Lithium-ion battery and electric device

Abstract

A lithium-ion battery and an electric device. The electrolyte filling ratio a of the lithium-ion battery satisfies: 2.2 g / Ah≤a≤2.8 g / Ah. The lithium-ion battery comprises an electrolyte, which comprises a first solvent and an additive, wherein the viscosity η of the first solvent satisfies: η≤0.6 mPa / s; the additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, ethylene sulfate and 1,3-propane sultone; and the mass content m of the additive in the electrolyte satisfies: 5%≤m≤12%. The electrolyte filling ratio is small, and the lithium-ion battery having the electrolyte that comprises a carboxylic ester solvent, an ether solvent and / or a nitrile solvent has good cycle performance.

Description

Lithium-ion batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202410303747.8, filed on March 18, 2024, entitled “Lithium-ion battery and power-consuming device.” The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

[0003] The present application relates to the field of batteries, and more specifically, to a lithium-ion battery and an electrical device. Background Art

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

[0005] As a crucial component of lithium-ion batteries, the electrolyte significantly impacts their performance. However, solvents with lower viscosity are beneficial for improving the electrolyte's ionic conductivity, thereby enhancing the fast-charging performance of lithium-ion batteries. However, low-viscosity solvents often suffer from poor compatibility with the anode, and some components are prone to gassing, which can severely impact the cycling performance of lithium-ion batteries. Therefore, improving the cycling performance of lithium-ion batteries is a pressing technical challenge.

[0006] Summary of the Invention

[0007] The present application is made in view of the above technical problems, and its purpose is to provide a lithium ion battery and an electrical device, wherein the lithium ion battery has good cycle performance.

[0008] In a first aspect, a lithium-ion battery is provided, wherein the filling coefficient a of the lithium-ion battery satisfies the following conditions: 2.2 g / Ah ≤ a ≤ 2.8 g / Ah; the lithium-ion battery includes an electrolyte, the electrolyte including a first solvent and an additive; the viscosity η of the first solvent satisfies the following conditions: η ≤ 0.6 mPa / s; the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, and 1,3-propane sultone; and the mass content m of the additive in the electrolyte satisfies the following conditions: 5% ≤ m ≤ 12%. In an embodiment of the present application, the lithium-ion battery has a small filling coefficient and the electrolyte includes a low-viscosity solvent with poor compatibility with the negative electrode. By controlling the mass content of the additive within a wide range, the poor compatibility of the low-viscosity solvent with the negative electrode can be improved, thereby improving the cycling performance of the lithium-ion battery having a small filling coefficient and an electrolyte including a low-viscosity solvent.

[0009] If the mass content of the additive is too high, the direct current resistance (DCR) of the lithium-ion battery may be increased. Therefore, in the embodiments of the present application, by controlling the content of the additive to be relatively large and within an appropriate range, the cycle performance of the lithium-ion battery can be improved and the effect of the additive on the DCR of the lithium-ion battery can be controlled.

[0010] In one possible implementation, 2.4 g / Ah≤a≤2.6 g / Ah.

[0011] In a possible implementation, the additive includes at least one of ethylene carbonate and fluoroethylene carbonate.

[0012] In a possible implementation, the first solvent includes at least one of a carboxylate solvent, an ether solvent, and a nitrile solvent.

[0013] Carboxylate, ether, and nitrile solvents are prone to generating gas at the negative electrode, further impacting the battery's cycling performance. By controlling the additive content within a wide range in lithium-ion batteries with a small filling coefficient and containing these solvents as electrolytes, the problem of gassing at the negative electrode can be mitigated, thereby improving the cycling performance of lithium-ion batteries with small filling coefficients and containing these solvents as electrolytes.

[0014] In a possible implementation, the carboxylate solvent includes: R1-COO-R2, wherein R1 and R2 independently include at least one of an alkyl group with 1 to 5 carbon atoms and a halogenated alkyl group with 1 to 5 carbon atoms.

[0015] In a possible implementation, the ether solvent includes at least one of diethyl ether, ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0016] In a possible implementation, the nitrile solvent includes at least one of succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile.

[0017] In a possible implementation, the mass content X of the first solvent in the electrolyte satisfies: 10%≤X≤70%.

[0018] In one possible implementation, 20%≤X≤60%.

[0019] In a possible implementation, the electrolyte further includes a second solvent, and the second solvent includes at least one of ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

[0020] In a possible implementation, the second solvent includes ethylene carbonate.

[0021] In a possible implementation, the mass content Y of the second solvent in the electrolyte satisfies: 15%≤Y≤35%.

[0022] In a possible implementation, 25%≤Y≤35%.

[0023] In the embodiments of the present application, by selecting a carbonate solvent with a higher dielectric constant as the second solvent, it is beneficial to further improve the conductivity of the electrolyte; and, the carbonate solvent has good electrochemical stability, and it and the first solvent form a solvent for the electrolyte through a suitable ratio, which can form an electrolyte system with suitable viscosity and high conductivity, thereby improving the fast charging capability of the lithium-ion battery, that is, the fast charging performance.

[0024] In a possible implementation, the conductivity σ of the electrolyte satisfies: 13 mS / cm≤σ≤20 mS / cm.

[0025] In a possible implementation, the volume energy density VED of the lithium-ion battery satisfies: VED ≥ 425Wh / L.

[0026] In a possible implementation, the group margin x of the lithium-ion battery satisfies: x≥97.5%.

[0027] In one possible implementation, the lithium-ion battery includes a positive electrode sheet, and the compaction density ρ1 of the positive electrode sheet satisfies: ρ1 ≥ 2.6 g / cm 3 .

[0028] In a possible implementation, the positive electrode plate includes a positive electrode active material, and the loading amount m of the positive electrode active material per unit area of ​​the positive electrode plate satisfies: m1 ≥ 0.22 mg / mm 2 .

[0029] In one possible implementation, the ion battery includes a negative electrode sheet, and the compaction density ρ2 of the negative electrode sheet satisfies: ρ2≥1.7g / cm 3 .

[0030] In one possible implementation, the negative electrode plate includes a negative electrode active material, and the loading amount of the negative electrode active material per unit area of ​​the negative electrode plate satisfies: m1≥0.07 mg / mm 2 .

[0031] In one possible implementation, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector; at a position close to the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50 of the negative electrode active material satisfies: 14.5μm≤Dv50≤19.5μm; at a position away from the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50' of the negative electrode active material satisfies: 10.2μm≤Dv50'≤15.5μm.

[0032] In a second aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in any possible implementation of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0034] FIG1 is a schematic diagram of a battery cell.

[0035] FIG2 is a schematic diagram of a battery module.

[0036] FIG3 is a schematic diagram of a battery pack.

[0037] FIG4 is another schematic diagram of a battery pack. DETAILED DESCRIPTION

[0038] Below, the embodiments of the lithium-ion battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0039] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0042] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0045] As mentioned, the "filling coefficient" refers to the ratio of the electrolyte filling volume to the rated capacity of the battery. In the embodiments of this application, the filling volume can be approximated as the electrolyte retention volume. The rated capacity of a battery refers to the amount of electricity discharged when the battery is discharged to the cutoff voltage under specified charge and discharge conditions. The specified charge and discharge conditions can be referenced to the ICE standard.

[0046] Where mentioned, "carboxylate solvent" refers to an organic solvent including a -COO- group; "ether solvent" refers to an organic solvent including an -O- group; and "nitrile solvent" refers to an organic solvent including a -CN group.

[0047] As mentioned, "group margin" refers to the ratio of the internal cross-sectional area of ​​a battery cell to its maximum internal cross-sectional area. For example, if a wound battery cell is cut horizontally, the ratio of the cross-sectional area of ​​each component of the wound electrode assembly to the cross-sectional area of ​​the battery cell is the group margin for that battery cell.

[0048] Next, embodiments of the present application are introduced.

[0049] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have thus achieved great development. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0050] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, they are also called rocking-chair batteries. During the charging process, lithium ions are released from the positive electrode active material, transferred through the electrolyte to the negative electrode, and then embedded in the negative electrode active material. During the discharge process, lithium ions are released from the negative electrode active material, transferred through the electrolyte to the positive electrode, and then embedded in the positive electrode active material.

[0051] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to electrochemical reactions, and the "extraction", "delithiation" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to electrochemical reactions. As the application scope of lithium-ion batteries becomes wider and wider, and the usage scenarios become more and more diverse, new demands are put forward for the energy density of lithium-ion batteries, and lithium-ion batteries are developing towards high energy density. As an important component of lithium-ion batteries, the electrolyte plays the role of conducting ions, and the composition and properties of the electrolyte directly affect the performance of the lithium-ion battery. At present, single-component solvents can no longer meet the application requirements of lithium-ion batteries. The performance of a solvent system composed of two or more solvents is better than that of a single-component solvent, and it has become a way to optimize the performance of the electrolyte and improve the performance of lithium-ion batteries.

[0052] Solvents with lower viscosity help improve electrolyte conductivity, thereby enhancing the fast-charging performance of lithium-ion batteries. However, in practical applications, low-viscosity solvents suffer from poor compatibility with the negative electrode, which can negatively impact the cycling performance of lithium-ion batteries. This issue is particularly pronounced for lithium-ion batteries with low filling coefficients.

[0053] Among the many solvents with lower viscosities, carboxylate, ether, and nitrile solvents are often added to electrolytes as co-solvents due to their low viscosity and low freezing point. This allows them to form highly conductive electrolyte systems, helping to improve the charging capacity and low-temperature performance of lithium-ion batteries. However, carboxylate, ether, and nitrile solvents are prone to film-forming side reactions with the negative electrode during battery cycling, producing gas, which is detrimental to the cycling performance of lithium-ion batteries. For lithium-ion batteries with smaller injection coefficients, the cycling drop problem caused by electrolyte gas production is even more prominent.

[0054] Typically, the filling coefficient of lithium-ion batteries is greater than or equal to 3.0g / Ah; at this filling coefficient, the mass content of additives in the electrolyte is approximately 2%. However, for lithium-ion batteries with lower filling coefficients, the additive content is less than 2%, and a cycle drop occurs when the additive content in the electrolyte is completely consumed. In high-conductivity electrolyte systems, a competitive reaction between low-viscosity solvents and additives occurs for film formation. When the filling coefficient of lithium-ion batteries is low, the additive content is too low, causing the solvent to primarily participate in the film formation reaction, and a cycle drop occurs when the additive content in the electrolyte is not completely consumed.

[0055] In view of this, embodiments of the present application provide a lithium-ion battery and an electrical device. In this lithium-ion battery, when the electrolyte contains a low-viscosity solvent and a low-filling coefficient, a high-mass content additive is introduced into the electrolyte. This improves the compatibility of the low-viscosity solvent with the negative electrode in lithium-ion batteries with a low filling coefficient, reduces side reactions between the low-viscosity solvent and the negative electrode in lithium-ion batteries with low filling coefficients, enhances the stability between the solvent and the negative electrode, and thus improves the cycling performance of the lithium-ion battery.

[0056] A lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium-ion battery provided in this application and its various components are introduced.

[0057] First, a lithium-ion battery is provided, wherein an injection coefficient a of the lithium-ion battery satisfies the following: 2.2 g / Ah≤a≤2.8 g / Ah; the lithium-ion battery includes an electrolyte, the electrolyte includes a first solvent, and the viscosity η of the first solvent satisfies the following: η≤0.6 mPa / s; the electrolyte also includes an additive, the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, and 1,3-propane sultone, and the mass content m of the additive in the electrolyte satisfies the following: 5%≤m≤12%.

[0058] Specifically, the above viscosity refers to the viscosity of the first solvent at 20°C. The injection coefficient a of the lithium-ion battery can be 2.2 g / Ah, 2.22 g / Ah, 2.3 g / Ah, 2.35 g / Ah, 2.4 g / Ah, 2.45 g / Ah, 2.5 g / Ah, 2.55 g / Ah, 2.6 g / Ah, 2.65 g / Ah, 2.7 g / Ah, 2.75 g / Ah, or 2.8 g / Ah, or any value within the range obtained by combining any two of the above values. The viscosity η of the first solvent can be any value below 0.6 mPa / s.

[0059] In another embodiment, 2.4 g / Ah≤a≤2.6 g / Ah.

[0060] The manufacturing process for lithium-ion batteries typically involves first placing an electrode assembly soaked in electrolyte into a casing, then injecting electrolyte into the casing before encapsulation. The filling coefficient, determined by the amount of electrolyte injected, is a key parameter in lithium-ion battery manufacturing. Typically, the filling coefficient for lithium-ion batteries is no less than 3.0 g / Ah, given that too little electrolyte can result in high internal resistance, severe polarization, and poor cycling performance. High-energy-density lithium-ion batteries are typically paired with a high-conductivity electrolyte system, and the positive and negative electrodes typically carry more active material. In theory, this should provide more electrolyte to match the active material. However, given a given battery casing volume, the space occupied by the active material increases, leaving less room for the electrolyte. This results in a lower filling coefficient for high-energy-density lithium-ion batteries.

[0061] Additives such as vinylene carbonate, fluoroethylene carbonate, vinyl carbonate, vinyl sulfate, and 1,3-propane sultone can participate in the film-forming reaction on the negative electrode surface to form a dense and stable SEI film, and have the advantages of good compatibility with the positive electrode and excellent thermal stability. The above additives can reduce side reactions between the solvent and the negative electrode, helping to improve the gas production problem of the above solvents. As mentioned earlier, considering the DCR, rate performance, and other performance of lithium-ion batteries, the mass content of such additives in the electrolyte needs to be controlled within a small range, usually not exceeding 2%. In lithium-ion batteries with a small injection coefficient, the total amount of electrolyte is less than that of ordinary lithium-ion batteries. When the mass content is the same, the amount of the above additives in the electrolyte is lower. Because the reduction peak positions of the first solvent and the additive are close, there is a competitive reaction. Once the amount of additive is insufficient, the first solvent will mainly participate in the film-forming reaction in the competitive reaction, resulting in the first solvent being reduced on the negative electrode surface and producing gas.

[0062] Therefore, in this embodiment, when the lithium-ion battery injection coefficient is small and the electrolyte includes a low-viscosity solvent, the mass content of the additive is controlled within a larger range so that there are enough additives in the electrolyte to compete with the solvent, improve the compatibility between the solvent and the negative electrode, and help reduce the probability of the solvent producing gas at the negative electrode. At the same time, the solvent with lower viscosity contributes to the charging performance of the lithium-ion battery; thus, this embodiment can enable the lithium-ion battery to have good cycle performance and fast charging performance. In one embodiment, the additive is preferably at least one of ethylene carbonate and fluoroethylene carbonate. In one embodiment, the first solvent includes at least one of a carboxylic acid ester solvent, an ether solvent, and a nitrile solvent.

[0063] Specifically, carboxylate solvents, ether solvents, and nitrile solvents have low viscosities, all less than or equal to 0.6 mPa / s, and are widely used in high-conductivity electrolyte systems. However, carboxylate solvents, ether solvents, and nitrile solvents are prone to side reactions and gas production at the negative electrode. Although this improves the fast charging performance of lithium-ion batteries, it seriously affects their cycle performance. In this embodiment, for lithium-ion batteries whose electrolytes specifically include carboxylate solvents, ether solvents, and nitrile solvents, the problem that carboxylate solvents, ether solvents, and nitrile solvents are prone to gas production at the negative electrode can be improved by controlling the mass content of the additives within a larger range, thereby improving the cycle performance of lithium-ion batteries whose injection coefficient is small and whose electrolytes include carboxylate solvents, ether solvents, and nitrile solvents.

[0064] As mentioned above, 5%≤m≤12%.

[0065] Specifically, the mass content m of the additive in the electrolyte can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, or its value is within the range obtained by combining any two of the above values.

[0066] Normally, the amount of additives will decrease as the injection coefficient decreases. In this embodiment, in a lithium-ion battery with an injection coefficient of 2.2g / Ah to 2.8g / Ah, by increasing the amount of additives so that the mass content of the additives is within a larger range, the compatibility problem between the low-viscosity solvent and the negative electrode in the electrolyte, especially the gas production problem of carboxylic acid ester solvents, ether solvents, and nitrile solvents, can be effectively improved, thereby improving the cycle performance of the lithium-ion battery. In addition, an excessive mass content of the additive is not conducive to the DCR of the lithium-ion battery. Therefore, this embodiment can improve the cycle performance of the lithium-ion battery and enable the lithium-ion battery to have good DCR performance by controlling the mass content of the additive within an appropriate range.

[0067] In one embodiment, the carboxylate solvent includes: R1-COO-R2, wherein R1 and R2 independently include at least one of an alkyl group having 1 to 5 carbon atoms and a haloalkyl group having 1 to 5 carbon atoms. For example, R1-COO-R2 can be methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (NPAC), methyl acrylate (MA), ethyl acrylate (EA), etc.

[0068] In one embodiment, the ether solvent includes at least one of diethyl ether, ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0069] In one embodiment, the nitrile solvent includes at least one of succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile.

[0070] Carboxylate, ether, and nitrile solvents have low viscosity, density, and high conductivity, which facilitate the rapid transport of lithium ions. Therefore, using carboxylate, ether, and nitrile solvents as co-solvents can improve electrolyte conductivity and reduce electrolyte density, resulting in good charging performance for lithium-ion batteries.

[0071] In one embodiment, the electrolyte further includes a second solvent, which is a carbonate solvent. Specifically, the second solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (MEC). For another example, the second solvent may also include dimethyl carbonate (DMC), diethyl carbonate (DEC), etc.

[0072] The second solvent is a carbonate solvent with a high dielectric constant and good electrochemical stability. Choosing a carbonate solvent as a co-solvent helps further improve the conductivity of the electrolyte, forming a high-conductivity electrolyte system. Its excellent electrochemical stability also helps extend the operating voltage range of lithium-ion batteries and provides good compatibility with both positive and negative electrodes.

[0073] In one embodiment, the mass content X of the first solvent in the electrolyte satisfies: 10%≤X≤70%; optionally, 20%≤X≤60%.

[0074] In one embodiment, the mass content Y of the second solvent in the electrolyte satisfies: 15%≤Y≤35%; optionally, 25%≤Y≤35%.

[0075] Specifically, X may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any combination thereof. Y may be 25%, 30%, 35%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any combination thereof.

[0076] In one embodiment, the conductivity σ of the electrolyte satisfies: 13 mS / cm≤σ≤20 mS / cm.

[0077] In one embodiment, the volumetric energy density (VED) of the lithium-ion battery satisfies the requirement of VED ≥ 425Wh / L. For high-energy-density lithium-ion batteries, the injection coefficient is small and a high-conductivity electrolyte system is required. The lithium-ion battery provided in the embodiments of the present application, by controlling the mass content of the additive in the high-conductivity electrolyte, can achieve good cycling performance in a lithium-ion battery with a high volumetric energy density.

[0078] Lithium-ion batteries with high energy density generally have a higher population margin. In one embodiment, the population margin x of the lithium-ion battery satisfies: x≥97.5%.

[0079] In one embodiment, the lithium-ion battery includes a positive electrode sheet, and the compaction density ρ1 of the positive electrode sheet satisfies: ρ1 ≥ 2.6 g / cm 3 .

[0080] In one embodiment, the positive electrode plate includes a positive electrode active material, and the loading amount m of the positive electrode active material per unit area of ​​the positive electrode plate satisfies: m1 ≥ 0.22 mg / mm 2 .

[0081] In one embodiment, the lithium-ion battery includes a negative electrode sheet, and the compaction density ρ2 of the negative electrode sheet satisfies: ρ2≥1.7g / cm 3 .

[0082] In one embodiment, the negative electrode plate includes a negative electrode active material, and the loading amount of the negative electrode active material per unit area of ​​the negative electrode plate satisfies: m2≥0.07 mg / mm 2 .

[0083] Next, the positive electrode sheet, negative electrode sheet, separator and electrolyte in the above-mentioned fast-charging lithium-ion battery are introduced in detail.

[0084] [Electrolyte]

[0085] The above text has partially mentioned some properties of the electrolyte in the lithium-ion battery of this application. The electrolyte will be introduced in more detail below.

[0086] The electrolyte conducts ions between the positive and negative electrodes. It primarily consists of an electrolyte salt and a solvent. In lithium-ion batteries, the electrolyte salt is primarily lithium salt, and may also include other additives.

[0087] The selection of lithium salts has been introduced in the previous article and will not be repeated here.

[0088] In one embodiment, in addition to the examples mentioned above, the solvent may also include at least one of ethylene carbonate, propylene carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0089] As mentioned above, the conductivity σ of the electrolyte satisfies: 13mS / cm≤σ≤20mS / cm.

[0090] Specifically, σ can be 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, or 20 mS / cm, or any value within the range obtained by combining any two of the above values. In this embodiment, the conductivity of the electrolyte can be adjusted to meet the above range by selecting the solvent and controlling the solvent ratio.

[0091] In one embodiment, the electrolyte further includes positive electrode film-forming additives and other additives capable of improving certain battery properties, such as additives for improving battery overcharge performance, additives for improving battery high or low temperature performance, etc.

[0092] [Negative electrode]

[0093] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0094] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0095] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In one embodiment, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0097] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0100] As mentioned above, the compaction density ρ2 of the negative electrode sheet satisfies: ρ2 ≥ 1.7 g / cm 3 The loading amount of negative electrode active material per unit area of ​​negative electrode sheet shall meet the following requirements: m2≥0.07mg / mm 2 .

[0101] For example, ρ2 may be 1.7 g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 Equal to or greater than 1.7g / cm 3 Value. m2 can be 0.07mg / mm 2 , 0.08mg / mm 2 , 0.09mg / mm 2 , 0.1mg / mm 2 Equal to or greater than 0.07mg / mm 2 Numeric value.

[0102] Specifically, during the preparation of lithium-ion batteries, to meet design parameters such as energy density, the prepared pole pieces undergo a rolling process to achieve a compacted density. The compaction of the pole pieces is closely related to a variety of factors, including the particle morphology, particle size distribution, and specific surface area of ​​the active material itself, as well as the component ratios of the slurry during the pole piece coating process, coating weight, and current collector thickness. The compaction density of the pole pieces is crucial for the capacity, rate capability, and cycle performance of lithium-ion batteries. For example, all other conditions being equal, the greater the compaction density of the pole piece, the greater the volumetric energy density of the lithium-ion battery. Furthermore, the greater the compaction density of the pole piece, the slower the rate of electrolyte wetting into the pole piece, and the weaker the pole piece's ability to absorb electrolyte. For lithium-ion batteries with a low injection coefficient, this can help reduce the rate of electrolyte consumption, minimizing the risk of cycling failures due to rapid electrolyte consumption or insufficient electrolyte.

[0103] Taking the negative electrode sheet as an example, the compacted density of the negative electrode sheet ρ2 = negative electrode sheet area density / (negative electrode sheet thickness - current collector thickness). Among them, the negative electrode sheet area density refers to the mass of the negative electrode film layer per unit area. The loading amount of negative electrode active material per unit negative electrode sheet can be controlled by adjusting the coating slurry weight, coating thickness, etc. during the preparation process of the negative electrode sheet. Under the same other conditions, the greater the loading amount of negative electrode active material, the greater the volume energy density of the lithium-ion battery.

[0104] That is to say, the embodiments of the present application can help improve the volume energy density of lithium-ion batteries by controlling the compaction density of the negative electrode sheet and the loading amount of the negative electrode active material on the negative electrode sheet.

[0105] In one embodiment, at a position close to the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50 of the negative electrode active material satisfies: 14.5 μm ≤ Dv50 ≤ 19.5 μm; at a position far from the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50' of the negative electrode active material satisfies: 10.2 μm ≤ Dv50' ≤ 15.5 μm.

[0106] Exemplarily, the negative electrode active material is graphite. Along the thickness of the negative electrode sheet, in the negative electrode film layer near the negative electrode current collector, i.e., the "lower layer" of the negative electrode film layer, the average volume particle size Dv50 of the graphite is 14.5 μm to 19.5 μm; in the negative electrode film layer away from the negative electrode current collector, i.e., the "upper layer" of the negative electrode film layer, the average volume particle size Dv50 of the graphite is 10.2 μm to 15.5 μm.

[0107] In this embodiment, graphite with different DV50 values ​​can be placed at different locations in the negative electrode film. This combination of graphite with different particle sizes can help improve the compaction density of the negative electrode sheet. Furthermore, controlling the DV50 value of graphite at different locations in the negative electrode film can further control the electrolyte consumption rate. This can reduce the cycle drop caused by rapid electrolyte consumption in lithium-ion batteries with low filling coefficients, thereby improving the cycling performance of lithium-ion batteries.

[0108] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the aforementioned components for preparing the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and cold pressing, the negative electrode sheet is obtained.

[0109] [Positive electrode]

[0110] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0111] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0112] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In one embodiment, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery will be accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0114] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0115] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] As mentioned above, the compaction density ρ1 of the positive electrode sheet satisfies: ρ1 ≥ 2.65g / cm 3 The loading amount m1 of the positive electrode active material per unit area of ​​the positive electrode sheet satisfies: m1 ≥ 0.22 mg / mm 2 .

[0117] For example, ρ1 can be 2.65 g / cm 3 , 2.68g / cm 3 , 2.7g / cm 3 , 2.72g / cm 3 , 2.75g / cm 3 , 2.78g / cm 3 , 2.8g / cm 3 Equal to or greater than 2.65g / cm 3 m1 can be 0.22mg / mm 2 , 0.24mg / mm 2 , 0.26mg / mm 2 , 0.28mg / mm 2 , 0.3mg / mm 2 , 0.32mg / mm 2 Equal to or greater than 0.22mg / mm 2 The numerical value of .

[0118] Similar to the negative electrode sheet, controlling the compaction density of the positive electrode sheet and the loading amount of the positive electrode active material can also help improve the volume energy density of the lithium-ion battery.

[0119] In one embodiment, the positive electrode sheet can be prepared by separately forming a positive electrode slurry from the components used to prepare the positive electrode sheet. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector. After drying and cold pressing, the positive electrode sheet can be obtained.

[0120] [Isolator]

[0121] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator. For example, any known porous structure separator with good chemical and mechanical stability can be selected.

[0122] In one embodiment, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0123] In one embodiment, the negative electrode sheet, the positive electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0124] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0125] In one embodiment, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0126] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 100 having a square structure as an example.

[0127] It should be understood that the battery cell 100 may be the lithium-ion battery in the aforementioned embodiment.

[0128] Figure 2 shows an example battery module 200. Referring to Figure 2 , in the battery module 200, multiple battery cells 100 may be arranged sequentially along the length of the battery module 200. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 100 may be secured by fasteners. The multiple battery cells 100 may be of the same chemical system or of different chemical systems.

[0129] Optionally, in one embodiment, the battery module 200 may further include a housing having an accommodation space, and the plurality of battery cells 100 may be accommodated in the accommodation space.

[0130] Optionally, in one embodiment, the battery modules 200 may be assembled into a battery. The battery may contain one or more battery modules 200. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0131] Figures 3 and 4 illustrate an example battery pack 300. Referring to Figures 3 and 4, the battery pack 300 may include a battery box and multiple battery modules 200 disposed within the battery box. The battery box includes an upper case 301 and a lower case 302. The upper case 301 can be placed over the lower case 302 to form an enclosed space for accommodating the battery modules 200. The multiple battery modules 200 can be arranged in any manner within the battery box.

[0132] It should be understood that the battery cells 100 can first be assembled into the battery module 200, and the battery pack 300 can be assembled from the battery module 200. Alternatively, the battery pack 300 can be directly assembled from the battery cells 100, omitting the intermediate form of the battery module 200.

[0133] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0134] In another embodiment, the electrical device includes at least one of the battery cell 100, battery module 200, or battery pack 300 provided in the present application. The battery cell 100, battery module 200, or battery pack 300 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. As an electrical device, the number of battery cells 100, battery modules 200, or battery packs 300 can be selected according to its usage requirements.

[0135] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0136] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0137] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0138] [Examples 1-12 and Comparative Examples 1-5]

[0139] Example 1

[0140] (1) Preparation of negative electrode sheet

[0141] The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose were dissolved in deionized water at a mass ratio of 96:0.5:2.5:1 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was then evenly coated on the negative electrode current collector copper foil. After drying, cold pressing, and slitting, the negative electrode sheet was obtained. The coating weight of the negative electrode film on the negative electrode sheet was 0.12 mg / mm 2 After cold pressing, the powder compaction density of the negative electrode sheet is 1.72g / cm 3 .

[0142] (2) Preparation of positive electrode sheet

[0143] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent acetylene black were dissolved in the solvent N-methylpyrrolidone at a mass ratio of 97:2:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector aluminum foil. After drying, rolling, and slitting, the positive electrode sheet was obtained. The coating weight of the positive electrode film on the positive electrode sheet was 0.26 mg / mm 2 The powder compaction density of the positive electrode sheet is 2.65g / cm 3 .

[0144] (3) Preparation of electrolyte

[0145] In an argon atmosphere glove box with a water content of less than 10 ppm, an electrolyte solution was prepared. The specific process was as follows: ethyl acetate (EA), ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 50:30:20. An appropriate amount of lithium hexafluorophosphate (LiPF6) was slowly added, stirred thoroughly until completely dissolved, and then vinylene carbonate (VC) was added as an additive. The mass content of VC, m, was 4%, the lithium salt concentration in the electrolyte was c, 1 mol / L, the mass content of the first solvent in the electrolyte was X, 46%, and the mass content of the second solvent in the electrolyte was Y, 27.6%. The viscosity of the first solvent, EA, was η, 0.45 mPa / s.

[0146] (4) Preparation of lithium-ion batteries

[0147] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between and separating the positive and negative electrode sheets. The stacked components were then wound and placed in a square aluminum casing. After drying, electrolyte was injected. After packaging, standing, and chemical formation, the lithium-ion battery of Example 1 was obtained. The lithium-ion battery of Example 1 had a measured filling coefficient a = 2.8 g / Ah, and a volumetric energy density VED = 438 Wh / L.

[0148] Example 2

[0149] Compared with Example 1, the filling coefficient a of the lithium ion battery of Example 2 is 2.5 g / Ah.

[0150] Example 3

[0151] Compared with Example 1, the filling coefficient a of the lithium ion battery of Example 3 is 2.2 g / Ah.

[0152] Example 4

[0153] Compared with Example 1, in the lithium ion battery of Example 4, m=5%.

[0154] Example 5

[0155] Compared with Example 1, in the lithium ion battery of Example 5, m=8%.

[0156] Example 6

[0157] Compared with Example 1, in the lithium ion battery of Example 6, m=10%.

[0158] Example 7

[0159] Compared with Example 1, in the lithium ion battery of Example 7, m=12%.

[0160] Example 8

[0161] Compared with Example 1, in the lithium ion battery of Example 8, m=15%.

[0162] Example 9

[0163] Compared with Example 1, in the lithium ion battery of Example 9, the first solvent is acetonitrile, and η=0.37 mPa / s.

[0164] Example 10

[0165] Compared with Example 1, in the lithium ion battery of Example 10, X=20%.

[0166] Example 11

[0167] Compared with Example 1, in the lithium ion battery of Example 11, X=10%.

[0168] Example 12

[0169] Compared with Example 1, in the lithium ion battery of Example 12, the additive is fluoroethylene carbonate (FEC).

[0170] Comparative Example 1

[0171] Compared with Example 1, in the lithium ion battery of Comparative Example 1, the volume energy density is 400Wh / L, the injection coefficient a=3.0g / Ah, and m=3%.

[0172] Comparative Example 2

[0173] Compared with Example 1, in the lithium ion battery of Comparative Example 2, m=2%.

[0174] Comparative Example 3

[0175] Compared with Example 12, in the lithium ion battery of Comparative Example 3, m=2%.

[0176] Comparative Example 4

[0177] Compared with Example 10, in the lithium ion battery of Comparative Example 4, m=2%.

[0178] Comparative Example 5

[0179] Compared with Example 1, in the lithium ion battery of Comparative Example 5, the additive is vinyl ethylene carbonate (VEC).

[0180] Product parameters of Examples 1-12 and Comparative Examples 1-5.

[0181] Table 1: Products and performance parameters of Examples 1-12 and Comparative Examples 1-5

[0182] In Table 1, "a" represents the injection coefficient of the lithium-ion battery, "first solvent" represents the type of the first solvent in the electrolyte. "X" represents the mass content of the first solvent in the electrolyte, "additive" represents the type of additive in the electrolyte, "m" represents the mass content of the additive in the electrolyte, "discharge DCR" represents the DC impedance during the discharge process measured by performing a DCR test after the lithium-ion battery is cycled to 50% SOC at -20°C, "charge DCR" represents the DC impedance during the charge process measured by performing a DCR test after the lithium-ion battery is cycled to 50% SOC at -20°C, and "cycle number" represents the number of cycles of the lithium-ion battery cycled to 70% SOH at 60°C (it is generally believed that the capacity of the battery decays to 70% of the rated capacity and the SOH of the battery is 70% SOH).

[0183] By comparing the data of Examples 1-12 with Comparative Examples 2-4, it can be seen that the cycle performance of Examples 1-12 is significantly better than that of Comparative Examples 2-4. It can be seen that for lithium-ion batteries with low injection coefficients and electrolyte solvents including low-viscosity solvents, such as carboxylic acid ester solvents, ether solvents or nitrile solvents, adding specific additives to the electrolyte and controlling the additive content to be high can effectively improve the compatibility between the solvent and the negative electrode, inhibit the gas production of the above-mentioned solvent, and thus improve the cycle performance of lithium-ion batteries with low injection coefficients. The above-mentioned cycle test was carried out at a temperature of 60°C. At high temperatures, the gas production problem of the electrolyte is more serious. It can be seen that even at high temperatures, the lithium-ion battery in the embodiment has excellent cycle performance, which further proves the improvement effect of the solution of the present application on the solvent gas production problem.

[0184] A comparative analysis of the data from Comparative Example 1 and Comparative Examples 2-4 shows that for Comparative Example 1, which has a higher filling coefficient, even though the additive content is relatively low, the total amount of additive in the electrolyte is sufficient to participate in a competitive reaction with the solvent, thereby suppressing gassing of the carboxylate, ether, and nitrile solvents in the electrolyte, resulting in minimal impact on the cycling performance of the lithium-ion battery. In contrast, for Comparative Examples 2-4, which have lower filling coefficients, the lower additive content leads to a more pronounced problem of electrolyte gassing, which has a serious adverse effect on the cycling performance of the battery.

[0185] The DCR performance of lithium-ion batteries in Table 1 includes charging DCR and discharging DCR. Among them, charging DCR reflects the polarization size and heat generation capacity of the lithium-ion battery during the charging process; while discharging DCR reflects the polarization size and heat generation capacity of the lithium-ion battery during the discharging process. At low temperatures (-20°C), the internal resistance of the lithium-ion battery will increase sharply, the discharge capacity and rate performance of the battery will decrease, and low temperatures will also cause lithium precipitation. The precipitation of metallic lithium dendrites may pierce the diaphragm, affecting safety performance. According to the DCR data shown in Table 1, it can be seen that the DCR of Examples 1-12 is higher than that of Comparative Examples 1-3. This is because the large mass content of the additive will increase the DCR of the lithium-ion battery to a certain extent, but compared with the degree of improvement in the cycle performance, the adverse effects of the slight increase in DCR can be ignored. Comparative Example 5 shows the case where other types of additives are added to a lithium-ion battery with a low injection coefficient and an electrolyte including a low-viscosity solvent, and their mass content is controlled to 4%. It can be seen that although the mass content of VEC is also 4%, it cannot improve the compatibility of the solvent and the negative electrode, nor can it inhibit EA gassing at the negative electrode. The cycle performance of the lithium-ion battery of Comparative Example 5 is only 523 cycles. This demonstrates the effect of specific types of additives on improving the compatibility of low-viscosity solvents and negative electrodes, and the effect of specific types of additives on inhibiting solvent gassing.

[0186] By comparing the data of Examples 1-3, it can be seen that as the injection coefficient decreases, the number of cycles of the lithium-ion battery decreases. This shows that for lithium-ion batteries with high energy density (for example, volume energy density VED≥425Wh / L), the injection coefficient has a significant effect on its cycle performance. According to the comparison between Example 2 and Comparative Example 2, and the comparison between Example 11 and Comparative Example 4, the cycle performance of Comparative Example 2 and Comparative Example 4, in which the additive content is only 2%, is significantly worse than the cycle performance of Example 2 and Example 11, in which the additive content is 4%. The reason is that the carboxylic acid ester solvents, ether solvents, and nitrile solvents in the electrolyte are prone to side reactions with the negative electrode to produce gas during the battery cycle, which is not conducive to the cycle performance of the lithium-ion battery. The additives in the electrolyte can suppress the gas production of the solvent, but considering the effect of the additives on other properties of the lithium-ion battery (such as DCR), the mass content of the additives in the electrolyte is usually not higher than 2%. Through experiments, the present application discovered that low-viscosity solvents will compete with additives for film formation. For lithium-ion batteries with a smaller injection coefficient, the mass content of the additive is lower, and the solvent preferentially participates in film formation, thereby producing a large amount of gas, resulting in cycle drop, which is not conducive to the cycle performance of the lithium-ion battery. This is the case in Comparative Example 2: for a high-energy-density lithium-ion battery with an injection coefficient of only 2.5, the 2% additive mass content is obviously unable to inhibit solvent gas production. The number of cycles of the lithium-ion battery in Comparative Example 2 is only 243. Compared with Comparative Example 2, the mass content of the additive in Example 2 is increased to 4%. It can be seen that although the DCR of Example 2 is higher than that of Comparative Example 2, its cycle performance is improved to 2633 cycles. The situation in Example 11 is similar to that in Comparative Example 4, and the mass content of EA is 20%, which will have a certain impact on the charging performance of the lithium-ion battery. Therefore, it is proved that a low injection coefficient combined with a higher mass content of additives can give lithium-ion batteries excellent cycle performance. By comparing Examples 4-7, it can be seen that the number of cycles of the lithium-ion battery increases significantly, indicating that increasing the mass content of the additive in the electrolyte helps to further improve the cycle performance of the lithium-ion battery. In addition, as the mass content of the additive increases, the DCR of the lithium-ion battery also gradually increases. By comparing the performance of Examples 4-7 and 8, it can be seen that the mass content of the additive in Example 8 is higher than that in Example 7, but its DCR is higher than that in Example 4-7, and its cycle performance is far less than that in Example 4-7. This shows that the mass of the additive in the electrolyte in Example 8 is too high, the DCR of the lithium-ion battery is too large, the lithium-ion kinetics deteriorate, and the degree of influence on the cycle performance of the lithium-ion battery is greater than that of the additive. Therefore, it is shown that by controlling the mass content of the additive within an appropriate range, the cycle performance of the lithium-ion battery can be further improved. On the other hand, the higher the mass content of the first solvent, the greater the advantage of the first solvent in the competitive reaction between the first solvent and the additive. At this time, in order to suppress the first solvent from participating in the competitive reaction, it is also necessary to further increase the content of the additive.Although in the data shown in the embodiments and comparative examples, the mass content of the first solvent is mostly 46% and the mass content of the additive is mostly 4%, it can be reasonably speculated that when the mass content of the first solvent is further increased, in order to improve the cycle performance of the lithium-ion battery, the mass content of the additive will also increase.

[0187] It can be seen from Example 9 that when acetonitrile is selected as the first solvent and an electrolyte with a VC content of 4% by mass is used, a lithium-ion battery with a filling coefficient of 2.5 can also have good cycle performance.

[0188] It can be seen from Examples 2 and 10-11 that the mass content of the first solvent in the electrolyte in Example 10-11 is less than that in Example 2, and the cycle performance of the lithium-ion battery in Example 10-11 is better than that in Example 2. It is proved that the first solvent that easily produces gas during the battery cycle has an adverse effect on the cycle performance of the lithium-ion battery. But on the other hand, the charging DCR of the lithium-ion battery in Example 10-11 is significantly higher than that in Example 2, and the charging DCR of Comparative Example 4 is also higher than that of Comparative Example 2, indicating that the increase of the first solvent is beneficial to the conductivity of the electrolyte and can improve the charging capacity and low-temperature performance of the lithium-ion battery. Therefore, considering that the mass content of the additive is within a larger range, and considering that the mass content of the first solvent is controlled within a larger range, good fast charging performance and cycle performance can be achieved. It can be seen from Example 12 that FEC can also play a similar role as an additive.

[0189] The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the embodiments of this application. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0190] 1. Test method for battery filling coefficient

[0191] The filling coefficient of the battery can be tested by methods well known to those skilled in the art. For example, the filling coefficient of the lithium-ion battery can be measured according to the following process: 1) weigh the mass M0 of the lithium-ion battery; 2) disassemble the lithium-ion battery, pour out the electrolyte, and take out the electrode assembly; 3) soak and clean the electrode assembly and shell with DMC respectively, soak for 12 hours, and clean at least 3 times; 4) place the electrode assembly and shell in an oven until completely dried; 5) weigh the mass M1 of the electrode assembly and shell. Therefore, the filling coefficient of the lithium-ion battery is a = (M0-M1) / A. Wherein, A is the rated capacity of the lithium-ion battery. The value of A can be obtained from the nameplate information of the lithium-ion battery. It can also be obtained by testing using constant current discharge, constant power discharge, etc.

[0192] The rated capacity A of a lithium-ion battery can be read directly from the nameplate information or obtained by testing using the following method: Place a commercially available, unused lithium-ion battery at 25°C, charge it to 3.8V at a constant current of 0.33C, let it rest for 1 minute, then charge it to 3.8V at a constant current of 0.1C, let it rest for 30 minutes; discharge it to 2.0V at a constant current of 0.33C, and record the discharge capacity at this time as the rated capacity A.

[0193] 2. Test method for mass content

[0194] The components and contents in the solution can be detected by methods known to those skilled in the art. For example, the mass content of each component in the electrolyte can be measured by liquid chromatography, ultraviolet spectrophotometry, ultraviolet-visible spectrophotometry, etc.

[0195] Exemplarily, the mass content of the first solvent and additive can also be tested by the following method: weigh the battery and record the mass as M0. Disassemble the battery, pour out the free electrolyte, and take the free electrolyte to test the electrolyte composition. Take out the internal electrode assembly and separate the positive electrode sheet, negative electrode sheet, separator and mechanical parts. Use DMC solvent to soak and clean the positive electrode sheet, negative electrode sheet, separator and mechanical parts for 24h to 48h, and repeat the soaking for more than 3 times. Place the above-mentioned positive electrode sheet, negative electrode sheet, separator and mechanical parts in a 100°C oven for more than 24h until completely dried. Weigh the dried positive electrode sheet, negative electrode sheet, separator and mechanical parts, and record the mass as M1. Thus, the electrolyte weight d3 in the lithium-ion battery is obtained = M0-M1.

[0196] Use IC ion chromatograph to test the inorganic content in the electrolyte, weigh the quantitative electrolyte (the dilution concentration is in the middle of the standard curve), dilute to 100 mL with ultrapure water, perform automatic sampling detection on the ion chromatogram, test the inorganic ion chromatogram, compare the corresponding inorganic species according to the chromatogram peak position, calculate the corresponding inorganic ion concentration according to the peak area, and calculate the inorganic mass M2 in the electrolyte through the mass of the electrolyte. The free electrolyte is diluted 3 to 10 times with acetonitrile to obtain an electrolyte dilution to be tested. The electrolyte dilution is placed in a GC-MS 3100 organic component gas chromatograph for full scan qualitative analysis. The injection port temperature is 250°C, and the scanning range is 35 μm to 270 μm. After the test is completed, a total ion current chromatogram of each organic matter is obtained. The type of organic matter corresponding to the peak position of the chromatogram is compared, and the corresponding content percentage of each organic matter is calculated based on the peak area. The mass of each organic matter in the electrolyte d3-M2 and the content percentage of each organic matter can be calculated. For example, the mass d1 of the first solvent and the mass d2 of the additive in the electrolyte can be calculated.

[0197] Finally, the mass content of the first solvent and the mass content of the additive are calculated by d1 / d3 and d2 / d3.

[0198] 3. Volume energy density test method

[0199] Place a commercially available, unused lithium-ion battery at 25°C, charge it to 3.8V at a constant current of 0.33C, let it rest for 1 minute, then charge it to 3.8V at a constant current of 0.1C and let it rest for 30 minutes. Discharge it to 2.0V at a constant current of 0.33C, and record the discharge capacity A0 at this time in Ah. Use calipers to measure the length, width, and height of the lithium-ion battery's outer surface and calculate the volume of the single cell V0 in L. The volumetric energy density of the single cell, VED, is calculated as (A0 × discharge platform voltage of the lithium-ion battery) / V0 in Wh / L. It should be understood that lithium-ion batteries with different positive and negative electrode systems have different discharge platform voltages, which can be determined by testing their charge and discharge curves or referring to existing literature.

[0200] 4.DCR test method

[0201] The test method for DCR can refer to the method in GB / T 31467 "Performance test specification for high-power lithium-ion power batteries for HEV".

[0202] For example, at 25°C, charge the lithium-ion battery to 3.8V at a constant current of 0.33C and let it stand for 1 minute; then charge it to 3.8V at a constant current of 0.1C and let it stand for 30 minutes; discharge it to 2.0V at a constant current of 0.33C, record the discharge capacity A0 at this time, in Ah, and then charge it at a constant current of 0.33C for 0.5A0Ah, adjusting the SOC to 50%.

[0203] After the battery is placed at -20℃ for 2h, it is discharged at a constant current of 4C for 10s and ΔU is recorded. 放电 , ΔI 放电 Then charge at a constant current of 0.01C for 4000s, adjust the charge to 50% SOC, and place the battery at -20℃ for 2h, then charge at a constant current of 0.1C for 10s, and record ΔU 充电 , ΔI 充电 , the discharge and charge DCR data of lithium-ion batteries are calculated using the following formula. 放电 =ΔU 放电 / ΔI 放电 R 充电 =ΔU 充电 / ΔI 充电

[0204] Among them, ΔU 放电 Indicates the voltage change within 10s after the discharge starts, ΔI 放电Indicates the current value within 10s after the discharge starts, ΔU 充电 Indicates the voltage change within 10 seconds after the start of charging, ΔI 充电 Indicates the current change within 10 seconds after the start of charging.

[0205] 5. Cycle number test method

[0206] At 60°C, charge a commercially available, unused lithium-ion battery at a constant current of 1C to 3.8V. After 30 minutes of rest, discharge it at a constant current of 1C to 2.8V. Following this charge-discharge schedule, record the number of cycles required to achieve 70% SOH.

[0207] 6. Test method for solvent viscosity

[0208] The fluid material of this embodiment is tested based on the rotational viscometer in Appendix D of the national standard GB / T10247-2008. For details, please refer to the following test steps: Take a certain mass of electrolyte sample and place it in a sample container. Use the rotational viscometer with instrument model DV2TLV produced by Brookfield for testing. At a certain temperature, when the rotor rotates continuously at a constant speed in the sample, the shear force it is subjected to causes the spring to generate torque. The torque is proportional to the viscosity, and the viscosity value is obtained. The test equipment meets the following test environmental conditions: 1. External environment of the equipment: temperature: 15~28℃, humidity: RH<80%; 2. Internal environment of the equipment: 2 / 3 of the sample container is immersed in a water bath, the medium is water, and water is used to keep the sample at a constant temperature.

[0209] 7. Test method for electrolyte conductivity

[0210] The test method is in accordance with HG / T 4067-2015. The conductivity of the electrolyte to be tested is tested using a conductivity meter: about 100 ml of the sample to be tested is taken into a dry, clean, corrosion-resistant sample bottle, and sealed in a constant temperature water bath at 25±0.5℃. When the temperature of the sample to be tested is constant, the sample bottle cap is replaced with a rubber stopper with an electrode inserted. When the temperature is within the range of 25±0.5℃, the data is read, which is the conductivity of the sample to be tested.

[0211] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery has an injection coefficient a that satisfies: 2.2 g / Ah≤a≤2.8 g / Ah; the lithium-ion battery includes an electrolyte, and the electrolyte includes a first solvent and an additive; The viscosity η of the first solvent satisfies: η≤0.6 mPa / s; The additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, and 1,3-propane sultone, and the mass content m of the additive in the electrolyte satisfies: 5%≤m≤12%.

2. The lithium-ion battery according to claim 1, wherein 2.4g / Ah≤a≤2.6g / Ah.

3. The lithium-ion battery according to claim 1 or 2, characterized in that The additive includes at least one of vinylene carbonate and fluoroethylene carbonate.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that The first solvent includes at least one of a carboxylate solvent, an ether solvent, and a nitrile solvent.

5. The lithium-ion battery according to claim 4, characterized in that The carboxylate solvent includes: R1-COO-R2, wherein R1 and R2 independently include at least one of an alkyl group with 1 to 5 carbon atoms and a halogenated alkyl group with 1 to 5 carbon atoms.

6. The lithium-ion battery according to claim 4 or 5, characterized in that The ether solvent includes at least one of diethyl ether, ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, tetrahydrofuran, and 2-methyltetrahydrofuran.

7. The lithium-ion battery according to any one of claims 4 to 6, characterized in that The nitrile solvent includes at least one of succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile.

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that The mass content X of the first solvent in the electrolyte satisfies: 10%≤X≤70%.

9. The lithium-ion battery according to claim 8, characterized in that 20％≤X≤60％。 10. The lithium-ion battery according to any one of claims 1 to 9, characterized in that The electrolyte further includes a second solvent, and the second solvent includes at least one of ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

11. The lithium-ion battery according to claim 10, wherein: The second solvent includes ethylene carbonate.

12. The lithium-ion battery according to claim 10 or 11, characterized in that The mass content Y of the second solvent in the electrolyte satisfies: 15%≤Y≤35%.

13. The lithium-ion battery according to claim 12, wherein: 25％≤Y≤35％。 14. The lithium-ion battery according to any one of claims 1 to 13, characterized in that The conductivity σ of the electrolyte satisfies: 13 mS / cm≤σ≤20 mS / cm.

15. The lithium-ion battery according to any one of claims 1 to 14, characterized in that The volume energy density VED of the lithium-ion battery satisfies: VED≥425Wh / L.

16. The lithium-ion battery according to any one of claims 1 to 15, characterized in that The group margin x of the lithium-ion battery satisfies: x≥97.5%.

17. The lithium-ion battery according to any one of claims 1 to 16, characterized in that The lithium-ion battery includes a positive electrode sheet, and the compaction density ρ1 of the positive electrode sheet satisfies: ρ1≥2.6g / cm 3 .

18. The lithium-ion battery according to claim 17, wherein: The positive electrode plate includes a positive electrode active material, and the loading amount m1 of the positive electrode active material per unit area of ​​the positive electrode plate satisfies: m1 ≥ 0.22 mg / mm 2 .

19. The lithium-ion battery according to any one of claims 1 to 18, characterized in that The lithium-ion battery includes a negative electrode plate, and the compaction density ρ2 of the negative electrode plate satisfies: ρ2≥1.7g / cm 3 .

20. The lithium-ion battery according to claim 19, wherein The negative electrode plate includes a negative electrode active material, and the loading amount m2 of the negative electrode active material per unit area of ​​the negative electrode plate satisfies: m2 ≥ 0.07 mg / mm 2 .

21. The lithium-ion battery according to claim 20, characterized in that The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector; At a position close to the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50 of the negative electrode active material satisfies: 14.5 μm ≤ Dv50 ≤ 19.5 μm; at a position far from the negative electrode current collector in the negative electrode film layer, the average volume particle size Dv50' of the negative electrode active material satisfies: 10.2 μm ≤ Dv50' ≤ 15.5 μm.

22. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery according to any one of claims 1 to 21.

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