higher than that of LiFSI.

[0171] Since the lithium salt is consumed a lot in the process of forming SEI during the lithium ion battery cycle, especially the first charge and discharge, the application scheme monitors the lithium salt content in the finished lithium ion battery during the cycle. Specifically, when the lithium ion battery charge-discharge times are between 5 and 100 times, the volume molar content of lithium salt is between 0.8mol / L-1.5mol / L in the case of lithium salt including lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI); for the purpose of reducing the corrosion of aluminum foil, further limit the mass percentage of lithium bisfluorosulfonylimide (LiFSI) in the electrolyte to 0.1%-9%.

[0172] On the other hand, considering that the capacity of lithium ion battery is improved, the gas production is intensified, when the capacity of lithium ion battery is greater than 300Ah, the mass percentage of LiFSI in the electrolyte is not less than 1%.

[0173] According to the capacity and cost of lithium ion battery: when the capacity of lithium ion battery L is 200Ah≤L≤300Ah, the mass percentage of LiFSI in the electrolyte is 0.1%-9%, for the purpose of cost, the mass percentage of LiFSI in the electrolyte is preferably 0.1%-5%; when the capacity of lithium ion battery L is 300Ah<L≤500Ah, the mass percentage of LiFSI in the electrolyte is 1%-9%, for the purpose of cost, the mass percentage of LiFSI in the electrolyte is preferably 1%-5%; when the capacity of lithium ion battery L is 500Ah<L≤700Ah, the mass percentage of LiFSI in the electrolyte is 3%-9%; when the capacity of lithium ion battery L is 700Ah<L≤1100Ah, the mass percentage of LiFSI in the electrolyte is 5%-9%.

[0174] The solvent in the electrolyte of the present application includes EC, DMC, EMC, DEC, and the specific Chinese names are: ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Because EC is a cyclic carbonate, the cyclic carbonate has high dielectric constant and high ionic conductivity, and can form a stable SEI film on the negative electrode surface, 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%; wherein DMC and EMC are 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, the sum of the mass of DMC and EMC needs to be greater than the mass of EC, and the total content of EMC and DMC needs to be further controlled to be between 50% and 60%. In addition, compared with EMC, DMC has a lower boiling point and is prone to gas production. From the aspect of controlling high-temperature gas production, the mass of EMC needs to be higher than that of DMC. However, the lower viscosity of DMC is conducive to the climbing of the electrolyte on the long electrode and the diaphragm (lateral and longitudinal diffusion capacity), and the presence of DMC is required, and the content of DMC needs to be between 10% and 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, i.e. 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, i.e. 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, i.e. the mass of DMC / (the difference between the mass of the electrolyte and the mass of the lithium salt).

[0175] In some embodiments, a certain amount of carboxylic acid ester is also added to the electrolyte. The content of carboxylic acid ester refers to the mass of carboxylic acid ester divided by the difference between the mass of the electrolyte and the mass of the lithium salt, i.e. the content of carboxylic acid ester is the mass of carboxylic acid ester / (the difference between the mass of the electrolyte and the mass of the lithium salt). Carboxylic acid ester helps to form a film on 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, too much carboxylic acid ester will increase the amount of gas production, especially in a fast charging system. For some embodiments of the present application, the content of carboxylic acid ester is not more than 10%.

[0176] In some embodiments, carboxylic acid ester can also be used in combination with LiFSI, both combinations can reduce gas production, the most intuitive effect is that the use of LiFSI can be reduced, thereby reducing the cost. Specifically, when the content of carboxylic acid ester is 5%-10%, the capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, the mass percentage of LiFSI in the electrolyte is 0.1%-5%; the capacity L of the lithium ion battery is 300 Ah<L≤500 Ah, the mass percentage of LiFSI in the electrolyte is 1%-5%; the capacity L of the lithium ion battery is 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%.

[0177] Battery cell structure:

[0178] The battery cell structure of the present application includes a positive electrode sheet, a negative electrode sheet and a separator. The battery cell structure of the present application can be a laminated structure or a wound structure. The present application is suitable for large battery cells, and the capacity of the lithium ion battery is between 200 Ah and 1100 Ah.

[0179] Regardless of the laminated structure or the wound structure of the battery cell, the battery cell is often placed vertically during use. The wider the battery cell, the longer the distance the electrolyte needs to climb from the lower end of the battery cell to the upper end of the battery cell. The electrolyte climbs from the lower end of the battery cell to the upper end of the battery cell mainly through the separator, which is related to the porosity of the separator. Especially in the later stage of lithium ion battery cycling, the amount of electrolyte inside the shell decreases. If the electrolyte at the bottom of the shell cannot climb to the upper end of the battery cell, the electrode sheet at the upper end of the battery cell cannot be in contact with the electrolyte or the amount of electrolyte is small, which can cause uneven deposition of lithium ions at the negative electrode and generate a large amount of lithium dendrites, resulting in an increase in gas production. On the other hand, the wider the battery cell, the more difficult it is to dissipate heat in the middle of the battery cell, which can lead to an increase in gas production in the battery cell. A high porosity of the separator can also help dissipate heat to some extent. However, the porosity of the separator cannot be too high, otherwise it can cause an increase in negative electrode lithium dendrites due to uneven current density during charging, especially during high-rate charging. Under the electrolyte composition of the present application, when the width of the negative electrode sheet is between 100 mm and 150 mm, the porosity of the separator is between 30% and 50%; when the width of the negative electrode sheet is between 200 mm and 250 mm, the porosity of the separator is between 35% and 50%. According to the capacity requirement of the aforementioned battery cell, when the width of the negative electrode sheet is between 100 mm and 150 mm, the aspect ratio of the battery 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 battery cell is preferably between 2.8 and 4.

[0180] Lithium ion battery:

[0181] The lithium ion battery in the present application comprises a shell, an electric core, and an electrolyte, the electrolyte and the electric core are arranged inside the shell. The shell is arranged in a sealed manner, and the shell comprises a positive pole column, a negative pole column, and an explosion-proof valve. The positive pole column is electrically connected with the positive pole tab, and the negative pole column is electrically connected with the negative pole tab; the positive pole column and the negative pole column can be arranged at two ends of the shell respectively or can be arranged at the same end of the shell.

[0182] The explosion-proof valve is arranged at the first end of the shell, and at least one of the positive pole column and the negative pole column is also arranged at the first end of the shell.

[0183] Preferably, the explosion-proof valve is arranged at the edge of the end of the shell where the positive pole column is located, that is, the explosion-proof valve is arranged at the first end of the shell, and the positive pole column is also arranged at the first end of the shell. The upper end of the positive pole tab and the shell form a first upper exhaust passage, and along the airflow direction of the first upper exhaust passage, the projection area of the explosion-proof valve partially overlaps the projection area of the first upper exhaust passage. Furthermore, along the airflow direction of the first upper exhaust passage, the overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage exceeds 80%.

[0184] Or the explosion-proof valve is arranged at the edge of the end of the shell where the negative pole column is located, that is, the explosion-proof valve is arranged at the first end of the shell, and the negative pole column is also arranged at the first end of the shell. The upper end of the negative pole tab and the shell form a second upper exhaust passage, and along the airflow direction of the second upper exhaust passage, the projection area of the explosion-proof valve partially overlaps the projection area of the second upper exhaust passage, and furthermore, along the airflow direction of the second upper exhaust passage, the overlap degree of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage exceeds 80%.

[0185] The overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage refers to the ratio of the area of the overlapping region of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage to the area of the projection area of the first upper exhaust passage along the airflow direction of the first upper exhaust passage. Similarly, the overlap degree of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage refers to the ratio of the area of the overlapping region of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage to the area of the projection area of the second upper exhaust passage along the airflow direction of the second upper exhaust passage.

[0186] The projection area of the explosion-proof valve and the first upper exhaust passage or the second upper exhaust passage partially overlaps in terms of air flow, so that in the event of an abnormal situation, when the internal air pressure of the lithium ion battery is too large, the explosion-proof valve can be quickly opened, preventing the accumulation of air pressure inside the shell and causing an explosion. However, the overlap between the explosion-proof valve and the first upper exhaust passage or the second upper exhaust passage is more than 80%, because the large-capacity battery (lithium ion battery capacity greater than or equal to 200Ah) in this application produces a large amount of gas in abnormal situations. Through the applicant's experiments and simulations, if the overlap is less than 80%, some lithium ion batteries may explode. In order to further prevent the lithium ion battery from exploding, for the large-capacity battery (lithium ion battery capacity greater than or equal to 200Ah) in this application, the applicant further optimizes 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 limited, 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 lithium ion battery from exploding, for the large-capacity battery (lithium ion battery capacity greater than or equal to 200Ah) in this application, the applicant further optimizes that when the aspect ratio of the battery is greater than 2.8, there are multiple explosion-proof valves, and all of the multiple explosion-proof valves are 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 in the initial 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 situation occurs at this time and causes the explosion-proof valve to open, the applicant does not want the electrolyte to be ejected from the explosion-proof valve along with the generated gas, because the ejected electrolyte can further cause other external short circuits, so the explosion-proof valve should be placed in the upper half of the lithium ion battery, and even if there are multiple explosion-proof valves, each explosion-proof valve should be placed in the upper half of the lithium ion battery.

[0187] The explosion-proof valve can be located on the short side of the lithium ion battery (as shown in Figure 3 of the present application), or it can be located on the long side of the lithium ion battery. At this time, there are various ways of setting, one of which is shown in Figure 9 of the present application.

[0188] The explosion-proof valve can also be arranged on the long side of the shell, the positive electrode tab can be arranged on the short side of the positive electrode current collector, the negative electrode tab can be arranged on the short side of the negative electrode current collector, the positive electrode tab and the negative electrode tab can be arranged at two ends of the battery cell respectively, and the positive electrode tab and / or the negative electrode tab can be arranged symmetrically with respect to the pole piece (in other arrangement modes, at least one side is arranged asymmetrically, for at least one of the following reasons: to leave space for the explosion-proof valve or other devices (such as a liquid injection channel), and to take into account the flow capacity of the tab, which needs to have a certain width, so the tab is often moved downward with respect to the upper end of the pole piece, but the tab may come into contact with the shell, so the distance between the lower edge of the tab and the shell needs to be controlled. After the explosion-proof valve is arranged on the short side of the shell and the tab is arranged on the short side of the current collector (the pole is also arranged on the short side of the shell), the tab can be arranged symmetrically with respect to the short side of the current collector, and the ratio of the width of the tab to the short side of the current collector can be increased, which can be set to 0.7-0.8, thereby increasing the flow capacity of the tab.

[0189] The present application does not limit the specific structure of the explosion-proof valve, and any part of the shell that can be broken under abnormal conditions can play the role of the explosion-proof valve. For example, when the shell is an aluminum plastic film shell, the weak area of the aluminum plastic film package can play the role of the explosion-proof valve. At this time, the weak area can be a line structure, and the area calculation method of the explosion-proof valve is the area of a square with the length of the weak area as the circumference.

[0190] For multiple explosion-proof valves, there are multiple design schemes. For example, there are two explosion-proof valves, and the two explosion-proof valves are arranged on two opposite short sides of the lithium ion battery. At this time, the two explosion-proof valves need to be arranged symmetrically, otherwise one explosion-proof valve may not be activated after the other explosion-proof valve is activated. For another example, there are two explosion-proof valves, and the two explosion-proof valves are arranged on the long side of the upper end of the lithium ion battery. At this time, the two explosion-proof valves need to be arranged symmetrically with respect to the long side of the lithium ion battery. The symmetrically arranged here means that the distance from each explosion-proof valve to the midpoint of the long side of the lithium ion battery is equal. 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 generated rapidly at the collision position, which may not be quickly transmitted to the explosion-proof valves at both ends of the battery cell, thereby possibly causing the lithium ion battery to explode. For another example, there can be three explosion-proof valves, two explosion-proof valves are arranged symmetrically 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 at the middle of the long side. 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 generated rapidly at the collision position, which may not be quickly transmitted to the explosion-proof valves at both ends of the battery cell, thereby possibly causing the lithium ion battery to explode.

[0191] When the battery cell is a jelly-roll battery cell, the positive pole and the negative pole are preferably arranged at the same end of the shell.

[0192] Gas analysis:

[0193] During the preparation of the lithium ion battery, the first charge and discharge will form a SEI layer on the surface of the active material of the negative electrode sheet. A large amount of gas is generated in this process, and the gas needs to be pumped out of the lithium ion battery. After that, the shell is sealed as a finished lithium ion battery. The use process of the finished lithium ion battery includes normal charge and discharge cycle use, and also includes abnormal use environment, such as high temperature, collision, etc. Under normal use environment, with the process of charge and discharge cycle, the interlayer of graphite in the negative electrode continuously deintercalates lithium, which will cause the volume expansion of graphite and also may cause the peeling of the interlayer of graphite, etc. These factors will cause the destruction of the SEI on the surface of the negative electrode active material and also accompanied by re-generation. The process of re-generating SEI will generate gas. In addition, with the intercalation of lithium into graphite, especially for thick electrode sheets, part of the lithium ions cannot be intercalated into the interlayer of graphite, thereby lithium dendrites are precipitated on the surface of the negative electrode active material. Part of the precipitated lithium dendrites will react with the electrolyte, generate SEI, consume electrolyte and generate gas. The positive electrode sheet will also generate gas during the charge and discharge process. The ternary material as the positive electrode active material generates more gas, but the technical solution of the present application adopts lithium-containing phosphate, so the gas generation of the positive electrode is less. When the lithium ion battery is abnormally used, such as high temperature, the specific reactions in the lithium ion battery are as follows:

[0194] When the temperature of the lithium ion battery exceeds 80℃, the organic lithium in the SEI film will decompose and generate gas, and lithium hexafluorophosphate will decompose and react with the solvent to generate gas;

[0195] When the temperature of the lithium ion battery exceeds 120℃, the SEI film on the surface of the negative electrode has been mostly decomposed, so that the lithium and other substances in the negative electrode react with the organic solvent to generate gas;

[0196] When the temperature of the lithium ion battery is between 110℃ and 300℃, lithium hexafluorophosphate decomposes in large quantities, and the electrolyte also reacts in large quantities to generate gas;

[0197] When the temperature of the lithium ion battery exceeds 300℃, the lithium-containing phosphate decomposes and generates gas, and further induces the decomposition of the electrolyte to generate gas;

[0198] In addition, when the temperature of the lithium ion battery exceeds 235℃, the binder PVDF used in the positive and negative electrode sheets also begins to decompose.

[0199] The pre-gas of thermal runaway is relatively mild, at this time, if the charging and discharging of the lithium ion battery is stopped as soon as possible and the lithium ion battery is cooled, the further occurrence of thermal runaway can be prevented, and the negative electrode of the lithium ion battery can be reformed SEI film, and the lithium ion battery can continue to be used; but if the thermal runaway is not stopped in time, in the middle and late stage of thermal runaway, with the accumulation of a large amount of heat, a large amount of gas is generated, which makes the gas pressure in the lithium ion battery increase a lot and the explosion-proof valve is opened, although the explosion-proof valve prevents the explosion reaction of the lithium ion battery, but after the explosion-proof valve is opened, the lithium ion battery cannot be used again.

[0200] Therefore, the technical scheme of the present application continuously optimizes the features of the positive plate, negative plate, separator, electrolyte, and cell structure in the lithium ion battery, so as to minimize the amount of gas generated under normal use conditions, thereby first ensuring that the gas generated during the normal use life cycle of the lithium ion battery (such as 3000 cycles of charging and discharging) is not enough to open the explosion-proof valve; and further ensuring that as much space as possible is left for the gas generated by thermal runaway, so that the lithium ion battery does not open the explosion-proof valve in the early stage of thermal runaway. Specifically, if the amount of gas generated during normal cycling is small, the gas generated in the early stage of thermal runaway is still not enough to reach the opening pressure of the explosion-proof valve, so the explosion-proof valve does not open, at this time, if the thermal runaway is prevented from further occurring, the lithium ion battery can still be used. More specifically, the opening pressure of the explosion-proof valve is generally between 0.6Mpa-1Mpa, in order to ensure the safety of the lithium ion battery, the opening pressure of the explosion-proof valve is designed to be 0.55Mpa-0.65Mpa, in order to leave space for the gas generated by thermal runaway, the internal pressure of the lithium ion battery of the present application after 3000 cycles of charging and discharging at 40℃ is not more than 0.35Mpa.

[0201] Theoretically, the space is formed by the space between the battery cell and the shell which is not filled by the electrolyte during the preparation of the lithium ion battery, and the space which is formed by the electrolyte consumed during the cycle of the lithium ion battery. Especially in the later stage of the cycle of the lithium ion battery, the electrolyte is largely consumed, and most of the electrolyte is located in the pores of the diaphragm, so that the electrolyte between the battery cell and the shell is very little. Therefore, when designing the theoretical gas storage space, the space between the battery cell and the shell in the thickness direction of the battery cell is ignored, because the thickness of the battery cell is similar to the thickness of the shell during the preparation of the lithium ion battery, and the space reserved is very little. The space between the battery cell and the shell in the thickness direction of the battery cell is ignored because the thickness of the battery cell is almost the same as the thickness of the shell after the cycle of the battery cell and the filling of the electrolyte in the battery cell. On the other hand, with the cycle, especially in the later stage of the cycle of the battery, the electrolyte is largely consumed, and most of the electrolyte is located in the pores of the diaphragm, so that the electrolyte between the battery cell and the shell is very little. 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.

[0202] Specifically, when designing the battery cell, the capacity is first preset, and then the required theoretical gas storage space V0 can be calculated according to the relationship between the volume and the capacity. For the finished lithium ion battery, the capacity of the lithium ion battery is the capacity under the 0.33C charge-discharge rate.

[0203] The scheme of the present application is suitable for various structures of lithium ion batteries, and is described below only by way of example in combination with the accompanying drawings:

[0204] As shown in FIG. 1, FIG. 2, FIG. 3, and FIG. 4, the square laminated lithium ion battery has a length-width ratio of 6.5, and includes a shell 40, a battery cell 30 and an electrolyte (not shown in the figure) located inside the shell 40. The positive electrode sheet 10 in FIG. 1 and the negative electrode sheet 20 in FIG. 2 and the diaphragm (not shown in the figure) are laminated to form the battery cell 30. The shell 40 further includes a positive electrode column 41, a negative electrode column 42, and a pressure relief valve 43.

[0205] The positive electrode sheet 10 and the negative electrode sheet 20 are both square structures, which refers to the overall shape ignoring the tab. The positive electrode sheet 10 includes a positive electrode tab 11, a positive electrode current collector, and a positive electrode active material layer. The positive electrode current collector is in a rectangular structure. The positive electrode tab 11 is arranged on one short side of the positive electrode current collector. The positive electrode tab 11 is asymmetrically distributed on the short side of the positive electrode current collector. In the width direction of the battery cell, that is, in the direction of the short side of the positive electrode current collector, the vertical distance from the upper end of the positive electrode 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 electrode tab 11 to the lower end of the positive electrode sheet 10 is a second distance h2. Here, h1 is greater than h2, and the ratio of the width of the positive electrode tab 11 to the short side width of the positive electrode 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 in a rectangular structure. The negative electrode tab 21 is arranged on one short side of the negative electrode current collector. The negative electrode tab 21 is asymmetrically distributed on the short side of the negative electrode current collector. In the width direction of the battery cell, that is, in the direction of the short side 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. Here, 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.

[0206] The battery cell 30 is formed by stacking a plurality of positive electrode sheets 10 and a plurality of negative electrode sheets 20 and a separator. Each positive electrode sheet 10 has a positive electrode tab 11 arranged on one short side. Each negative electrode sheet 20 has a negative electrode tab 21 arranged on one short side. The positive electrode tab 11 and the negative electrode tab 21 are respectively located at two ends of the battery cell 30.

[0207] The positive pole 41 is electrically connected with the positive tab 11, and the negative pole 42 is electrically connected with the negative tab 21. The positive pole 41 and the negative pole 42 are arranged at both ends of the shell 40, and the explosion-proof valve 43 is arranged at the edge of the end of the shell 40 where the positive pole 41 is located. As shown in FIG. 3 and FIG. 4, the upper end of the positive tab 11 and the shell 40 form a first upper exhaust passage 51, and the end of the shell 40 connected with the positive tab 11 includes the explosion-proof valve 43. Along the airflow direction of the first upper exhaust passage 51 (the horizontal direction in FIG. 4, which is also the length direction Ld of the battery cell), the explosion-proof valve 43 partially overlaps with the first upper exhaust passage 51. Specifically, along the airflow direction of the first upper exhaust passage 51, the overlap degree of the explosion-proof valve 43 and the first upper exhaust passage 51 is 85%, that is, the ratio of the width of the explosion-proof valve 43 to the width of the first upper exhaust passage 51 is 85% along the vertical direction (which is also the height direction Hd) in FIG. 4. As shown in FIG. 4, the flow direction of the gas inside the lithium ion battery is shown. The gas generated inside the battery cell 30 is mostly discharged from the battery cell 30 along the edge of the pole piece through the pores or diaphragm between the pole pieces. In the normal cycle, due to the continuous and relatively slow generation of gas, the generated gas is relatively uniformly dispersed inside the shell 40 due to the flowability, including part of the gas concentrated at the position of the first upper exhaust passage 51; in the abnormal situation, the gas is rapidly generated, thereby causing the gas pressure in the shell 40 to rise, and the gas pressure at the position of the first upper exhaust passage 51 to rise, thereby breaking the explosion-proof valve 43.

[0208] As shown in FIG. 3, due to the small gap between the battery cell 30 and the shell 40 in the thickness direction of the pole piece, which is also the thickness direction of the battery cell 30 (the thickness direction in the figure is the direction perpendicular to the plane of the view, that is, the direction perpendicular to Hd and Ld), and as the battery cell 30 expands in 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. In the calculation of 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 of the battery cell 30 and the height direction (which is also the width direction) of the battery cell 30 is calculated, that is, the space at the positions marked by ①②③④ in FIG. 3.

[0209] FIG. 1 to FIG. 4 are only schematic, and the explosion-proof valve 43 can also be arranged at the edge of the end of the shell 40 where the negative pole 42 is located, that is, the explosion-proof valve 43 is arranged on the right side short side of the lithium ion battery in FIG. 3 or FIG. 4.

[0210] As shown in FIG. 5, FIG. 6, FIG. 9, FIG. 10, another structure of the lithium ion battery of the present application is shown, the length-width ratio of the lithium ion battery is 3, the lithium ion battery also comprises a shell 40, and an electrode 30 and an electrolyte (not shown in the figure) in the shell 40, the negative electrode sheet 20 in FIG. 5 and the positive electrode sheet 10 in FIG. 6 and the separator (not shown in the figure) are stacked to form the electrode 30, the shell 40 further comprises a positive electrode column 41, a negative electrode column 42, and a safety valve 43. The positive electrode sheet 10 and the negative electrode sheet 20 are both square structures, here the square structure refers to the overall shape ignoring the tab. The positive electrode sheet comprises a positive electrode tab 11, a positive electrode current collector, and a positive electrode active material layer, the positive electrode current collector is a rectangular structure, and the positive electrode tab 11 is arranged on one long side of the positive electrode current collector. The negative electrode sheet 20 comprises 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, and the negative electrode tab 21 is arranged on one long side of the negative electrode current collector. The electrode 30 is formed by stacking a plurality of positive electrode sheets 10 and a plurality of negative electrode sheets 20 and a separator, the positive electrode tab 11 is arranged on one long side of each positive electrode sheet 10, the negative electrode tab 21 is arranged 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 electrode 30. The positive electrode column 41 is electrically connected with the positive electrode tab 11, the negative electrode column 42 is electrically connected with 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 safety valve 43 is arranged between the positive electrode column 41 and the negative electrode column 42. FIG. 10 also shows a schematic diagram of the flow direction of the gas flow. As shown in FIG. 9, since the gap between the electrode sheet and the shell 40 in the thickness direction of the electrode sheet, that is, the thickness direction of the electrode 30 (the thickness direction in the figure is the direction perpendicular to the plane of the view, that is, the direction perpendicular to Hd and Ld), is small, and as the electrode 30 expands in the cycle, and the expansion mainly occurs in the thickness direction of the electrode 30, the gap between the electrode 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 electrode 30 and the shell 40 in the length direction of the electrode 30 and the height direction of the electrode 30, that is, the space at the positions marked by ①②③④ in FIG. 9, is calculated. More specifically, the space volume in the length direction of the electrode 30 (that is, the sum of the space volumes marked by ① and ②): the difference between the inner cavity length of the shell 40 and the length of the electrode 30 multiplied by the inner cavity width of the shell 40 and then multiplied by the inner cavity thickness of the shell 40; the space volume in the height direction of the electrode 30 (that is, the space volume in the width direction, that is, the sum of the space volumes marked by ③ and ④): the difference between the inner cavity width of the shell 40 and the width of the electrode 30 multiplied by the length of the electrode 30 and then multiplied by the inner cavity thickness of the shell 40. The actual gas storage space is the sum of the space volume in the length direction of the electrode 30 and the space volume in the width direction of the electrode 30.

[0211] The inner cavity thickness of the shell 40 is also referred to as the inner thickness of the shell 40 (i.e. the distance between the inner wall on one side of the shell 40 and the inner wall on 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 on one side of the shell 40 and the inner wall on 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 on one side of the shell 40 and the inner wall on the other side of the shell 40 in the length direction). In addition, the width of the negative current collector (excluding the tab) is used instead of the width of the battery cell 30, and the length of the negative current collector (excluding the tab) is used instead of the length of the battery cell 30. Although the tab also occupies a certain space, the space volume occupied by the tab is ignored in the present application.

[0212] 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 by ①, ②, ③ and ④, and further, other components such as support structures between the shell 40 and the battery cell 30 are not included. Such components also occupy a volume, and the actual gas storage space is reduced by the volume of other components.

[0213] As shown in FIG. 7, FIG. 8, FIG. 9, FIG. 10, another structure of the lithium ion battery of the present application is shown, the length-width ratio of the lithium ion battery is 3, the lithium ion battery also comprises a shell 40, and an electrode 30 and an electrolyte (not shown in the figure) inside the shell 40, the positive plate 10 in FIG. 7 and the negative plate 20 in FIG. 8 and the separator (not shown in the figure) are wound to form the electrode 30, the shell 40 further comprises a positive pole 41, a negative pole 42, and an explosion-proof valve 43. The positive plate 10 and the negative plate 20 are both square structures, which refers to the overall shape ignoring the tabs. The positive plate comprises 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 one long side of the positive current collector, and a plurality of positive tabs 11 are uniformly arranged on one positive current collector. The negative plate 20 comprises a negative tab 21, a negative current collector, and a negative active material layer, the negative current collector is a rectangular structure, the negative tab 21 is arranged on one long side of the negative current collector, and a plurality of negative tabs 21 are uniformly arranged on one negative current collector. The electrode 30 is formed by winding one positive plate 10 and one negative plate 20 and a separator, the positive tab 11 and the negative tab 21 are both located at the upper end of the electrode 30; the positive pole 41 is electrically connected with the positive tab 11, the negative pole 42 is electrically connected with the negative tab 21, the positive pole 41 and the negative pole 42 are arranged on the upper end of the shell 40, and the explosion-proof valve 43 is arranged between the positive pole 41 and the negative pole 42. FIG. 10 also shows the schematic diagram of the airflow direction. As shown in FIG. 9, since the gap between the electrode 30 and the shell 40 in the thickness direction of the plate, which is also the thickness direction of the electrode 30 (the thickness direction in the figure is the direction perpendicular to the plane of the view, that is, the direction perpendicular to Hd and Ld), is small, and as the electrode 30 expands in the cycle, and the expansion mainly occurs in the thickness direction of the electrode 30, the gap between the electrode 30 and the shell 40 after the cycle is further reduced, when calculating the actual gas storage space, the thickness direction can be ignored, only the space between the electrode 30 and the shell 40 in the length direction and the height direction is calculated, that is, the space at the positions marked by ①②③④ in FIG. 9.

[0214] In order to further study the actual gas storage space required by different materials in different lithium ion battery systems, the applicant designed a series of experiments in combination with his own design experience in small-capacity lithium ion batteries and previous exploration, wherein the experimental groups are as follows:

[0215] [First basic group]

[0216] The applicant first sets up the first basic group of 100 lithium ion batteries. The design purpose of the first basic group is to obtain the capacity and gas production ratio of large-capacity battery cells. The raw materials added to the first basic group of lithium ion batteries and the structure of the lithium ion batteries are as follows: the negative active material uses carbon-coated graphite, the OI value of the graphite is 10, the graphitization degree is 92%, the Dv50 of the graphite is 15 μm, the Dv10 is 6 μm, the Dv90 is 26 μm, the Dv99 is 42 μm, the graphite is non-agglomerated single particle, the areal density of the single-sided active material layer of the negative plate is 0.11 mg / mm 2 , the compaction density of the single-sided active material layer of the negative plate is 1.4 g / cc, the single-sided thickness of the negative active material layer is 79 μm, the negative current collector is a copper foil with a thickness of 6 μm, the negative active material layer is arranged on both sides of the negative current collector, the negative tab is arranged at one end of the length direction of the negative plate, that is, on the short side, and the negative tab and the negative plate are in an integrated structure, the width of the negative plate is 120 mm, the width of the negative tab is 75 mm, and along the width direction of the negative plate, the distance h3 from the upper end of the negative tab to the upper end of the negative plate is 28 mm, and the distance h4 from the lower end of the negative tab to the lower end of the negative plate is 17 mm; the negative plate has a plurality of negative tabs arranged thereon, the plurality of negative tabs are electrically connected to the negative column on the second end of the shell, and the first end of the shell is provided with an explosion-proof valve.

[0217] The positive active material is carbon-coated lithium iron phosphate (LFP), the compaction density of the single-sided active material layer of the positive plate is 2.6 g / cc, the areal density of the single-sided active material layer of the positive plate is 0.24 mg / mm 2 , the thickness of the single-sided active material layer of the positive plate is 92 μm, the positive tab is arranged at one end of the length direction of the positive plate, that is, on the short side, and the positive tab and the positive plate are in an integrated structure, the width of the positive plate is 116 mm, the width of the positive tab is 75 mm, the distance h1 from the upper end of the positive tab to the upper end of the positive plate is 26 mm, the distance h2 from the lower end of the positive tab to the lower end of the positive plate is 15 mm, the positive plate has a plurality of positive tabs arranged thereon, and the plurality of positive tabs are electrically connected to the positive column on the second end of the shell; the upper end of the positive tab and the shell form a first upper exhaust passage; the first end of the shell is provided with an explosion-proof valve, and the explosion-proof valve is arranged above the positive column; along the airflow direction of the first upper exhaust passage, the overlap degree of the explosion-proof valve and the first upper exhaust passage is 85%; the average particle size of the primary particles of the LFP positive active material is 0.1 μm-5 μm (since the LFP particles themselves are prone to agglomeration, the average particle size of the particles cannot be accurately measured, but since the LFP has a very small gas production compared to the ternary positive material, and the gas production at the negative graphite position is much larger than that at the positive LFP position when the LFP and graphite are used to form a lithium ion battery, the particle size of the LFP as the positive material is not limited in the present application).

[0218] The diaphragm comprises a PE base film, and an aluminum oxide coating is arranged on the base film, and the diaphragm porosity is 40%.

[0219] The lithium salt of the electrolyte is LiPF6, and the mass percentage is 16% relative to the electrolyte; the solvents of the electrolyte include EC, DMC, EMC and DEC, and the mass percentages are 30%, 13%, 38% and 8% respectively.

[0220] The structure of the battery cell is a laminated structure, and the capacity of the lithium ion battery is designed to be 300 Ah, and the gas storage space of the first basic group of lithium ion batteries is 1500 cm 3 ; The gas storage space of the first basic group of lithium ion batteries is designed to be much larger than the required space, and there are multiple considerations as follows: on the one hand, in order to cycle 3000 times for each basic group test without starting the explosion-proof valve, so as to calculate the relationship between the capacity of the lithium ion battery in different basic groups and the gas production; on the other hand, the gas storage space of the lithium ion battery in the first basic group is large, which is convenient for arranging the gas pressure sensor inside the shell.

[0221] After the lithium ion battery is injected, it will undergo formation and degassing processes.

[0222] The burst pressure of the explosion-proof valve is 0.6 MPa.

[0223] The shell of the lithium ion battery is an aluminum alloy, and the gas pressure sensor is arranged inside the shell.

[0224] The 100 lithium ion batteries of the first basic group are charged and discharged, the external environment temperature of the lithium ion battery is 40℃, the charge and discharge cut-off voltage is 2.5V-3.65V, the charging process includes a constant current segment and a constant voltage segment, in the constant current segment: the lithium ion battery is first charged to the cut-off voltage (3.65V) at a rate of 1C, and in the constant voltage segment: constant voltage charging; the discharge process is to discharge the lithium ion battery to the discharge cut-off voltage (2.5V) at a rate of 1C. After 50 cycles of charge and discharge of the basic group, 5 lithium ion batteries are taken out for analysis of the changes of the components of the lithium ion battery, and the remaining 95 lithium ion batteries continue to cycle to 3000 cycles. Analysis of the 5 lithium ion batteries taken out shows that most of the positive and negative electrode materials and the positive and negative electrode sheets have not changed much, except that the compaction density of the negative electrode sheet and the thickness of the negative electrode sheet will change, the compaction density of the single-sided active material layer of the negative electrode sheet is measured to be 1.35 g / cc, and the thickness of the single-sided active material layer of the negative electrode sheet is 85 μm; the compaction density and thickness of the single-sided active material layer of the positive electrode sheet change relatively small, and the compaction density of the single-sided active material layer of the positive electrode sheet is measured to be 2.59 g / cc, and the thickness of the single-sided active material layer of the positive electrode sheet is 93 μm.

[0225] The remaining 95 lithium ion batteries did not have the explosion-proof valve burst after 3000 cycles. After the lithium ion batteries were cycled for 3000 times, the gas pressure sensor pressure P of each lithium ion battery was recorded (the gas pressure P of different lithium ion batteries was different), and according to PV=NRT, T was 40℃, R was 8.314, V was 1500cm 3 , the gas pressure P was in units of Mpa, the corresponding gas production N of each lithium ion battery was obtained, 95 data were collected, and when the capacity L of the lithium ion battery was 300Ah, the ratio N / L of the gas production N of the lithium ion battery to the capacity of the lithium ion battery was between 0.02554mmol / Ah (millimoles per ampere) and 0.03495mmol / Ah.

[0226] Further according to Pv=NRT, when the gas pressure P is fixed at 0.35Mpa, the ratio of the gas storage space v to the capacity L of the lithium ion battery: v / L=NRT / PL is obtained; T is 40℃, R is 8.314, N / L is 0.02554mmol / Ah (millimoles per ampere) to 0.03495mmol / Ah, and thus 0.19cm 3 / Ah≤v / L≤0.26cm 3 / Ah, that is, 0.19L≤v≤0.26L, v is in units of cubic centimeters (cm 3 ).

[0227] [First adjustment group]

[0228] On the basis of the first basic group, the first adjustment group is set. The design idea of the first adjustment group is to design a series of lithium ion batteries with different graphite OI values on the basis of the first basic group, and to control other characteristics to be the same as the first basic group.

[0229] After this series of lithium ion batteries were cycled for 3000 times, the ratio of the gas production to the capacity of the lithium ion batteries was obtained, it was found that when the graphite OI value was 3, the average value of the ratio of the gas production to the capacity of the corresponding lithium ion batteries of the first adjustment group was close to the upper limit of the first basic group (0.03495mmol / Ah); when the graphite OI value was lower than 3, the average value of the ratio of the gas production to the capacity of the corresponding lithium ion batteries of the first adjustment group 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 (due to cost considerations, the OI value higher than 30 was not verified in this application, but according to the inventor's speculation, the higher the graphite OI value, the better the fast charging performance and the less the gas production), the average value of the ratio of the gas production to the capacity of the corresponding lithium ion batteries of the first adjustment group was lower than the upper limit of the first basic group (0.03495mmol / Ah).

[0230] [First secondary adjustment group]

[0231] On the basis of the first adjustment group, a first secondary adjustment group is further set. The first secondary adjustment group is only different from the first adjustment group in that the charge rate is changed to 2C.

[0232] It is found that the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first secondary adjustment group corresponding to the graphite OI value of 10 is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first secondary adjustment group corresponding to the graphite OI value of less than 10 exceeds the upper limit (0.03495 mmol / Ah) of the first basic group, it is found that the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first secondary adjustment group corresponding to the graphite OI value of more than 10 and less than or equal to 30 is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0233] [First tertiary adjustment group]

[0234] On the basis of the first adjustment group, a first tertiary adjustment group is further set. The first tertiary adjustment group is only different from the first adjustment group in that the charge rate is changed to 3C.

[0235] It is found that the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first tertiary adjustment group corresponding to the graphite OI value of 15 is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first tertiary adjustment group corresponding to the graphite OI value of less than 15 exceeds the upper limit (0.03495 mmol / Ah) of the first basic group, it is found that the average value of the ratio of the gas production to the capacity of a plurality of lithium ion batteries in the first tertiary adjustment group corresponding to the graphite OI value of more than 15 and less than or equal to 30 is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0236] Therefore, according to 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 needs to have high rate charging capability, such as a rate of 2C or more, the graphite OI value range can be designed to be 10-30, and when the rate is 3C or more, the graphite OI value range can be designed to be 15-30.

[0237] [Second adjustment group]

[0238] On the basis of the first basic group, a second adjustment group is set. The design idea of the second adjustment group is to design a series of lithium ion batteries with different graphitization degrees on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0239] The ratio of the gas production to the capacity of the series of lithium ion batteries is obtained after 3000 cycles of the series of lithium ion batteries. It is found that the average value of the ratio of the gas production to the capacity of the several second adjustment group lithium ion batteries corresponding to the graphitization degree of 90% is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and the average value of the ratio of the gas production to the capacity of the several second adjustment group lithium ion batteries corresponding to the graphitization degree less than 90% exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the graphitization degree is higher than 90% and less than or equal to 95 (for cost consideration, the present application does not verify the case where the graphitization degree is higher than 95, but according to the inventor's speculation, the higher the graphitization degree, the better the fast charging performance and the less the gas production), the average value of the ratio of the gas production to the capacity of the several second adjustment group lithium ion batteries is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0240] [Second adjustment group]

[0241] On the basis of the second adjustment group, a second adjustment group is set, and the design idea of the second adjustment group is to set the charge rate to 2C on the basis of the second adjustment group, and control other characteristics to be the same as the second adjustment group.

[0242] The ratio of the gas production to the capacity of the series of lithium ion batteries is obtained after 3000 cycles of the series of lithium ion batteries. It is found that the average value of the ratio of the gas production to the capacity of the several second adjustment group lithium ion batteries corresponding to the graphitization degree of 91% is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and the average value of the ratio of the gas production to the capacity of the several second adjustment group lithium ion batteries corresponding to the graphitization degree less than 91% exceeds the upper limit (0.03495 mmol / Ah) of the first basic group.

[0243] [Third adjustment group]

[0244] On the basis of the first basic group, a third adjustment group is set, and the design idea of the third adjustment group is to design a series of Dv50 different graphite lithium ion batteries on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0245] The ratio of the gas production to the capacity of the series of lithium ion batteries is obtained after 3000 cycles of the series of lithium ion batteries. It is found that when the graphite Dv50 is 10 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third adjustment groups is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the graphite Dv50 is less than 10 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third adjustment groups exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; it is found that when the graphite Dv50 is 30 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third adjustment groups is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the graphite Dv50 is higher than 30 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third adjustment groups exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the graphite Dv50 is between 10 μm and 30 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third adjustment groups is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0246] [Third second adjustment group]

[0247] On the basis of the third adjustment group, a third second adjustment group is further provided, and the difference from the third adjustment group is that the charge rate is changed to 2C.

[0248] It is found that when the graphite Dv50 is 20 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third second adjustment groups is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the graphite Dv50 exceeds 20 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third second adjustment groups exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the graphite Dv50 is between 10 μm and 20 μm, the average value of the ratio of the gas production to the capacity of the series of lithium ion batteries corresponding to the several third second adjustment groups is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0249] [Third third adjustment group]

[0250] On the basis of the third adjustment group, a third third adjustment group is further provided, and the difference from the third adjustment group is that the graphite used is the carbon-coated graphite secondary particles.

[0251] It is found that the Dv50 of the carbon-coated graphite secondary particles is 30 μm, and the average value of the ratio of the gas production to the capacity of the corresponding number of the third third adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group. When the Dv50 of the carbon-coated graphite secondary particles exceeds 30 μm, the average value of the ratio of the gas production to the capacity of the corresponding number of the third third adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group. When the Dv50 of the carbon-coated graphite secondary particles is between 10 μm and 30 μm, the average value of the ratio of the gas production to the capacity of the corresponding number of the third third adjustment group lithium ion batteries is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0252] [Third fourth adjustment group]

[0253] On the basis of the first basic group, the third fourth adjustment group is set. The design idea of the third fourth adjustment group is to design a series of Dv10 different graphite lithium ion batteries on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0254] After 3000 cycles of this series of lithium ion batteries, the ratio of the gas production to the capacity of this series of lithium ion batteries is obtained. It is found that the graphite Dv10 is 3 μm, and the average value of the ratio of the gas production to the capacity of the corresponding number of the third fourth adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group. When the graphite Dv10 is lower than 3 μm, the average value of the ratio of the gas production to the capacity of the corresponding number of the third fourth adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group.

[0255] [Third fifth adjustment group]

[0256] On the basis of the first basic group, the third fifth adjustment group is set. The design idea of the third fifth adjustment group is to design a series of Dv90 different graphite lithium ion batteries on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0257] After 3000 cycles of this series of lithium ion batteries, the ratio of the gas production to the capacity of this series of lithium ion batteries is obtained. It is found that the graphite Dv90 is 40 μm, and the average value of the ratio of the gas production to the capacity of the corresponding number of the third fifth adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group. When the graphite Dv90 is higher than 40 μm, the average value of the ratio of the gas production to the capacity of the corresponding number of the third fifth adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group.

[0258] [Third sixth adjustment group]

[0259] On the basis of the first basic group, a third sixth adjustment group is set, and the design idea of the third sixth adjustment group is to design a series of lithium ion batteries with different Dv99 graphite on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0260] 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, and it is found that when the Dv99 of graphite is 49 μm, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the third sixth adjustment group is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the Dv99 of graphite is higher than 49 μm, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the third sixth adjustment group exceeds the upper limit (0.03495 mmol / Ah) of the first basic group.

[0261] [Fourth adjustment group]

[0262] On the basis of the first basic group, a fourth adjustment group is set, and the design idea of the fourth adjustment group is to design a series of lithium ion batteries with different surface densities of negative electrode sheets on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0263] 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, and it is found that when the surface density of the single-face active material layer of the negative electrode sheet is 0.13 mg / mm 2 , the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the fourth adjustment group is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the surface density of the single-face active material layer of the negative electrode sheet exceeds 0.13 mg / mm 2 , the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the fourth adjustment group exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the surface density of the single-face active material layer of the negative electrode sheet is between 0.07 mg / mm 2 -0.13 mg / mm 2 , the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the fourth adjustment group is lower than the upper limit (0.03495 mmol / Ah) of the first basic group; in addition, when the surface density of the single-face active material layer of the negative electrode sheet is lower than 0.07 mg / mm 2At this time, for the whole negative plate, due to the presence of the negative current collector, the active material on the negative plate is relatively less, especially for the large-capacity battery exceeding 200 Ah, more negative plates are needed to realize large capacity, so for the large-capacity battery, the volume ratio of the current collector will increase, therefore, according to the previous practice of the inventor, the surface density of the single-face active material layer of the negative plate is not less than 0.07 mg / mm 2 .

[0264] [The fifth adjustment group]

[0265] On the basis of the first basic group, the fifth adjustment group is set, and the design idea of the fifth adjustment group is to design a series of lithium ion batteries composed of negative plates 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.

[0266] After 3000 cycles of this series of lithium ion batteries, the ratio of the gas production to the capacity of this series of lithium ion batteries is obtained, it is found that when the compaction density of the single-face active material layer of the negative plate after rolling is 1.74 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion battery of the corresponding several fifth adjustment groups is close to the upper limit (0.03495 mmol / Ah) of the first basic group, when the compaction density of the single-face active material layer of the negative plate after rolling is more than 1.74 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion battery of the corresponding several fifth adjustment groups exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the compaction density of the single-face active material layer of the negative plate after rolling is between 1.32 g / cc and 1.74 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion battery of the corresponding several fifth adjustment groups is lower than the upper limit (0.03495 mmol / Ah) of the first basic group; in addition, when the compaction density of the single-face active material layer of the negative plate after rolling is less than 1.32 g / cc, the principle is similar to the surface density, for the whole negative plate, the mass ratio of the negative current collector is high, especially for the large-capacity battery exceeding 200 Ah, more negative plates are needed to realize large capacity, so for the large-capacity battery, the mass ratio of the current collector will increase, therefore, according to the previous practice of the inventor, the compaction density of the single-face active material layer of the negative plate is not less than 1.32 g / cc. In the fifth adjustment group, the compaction density of the single-face active material layer of the negative plate is 1.7 g / cc after 50 cycles of the lithium ion battery with the compaction density of the single-face active material layer of the negative plate after rolling being 1.74 g / cc; the compaction density of the single-face active material layer of the negative plate is 1.3 g / cc after 50 cycles of the lithium ion battery with the compaction density of the single-face active material layer of the negative plate after rolling being 1.32 g / cc.

[0267] [Sixth adjustment group]

[0268] On the basis of the first basic group, the sixth adjustment group is set, and the design idea of the sixth adjustment group is that, on the basis of the first basic group, a series of lithium ion batteries composed of positive plates with different densities after a series of rolling processes are designed, and other characteristics are controlled to be the same as those of the first basic group.

[0269] After 3000 cycles of this series of lithium ion batteries, the ratio of the gas production amount to the capacity of this series of lithium ion batteries is obtained, and it is found that when the areal density of the single-sided active material layer of the positive plate after rolling is 0.26mg / mm 2 , the average value of the ratio of the gas production amount to the capacity of the corresponding several lithium ion batteries of the sixth adjustment group is close to the upper limit (0.03495mmol / Ah) of the first basic group, when the areal density of the single-sided active material layer of the positive plate after rolling is more than 0.26mg / mm 2 , the average value of the ratio of the gas production amount to the capacity of the corresponding several lithium ion batteries of the sixth adjustment group exceeds the upper limit (0.03495mmol / Ah) of the first basic group; when the areal density of the single-sided active material layer of the positive plate after rolling is between 0.16mg / mm 2 -0.26mg / mm 2 , the average value of the ratio of the gas production amount to the capacity of the corresponding several lithium ion batteries of the sixth adjustment group is lower than the upper limit (0.03495mmol / Ah) of the first basic group. In addition, when the areal density of the single-sided active material layer of the positive plate is less than 0.16mg / mm 2 , for the whole positive plate, due to the existence of the positive current collector, the active material on the positive plate is relatively less, especially for the large-capacity battery exceeding 200Ah, more positive plates are needed to realize large capacity, so the volume ratio of the current collector will increase for the large-capacity battery, therefore, according to the previous practice of the inventor, the application provides that the areal density of the single-sided active material layer of the positive plate is not less than 0.16mg / mm 2 .

[0270] [Seventh adjustment group]

[0271] On the basis of the first basic group, the seventh adjustment group is set, and the design idea of the seventh adjustment group is that, on the basis of the first basic group, a series of lithium ion batteries composed of positive plates with different compaction densities after a series of rolling processes are designed, and other characteristics are controlled to be the same as those of the first basic group.

[0272] The ratio of the gas production to the capacity of the series of lithium ion batteries is obtained after 3000 cycles, and it is found that when the compaction density of the single-sided active material layer of the rolled positive plate is 2.71 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion batteries corresponding to the seventh adjustment group is close to the upper limit of the first basic group (0.03495 mmol / Ah), and when the compaction density of the single-sided active material layer of the rolled positive plate exceeds 2.71 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion batteries corresponding to the seventh adjustment group exceeds the upper limit of the first basic group (0.03495 mmol / Ah); when the compaction density of the single-sided active material layer of the rolled positive plate is between 2.3 g / cc and 2.71 g / cc, the average value of the ratio of the gas production to the capacity of the lithium ion batteries corresponding to the seventh adjustment group is lower than the upper limit of the first basic group (0.03495 mmol / Ah); in addition, when the compaction density of the single-sided active material layer of the rolled positive plate is less than 2.3 g / cc, the mass ratio of the positive current collector is high, especially for large-capacity batteries exceeding 200 Ah, more positive plates are needed to achieve large capacity, so the mass ratio of the current collector will increase for large-capacity batteries, therefore, according to the previous practice of the inventor, the compaction density of the single-sided active material layer of the positive plate is not less than 2.3 g / cc. In the seventh adjustment group, the compaction density of the single-sided active material layer of the rolled positive plate is 2.71 g / cc, and the compaction density of the single-sided active material layer of the negative plate is 2.7 g / cc after 50 cycles; the compaction density of the single-sided active material layer of the rolled positive plate is 1.3 g / cc, and the compaction density of the single-sided active material layer of the positive plate is 1.3 g / cc after 50 cycles, when the compaction density is low, the compaction of the positive plate changes little.

[0273] [The eighth adjustment group]

[0274] On the basis of the first basic group, the eighth adjustment group is set, and the design idea of the eighth adjustment group is to design a series of lithium ion batteries with different porosities of the separator on the basis of the first basic group, and control other characteristics to be the same as the first basic group.

[0275] The ratio of the gas production to the capacity of the series of lithium ion batteries is obtained after 3000 cycles of the series of lithium ion batteries, and it is found that when the porosity of the separator is 50%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the porosity of the separator exceeds 50%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; and it is found that when the porosity of the separator is 30%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group, and when the porosity of the separator is less than 30%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; it is found that when the porosity of the separator is between 30%-50%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth adjustment group lithium ion batteries is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.03495mmol / Ah); on the basis of the first basic group, a eighth third adjustment group is further set, the eighth third adjustment group is different from the first basic group in that the negative plate width is 200 mm (the corresponding cell width, the positive plate width, the negative tab width, and the positive tab width are all different), a series of lithium ion batteries composed of separators with different porosities are designed, after the series of lithium ion batteries are cycled for 3000 times, the ratio of the gas production to the capacity of the series of lithium ion batteries is obtained, it is found that when the separator porosity is 35%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth third adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group, when the separator porosity is lower than 35%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth third adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the separator porosity is between 35%-50%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth third adjustment group lithium ion batteries is lower than the upper limit (0.03495 mmol / Ah) of the first basic group; on the basis of the first basic group, a eighth fourth adjustment group is further set, the eighth fourth adjustment group is different from the first basic group in that the negative plate width is 150 mm (the corresponding cell width, the positive plate width, the negative tab width, and the positive tab width are all different), a series of lithium ion batteries composed of separators with different porosities are designed, after the series of lithium ion batteries are cycled for 3000 times, the ratio of the gas production to the capacity of the series of lithium ion batteries is obtained, it is found that when the separator porosity is 30%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth fourth adjustment group lithium ion batteries is close to the upper limit (0.03495 mmol / Ah) of the first basic group, when the separator porosity is lower than 30%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth fourth adjustment group lithium ion batteries exceeds the upper limit (0.03495 mmol / Ah) of the first basic group; when the separator porosity is between 30%-50%, the average value of the ratio of the gas production to the capacity of the corresponding several eighth fourth adjustment group lithium ion batteries is lower than the upper limit (0.03495 mmol / Ah) of the first basic group.

[0276] [the ninth adjustment group]

[0277] On the basis of the first base group, the ninth adjustment group is set. The design idea of the ninth adjustment group is that, on the basis of the first base group, a series of lithium ion batteries with different DMC contents of electrolyte are designed. The DMC content refers to the mass of DMC divided by the difference between the mass of electrolyte and the mass of lithium salt. The change of DMC content will correspondingly bring about the change of the proportion of EC, DMC, EMC, DEC and other electrolyte solvents, but according to the experience and experimental exploration of the inventor, it is necessary to let the EC content be 30%-40%, and the sum of the mass of EMC and DMC divided by the difference between the mass of electrolyte and the mass of lithium salt be 50%-60% (at this content, since there will be other additives in the electrolyte, therefore in some cases, the sum of the mass of EC, EMC and DMC divided by the difference between the mass of electrolyte and the mass of lithium salt will be less than 100%). Since high DMC content will reduce the viscosity of electrolyte, which is beneficial to reduce gas production and fast charging, but DMC produces a large amount of gas during the charging and discharging process of lithium ion battery, so for the lithium ion battery of the present application, DMC needs a range.

[0278] 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 DMC content is 10%, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the ninth adjustment group is close to the upper limit (0.03495 mmol / Ah) of the first base group, when the DMC content is less than 10%, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the ninth adjustment group exceeds the upper limit (0.03495 mmol / Ah) of the first base group; it is found that when the DMC content is 15%, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the ninth adjustment group is close to the upper limit (0.03495 mmol / Ah) of the first base group, when the DMC content is higher than 15%, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the ninth adjustment group exceeds the upper limit (0.03495 mmol / Ah) of the first base group; when the DMC content is 10%-15%, the average value of the ratio of gas production to capacity of the corresponding several lithium ion batteries of the ninth adjustment group is lower than the upper limit (0.03495 mmol / Ah) of the first base group.

[0279] [Tenth adjustment group]

[0280] On the basis of the first basic group, the tenth adjustment group is set. The design idea of the tenth adjustment group is to design a series of lithium ion batteries with different carboxylic ester contents on the basis of the first basic group. The carboxylic ester content refers to the mass of carboxylic ester divided by the difference between the mass of electrolyte and the mass of lithium salt. Carboxylic ester helps to form a film on the negative electrode during the charging and discharging process of lithium ion battery, improves the ionic conductivity, helps fast charging and reduces gas production at the negative electrode interface, but too much carboxylic ester content will increase the gas production, especially in the fast charging system, the content of carboxylic ester needs to be within a certain range.

[0281] 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, and it is found that when the carboxylic ester content is less than 10%, the average value of the gas production to capacity ratio of the corresponding several tenth adjustment group lithium ion batteries is lower than the upper limit of the first basic group (0.03495 mmol / Ah), it is found that when the carboxylic ester content is 10%, the average value of the gas production to capacity ratio of the corresponding several tenth adjustment group lithium ion batteries is close to the upper limit of the first basic group (0.03495 mmol / Ah), and it is found that when the carboxylic ester content is higher than 10%, the average value of the gas production to capacity ratio of the corresponding several tenth adjustment group lithium ion batteries exceeds the upper limit of the first basic group (0.03495 mmol / Ah).

[0282] [Eleventh adjustment group]

[0283] On the basis of the first basic group, the eleventh adjustment group is set. The eleventh adjustment group only needs 10 lithium ion batteries, and the difference from the first basic group is that the charging method is different. In the constant current stage, instead of charging at a constant current, it is charged at high and low currents alternately. The specific method is: 1C rate charging for 2 minutes, then connecting 0.2C charging for 0.5 minutes, then 1C charging for 2 minutes again, so as to alternate and reciprocate until the charging voltage is reached, and the constant voltage charging is started.

[0284] After 3000 cycles of the high and low current staggered charging method of this group, the gas production of each lithium ion battery in the eleventh adjustment group is reduced compared with the corresponding lithium ion battery in the first basic group, and other conditions are the same as the first basic group.

[0285] [Eleventh adjustment group]

[0286] On the basis of the first basic group, the twelfth adjustment group is set, and only 10 lithium ion batteries are needed, and the difference from the first basic group is that the charging method is different. In the constant current segment, it is no longer charged with a constant current, but is charged with high and low current staggered distribution. The specific method is: 1C rate charging for 2 minutes, then 0.2C charging for 0.5 minutes, then 0.8C charging for 2 minutes, and then 0.2C charging for 0.5 minutes. In this way, the current value of the high current is gradually reduced until the charging cut-off voltage, and the constant voltage charging is started.

[0287] After 3000 cycles of the high and low current staggered distribution charging method of this group, the gas production of each lithium ion battery in the twelfth adjustment group is reduced compared with the corresponding lithium ion battery in the corresponding first basic group, and other conditions are the same as the first basic group.

[0288] [Thirteenth adjustment group]

[0289] On the basis of the first basic group, the thirteenth adjustment group is set, and only 10 lithium ion batteries are needed, and the difference from the first basic group is that the charging method is different. In the constant current segment, it is no longer charged with a constant current, but is charged with high and low current staggered distribution. The specific method is: 1C rate charging for 2 minutes, then stopping charging for 0.1 minutes, then 1C charging for 2 minutes, and then alternating back and forth until the charging cut-off voltage, and the constant voltage charging is started.

[0290] The inventor surprisingly found that after 3000 cycles of the high and low current staggered distribution charging method of this group, the gas production of each lithium ion battery in the thirteenth adjustment group is reduced compared with the corresponding lithium ion battery in the corresponding first basic group, and other conditions are the same as the first basic group.

[0291] Based on the eleventh adjustment group, the twelfth adjustment group and the thirteenth adjustment group, the inventor further summarizes a charging method for reducing gas production, which includes a constant current charging segment and a constant voltage charging segment. In the constant current charging segment, 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, then charging with a third current for a third time, and then 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 further preferably the second current is equal to the fourth current.

[0292] [Second basic group to twelfth basic group]

[0293] On the basis of the first basic group, a second basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 100 Ah by reducing the number of positive and negative electrode sheets, and other conditions are the same. After 3000 cycles, the ratio of the gas production amount N of the lithium ion battery to the capacity L is between 0.01479 mmol / Ah (millimoles per ampere) and 0.02285 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.01479 mmol / Ah (millimoles per ampere) -0.02285 mmol / Ah, 0.11 cm 3 / Ah≤v / L≤0.17 cm 3 / Ah, that is, 0.11L≤v≤0.17L, v is in cubic centimeters (cm 3 ).

[0294] On the basis of the first basic group, a third basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 200 Ah by reducing the number of positive and negative electrode sheets, and other conditions are the same. After 3000 cycles, the ratio of the gas production amount of the lithium ion battery to the capacity is between 0.01882 mmol / Ah (millimoles per ampere) and 0.02689 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.01882 mmol / Ah (millimoles per ampere) -0.02689 mmol / Ah, 0.14 cm 3 / Ah≤v / L≤0.2 cm 3 / Ah, that is, 0.14L≤v≤0.2L, v is in cubic centimeters (cm 3 ).

[0295] On the basis of the first basic group, a fourth basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 400 Ah by increasing the number of positive and negative electrode sheets, and other conditions are the same. After 3000 cycles, the ratio of the gas production amount of the lithium ion battery to the capacity is between 0.03226 mmol / Ah (millimoles per ampere) and 0.04571 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.03226 mmol / Ah (millimoles per ampere) -0.04571 mmol / Ah, 0.24 cm 3Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 )..

[0296] On the basis of the first basic group, the fifth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative plates, the capacity of the lithium ion battery is adjusted to 500 Ah, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.03899 mmol / Ah (millimoles per ampere-hour) and 0.05377 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.03899 mmol / Ah (millimoles per ampere-hour) to 0.05377 mmol / Ah, 0.29 cm 3 Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 )..

[0297] On the basis of the first basic group, the sixth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative plates, the capacity of the lithium ion battery is adjusted to 600 Ah, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.04436 mmol / Ah (millimoles per ampere-hour) and 0.06318 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.04436 mmol / Ah (millimoles per ampere-hour) to 0.06318 mmol / Ah, 0.33 cm 3 Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 Ah, i.e. 0.24L≤v≤0.34L, v is in cubic centimeter (cm 3 )..

[0298] On the basis of the first basic group, a seventh basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 700 Ah by increasing the number of positive and negative plates, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.05109 mmol / Ah (millimoles per ampere) and 0.07259 mmol / 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℃, R as 8.314, gas pressure P as 0.35Mpa, and N / L as 0.05109 mmol / Ah (millimoles per ampere) -0.07259 mmol / Ah, 0.38 cm 3 / Ah≤v / L≤0.54 cm 3 / Ah, that is, 0.38L≤v≤0.54L, v is in cubic centimeters (cm 3 ).

[0299] On the basis of the first basic group, an eighth basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 800 Ah by increasing the number of positive and negative plates, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.05915 mmol / Ah (millimoles per ampere) and 0.08738 mmol / 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℃, R as 8.314, gas pressure P as 0.35Mpa, and N / L as 0.05915 mmol / Ah (millimoles per ampere) -0.08738 mmol / Ah, 0.44 cm 3 / Ah≤v / L≤0.65 cm 3 / Ah, that is, 0.44L≤v≤0.65L, v is in cubic centimeters (cm 3 ).

[0300] On the basis of the first basic group, a ninth basic group is set, which is different from the first basic group in that the capacity of the lithium ion battery is adjusted to 900 Ah by increasing the number of positive and negative plates, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.06856 mmol / Ah (millimoles per ampere) and 0.09545 mmol / 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℃, R as 8.314, gas pressure P as 0.35Mpa, and N / L as 0.06856 mmol / Ah (millimoles per ampere) -0.09545 mmol / Ah, 0.51 cm 3 / Ah≤v / L≤0.71cm 3 / Ah, i.e. 0.51L≤v≤0.71L, v is in cubic centimeters (cm 3 ).

[0301] On the basis of the first basic group, the tenth basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative plates, the capacity of the lithium ion battery is adjusted to 1000 Ah, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.07932 mmol / Ah (millimoles per ampere-hour) and 0.10486 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.07932 mmol / Ah (millimoles per ampere-hour) -0.10486 mmol / Ah, 0.59 cm 3 / Ah≤v / L≤0.78cm 3 / Ah, i.e. 0.59L≤v≤0.78L, v is in cubic centimeters (cm 3 ).

[0302] On the basis of the first basic group, the eleventh basic group is set, which is different from the first basic group in that: by increasing the number of positive and negative plates, the capacity of the lithium ion battery is adjusted to 1100 Ah, and other conditions are the same. Ultimately, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.09141 mmol / Ah (millimoles per ampere-hour) and 0.11696 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.09141 mmol / Ah (millimoles per ampere-hour) -0.11696 mmol / Ah, 0.68 cm 3 / Ah≤v / L≤0.87cm 3 / Ah, i.e. 0.68L≤v≤0.87L, v is in cubic centimeters (cm 3 ).

[0303] On the basis of the first base group, a twelfth base group is set, which is different from the first base group in that the capacity of the lithium ion battery is adjusted to 1200 Ah by increasing the number of positive and negative plates, and other conditions are the same. Finally, the ratio of the gas production amount to the capacity of the lithium ion battery after 3000 cycles is between 0.1062 mmol / Ah (millimoles per ampere-hour) and 0.13174 mmol / 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℃, R as 8.314, the gas pressure P as 0.35Mpa, and N / L as 0.1062 mmol / Ah (millimoles per ampere-hour) to 0.13174 mmol / Ah, 0.79 cm 3 / Ah≤v / L≤0.98 cm 3 / Ah, that is, 0.79L≤v≤0.98L, v is in cubic centimeters (cm 3 ).

[0304] In combination with the above adjustment group and the base group, the inventors further analyze that the ratio of the gas production amount to the capacity of the lithium ion battery increases with the increase of the capacity; in order to give design guidance on the theoretical gas storage space of lithium ion batteries with different capacities, from the perspective of safety as much as possible, the inventors give different design standards for lithium ion batteries with different capacities. For lithium ion batteries with a capacity below 200 Ah, there is no need to pay attention to the problem of theoretical gas storage space, because during the cell assembly process, due to the fact that the tabs are to be welded on the pole, and the width of the tabs is shorter than the width of the plates, there must be a certain space around the tabs due to the cell assembly. This inevitable space is generally around 35 cm 3 , and the maximum gas production amount of the second base group is 17 cm 3 , and the maximum gas production amount of the third base group is 40 cm 3 , so for lithium ion batteries below 200 Ah, the assembly space around the tabs is basically enough for gas accumulation. Therefore, the present application pays more attention to lithium ion batteries of 200 Ah and above, and the theoretical gas storage space of lithium ion batteries of 200 Ah and above is more meaningful.

[0305] For cells of 200 Ah and above:

[0306] In order to be safer and also to improve the accommodation capacity of high temperature abnormalities, it is necessary to enlarge the standard of gas storage space. Specifically, for lithium ion batteries with a capacity of 200 Ah≤L≤300 Ah, the actual gas storage space is not less than the lower limit of the ratio of the gas storage space v to the capacity L of the lithium ion battery of the fourth base group 0.24 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 fourth base group 0.24 cm 3 / Ah is used to calculate the theoretical gas storage space;

[0307] To further reduce the problems caused by gas production, the actual gas storage space should be optimized to be no less than the upper limit of the ratio of gas storage space v to capacity L of the lithium-ion battery in the fourth basic group, which is 0.34 cm. 3 / Ah, the upper limit of the ratio of gas storage space v to capacity L for lithium-ion batteries using the fourth basic group is 0.34cm. 3 / Ah is used to calculate the theoretical gas storage space;

[0308] To balance energy density, the lower limit of the ratio of gas storage space v to capacity L in the fourth basic group of lithium-ion batteries is 0.24 cm². 3 Based on the calculation of the theoretical gas storage space using / Ah, the actual gas storage space is further optimized to be no greater than the upper limit of the ratio of gas storage space v to capacity L of the lithium-ion battery in the fourth basic group, which is 0.34cm. 3 / Ah, the upper limit of the ratio of gas storage space v to capacity L for lithium-ion batteries using the fourth basic group is 0.34cm. 3 / Ah is used to calculate the theoretical maximum gas storage space.

[0309] Similarly, for lithium-ion batteries with a capacity of 300Ah < L ≤ 400Ah:

[0310] The actual gas storage space must be no less than the lower limit of the ratio of gas storage space v to 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 gas storage space v to capacity L for lithium-ion batteries using the fifth basic group is 0.29cm. 3 / Ah is used to calculate the theoretical gas storage space;

[0311] Further optimization requires that the ratio of the gas storage space v to the capacity L of the lithium-ion battery in the fifth basic group be no less than the upper limit of 0.4 cm. 3 / Ah, the upper limit of the ratio of gas storage space v to capacity L for lithium-ion batteries using the fifth basic group is 0.4cm. 3 / Ah is used to calculate the theoretical gas storage space;

[0312] To balance energy density, the lower limit of the ratio of gas storage space v to capacity L for lithium-ion batteries using the fifth basic group is 0.29 cm². 3 Based on the calculation of the theoretical gas storage space using / Ah, the actual gas storage space is further optimized to be no greater than the upper limit of the ratio of gas storage space v to capacity L of the fifth basic group of lithium-ion batteries, which is 0.4cm. 3 / Ah, the upper limit of the ratio of gas storage space v to capacity L for lithium-ion batteries using the fifth basic group is 0.4cm. 3Ah is used to calculate the theoretical maximum gas storage space.

[0313] Other capacity intervals are designed similarly.

[0314] Specifically:

[0315] 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: 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 the lithium ion battery is 200Ah, the theoretical gas storage space is 0.24cm 3 / Ah·200Ah=48cm 3 . Therefore, for the capacity L of the lithium ion battery L≥200Ah, preferably 200Ah≤L≤300Ah, the actual gas storage space v≥48cm 3 .

[0316] In order to further reduce the problems caused by gas production, it is further preferred that the corresponding theoretical gas storage space V0=0.34cm 3 / Ah·L, unit: 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 the lithium ion battery is 200Ah, the theoretical gas storage space is 0.34cm 3 / Ah·200Ah=68cm 3 .

[0317] In order to take into account the energy density of the lithium ion battery, the theoretical maximum gas storage space V0max=0.34cm 3 / Ah·L, unit: cm 3 . Therefore, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0=0.24cm 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 L of the lithium ion battery is 200Ah, the theoretical maximum gas storage space is 68cm 3 .

[0318] 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: 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 > 300 Ah, the theoretical gas storage space V0> 0.29 cm 3 / Ah·300 Ah = 87 cm 3 . That is, when the capacity L of the lithium ion battery satisfies 300 Ah < L≤ 400 Ah, the actual gas storage space v > 87 cm 3 .

[0319] In order to further reduce the problems caused by gas production, it is further preferred that the corresponding theoretical gas storage space V0= 0.4 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.4 cm 3 / Ah·L.

[0320] In order to take into account the energy density of the lithium ion battery, the theoretical maximum gas storage space V0max= 0.4 cm 3 / Ah·L, unit: 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, and at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max= 0.4 cm 3 / Ah·L.

[0321] 3) When the capacity L of the lithium ion battery satisfies 400 Ah < L≤ 500 Ah, the corresponding theoretical gas storage space V0= 0.33 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.33 cm 3 / Ah·L; in order to further reduce the problems caused by gas production, it is further preferred that the corresponding theoretical gas storage space V0= 0.47 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.47 cm 3 / Ah·L.

[0322] In order to take into account the energy density of the lithium ion battery, the theoretical maximum gas storage space V0max= 0.47 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.33 cm 3 / Ah·L, and at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max= 0.47 cm 3 / Ah·L.

[0323] Understandably, in combination with the above 2) and 3), when the capacity L of the lithium ion battery satisfies 300 Ah < L≤ 500 Ah, the actual gas storage space v also satisfies v > 87 cm 3 .

[0324] 4) When the capacity L of the lithium ion battery satisfies 500 Ah < L≤ 600 Ah, the corresponding theoretical gas storage space V0= 0.38 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.38 cm 3 / Ah·L. Considering that L > 500 Ah, the theoretical gas storage space V0> 0.38 cm 3 / Ah·500 Ah = 190 cm 3 . That is, when the capacity L of the lithium ion battery satisfies 500 Ah < L≤ 600 Ah, the actual gas storage space v > 190 cm 3 .

[0325] In order to further reduce the problems brought by gas production, it is further preferred that the corresponding theoretical gas storage space V0= 0.54 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.54 cm 3 / Ah·L.

[0326] In order to take into account the energy density of the lithium ion battery, the theoretical maximum gas storage space V0max= 0.54 cm 3 / Ah·L, unit: cm 3 , then, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.38 cm 3 / Ah·L, and at the same time, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max= 0.54 cm 3 / Ah·L.

[0327] 5) When the capacity L of the lithium ion battery satisfies 600 Ah < L≤ 700 Ah, the corresponding theoretical gas storage space V0= 0.44 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.44 cm 3 / Ah·L; in order to further reduce the problems brought by gas production, it is further preferred that the corresponding theoretical gas storage space V0= 0.65 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0= 0.65 cm 3 / Ah·L.

[0328] In order to balance the energy density of lithium ion battery, the theoretical maximum gas storage space V0max=0.65cm 3 / Ah·L, unit: cm 3 Therefore, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0=0.44cm 3 / Ah·L, and 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.

[0329] Understandably, in combination with the above 4) and 5), when the capacity L of the lithium ion battery satisfies 500Ah 3 .

[0330] 6) When the capacity L of the lithium ion battery satisfies 700Ah 3 / Ah·L, unit: 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 problem brought by gas production, it is further preferred that the corresponding theoretical gas storage space V0=0.71cm 3 / Ah·L, unit: 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.

[0331] In order to balance the energy density of lithium ion battery, the theoretical maximum gas storage space V0max=0.71cm 3 / Ah·L, unit: 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, and 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.

[0332] 7) When the capacity L of the lithium ion battery satisfies 800Ah 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0=0.59cm 3 / Ah·L; in order to further reduce the problem brought by gas production, it is further preferred that the corresponding theoretical gas storage space V0=0.78cm 3 / Ah·L, unit: cm 3, the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.78 cm 3 / Ah·L.

[0333] In order to balance the energy density of lithium ion battery, the theoretical maximum gas storage space V0max = 0.78 cm 3 / Ah·L, unit: 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, and the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max = 0.78 cm 3 / Ah·L.

[0334] 8) When the lithium ion battery capacity L satisfies 900 Ah < L ≤ 1000 Ah, the corresponding theoretical gas storage space V0 = 0.68 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.68 cm 3 / Ah·L; in order to further reduce the problem caused by gas production, the further preferred corresponding theoretical gas storage space V0 = 0.87 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.87 cm 3 / Ah·L.

[0335] In order to balance the energy density of lithium ion battery, the theoretical maximum gas storage space V0max = 0.87 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.68 cm 3 / Ah·L, and the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max = 0.87 cm 3 / Ah·L.

[0336] 9) When the lithium ion battery capacity L satisfies 1000 Ah < L ≤ 1100 Ah, the corresponding theoretical gas storage space V0 = 0.79 cm 3 / Ah·L, unit: cm 3 , 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; in order to further reduce the problem caused by gas production, the further preferred corresponding theoretical gas storage space V0 = 0.98 cm 3 / Ah·L, unit: cm 3 , the actual gas storage space v should be greater than or equal to the theoretical gas storage space V0 = 0.98 cm 3Ah·L.

[0337] In order to take into account the energy density of the lithium ion battery, the theoretical maximum gas storage space V0max=0.98 cm 3 Ah·L, the unit is cm 3 Therefore, 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, and the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max=0.98 cm 3 Ah·L.

[0338] In the actual design of the 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, and the actual gas storage space v 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, the actual gas storage space v should be less than or equal to the theoretical maximum gas storage space V0max;

[0339] The actual gas storage space does not include other components such as support structures between the shell and the battery cell, which will also occupy the volume.

[0340] The above basic groups and adjustment groups are exemplary and are used only to explain the present application and cannot be understood as limiting the present application.

[0341] 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 72 cm 3 , and there is no gas pressure sensor inside the shell. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this embodiment is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycle is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and is cycled to 3000 times.

[0342] Example 2, the difference from the third basic group is that the gas storage space of the lithium ion battery is equal to the theoretical gas storage space 48 cm 3 , and there is no gas pressure sensor inside the shell. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this embodiment is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycle is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and is cycled to 3000 times.

[0343] Example 3, the difference from the eleventh base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 869 cm 3 , and the shell interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this example is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this example is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times.

[0344] Example 4, the difference from the fourth base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 116 cm 3 , and the shell interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this example is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this example is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times.

[0345] Example 5, the difference from the fifth base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 165 cm 3 , and the shell interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this example is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this example is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times.

[0346] Example 6, the difference from the sixth base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 228 cm 3 , and the shell interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this example is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this example is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added during the 40°C charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times.

[0347] Example 7, the difference from the seventh base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 308 cm 3and the housing interior is free of a gas pressure sensor. Additionally, the first portion of 50 lithium ion cells in this example were cycled 3000 cycles at 40 degrees Celsius, and the second portion of 50 lithium ion cells in this example were cycled to 1500 cycles at 40 degrees Celsius, after which each subsequent charge process was: charge to cut-off voltage, prior to the 40 degrees Celsius charge process, add a 3 minute 90°C cycle, otherwise the same conditions as the first portion of 50 lithium ion cells, and cycle to 3000 cycles.

[0348] Example 8, which differs from the eighth base set by the lithium ion cell gas storage space being equal to the theoretical gas storage space 408 cm 3 and the housing interior is free of a gas pressure sensor. Additionally, the first portion of 50 lithium ion cells in this example were cycled 3000 cycles at 40 degrees Celsius, and the second portion of 50 lithium ion cells in this example were cycled to 1500 cycles at 40 degrees Celsius, after which each subsequent charge process was: charge to cut-off voltage, prior to the 40 degrees Celsius charge process, add a 3 minute 90°C cycle, otherwise the same conditions as the first portion of 50 lithium ion cells, and cycle to 3000 cycles.

[0349] Example 9, which differs from the ninth base set by the lithium ion cell gas storage space being equal to the theoretical gas storage space 531 cm 3 and the housing interior is free of a gas pressure sensor. Additionally, the first portion of 50 lithium ion cells in this example were cycled 3000 cycles at 40 degrees Celsius, and the second portion of 50 lithium ion cells in this example were cycled to 1500 cycles at 40 degrees Celsius, after which each subsequent charge process was: charge to cut-off voltage, prior to the 40 degrees Celsius charge process, add a 3 minute 90°C cycle, otherwise the same conditions as the first portion of 50 lithium ion cells, and cycle to 3000 cycles.

[0350] Example 10, which differs from the tenth base set by the lithium ion cell gas storage space being equal to the theoretical gas storage space 680 cm 3 and the housing interior is free of a gas pressure sensor. Additionally, the first portion of 50 lithium ion cells in this example were cycled 3000 cycles at 40 degrees Celsius, and the second portion of 50 lithium ion cells in this example were cycled to 1500 cycles at 40 degrees Celsius, after which each subsequent charge process was: charge to cut-off voltage, prior to the 40 degrees Celsius charge process, add a 3 minute 90°C cycle, otherwise the same conditions as the first portion of 50 lithium ion cells, and cycle to 3000 cycles.

[0351] Comparative Example 1, which differs from the first base set by the lithium ion cell gas storage space being equal to 54 cm 3 (corresponding to a lithium ion cell gas storage space v to capacity L relationship of 0.18 cm 3 / Ah, less than the lower limit of the first basal group by 0.19cm 3 / Ah), and there is no gas pressure sensor inside the casing. In addition, in this embodiment, the first part of 50 lithium-ion batteries is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium-ion batteries is cycled 1500 times at 40 degrees Celsius. The subsequent charging process is as follows: before charging to the cutoff voltage, during the charging process at 40 degrees Celsius, an additional 3 minutes of 90°C cycling is added. Other conditions are the same as those for the first part of 50 lithium-ion batteries, and the cycle is repeated 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, charging and discharging are stopped).

[0352] Comparative Example 2 differs from the third basic group in that the lithium-ion battery gas storage space is equal to 26 cm³. 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 relationship of the third basic group by 0.14cm 3 / Ah), and there is no gas pressure sensor inside the casing. In addition, in this embodiment, the first part of 50 lithium-ion batteries is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium-ion batteries is cycled 1500 times at 40 degrees Celsius. The subsequent charging process is as follows: before charging to the cutoff voltage, during the charging process at 40 degrees Celsius, an additional 3 minutes of 90°C cycling is added. Other conditions are the same as those for the first part of 50 lithium-ion batteries, and the cycle is repeated 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, charging and discharging are stopped).

[0353] Comparative Example 3 differs from the eleventh basic group in that the lithium-ion battery has a gas storage space of 737 cm³. 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 the eleventh basic group (0.68cm). 3 / Ah), and there is no gas pressure sensor inside the casing. In addition, in this embodiment, the first part of 50 lithium-ion batteries is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium-ion batteries is cycled 1500 times at 40 degrees Celsius. The subsequent charging process is as follows: before charging to the cutoff voltage, during the charging process at 40 degrees Celsius, an additional 3 minutes of 90°C cycling is added. Other conditions are the same as those for the first part of 50 lithium-ion batteries, and the cycle is repeated 3000 times (if the explosion-proof valve of a lithium-ion battery is opened, charging and discharging are stopped).

[0354] Comparative Example 4 differs from the fourth basic group in that the lithium-ion battery has a gas storage space of 92 cm³. 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 base group 0.24 cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius for 3000 times, and the second part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius to 1500 times, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycle is added during the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is opened, the charging and discharging is stopped).

[0355] Comparative Example 5, the difference from the fifth base group is that the lithium ion battery gas storage space is equal to 140 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery 0.28 cm 3 / Ah, less than the lower limit of the fifth base group 0.29 cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius for 3000 times, and the second part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius to 1500 times, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycle is added during the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is opened, the charging and discharging is stopped).

[0356] Comparative Example 6, the difference from the sixth base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 192 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery 0.32 cm 3 / Ah, less than the lower limit of the sixth base group 0.33 cm 3 / Ah), and there is no gas pressure sensor inside the shell. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius for 3000 times, and the second part of 50 lithium ion batteries in this embodiment is cycled at 40 degrees Celsius to 1500 times, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycle is added during the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and it is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is opened, the charging and discharging is stopped).

[0357] Comparative Example 7, the difference from the seventh base group is that the lithium ion battery gas storage space is equal to the theoretical gas storage space 259 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery 0.37 cm3 / Ah, less than the lower limit of the seventh basic group 0.38 cm 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 at 40 degrees Celsius for 3000 cycles, and the 50 lithium ion batteries in the second part of this embodiment are cycled at 40 degrees Celsius to 1500 cycles, and then each charging process is: charged to the cut-off voltage before, increase 3 minutes of 90°C cycle during the 40 degrees Celsius charging process, other conditions are the same as the 50 lithium ion batteries in the first part, and cycle to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery bursts, stop charging and discharging); In addition, the 50 lithium ion batteries in the first part of this embodiment are cycled at 40 degrees Celsius for 3000 cycles, and the 50 lithium ion batteries in the second part of this embodiment are cycled at 40 degrees Celsius to 1500 cycles, and then each charging process is: charged to the cut-off voltage before, increase 3 minutes of 90°C cycle during the 40 degrees Celsius charging process, other conditions are the same as the 50 lithium ion batteries in the first part, and cycle to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery bursts, stop charging and discharging).

[0358] Comparative Example 8, the difference from the eighth basic group is that the lithium ion battery gas storage space is equal to 344 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery 0.43 cm 3 / Ah, less than the lower limit of the eighth basic group 0.44 cm 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 at 40 degrees Celsius for 3000 cycles, and the 50 lithium ion batteries in the second part of this embodiment are cycled at 40 degrees Celsius to 1500 cycles, and then each charging process is: charged to the cut-off voltage before, increase 3 minutes of 90°C cycle during the 40 degrees Celsius charging process, other conditions are the same as the 50 lithium ion batteries in the first part, and cycle to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery bursts, stop charging and discharging).

[0359] Comparative Example 9, the difference from the ninth basic group is that the lithium ion battery gas storage space is equal to 450 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery 0.50 cm 3 / Ah, less than the lower limit of the ninth basic group 0.51 cm 3 / Ah, and the housing interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this embodiment is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added in the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is broken, the charging and discharging is stopped).

[0360] Comparative Example 10, the difference from the tenth basic group is that the lithium ion battery gas storage space is equal to 580 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery is 0.58 cm 3 / Ah, less than the lower limit of the tenth basic group 0.59 cm 3 / Ah, and the housing interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this embodiment is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added in the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is broken, the charging and discharging is stopped).

[0361] Comparative Example 11, the difference from the first basic group is that the lithium ion battery gas storage space is equal to 66 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery is 0.22 cm 3 / Ah, less than the upper limit of the first basic group 0.26 cm 3 / Ah, and the housing interior has no gas pressure sensor. In addition, the first part of 50 lithium ion batteries in this embodiment is cycled 3000 times at 40 degrees Celsius, and the second part of 50 lithium ion batteries in this embodiment is cycled to 1500 times at 40 degrees Celsius, and then each charging process is: before charging to the cut-off voltage, 3 minutes of 90°C cycling is added in the 40 degrees Celsius charging process, other conditions are the same as the first part of 50 lithium ion batteries, and is cycled to 3000 times (if the explosion-proof valve of a certain lithium ion battery is broken, the charging and discharging is stopped).

[0362] Comparative Example 12, the difference from the third basic group is that the lithium ion battery gas storage space is equal to 36 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery is 0.18 cm 3 / Ah, less than the upper limit of the third basic group 0.2 cm 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, an increase of 3 minutes of 90°C cycling, the same conditions as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery bursts, stop charging and discharging).

[0363] Comparative Example 13, which differs from the eleventh basic group in that the lithium-ion battery gas storage space is equal to 836 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium-ion battery of 0.76 cm 3 / Ah, less than the upper limit of the eleventh basic group of 0.87 cm 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, an increase of 3 minutes of 90°C cycling, the same conditions as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery bursts, stop charging and discharging).

[0364] Comparative Example 14, which differs from the fourth basic group in that the lithium-ion battery gas storage space is equal to 114 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium-ion battery of 0.28 cm 3 / Ah, less than the upper limit of the fourth basic group of 0.34 cm 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, an increase of 3 minutes of 90°C cycling, the same conditions as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery bursts, stop charging and discharging).

[0365] Comparative Example 15, which differs from the fifth basic group in that the lithium-ion battery gas storage space is equal to 155 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium-ion battery of 0.31 cm 3 / Ah, less than the upper limit of the fifth basic group of 0.4 cm 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90°C cycling was added, other conditions were the same as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery was blown off, the charging and discharging was stopped).

[0366] Comparative Example 16, the difference from the sixth basic group is that the gas storage space of the lithium-ion battery is equal to 216 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.36 cm 3 / Ah, less than the upper limit 0.47 cm of the sixth basic group 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90°C cycling was added, other conditions were the same as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery was blown off, the charging and discharging was stopped).

[0367] Comparative Example 17, the difference from the seventh basic group is that the gas storage space of the lithium-ion battery is equal to 294 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium-ion battery is 0.42 cm 3 / Ah, less than the upper limit 0.54 cm of the seventh basic group 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium-ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, after which each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90°C cycling was added, other conditions were the same as the first part of 50 lithium-ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium-ion battery was blown off, the charging and discharging was stopped).

[0368] Comparative Example 18, the difference from the eighth basic group is that the gas storage space of the lithium-ion battery is equal to 392 cm 3 (corresponding to the 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 0.65 cm of the eighth basic group 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, and then each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90 degrees Celsius cycling was added, other conditions were the same as the first part of 50 lithium ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery was blown off, the charging and discharging was stopped).

[0369] Comparative Example 19, the difference from the ninth basic group is that the lithium ion battery gas storage space is equal to 513 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery is 0.57 cm 3 / Ah, less than the upper limit 0.71 cm of the ninth basic group 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, and then each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90 degrees Celsius cycling was added, other conditions were the same as the first part of 50 lithium ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery was blown off, the charging and discharging was stopped).

[0370] Comparative Example 20, the difference from the tenth basic group is that the lithium ion battery gas storage space is equal to 660 cm 3 (corresponding to the relationship between the gas storage space v and the capacity L of the lithium ion battery is 0.66 cm 3 / Ah, less than the upper limit 0.78 cm of the tenth basic group 3 / Ah) and without a gas pressure sensor inside the housing. In addition, the first part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius for 3000 cycles, and the second part of 50 lithium ion batteries in this example were cycled at 40 degrees Celsius to 1500 cycles, and then each charging process was: charged to the cut-off voltage, before the 40 degrees Celsius charging process, 3 minutes of 90 degrees Celsius cycling was added, other conditions were the same as the first part of 50 lithium ion batteries, and cycled to 3000 cycles (if the explosion-proof valve of a certain lithium ion battery was blown off, the charging and discharging was stopped).

[0371] Comparative Example 21, the difference from the first basic group is that the positive active material uses lithium nickel cobalt manganese oxide with an atomic ratio of nickel content to the total content of nickel, cobalt and manganese of 0.8, and the corresponding adjustment of the cut-off voltage of charging and discharging, and the thickness and compaction density of the positive electrode film, other conditions are similar to the first basic group.

[0372] The explosion-proof valves of the lithium ion batteries in Examples 1-10 were not burst after 3000 cycles;

[0373] In Comparative Examples 1-10, the first part of lithium ion batteries in each of the comparative examples were not burst, and the second part of lithium ion batteries in each of the comparative examples had 15-25 lithium ion batteries burst;

[0374] In Comparative Examples 11-20, the first part of lithium ion batteries in each of the comparative examples were not burst, and the second part of lithium ion batteries in each of the comparative examples had 1-10 lithium ion batteries burst;

[0375] In Comparative Example 21, 70 lithium ion batteries were burst;

[0376] Comparative Example 21 and Example 1 show 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 burst. From the perspective of gas production, a lithium-containing phosphate material is preferred;

[0377] Examples 1-10, Comparative Examples 1-10 and Comparative Examples 11-20 show that when the actual gas storage space is not less than the theoretical gas storage space, not only the normally cycled lithium ion batteries will not be burst, but also the lithium ion batteries have the ability to resist high-temperature abnormalities, thereby making the lithium ion batteries safer. Comparative Examples 1-10 and Comparative Examples 11-20 show that although the actual gas storage space is less than the theoretical gas storage space, the closer to the theoretical gas storage space, the higher the ability to resist high-temperature abnormalities.

[0378] The present application considers multiple factors from the positive electrode active material and the negative electrode active material, to the positive electrode sheet and the negative electrode sheet, to the separator and the electrolyte, to minimize gas production, thereby reducing unnecessary internal space, so as to be able to set more active materials and improve the capacity of the lithium ion battery. At the same time, on the basis of the foregoing measures to reduce gas production, the gas storage space is also optimized, so that the explosion-proof valve of the lithium ion battery of the present application will not be burst under normal use conditions, and has the ability to resist high-temperature abnormalities, thereby being able to reduce the risk of lithium ion battery scrap caused by the burst of the explosion-proof valve.

[0379] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium ion battery, comprising a shell, an electrode core, and an electrolyte, the electrode core and the electrolyte being arranged in the interior of the shell, the electrode core comprising a positive electrode sheet, a negative electrode sheet, and a separator, the separator being arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer being electrically connected with the positive electrode current collector, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being electrically connected with the negative electrode current collector; at least one side of the negative electrode current collector is provided with the negative electrode active material layer, 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 comprises a negative electrode active material, the negative electrode active material comprises 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%; at least one side of the positive electrode current collector is provided with the positive electrode active material layer, 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, the positive electrode active material comprises lithium-containing phosphates and a carbon layer on the surface of the lithium-containing phosphates; 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. characterized in that The capacity L of the lithium ion battery is in the range of 600 Ah < L ≤ 700 Ah, the theoretical gas storage space V0 of the lithium ion battery is V0, 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. 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. The capacity L of the lithium ion battery is ≥ 200 Ah, and the actual gas storage space v of the lithium ion battery is ≥ 48 cm 3 .

2. The lithium-ion battery of claim 1, wherein, The capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0=0.24 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 300 Ah < L≤ 400 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.29 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 400 Ah < L≤ 500 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.33 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 500 Ah < L≤ 600 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0= 0.38 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 600 Ah < L≤ 700 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0= 0.44 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 700 Ah < L < 800 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.51 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 800 Ah < L≤ 900 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0= 0.59 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 900 Ah < L < 1000 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.68 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 1000 Ah < L < 1100 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.79 cm 3 / Ah·L; The actual gas storage space v of the lithium ion battery is less than or equal to the maximum theoretical gas storage space V0max of the lithium ion battery.

3. The lithium-ion battery of claim 1, wherein, The capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0=0.34 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 300 Ah < L≤ 400 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.4 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 400 Ah < L≤ 500 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.47 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 500 Ah < L≤ 600 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0= 0.54 cm 3 / Ah·L; or, At least part of the surface of the graphite is coated with a carbon layer, the Dv90 of the graphite is less than or equal to 40 μm, the Dv10 of the graphite is greater than or equal to 3 μm, and the Dv99 of the graphite is less than or equal to 49 μm; and / or, the OI value of the graphite is in the range of 3 to 30; and / or, the graphitization degree of the graphite is in the range of 90% to 95%. V0 = 0.65 cm 3 / Ah-L; or, The capacity L of the lithium ion battery is 700 Ah < L < 800 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.71 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 800 Ah < L≤ 900 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0= 0.78 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 900 Ah < L < 1000 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.87 cm 3 / Ah·L; or, The capacity L of the lithium ion battery is 1000 Ah < L < 1100 Ah, the theoretical gas storage space of the lithium ion battery is V0, V0 = 0.98 cm 3 / Ah·L; The OI value of the graphite is in the range of 10 to 30.

4. The lithium-ion battery of claim 2, wherein, The capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max=0.34 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 300 Ah < L ≤ 400 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.4 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 400 Ah < L ≤ 500 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.47 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 500 Ah < L ≤ 600 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.54 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 600 Ah < L < 700 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.65 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 700 Ah < L < 800 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.71 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 800 Ah < L < 900 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.78 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 900 Ah < L < 1000 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.87 cm3 / Ah·L; or, 3 / Ah·L; or, The capacity L of the lithium ion battery is 1000 Ah < L < 1100 Ah, the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.98 cm3 / Ah·L; and the theoretical maximum gas storage space V0max of the lithium ion battery is V0max = 0.98 cm3 / Ah·L. 3 / Ah·L; The graphitization degree of the graphite is in the range of 91% to 95%; and / or, the OI value of the graphite is in the range of 15 to 30.

5. The lithium-ion battery of any one of claims 1-4, wherein, The compaction density of the single-side active material layer of the negative electrode sheet is in the range of 1.3 g / cc to 1.7 g / cc. The compaction density of the single-side active material layer of the positive electrode sheet is in the range of 2.3 g / cc to 2.7 g / cc. The separator comprises a base film and a coating layer, the coating layer is bonded to the surface of the base film and partially located in the interior of the base film, and the porosity of the separator is in the range of 30% to 50%.

6. The lithium-ion battery of claim 5, wherein, The thickness of the carbon layer on the surface of the graphite is in the range of 0.5 μm to 2 μm.

7. The lithium-ion battery of claim 5, wherein, The negative electrode active material layer further comprises carbon tubes, the carbon tubes comprise at least one of oligomeric wall carbon tubes and single-wall carbon tubes. The negative electrode active material layer further comprises silicon, when the capacity L of the lithium ion battery is in the range of 200 Ah ≤ L ≤ 500 Ah, the mass content of the silicon in the negative electrode active material layer is in the range of 1% to 10%.

8. The lithium-ion battery of any one of claims 1-4, wherein, The areal density of the single-sided active material layer of the negative electrode sheet is between 0.07 mg / mm 2 -0.13 mg / mm 2 .

9. The lithium-ion battery of any one of claims 1-4, wherein, ​ 10. The lithium-ion battery of any one of claims 1-4, wherein, The areal density of the single-sided active material layer of the positive electrode sheet is between 0.16 mg / mm 2 -0.26 mg / mm 2 .

11. The lithium-ion battery of any one of claims 1-4, wherein, ​ 12. The lithium-ion battery of any one of claims 1-4, wherein, ​ 13. The lithium-ion battery of claim 5, wherein, ​ 14. The lithium-ion battery of any one of claims 1-4, wherein, ​ 15. The lithium-ion battery of any one of claims 1-4, wherein, ​ 16. The lithium-ion battery of claim 15, wherein, In the thickness direction of the negative electrode active material layer, the silicon is distributed on the side of the negative electrode active material layer close to the negative electrode current collector.

17. The lithium-ion battery of any one of claims 1-4, wherein, The lithium-containing phosphate includes lithium iron phosphate, and a metal element is doped in the lithium iron phosphate, the metal element being selected from at least one of titanium or vanadium.

18. The lithium-ion battery of claim 17, wherein, The mass ratio of the doped metal element to the mass of the positive electrode active material is not more than 0.4%.

19. The lithium-ion battery of claim 18, wherein, The doped metal element includes titanium, and the mass ratio of the titanium to the mass of the positive electrode active material is 0.2%-0.4%.

20. The lithium-ion battery of claim 18, wherein, The doped metal element includes titanium and vanadium, the mass ratio of the titanium to the mass of the positive electrode active material is 0.1%-0.2%, and the mass ratio of the vanadium to the mass of the positive electrode active material is 0.01%-0.05%.

21. The lithium-ion battery of any one of claims 1-4, wherein, The positive electrode active material layer includes carbon tubes, and the carbon tubes include at least one of few-walled carbon tubes and single-walled carbon tubes.

22. The lithium-ion battery of any one of claims 1-4, wherein, 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.

23. The lithium-ion battery of claim 22, wherein, The lithium salt further includes lithium bisfluorosulfonylimide.

24. The lithium-ion battery of claim 23, wherein, The volume molar content of the lithium hexafluorophosphate is higher than the volume molar content of the lithium bisfluorosulfonylimide.

25. The lithium-ion battery of claim 24, wherein, The capacity L of the lithium ion battery is 200 Ah≤L≤300 Ah, and the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is 0.1%-9%.

26. The lithium-ion battery of claim 25, wherein, The mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is 0.1%-5%.

27. The lithium-ion battery of claim 24, wherein, The capacity L of the lithium ion battery is 300 Ah 28. The lithium-ion battery of claim 27, wherein, The mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is 1%-5%.

29. The lithium-ion battery of claim 23, wherein, The solvent includes EC, DMC, EMC, and DEC, the content of the EC is 30%-40%, the sum of the mass of the DMC and the EMC is greater than the mass of the EC, and 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).

30. The lithium-ion battery of claim 29, wherein, The total content of the EMC and the DMC is 50%-60%, and 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).

31. The lithium-ion battery of claim 30, wherein, The content of the DMC is 10%-15%, and 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).

32. The lithium-ion battery of claim 23, wherein, The electrolyte further includes a carboxylic acid ester, and the content of the carboxylic acid ester is not more than 10%, and the content of the carboxylic acid ester is the mass of the carboxylic acid ester / (the difference between the mass of the electrolyte and the mass of the lithium salt).

33. The lithium-ion battery of any one of claims 23-32, wherein, The negative electrode sheet has a square structure, the width of the negative electrode sheet is 100 mm-150 mm, and the porosity of the separator is 30%-50%.

34. The lithium-ion battery of any one of claims 23-32, wherein, The negative electrode sheet has a square structure, the width of the negative electrode sheet is 200 mm-250 mm, and the porosity of the separator is 35%-50%.

35. The lithium-ion battery of claim 33, wherein, The aspect ratio of the battery cell is 6-8.

36. The lithium-ion battery of claim 34, wherein The length-width ratio of the battery cell is between 2.8 and 4.

37. The lithium-ion battery of any one of claims 1-4, wherein, The negative electrode tab is electrically connected to the negative electrode current collector, and the positive electrode tab is electrically connected to the positive electrode current collector. The shell comprises a positive pole column, a negative pole column, and an explosion-proof valve, the positive pole column is electrically connected with the positive pole tab, the negative pole column is electrically connected with the negative pole tab, the explosion-proof valve is arranged at the first end of the shell, at least one of the positive pole column and the negative pole column is also arranged at the first end of the shell, the opening air pressure of the explosion-proof valve is 0.55-0.65 Mpa, the ratio of the area of the explosion-proof valve to the capacity of the lithium ion battery ranges from 0.5 mm 2 / Ah-1.5 mm 2 / Ah.

38. The lithium-ion battery of claim 37, wherein, The positive electrode post is arranged at the first end of the shell, the positive electrode tab is arranged on the short side of the positive electrode current collector, and a first upper exhaust passage is formed between the upper end of the positive electrode tab and the shell.

39. The lithium-ion battery of claim 38, wherein, The overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage is more than 80% along the airflow direction of the first upper exhaust passage.

40. The lithium-ion battery of claim 38 or 39, wherein, The overlap degree of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage is the ratio of the area of the overlapping area of the projection area of the explosion-proof valve and the projection area of the first upper exhaust passage to the area of the projection area of the first upper exhaust passage.

41. The lithium-ion battery of claim 40, wherein, The positive electrode tabs are asymmetrically distributed on the short side of the positive electrode current collector.

42. The lithium-ion battery of claim 37, wherein, 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 along the width direction of the battery cell, and the first distance is greater than the second distance.

43. The lithium-ion battery of claim 42, wherein, The negative electrode post is arranged at the first end of the shell, the negative electrode tab is arranged on the short side of the negative electrode current collector, and a second upper exhaust passage is formed between the upper end of the negative electrode tab and the shell.

44. The lithium-ion battery of any one of claims 42 or 43, wherein, The overlap degree of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage is more than 80% along the airflow direction of the second upper exhaust passage.

45. The lithium-ion battery of claim 44, wherein, The overlap degree of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage is the ratio of the area of the overlapping area of the projection area of the explosion-proof valve and the projection area of the second upper exhaust passage to the area of the projection area of the second upper exhaust passage.

46. The lithium-ion battery of any one of claims 42 or 43, wherein, The ratio of the width of the negative electrode tab to the width of the short side of the negative electrode current collector is within the range of 0.5-0.

8.

47. The lithium-ion battery of claim 46, wherein, The ratio of the width of the negative electrode tab to the width of the short side of the negative electrode current collector is within the range of 0.6-0.

8.

48. The lithium-ion battery of any one of claims 1-4, wherein, The negative electrode tabs are asymmetrically distributed on the short side of the negative electrode current collector.

49. The lithium-ion battery of any one of claims 1-4, wherein, 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 along the width direction of the battery cell, and the third distance is greater than the fourth distance. 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. The positive electrode current collector is an aluminum foil, the thickness of the single-sided active material layer of the positive electrode sheet is ≤95 μm, and the thickness of the positive electrode current collector is D1, and the numerical range of D1 is 11 μm-13.5 μm.

50. The lithium-ion battery of any one of claims 1-4, wherein, The thickness of the single-sided active material layer of the positive electrode sheet is > 95 μm, and the thickness of the positive electrode current collector is D2, the value of D2 is in the range of 13.5 μm-16 μm.

51. The lithium-ion battery of any one of claims 1-4, wherein, The negative electrode active material layer further comprises silicon; the thickness of the single-sided active material layer of the negative electrode sheet is in the range of 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%.

52. The lithium-ion battery of any one of claims 1-4, wherein, The negative electrode active material layer further comprises silicon; the thickness of the single-sided active material layer of the negative electrode sheet is in the range of 70 μm-80 μm, and the mass content of the silicon in the negative electrode active material layer is in the range of 1%-8%.

53. The lithium-ion battery of any one of claims 1-4, wherein, The negative electrode active material layer further comprises silicon; the thickness of the single-sided active material layer of the negative electrode sheet is in the range of 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%.

54. The lithium-ion battery of claim 32, wherein, The capacity L of the lithium ion battery is in the range of 200 Ah≤L≤300 Ah, the content of the carboxylic acid ester is in the range of 5%-10%, and the mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is in the range of 0.1%-5%.

55. The lithium-ion battery of claim 32, wherein, The capacity L of the lithium ion battery is in the range of 300 Ah 56. The lithium-ion battery of claim 5, wherein, The negative electrode active material comprises primary particles composed of the graphite and the carbon layer on the surface of the graphite, and the Dv50 of the primary particles is in the range of 10 μm-20 μm.

57. The lithium-ion battery of claim 56, wherein, The negative electrode active material comprises secondary particles, the secondary particles comprise agglomerates of the primary particles, and the Dv50 of the secondary particles is in the range of 10 μm-30 μm.

58. The lithium-ion battery of claim 57, wherein, The surface of the agglomerates comprises a carbon layer.

59. A charging method characterized by, The charging method is used for charging the lithium ion battery in any one of claims 1-58, and the charging method comprises a first charging stage and a second charging stage, the voltage of the first charging stage is less than the voltage of the second charging stage, the voltage of the first charging stage increases with the increase of the charging time, the voltage of the second charging stage is constant, and the first charging stage comprises the following charging process: charging the lithium ion battery with a first current for a first time; charging the lithium ion battery with a second current for a second time; charging the lithium ion battery with a third current for a third time; charging the lithium ion battery 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.

60. The charging method of claim 59, wherein, The second current is equal to the fourth current.

61. A lithium-ion battery system, characterized by, The lithium ion battery in any one of claims 1-58 and a management module are included, the management module comprises a charging program for the lithium ion battery, and the charging program implements the charging method in claim 59 or 60.

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