Lithium cell and battery pack comprising same

Abstract

The invention provides a lithium battery cell and a battery pack comprising the same. According to the lithium battery cell disclosed by the invention, aiming at the problem of poor battery cell performance caused by large side reaction between carboxylic ester and active lithium due to introduction of the carboxylic ester, the stability between a negative electrode side and the carboxylic ester is improved and the side reaction between the active lithium and the carboxylic ester is reduced by adding the first additive and the second additive which have a synergistic effect; and by limiting the relationship between the contents of the carboxylic ester, the first additive and the second additive and the specific surface area of the negative electrode active layer, the low-temperature fast charging performance of the lithium battery cell is effectively improved under the condition of ensuring that other performances of the lithium battery cell are not deteriorated, and the lithium battery cell has a relatively good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium battery cell and a battery pack containing the same. Background Art

[0002] Compared with ternary positive electrode materials, lithium iron phosphate materials have a lower lithium ion diffusion rate and poor electronic conductivity, which makes LFP batteries (LiFePO4 batteries) prone to polarization during low-temperature and room-temperature charging, greatly limiting their application in the field of fast charging. In order to improve the fast charging capability of LFP batteries, it is necessary to improve the kinetics of liquid-phase transmission of the electrolyte. At present, carboxylic acid ester solvents with lower viscosity and higher conductivity at low temperatures are usually selected to reduce viscosity. However, carboxylic acid esters have high activity and are very easy to react with active lithium, causing the battery cell to dive during cycling at low temperatures, seriously deteriorating the performance and safety of the battery. On this basis, in order to improve the kinetics of LFP batteries, low-viscosity carboxylic acid esters are added to the electrolyte. At the same time, it is also necessary to improve the kinetics of the negative electrode by increasing the specific surface area of ​​the negative electrode active layer, reducing the particle size of the negative electrode material, etc. However, these methods will further deteriorate the interface between the negative electrode and the electrolyte, and further intensify the degree of reaction between the electrolyte and the active lithium on the negative electrode side.

[0003] Therefore, how to contain carboxylic acid ester in the electrolyte and have a high specific surface area (1.2m 2 / g or above), reducing the side reaction between active lithium and carboxylate, improving the low-temperature fast charging performance of LFP batteries, and ensuring that other performances are not affected have become urgent issues to be solved. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a lithium battery cell and a battery pack containing the same.

[0005] In the first aspect, the present invention provides a lithium battery cell, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein a negative electrode active layer is provided on the surface of the negative electrode sheet, and the specific surface area of ​​the negative electrode active layer is 1.3-1.6 m 2 / g;

[0006] The electrolyte includes a solvent, a lithium salt, a first additive and a second additive;

[0007] The solvent includes a carboxylate solvent; the first additive includes vinylene carbonate and / or fluoroethylene carbonate; the second additive includes a sulfur-containing organic compound; the sulfur-containing organic compound includes one or more of 1,3-propane sultone, vinyl sulfite or 1,3-propene sultone;

[0008] In the electrolyte, the content of the carboxylate solvent is 10-65 wt %; the content of the first additive is 1-6 wt %; and the content of the second additive is 0.05-1 wt %;

[0009] The content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship:

[0010] 0.02g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2

[0011] Wherein, W1 is the content of the carboxylate solvent;

[0012] M1 is the content of the first additive;

[0013] M2 is the content of the second additive;

[0014] D is the specific surface area of ​​the negative electrode active layer, m 2 / g.

[0015] In some embodiments of the present invention, the content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship:

[0016] 0.06g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2 .

[0017] In some embodiments of the present invention, the solvent further comprises a carbonate solvent.

[0018] In some embodiments of the present invention, the carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate or dimethyl carbonate.

[0019] In some embodiments of the present invention, the carboxylate solvent includes one or more of ethyl acetate, ethyl propionate, methyl acetate or methyl propionate, preferably ethyl acetate.

[0020] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate or lithium tetrafluorooxalatophosphate.

[0021] In some embodiments of the present invention, the content of the lithium salt in the electrolyte is 10-18 wt %.

[0022] In some embodiments of the present invention, the electrolyte further includes a third additive, and the third additive includes one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, lithium difluorooxalatoborate, or lithium difluorophosphate.

[0023] In the electrolyte, the content of the third additive is 0.3-1.5 wt %.

[0024] In some embodiments of the present invention, the negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes a carbon-based material or a silicon-based material.

[0025] In some embodiments of the present invention, the components of the negative electrode active layer include graphite, a conductive agent and a binder;

[0026] The mass ratio of the graphite, the conductive agent and the binder is (94-98):(1-4):(1-2).

[0027] In some embodiments of the present invention, the lithium battery cell includes a lithium iron phosphate battery cell.

[0028] In some embodiments of the present invention, the charging cut-off voltage of the lithium iron phosphate battery cell does not exceed 3.75V.

[0029] In a second aspect, the present invention provides a battery pack, comprising the lithium battery cell as described in the first aspect.

[0030] In a third aspect, the present invention provides a vehicle, comprising the lithium battery cell as described in the first aspect or the battery pack as described in the second aspect.

[0031] The technical solution provided by the embodiment of the present invention has the following advantages compared with the existing technology:

[0032] (1) The lithium battery cell of the present invention addresses the problem of poor battery performance caused by the introduction of carboxylate, which results in a large side reaction between the carboxylate and active lithium. By introducing a first additive and a second additive, the two additives work synergistically to inhibit the interaction between the α-H of the carboxylate and the active lithium, thereby improving the stability between the negative electrode and the carboxylate and reducing the side reaction between the active lithium and the carboxylate.

[0033] (2) The present invention also limits the relationship between the content of the carboxylic acid ester, the first additive, and the second additive and the specific surface area of ​​the negative electrode active layer, thereby more effectively improving the low-temperature fast charging performance of the lithium battery cell while ensuring that other properties of the lithium battery cell do not deteriorate, and has good application prospects. DETAILED DESCRIPTION

[0034] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0037] In the first aspect, this embodiment provides a lithium battery cell, including a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein a negative electrode active layer is provided on the surface of the negative electrode sheet, and the specific surface area of ​​the negative electrode active layer is 1.3-1.6m 2 / g;

[0038] The electrolyte includes a solvent, a lithium salt, a first additive, and a second additive;

[0039] The solvent includes a carboxylate solvent; the first additive includes vinylene carbonate and / or fluoroethylene carbonate; the second additive includes a sulfur-containing organic compound; the sulfur-containing organic compound includes one or more of 1,3-propane sultone, vinyl sulfite or 1,3-propene sultone;

[0040] In the electrolyte, the content of the carboxylate solvent is 10-65 wt %, the content of the first additive is 1-6 wt %, and the content of the second additive is 0.05-1 wt %;

[0041] The content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship:

[0042] 0.02g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2

[0043] Wherein, W1 is the content of carboxylic acid ester solvent;

[0044] M1 is the content of the first additive;

[0045] M2 is the content of the second additive;

[0046] D is the specific surface area of ​​the negative electrode active layer, m 2 / g.

[0047] Among them, the specific surface area of ​​the negative electrode active layer is 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or 1.6m 2 / g, etc.; the content of the carboxylic acid ester solvent is such as 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt% or 65wt%; the content of the first additive is such as 1wt%, 2wt%, 3wt%, 4wt%, 5wt% or 6wt%; the content of the second additive is such as 0.05wt%, 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.5wt% or 1wt%, etc., but is not limited to the listed values, and other values ​​not listed within the above range are equally applicable.

[0048] On the one hand, the present invention uses a carboxylate solvent with low viscosity in the electrolyte, which reduces the transmission resistance of lithium ions at low temperatures, thereby improving the low-temperature fast charging and room-temperature fast charging performance of the battery; on the other hand, a negative electrode with a high specific surface area is selected to improve the kinetics. Based on the problem of the intensified reaction between the electrolyte and the active lithium on the negative electrode side in the above technical solution, the present invention improves the stability between the negative electrode side and the carboxylate by adding two different film-forming additives, and reduces the side reaction between the active lithium and the carboxylate. Among them, the first additive can form a thicker polymer film and also form an interface film rich in lithium carbonate and lithium fluoride. On the one hand, this can significantly improve the effect of Fe dissolution of the LFP battery cell on the negative electrode interface, and on the other hand, it can also inhibit the reactivity of the negative electrode interface with the electrolyte; while the second additive can react on the negative electrode side before the carboxylate, forming a thin and dense SEI film with Li2SO4 as the main component. The two work synergistically, thereby effectively solving the problem of poor low-temperature fast charging performance of lithium batteries using carboxylate as an electrolyte and having a high specific surface area negative electrode.

[0049] Furthermore, the present invention more effectively improves the low-temperature fast charging performance of the lithium battery cell by exploring the relationship between the content of the carboxylate, the first additive, and the second additive and the specific surface area of ​​the negative electrode active layer, while ensuring that other properties of the lithium battery cell do not deteriorate. According to the results of the exploration, when the specific surface area of ​​the negative electrode active layer is constant, as the content of the carboxylate in the electrolyte increases, the degree of the side reaction between the carboxylate and the negative electrode material increases, and it is necessary to add more first additives and second additives to participate in the film formation at the negative electrode interface and inhibit the occurrence of negative electrode side reactions. At the same time, the increase in the carboxylate content can also make up for the impact on the low-temperature fast charging performance caused by the increase in the first additive and the second additive. However, if the content of the carboxylate, the first additive, and the second additive increases at the same time and exceeds the range of the relationship, it will cause the film formation impedance of the battery cell to be larger, making the concentration difference caused by the increase in the carboxylate content extremely large. The improvement in kinetics brought about by the increase in film formation impedance is difficult to offset, which in turn significantly deteriorates the fast-charging performance of the battery cell. When the carboxylate content is too low, the degree of side reaction between the carboxylate and the negative electrode side is reduced. Correspondingly, the content of the first additive and the second additive needs to be reduced to reduce the interfacial impedance. However, if the content of the carboxylate, the first additive, and the second additive is reduced at the same time and exceeds the range of the relationship, the film formation effect will be poor, and it will be difficult to suppress the side reaction caused by the carboxylate. At the same time, a low carboxylate content will also lead to insufficient fast-charging capacity of the battery cell, ultimately resulting in no advantage over traditional electrolyte solutions. If the specific surface area of ​​the negative electrode active layer increases, the content of the first additive and the second additive needs to be increased accordingly. Simultaneously, the content of the carboxylate can also be reduced to reduce the side reactions caused by the increase in the specific surface area of ​​the negative electrode active layer.

[0050] In addition, the present invention also found that if the content of the carboxylic acid ester and the specific surface area of ​​the negative electrode active layer are large, and the content of the first additive and the second additive is small (that is, when the result of the relationship is lower than the specified lower limit), although the low-temperature performance and fast-charging performance of the battery cell can be improved to a certain extent, the protective effect of the interface film is reduced, and the interface side reaction is intensified, which will aggravate the decomposition of the interface film and reduce the cycle performance and storage performance of the battery cell; if the content of the carboxylic acid ester and the specific surface area of ​​the negative electrode active layer are small, and the content of the first additive and the second additive is large (that is, when the result of the relationship exceeds the specified upper limit), the viscosity of the electrolyte will increase, the ion migration rate will decrease, and the film formation impedance will increase. Although the cycle and storage performance of the battery cell are improved, the low-temperature performance and fast-charging performance of the battery cell will decrease.

[0051] In summary, the present invention makes the electrolyte have a lower viscosity through the overall design of the solvent, additives and negative electrode plate in the electrolyte, overcomes the problem of large side reactions between carboxylic acid esters and active lithium, and enables the battery cell to have excellent fast charging capability without sacrificing high-temperature performance, cycle life and calendar life.

[0052] In some embodiments of the present invention, the content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship:

[0053] 0.06g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2 .

[0054] In some embodiments of the present invention, the solvent further includes a carbonate solvent.

[0055] In some embodiments of the present invention, the carbonate solvent includes one or more of ethyl methyl carbonate (EMC), ethylene carbonate (EC) or dimethyl carbonate (DMC).

[0056] In some embodiments of the present invention, the carboxylate solvent includes one or more of ethyl acetate (EA), ethyl propionate (EP), methyl acetate (MA) or methyl propionate (MP), preferably ethyl acetate (EA).

[0057] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, or lithium tetrafluorooxalatophosphate.

[0058] In some embodiments of the present invention, the content of lithium salt in the electrolyte is 10-18wt%, for example, 10wt%, 12wt%, 14wt%, 15wt% or 18wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0059] In the embodiments of the present invention, an appropriate lithium salt concentration helps improve the fast-charging capability of the battery cell. If the lithium salt concentration is too low, although it will significantly reduce the viscosity of the electrolyte, it will also significantly reduce the electrolyte conductivity, resulting in increased electrolyte concentration polarization, which in turn affects the fast-charging performance. On the other hand, if the lithium salt content is too high, it will increase the electrolyte viscosity and reduce the electrolyte conductivity, which will also affect the fast-charging performance of the battery cell.

[0060] In some embodiments of the present invention, the electrolyte further includes a third additive, the third additive including one or more of tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)borate (TMSB), lithium difluorooxalatoborate (LiODFB) or lithium difluorophosphate (LiPO2F2).

[0061] The content of the third additive in the electrolyte is 0.3-1.5wt%, for example, 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt% or 1.5wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] In the embodiment of the present invention, the content of the third additive is controlled within the above range, which helps to reduce the impedance of the battery cell and improve the fast charging performance. If the content of the third additive is too high, it will lead to a large film formation impedance of the battery cell and deteriorate the fast charging performance.

[0063] In some embodiments of the present invention, the negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes a carbon-based material or a silicon-based material.

[0064] In some embodiments of the present invention, the components of the negative electrode active layer include graphite, a conductive agent and a binder;

[0065] The mass ratio of graphite, conductive agent and binder is (94-98):(1-4):(1-2), such as 94:4:2, 95:4:1, 96:3:1, 97:2:1 or 98:1:1, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0066] In some embodiments of the present invention, the lithium battery cell includes a lithium iron phosphate battery cell.

[0067] In some embodiments of the present invention, the charging cut-off voltage of the lithium iron phosphate battery cell does not exceed 3.75V, for example, 3.5V, 3.55V, 3.6V, 3.65V or 3.75V, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0068] In a second aspect, the present invention further provides a battery pack comprising the lithium battery cell proposed in the first aspect.

[0069] In a third aspect, the present invention further provides a vehicle comprising the lithium battery cell as proposed in the first aspect or the battery pack as proposed in the second aspect.

[0070] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail with reference to the following embodiments. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way serves as any limitation on the present invention and its applications. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to conventional techniques or conditions in the art, or those described in the literature, or the product instructions. Reagents or instruments used without manufacturer specified were all commercially available conventional products.

[0072] It should be noted that the lithium battery cell in the following embodiment is only an example listed for testing the performance of the lithium battery cell of the present invention. The present invention is not limited to this type of battery cell. The raw materials, proportions, parameters and processes of the positive electrode plate, the negative electrode plate (except the specific surface area of ​​the negative electrode active layer) and the diaphragm can be replaced with other conventional raw materials, proportions, parameters and processes in the field, thereby forming a battery cell different from the test lithium battery cell.

[0073] Example 1

[0074] This embodiment provides a lithium battery cell, including a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein:

[0075] Preparation of positive electrode sheet: LiFePO4, PVDF, and acetylene black were mixed in a mass ratio of 96.5:2.5:1, and N-methylpyrrolidone (NMP) solvent was added until the system became uniform and transparent. The positive electrode slurry was prepared by stirring with a vacuum mixer, and then evenly coated on the current collector aluminum foil (thickness of 13 μm). After drying at room temperature, it was transferred to a 120 ° C oven for drying for 1 hour, and then cold pressed (compacted density of 2.6 g / cm 3 , specific surface area 1.2m 2 / g), cutting to obtain the positive electrode sheet;

[0076] Preparation of negative electrode sheet: Graphite, sodium carboxymethyl cellulose solution and styrene-butadiene rubber emulsion were mixed in a mass ratio of 97:2:1, deionized water was added, and the negative electrode slurry was prepared by stirring with a vacuum mixer. The negative electrode slurry was then evenly coated on the current collector copper foil (thickness of 6 μm), dried at room temperature, and then transferred to a 120 ° C oven for drying for 1 hour. After that, it was cold pressed (compacted density of 1.6 g / cm 3 , specific surface area 1.4m 2 / g), cutting to obtain the negative electrode sheet;

[0077] Diaphragm: Polypropylene diaphragm is selected;

[0078] Electrolyte: The components and contents are shown in Table 1;

[0079] The positive electrode sheet, negative electrode sheet and separator are wound, wrapped with aluminum-plastic film, baked to remove water, injected with the above-mentioned electrolyte and sealed, and then subjected to processes such as standing, hot and cold pressing, formation, clamping, and capacity separation to prepare a soft-pack lithium battery cell.

[0080] Example 2

[0081] This embodiment provides a lithium battery cell, which refers to the lithium battery cell in Example 1, with the following differences:

[0082] The specific surface area of ​​the negative electrode sheet excluding the negative electrode active layer is 1.6m 2 Except for / g, the rest are the same;

[0083] The components and contents of the electrolyte are shown in Table 1.

[0084] Example 3

[0085] This embodiment provides a lithium battery cell, which refers to the lithium battery cell in Example 1, with the following differences:

[0086] The specific surface area of ​​the negative electrode sheet excluding the negative electrode active layer is 1.3m 2 Except for / g, the rest are the same;

[0087] The components and contents of the electrolyte are shown in Table 1.

[0088] Examples 4-9 and Comparative Examples 1-5 each provide a lithium battery cell, which refers to the lithium battery cell in Example 1, except that the components and contents of the electrolyte are different, as shown in Table 1. All contents are expressed in mass percentage.

[0089] Table 1

[0090]

[0091] Table 1

[0092]

[0093]

[0094] The calculation result of the relational expression should be rounded to two decimal places.

[0095] Performance Testing

[0096] 1. Lithium deposition test at 0.8C charge at -10℃

[0097] At -10°C, the lithium battery cells of Examples 1-9 and Comparative Examples 1-5 were first discharged at 0.33C to 2.0V and then subjected to a cycle test. The cycle test process included: first charging at a constant current of 0.8C to 3.75V, then charging at a constant voltage to a current of 0.05C, and then discharging at a constant current of 0.33C to 2.0V. After 20 cycles of charge / discharge, the cells were charged at 1C to 3.75V at 25°C, then charged at a constant voltage to a current of 0.05C. The cells were then disassembled, and the disassembly interface was observed and the data recorded.

[0098] 2. 6C cycle test at 25℃

[0099] At 25°C, the lithium batteries of Examples 1-9 and Comparative Examples 1-5 were first discharged at 1C to 2.0V and then subjected to a cycling test. The cycling test process included charging at a constant current of 6C to 3.75V, then charging at a constant voltage to a current of 0.05C, and then discharging at a constant current of 1C to 2.0V. The charge / discharge cycle was repeated in this manner. The capacity retention of the lithium batteries after 500 cycles of 6C discharge at 25°C was calculated.

[0100] 3. 60℃ storage test

[0101] At 25°C, the lithium batteries of Examples 1-9 and Comparative Examples 1-5 were first discharged at 1C to 2.0V, then charged at a constant current of 1C to 3.75V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.0V. The discharge capacity was recorded as C1.

[0102] The lithium battery cell is then charged at a constant current of 1C to 3.75V, then charged at a constant voltage to a current of 0.05C. The lithium battery cell is stored in a 60°C oven for 60 days. After that, it is returned to room temperature and discharged at a constant current of 1C to 2.0V. It is then charged at a constant current of 1C to 3.75V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 1C to 2.0V. The discharge capacity is recorded as C2. C2 / C1 × 100% = Capacity retention.

[0103] The results of the above performance tests are shown in Table 2.

[0104] Table 2

[0105]

[0106] Compared with Example 1, the contents of the first additive, the second additive and the carboxylic acid ester solvent in the electrolyte of Example 2 are reduced at the same time, and the specific surface area of ​​the negative electrode active layer is increased, so that the interfacial impedance is also reduced at the same time. Therefore, there is no lithium deposition during 0.8C charging at -10°C, but there is a slight deterioration in high temperature storage and 6C cycling at 25°C.

[0107] Compared with Example 1, in Example 3, the contents of the first additive, the second additive, and the carboxylate solvent are increased simultaneously, and the specific surface area of ​​the negative electrode active layer is increased, so that the interfacial impedance is also increased, resulting in a slight deterioration in the kinetics of the negative electrode side. However, due to the high content of carboxylate and the strong liquid phase transmission capacity, lithium deposition does not occur even when charging at 0.8C at -10°C, and there is a slight improvement in high-temperature storage.

[0108] Compared with Example 1, Examples 4-6 use ES, PST, and FEC as replacements, respectively, and have little difference in effects on room temperature fast charge cycle, 60°C storage capacity retention rate, and low-temperature lithium precipitation.

[0109] Compared with Example 1, Examples 7-9 use MA, EP, and MP to replace EA, respectively. EP and MP will affect the kinetics, so there is slight lithium deposition during low-temperature fast charging.

[0110] Compared with Comparative Example 1 (no carboxylate solvent is added to the electrolyte), the lithium battery cell in Example 1 has better kinetics, and the resulting lithium battery cell does not precipitate lithium when charged at 0.8C at -10°C. At the same time, the synergistic combination of the first additive and the second additive can effectively inhibit the side reaction of the carboxylate on the active lithium at high temperature. Furthermore, by optimizing the first additive, the second additive, the solvent, and the specific surface area of ​​the negative electrode active layer, the low-temperature fast charge and room-temperature fast charge capabilities can be improved, while maintaining the same level of high-temperature storage as the traditional electrolyte (as seen in the 60°C storage test). However, due to insufficient kinetics, Comparative Example 1 suffered from severe lithium precipitation during the 6C cycle, exacerbated the loss of active lithium, and caused the battery cell to dive.

[0111] Compared with Example 1, the relationship between the content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer in Comparative Example 2 does not satisfy the relationship proposed by the present invention, that is, it does not reach the lower limit value specified by the relationship, resulting in the side reaction between the carboxylate and the active lithium not being well suppressed, and thus the 60°C storage capacity retention rate deteriorates.

[0112] Compared with Example 1, the relationship between the content of the carboxylic acid ester solvent, the content of the first additive, the content of the second additive and the specific surface area of ​​the negative electrode active layer in Comparative Example 3 does not satisfy the relationship proposed by the present invention, that is, it exceeds the upper limit value specified by the relationship, resulting in severe lithium plating during low-temperature fast charging of the battery cell. This is because the film formation impedance of the battery cell becomes larger, while the liquid phase transmission capacity is not improved, and the negative electrode side kinetics are not improved, which seriously affects the kinetics.

[0113] Compared with Example 1, in Comparative Example 4, only the first additive was added, and the second additive was not added. The two additives could not play a synergistic role, resulting in the inability to inhibit the side reaction between the carboxylate and the fully charged negative electrode at high temperature, resulting in a significant deterioration in the high-temperature storage capacity retention rate of the battery cell.

[0114] Compared with Example 1, in Comparative Example 5, only the second additive was added without the first additive. The two additives also failed to exert a synergistic effect, resulting in the inability to inhibit the side reaction between the carboxylate and the fully charged negative electrode at high temperature, resulting in a significant deterioration in the high-temperature storage capacity retention rate and fast charge cycle of the battery cell.

[0115] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0116] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments described herein, but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A lithium battery cell comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, characterized in that: The surface of the negative electrode plate is provided with a negative electrode active layer, and the specific surface area of ​​the negative electrode active layer is 1.3-1.6m 2 / g; The electrolyte includes a solvent, a lithium salt, a first additive and a second additive; The solvent includes a carboxylate solvent; the first additive includes vinylene carbonate and / or fluoroethylene carbonate; the second additive includes a sulfur-containing organic compound; the sulfur-containing organic compound includes one or more of 1,3-propane sultone, vinyl sulfite or 1,3-propene sultone; In the electrolyte, the content of the carboxylate solvent is 10-65 wt %; the content of the first additive is 1-6 wt %; and the content of the second additive is 0.05-1 wt %; The content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship: 0.02g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2 Wherein, W1 is the content of the carboxylate solvent; M1 is the content of the first additive; M2 is the content of the second additive; D is the specific surface area of ​​the negative electrode active layer, m 2 / g.

2. The lithium battery cell according to claim 1, characterized in that The content of the carboxylate solvent, the content of the first additive, the content of the second additive, and the specific surface area of ​​the negative electrode active layer satisfy the following relationship: 0.06g / m 2 ≤(3×M1+1.16×M2-0.05×W1) / D≤0.12g / m 2 。 3. The lithium battery cell according to claim 1, characterized in that The carboxylate solvent includes one or more of ethyl acetate, ethyl propionate, methyl acetate or methyl propionate; And / or, the solvent further includes a carbonate solvent.

4. The lithium battery cell according to claim 3, characterized in that The carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate or dimethyl carbonate.

5. The lithium battery cell according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate or lithium tetrafluorooxalatophosphate; and / or, in the electrolyte, the content of the lithium salt is 10-18 wt%; And / or, the electrolyte further comprises a third additive, wherein the third additive comprises one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, lithium difluorooxalatoborate or lithium difluorophosphate; In the electrolyte, the content of the third additive is 0.3-1.5 wt %.

6. The lithium battery cell according to claim 1, characterized in that The negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes a carbon-based material or a silicon-based material.

7. The lithium battery cell according to claim 1, characterized in that The components of the negative electrode active layer include graphite, a conductive agent and a binder; The mass ratio of the graphite, the conductive agent and the binder is (94-98):(1-4):(1-2).

8. The lithium battery cell according to claim 1, characterized in that The lithium battery cell includes a lithium iron phosphate battery cell.

9. A battery pack, characterized in that: The battery pack comprises the lithium battery cell according to any one of claims 1 to 8.

10. A vehicle, characterized in that: The vehicle includes the lithium battery cell according to any one of claims 1 to 8 or the battery pack according to claim 9.

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