Lithium-ion battery

Abstract

Provided in the present application is a lithium-ion battery, comprising a solvent, a lithium salt and an electrolyte. The electrolyte comprises additives. The proportion of the additives in the electrolyte is denoted as Add, the unit of Add being parts; a charging cut-off voltage of the lithium battery is denoted as Vol, the unit of Vol being V; a CB value of the lithium battery, Add and Vol satisfy the relationship: 0.98≤CB×Vol / Add≤1.54; and the CB value of the lithium battery is a dimensionless value. The additives include a negative electrode film-forming additive, a positive electrode complexing additive, and a positive electrode high-voltage resistant additive.

Description

A lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 2024118043325, filed with the Chinese Patent Office on December 9, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium battery technology, and in particular to a lithium-ion battery. Background Technology

[0003] Batteries with high energy density can provide longer operating time and driving range under a certain weight, which is especially important for applications with high battery energy density requirements.

[0004] Currently, in order to improve the energy density of power batteries, the charging cut-off voltage can be appropriately increased, which helps the positive electrode to achieve a higher specific capacity. At this time, the CB value of the lithium battery is usually increased to avoid lithium deposition on the negative electrode. Technical issues

[0005] Increasing the CB value of a lithium battery leads to a higher oxidation potential at the positive electrode. At high potentials, the electrolyte undergoes oxidative decomposition, resulting in a deterioration in the cycle performance of the lithium battery. In addition, an increase in the charging cut-off voltage causes the dissolution of transition metals (Fe & Mn) at the positive electrode. The presence of transition metals in ionic form causes the reduction and decomposition of ethylene carbonate (EC) in the electrolyte, which is then reduced to a metallic state at the negative electrode. This continuously damages the SEI film on the surface of the negative electrode, which will further deteriorate the cycle performance of the lithium battery. Technical solutions

[0006] This application provides a lithium-ion battery, which adopts the following technical solution:

[0007] A lithium-ion battery includes an electrolyte comprising a solvent, a lithium salt, and an additive, wherein the additive comprises, in the proportion A of the electrolyte. dd A dd The unit is units, and the charging cut-off voltage of the lithium battery is denoted as V. ol V ol The unit is V;

[0008] The CB value of the lithium battery and the A dd The V ol Satisfying 0.98≤ ≤1.54; the CB value of the lithium battery is a dimensionless value;

[0009] The additives include negative electrode film-forming additives, positive electrode complexing additives, and positive electrode high-voltage resistant additives.

[0010] The CB value is the design CB value, which is the ratio of the reversible capacity per unit area of ​​the negative electrode to the reversible capacity per unit area of ​​the positive electrode. Beneficial effects

[0011] In this application, the type of additives in the electrolyte and the weight percentage of additives per 100 parts of electrolyte are controlled. dd The charging cutoff voltage V of a lithium battery ol When the CB value of a lithium battery meets the above conditions, it can prevent metal ions at the positive electrode from being reduced at the negative electrode, and ensure the complexation of transition metal ions at the positive electrode as much as possible. This improves the stability of the electrolyte and the SEI film on the negative electrode surface. At this time, the content of additives in the electrolyte can also be controlled within a suitable range. This not only avoids the SEI film damage and recombination caused by the dissolution of transition metal ions, but also avoids electrolyte decomposition caused by the increase of the CB value of the lithium battery. All of these factors help the lithium battery maintain excellent cycle performance while having high energy density.

[0012] when If the value is less than 0.98, it means that the charging cut-off voltage and CB value of the lithium battery are too low or the proportion of additives in the electrolyte is too high. In this case, the energy density of the lithium battery cannot be effectively utilized. Furthermore, lithium plating is likely to occur on the surface of the negative electrode during the cycle of the lithium battery. In addition, an excessively high proportion of additives in the electrolyte will also affect the film formation on the surface of the negative electrode. All of these are not conducive to improving the cycle performance of the lithium battery.

[0013] when If the value is greater than 1.54, it means that the charging cut-off voltage and CB value of the lithium battery are too high or the proportion of additives in the electrolyte is too low. In this case, the electrolyte will cause more transition metal ions to dissolve at the positive electrode. These dissolved transition metal ions will be reduced at the surface of the negative electrode, thereby destroying the integrity, uniformity and stability of the SEI film on the surface of the negative electrode. This will increase the internal resistance of the lithium battery. In addition, the over-dissolved metal ions will also reduce the structural interface of the positive electrode material. All of these are not conducive to improving the cycle performance of the lithium battery. Embodiments of the present invention

[0014] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0015] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0016] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.

[0017] All percentages in this application are weight percentages unless otherwise stated.

[0018] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0019] In some embodiments, the CB value of the lithium battery is related to the A value. dd The V ol satisfy

[0020] In some embodiments, the CB value of the lithium battery ranges from 1.1 to 1.19.

[0021] In some embodiments, the CB value of the lithium battery ranges from 1.11 to 1.17.

[0022] By adjusting the CB value of a lithium battery to meet the aforementioned range, electrolyte decomposition can be avoided, thus improving the battery's cycle performance. When the CB value is high, the ratio between the lithium insertion capacity of the negative electrode and the lithium extraction capacity of the positive electrode is large during charging and discharging. This leads to excessive lithium insertion at the negative electrode during charging, consuming a large amount of electrolyte and reducing its ion conductivity. This results in excessively high internal battery temperature under high voltage, negatively impacting cycle performance and safety. Conversely, when the CB value is too low, the lithium ion insertion and extraction rates at the negative electrode are rapid, leading to faster consumption of lithium salts in the electrolyte. Since lithium salts are the primary source of lithium ions in the electrolyte, rapid consumption reduces electrolyte conductivity, shortening the battery's cycle life, narrowing its operating temperature range, and even increasing safety risks.

[0023] In some embodiments, A is the number of parts by weight of the additive per 100 parts of the electrolyte. dd The value range is 3-5.2 parts.

[0024] In some embodiments, A is the number of parts by weight of the additive per 100 parts of the electrolyte. dd The value ranges from 3.3 to 4.7 parts.

[0025] By adjusting the proportion A in the additive electrolyte dd Meeting the above range can prevent the SEI film from being damaged and remodeled due to the dissolution of transition metal ions in lithium batteries, thus helping to improve the cycle performance of lithium batteries. When A ddA higher concentration of A will hinder the formation of the SEI film, resulting in a less stable SEI film and hindering the improvement of lithium battery cycle performance; when A dd A low SEI film will result in an incomplete or poor-quality SEI film formed on the negative electrode. An incomplete SEI film will hinder the transport of lithium ions inside the battery, increase the battery's internal resistance, reduce the battery's discharge capacity and charging efficiency, and the incomplete SEI film will not effectively protect the electrode materials, leading to a significant decrease in the cycle performance of the lithium battery.

[0026] In some embodiments, the charging cutoff voltage V of the lithium battery ol The value range is 4.2-4.3V.

[0027] In some embodiments, the charging cutoff voltage V of the lithium battery ol The value range is 4.21-4.28V.

[0028] By controlling the charging cutoff voltage of the lithium battery to meet the above-mentioned range, the capacity of the electrode material can be fully utilized, thereby maintaining the energy density of the lithium battery at a high level. Furthermore, at this point, the charging cutoff voltage is related to the CB value of the lithium battery and the proportion of additives in the electrolyte, which is A. dd The combination of these factors prevents the electrolyte from being oxidized and decomposed, and also prevents the reduction of transition metal ions at the negative electrode, thus avoiding the destruction and reorganization of the SEI film. This allows the lithium battery to achieve both high energy density and excellent cycle performance.

[0029] In some embodiments, the negative electrode film-forming additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene ethylene carbonate (VEC); the positive electrode complexing additive includes at least one of trimethylsilyl phosphate (TMSP) and succinate (SN); and the positive electrode high-voltage resistant additive includes at least one of 1,3-propane sulpholol (PS) and lithium difluorooxalate borate (LiDFOB).

[0030] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; the concentration of the lithium salt in the electrolyte is 0.85-1.5 mol / L.

[0031] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0032] In some embodiments, the solvent includes cyclic carbonates and chain carbonates; the solvent accounts for 80%-90% of the mass of the electrolyte.

[0033] In some embodiments, the volume ratio of the cyclic carbonate to the chain carbonate is 3-4.5:5.5-7.

[0034] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate (EC) and propylene carbonate (PC); the chain carbonate includes at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0035] In some embodiments, a positive electrode and a negative electrode are also included; the compaction density of the positive electrode is 2.0-2.6 g / cm³. 3 And / or, the areal density of the positive electrode sheet on one side is 200-260 g / m³. 2 .

[0036] In some embodiments, the compaction density of the positive electrode sheet is 2.1-2.5 g / cm³. 3 And / or, the areal density of the positive electrode sheet on one side is 210-250 g / m³. 2 .

[0037] In some embodiments, the compaction density of the negative electrode sheet is 1.55-1.75 g / cm³. 3 And / or, the areal density of the negative electrode sheet on one side is 80-110 g / m³. 2 .

[0038] In some embodiments, the electrolyte injection coefficient of the lithium battery is 2.3-3.8 g / Ah.

[0039] The electrolyte filling coefficient is the ratio of electrolyte consumption to the battery's own capacity under normal operating conditions.

[0040] By controlling the electrolyte injection coefficient of the lithium battery to meet the above-mentioned range, on the one hand, it is possible to adjust the electrolyte to produce a good wetting effect on the positive and negative electrode sheets, thereby significantly improving the capacity of the positive and negative electrode active materials and reducing the impedance of the positive and negative electrode sheets. This is not only beneficial to the energy density of the lithium battery, but also to improving the cycle performance of the lithium battery. On the other hand, it is possible to adjust the size of the gas storage space of the secondary battery, thereby reducing the swelling of the lithium battery during the cycle process, which helps to improve the cycle performance of the lithium battery.

[0041] Example 1

[0042] 1. Electrolyte preparation

[0043] The electrolyte consists of a solvent, a lithium salt, and additives.

[0044] The lithium salt is composed of LiFSI and LiPF6 (mass ratio 1:1), and the concentration of lithium salt in the electrolyte is 1.1 mol / L;

[0045] The solvent comprises ethylene carbonate (EC) and chain carbonate (ethyl methyl carbonate EMC), with the solvent accounting for 85% of the electrolyte by mass, wherein the volume ratio of cyclic carbonate to chain carbonate is 4:6.

[0046] The additive consists of vinylene carbonate (VC), fluoroethylene carbonate (FEC), succinate (SN), and lithium difluorooxalate borate (LiDFOB), with 3 parts by weight of additive per 100 parts of electrolyte.

[0047] 2. Preparation of positive electrode sheet

[0048] The positive electrode material (lithium manganese iron phosphate), conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 96:2:2. NMP solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After double-layer coating and air-drying at room temperature, the foil was transferred to an oven for further drying. Finally, it was cold-pressed and slit to obtain a surface density of 220 g / m³. 2 The compacted density is 2.4 g / cm³. 3 The positive electrode plate.

[0049] 3. Preparation of negative electrode sheet

[0050] The negative electrode material (graphite), conductive agent acetylene black, and binder CMC were mixed at a mass ratio of 97:1.5:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the negative electrode current collector copper foil. After double-layer coating and air drying at room temperature, it was transferred to an oven for further drying. Then, it was cold-pressed and slit to obtain an areal density of [missing information]. The compacted density is 1.6 g / cm³. 3 The negative electrode.

[0051] 4. Lithium-ion battery manufacturing

[0052] The positive electrode, separator, and negative electrode are stacked in sequence using a stacking machine. The separator is a polyethylene film, which acts as a separator between the positive and negative electrodes. After stacking, the battery cell is assembled into an aluminum-plastic bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery with an electrolyte injection coefficient of 3.5, a charging cut-off voltage of 4.2V, and a CB value of 1.1 is obtained.

[0053] Example 2

[0054] 1. Electrolyte preparation

[0055] The electrolyte consists of a solvent, a lithium salt, and additives.

[0056] The lithium salt is composed of LiFSI and LiPF6 (mass ratio 1:1), and the concentration of lithium salt in the electrolyte is 0.85 mol / L;

[0057] The solvent consists of cyclic carbonate (ethylene carbonate EC) and chain carbonate (dimethyl carbonate DMC), and the solvent accounts for 80% of the mass of the electrolyte, wherein the volume ratio of cyclic carbonate to chain carbonate is 3:5.5.

[0058] The additive consists of vinylene carbonate (VC), fluoroethylene carbonate (FEC), succinate (SN), and lithium difluorooxalate borate (LiDFOB), with the additive comprising 3.6 parts by weight per 100 parts of electrolyte.

[0059] 2. Preparation of positive electrode sheet

[0060] The positive electrode material (lithium manganese iron phosphate), conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 96:2:2. NMP solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After double-layer coating and air-drying at room temperature, the foil was transferred to an oven for further drying. Finally, it was cold-pressed and slit to obtain a surface density of 220 g / m³. 2 The compacted density is 2.4 g / cm³. 3 The positive electrode plate.

[0061] 3. Preparation of negative electrode sheet

[0062] The negative electrode material (graphite), conductive agent acetylene black, and binder CMC were mixed at a mass ratio of 97:1.5:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the negative electrode current collector copper foil. After double-layer coating and air drying at room temperature, it was transferred to an oven for further drying. Then, it was cold-pressed and slit to obtain an areal density of [missing information]. The compacted density is 1.6 g / cm³. 3 The negative electrode plate.

[0063] 4. Lithium-ion battery manufacturing

[0064] The positive electrode, separator, and negative electrode are stacked in sequence using a stacking machine. The separator is a polyethylene film, which acts as a separator between the positive and negative electrodes. After stacking, the battery cell is assembled into an aluminum-plastic bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery with an electrolyte injection coefficient of 3.5, a charging cut-off voltage of 4.23V, and a CB value of 1.13 is obtained.

[0065] Example 3

[0066] 1. Electrolyte preparation

[0067] The electrolyte consists of a solvent, a lithium salt, and additives.

[0068] The lithium salt is composed of LiFSI and LiPF6 (mass ratio 1:1), and the concentration of lithium salt in the electrolyte is 1.3 mol / L;

[0069] The solvent is composed of cyclic carbonate (ethylene carbonate EC and propylene carbonate PC in a volume ratio of 1:1) and chain carbonate (ethyl methyl carbonate EMC). The solvent accounts for 90% of the mass of the electrolyte, and the volume ratio of cyclic carbonate to chain carbonate is 4.5:7.

[0070] The additive consists of vinylene carbonate (VC), fluoroethylene carbonate (FEC), trimethylsilyl phosphate (TMSP), and 1,3-propane sulfonyl lactone (PS), with the additive comprising 4.4 parts by weight per 100 parts of electrolyte.

[0071] 2. Preparation of positive electrode sheet

[0072] The positive electrode material (lithium manganese iron phosphate), conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 96:2:2. NMP solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After double-layer coating and air-drying at room temperature, the foil was transferred to an oven for further drying. Finally, it was cold-pressed and slit to obtain a surface density of 220 g / m³. 2 The compacted density is 2.4 g / cm³. 3 The positive electrode plate.

[0073] 3. Preparation of negative electrode sheet

[0074] The negative electrode material (graphite), conductive agent acetylene black, and binder CMC were mixed at a mass ratio of 97:1.5:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the negative electrode current collector copper foil. After double-layer coating and air drying at room temperature, it was transferred to an oven for further drying. Then, it was cold-pressed and slit to obtain an areal density of [missing information]. The compacted density is 1.6 g / cm³. 3 The negative electrode plate.

[0075] 4. Lithium-ion battery manufacturing

[0076] The positive electrode, separator, and negative electrode are stacked in sequence using a stacking machine. The separator is a polyethylene film, which acts as a separator between the positive and negative electrodes. After stacking, the battery cell is assembled into an aluminum-plastic bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery with an electrolyte injection coefficient of 3.5, a charging cut-off voltage of 4.27V, and a CB value of 1.15 is obtained.

[0077] Example 4

[0078] 1. Electrolyte preparation

[0079] The electrolyte consists of a solvent, a lithium salt, and additives.

[0080] The lithium salt is composed of LiFSI and LiPF6 (mass ratio 1:1), and the concentration of lithium salt in the electrolyte is 1.1 mol / L;

[0081] The solvent consists of cyclic carbonates (ethylene carbonate EC and propylene carbonate PC in a volume ratio of 2:1) and chain carbonates (diethyl carbonate DEC). The solvent accounts for 83% of the mass of the electrolyte, and the volume ratio of cyclic carbonates to chain carbonates is 3.5:6.

[0082] The additive consists of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), succinate (SN), and lithium difluorooxalate borate (LiDFOB), with 5.2 parts by weight of additive per 100 parts of electrolyte.

[0083] 2. Preparation of positive electrode sheet

[0084] The positive electrode material (lithium manganese iron phosphate), conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 96:2:2. NMP solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After double-layer coating and air-drying at room temperature, the foil was transferred to an oven for further drying. Finally, it was cold-pressed and slit to obtain a surface density of 220 g / m³. 2 The compacted density is 2.4 g / cm³. 3 The positive electrode plate.

[0085] 3. Preparation of negative electrode sheet

[0086] The negative electrode material (graphite), conductive agent acetylene black, and binder CMC were mixed at a mass ratio of 97:1.5:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the negative electrode current collector copper foil. After double-layer coating and air drying at room temperature, it was transferred to an oven for further drying. Then, it was cold-pressed and slit to obtain an areal density of [missing information]. The compacted density is 1.6 g / cm³. 3 The negative electrode.

[0087] 4. Lithium-ion battery manufacturing

[0088] The positive electrode, separator, and negative electrode are stacked in sequence using a stacking machine. The separator is a polyethylene film, which acts as a separator between the positive and negative electrodes. After stacking, the battery cell is assembled into an aluminum-plastic bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery with an electrolyte injection coefficient of 3.5, a charging cut-off voltage of 4.3V, and a CB value of 1.19 is obtained.

[0089] Example 5

[0090] The difference between this embodiment and Example 1 is that the additives in the electrolyte include vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), trimethylsilyl phosphate (TMSP), succinate (SN), 1,3-propane sulpholol (PS), and lithium difluorooxalate borate (LiDFOB); the remaining steps and parameter settings are consistent with those in Example 1.

[0091] Example 6

[0092] The difference between this embodiment and Embodiment 1 is that the CB value of the lithium battery is 1.05, the charging cut-off voltage is 4.35V, and the weight percentage of additives per 100 parts of electrolyte is 2.98; all other steps and parameter settings are consistent with Embodiment 1.

[0093] Example 7

[0094] The difference between this embodiment and Embodiment 1 is that the CB value of the lithium battery is 1.25, the charging cut-off voltage is 4.15V, and the weight percentage of additives in every 100 parts of electrolyte is 5; all other steps and parameter settings are consistent with Embodiment 1.

[0095] Example 8

[0096] The difference between this embodiment and Embodiment 1 is that the electrolyte injection coefficient of the lithium battery is 2.0; the remaining steps and parameter settings are consistent with Embodiment 1.

[0097] Example 9

[0098] The difference between this embodiment and Embodiment 1 is that the electrolyte injection coefficient of the lithium battery is 4.0; the remaining steps and parameter settings are consistent with Embodiment 1.

[0099] Comparative Example 1

[0100] The difference between this embodiment and the previous embodiment is that the weight percentage of the additive per 100 parts of electrolyte is 5.25. =0.88; the remaining steps and parameter settings are consistent with those in Example 1.

[0101] Comparative Example 2

[0102] The difference between this embodiment and the previous embodiment is that the charging cutoff voltage Vol of the lithium battery is 4.34V. =1.59; the remaining steps and parameter settings are consistent with those in Example 1.

[0103] Comparative Example 3

[0104] The difference between this embodiment and Embodiment 1 is that the additive does not contain the negative electrode film-forming additive, and an equal weight of the positive electrode complexing additive is used instead of the negative electrode film-forming additive in Embodiment 1; the remaining steps and parameter settings are consistent with Embodiment 1.

[0105] Comparative Example 4

[0106] The difference between this embodiment and Embodiment 1 is that the additive does not contain a positive electrode complexing additive, and an equal weight of a positive electrode high voltage resistant additive is used instead of the positive electrode complexing additive in Embodiment 1; the remaining steps and parameter settings are consistent with Embodiment 1.

[0107] Comparative Example 5

[0108] The difference between this embodiment and Embodiment 1 is that the additive does not contain the positive electrode high voltage resistant additive, and an equal weight of the negative electrode film-forming additive is used instead of the positive electrode high voltage resistant additive in Embodiment 1; the remaining steps and parameter settings are consistent with Embodiment 1.

[0109] Test methods

[0110] I. Lithium-ion battery energy density test

[0111] The energy density of the lithium batteries in the above embodiments and comparative examples was tested. The specific test steps were as follows: weigh the battery to be tested and record the weight as m; place the battery in the fixture, apply a force of 3000N, charge the single battery with a constant current of 0.33C to 4.3V, let it rest for 30min, discharge it with a constant current of 0.33C to 2.5V, let it rest for 30min, and repeat the charge and discharge cycle 3 times. Calculate the third discharge capacity (in Ah) and energy E (take the average value of the three cells). Discharge energy density: E / m (in Wh / kg).

[0112] II. Lithium-ion battery cycle performance test

[0113] The lithium batteries in the above embodiments and comparative examples were subjected to cycle performance tests. The lithium batteries were fully charged and discharged at 25°C. The specific test steps were as follows: 30 minutes of rest; constant current and constant voltage charging (current 0.33C, constant voltage 4.2V, cut-off current 0.05C, where C is the battery design capacity), three cycles, with the capacity of the last cycle recorded as Q (calibrated capacity). 1 hour of rest; constant current and constant voltage charging (current 1Q, constant voltage 4.2V, cut-off current 0.05Q); 1 hour of rest; constant current discharge (current 1Q), 2000 cycles, and the cycle capacity retention rate of the lithium battery was recorded.

[0114] III. Negative Electrode ICP Test

[0115] The contents of Mn and Fe elements in the negative electrode material of the lithium battery after cycle treatment in the above embodiments and comparative examples were determined by ICP.

[0116] Table 1

[0117]

[0118] Based on Examples 1-5, Comparative Examples 1-2, and Table 1, it can be seen that this application achieves the desired effect by controlling the weight percentage of additives (Add) per 100 parts of electrolyte, the charging cut-off voltage (Vol) of the lithium battery, and the CB value of the lithium battery to be 0.98 ≤ With a concentration ≤1.54, the deposition of transition metal ions at the negative electrode can be reduced, and the complexation of transition metal ions at the positive electrode can be ensured as much as possible. This improves the stability of the electrolyte and the SEI film on the negative electrode surface, thereby ensuring the energy density of the lithium battery and its good cycle performance.

[0119] In Comparative Example 1, the amount of additives per 100 parts of electrolyte was excessive. Apart from the amount required for film formation at the positive and negative electrodes, the remaining additives underwent side reactions in the electrolyte, which increased the impedance of the lithium battery and reduced its cycle performance. However, the excessive amount of additives also provided some protection to the surfaces of the positive and negative electrodes, so the deposition of transition metal ions at the negative electrode was not significantly improved.

[0120] In Comparative Example 2, the charging cutoff voltage of the lithium battery increased while the weight percentage of additives per 100 parts of electrolyte remained unchanged. During the voltage increase, the CEI and SEI films were damaged, and no additional additives participated in film formation in time, thus failing to suppress the dissolution of transition metals. The deposition of transition metal ions at the negative electrode was significant. When the additives in the electrolyte were exhausted, the solvent in the electrolyte also began to decompose, which would deteriorate the cycle performance of the lithium battery.

[0121] In Comparative Examples 3-5, the absence of any one of the negative electrode film-forming additive, positive electrode complexing additive, or positive electrode high-voltage resistant additive will hinder the synergistic effect between additives to maintain electrolyte stability. In particular, the absence of the positive electrode high-voltage resistant additive will significantly increase the deposition of transition metal ions at the negative electrode, and the cycle performance of the lithium battery will also decrease significantly. While the absence of either the negative electrode film-forming agent or the positive electrode complexing agent can alleviate the dissolution of transition metal ions at the positive electrode to some extent and reduce the deposition of transition metal ions at the negative electrode, the protective effect of the additives on the positive and negative electrodes is greatly weakened, and the cycle performance of the lithium battery deteriorates severely.

[0122] Combining Examples 1, 6-7, and Table 1, it can be seen that when the CB value is too small, the charging cutoff voltage Vol is too large, and Add is too small, although the relationship between these three still satisfies 0.98 ≤ ≤1.54, but because Add is too small, the SEI film generated at the negative electrode will be incomplete or of poor quality, and the combination of CB value and Vol will be poor, resulting in a decrease in electrolyte stability. All of these are not conducive to adjusting the cycle performance of lithium battery. The phenomenon of transition metal ion deposition at the negative electrode is more significant than in Example 1. When the CB value is too large and the charging cut-off voltage Vol is too small, the energy density of lithium battery will decrease slightly, and the negative electrode will experience excessive lithium intercalation during charging, which will not only consume a large amount of electrolyte, but also reduce the ion conduction efficiency of the electrolyte, which will not be conducive to improving the cycle performance of lithium battery.

[0123] Combining Examples 1, 8-9 and Table 1, it can be seen that when the electrolyte injection coefficient is too small, it helps to increase the energy density of the lithium battery. However, during long-term cycling, the electrolyte is usually consumed continuously. If the electrolyte injection coefficient is too low, the electrolyte will not be sufficient to maintain long-term cycling, thereby deteriorating the cycle performance of the lithium battery. When the electrolyte injection coefficient is too high, the energy density of the lithium battery decreases, and there are more side reactions in the electrolyte, which will increase the impedance of the lithium battery and deteriorate the cycle performance.

Claims

1. A lithium-ion battery, comprising an electrolyte, said electrolyte comprising a solvent, a lithium salt, and an additive, wherein the weight parts of the additive per 100 parts of said electrolyte are denoted as A. dd A dd The unit is units, and the charging cut-off voltage of the lithium battery is denoted as V. ol V ol The unit is V; The CB value of the lithium battery and the A dd The V ol Satisfying 0.98≤ ≤1.54; the CB value of the lithium battery is a dimensionless value; in, The additives include negative electrode film-forming additives, positive electrode complexing additives, and positive electrode high-voltage resistant additives.

2. The lithium-ion battery according to claim 1, wherein: The CB value of the lithium battery and the A dd The V ol Satisfying 1.06≤ ≤1.

42.

3. The lithium-ion battery according to claim 1 or 2, wherein: The CB value of the lithium battery ranges from 1.1 to 1.

19.

4. The lithium-ion battery according to claim 1 or 2, wherein: The number of parts by weight A of the additive in every 100 parts of the electrolyte dd The value range is 3-5.2 parts.

5. The lithium-ion battery according to claim 1 or 2, wherein: The charging cutoff voltage V of the lithium battery ol The value range is 4.2-4.3V.

6. The lithium-ion battery according to claim 1, wherein: The negative electrode film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate. The positive electrode complexing additive includes at least one of trimethylsilyl phosphate and succinic acid; The positive electrode high-voltage resistant additive includes at least one of 1,3-propanesulfonyl lactone and lithium difluorooxalate borate.

7. The lithium-ion battery according to claim 1, wherein: The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; the concentration of the lithium salt in the electrolyte is 0.8-1.5 mol / L.

8. The lithium-ion battery according to claim 1, further comprising a positive electrode and a negative electrode; wherein the compaction density of the positive electrode is 2.0-2.6 g / cm³. 3 And / or, the areal density of the positive electrode sheet on one side is 200-260 g / m³. 2 .

9. The lithium-ion battery according to claim 8, wherein: The compaction density of the negative electrode sheet is 1.55-1.75 g / cm³. 3 And / or, the areal density of the negative electrode sheet on one side is 80-110 g / m³. 2 .

10. The lithium-ion battery according to claim 1, wherein: The electrolyte injection coefficient of the lithium battery is 2.3-3.8 g / Ah.

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