Lithium ion battery and application thereof

Abstract

The invention provides a lithium ion battery and application thereof. A positive electrode active layer of the lithium ion battery comprises a positive electrode active material and a lithium supplement agent, and the weight ratio of the positive electrode active material to the lithium supplement agent is a; the negative active layer comprises a silicon-carbon composite material and graphite, and the weight ratio of the silicon-carbon composite material to the graphite is recorded as b; recording the compaction density of the negative electrode active layer as c; and a, b and c meet the condition that a * c / b is more than or equal to 100 and less than or equal to 3000. According to the invention, a mathematical relationship model among the weight ratio a of the positive electrode active material to the lithium supplement agent, the weight ratio b of the negative electrode silicon-carbon composite material to the graphite and the compaction density c of the negative electrode active layer is established in a lithium ion battery system, so that the lithium ion battery which is more excellent in performance and safer and more reliable is provided; and an optimal balance point is effectively found among improvement of the energy density, the first effect and the cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a lithium-ion battery and its application. Background Technology

[0002] The new energy vehicle and electrochemical energy storage markets are expanding rapidly, and lithium-ion batteries are entering an unprecedented phase of high-speed development. New energy vehicles, especially pure electric vehicles, are gradually replacing traditional gasoline vehicles as the mainstream mode of transportation due to their advantages of zero emissions, high efficiency, and low operating costs. However, the driving range, charging speed, and overall cost of electric vehicles are still constrained by the development of battery technology. This means that developing lithium-ion batteries that can provide longer driving range, faster charging speeds, and lower manufacturing costs has become crucial for the progress of the automotive industry.

[0003] In lithium-ion batteries, the cathode material is a crucial factor determining the battery's energy density and cycle performance. In recent years, materials such as lithium iron phosphate (LFP), lithium cobalt oxide (LCO), nickel-cobalt-manganese ternary materials (NCM), and lithium nickel manganese oxide (NMC) have been widely researched and applied due to their respective advantages. However, these materials each have limitations in energy density, initial efficiency, and cycle life. To address the lithium-ion loss caused by the formation of a solid electrolyte interphase (SEI) film during the first charge and discharge cycle, lithium replenishment technology has emerged. The role of lithium replenishment agents is to replenish the lost lithium ions during the first charge cycle, thereby improving the battery's initial efficiency and overall energy density.

[0004] Meanwhile, anode materials also play a crucial role in the energy density and cycle life of lithium-ion batteries. While graphite, as a traditional anode material, boasts structural stability, its theoretical energy density is limited. In contrast, silicon-carbon composite materials, with a theoretical capacity as high as 4200 mAh / g, have become an ideal choice for improving energy density. However, silicon-carbon anodes expand in volume by over 300% during charge and discharge, which can lead not only to electrode pulverization but also to accelerated battery performance degradation. Therefore, controlling the compaction density of the anode has become an important approach to optimizing battery performance.

[0005] Despite significant advancements in energy density and cycle life, existing lithium-ion battery technology still faces numerous technological bottlenecks to meet the high demands of future new energy vehicles and energy storage markets. First, insufficient initial coulombic efficiency of the cathode material limits the battery's overall energy output and initial efficiency, while excessive lithium supplementation can trigger side reactions, compromising battery safety and lifespan. Second, the volume expansion problem of high-capacity anode materials remains unresolved, leading to battery structural instability and decreased cycle performance. Finally, insufficient matching between cathode and anode materials often sacrifices the performance of one for the other, making it difficult to maximize the overall battery performance.

[0006] Therefore, how to balance the content of positive electrode lithium replenishment agent and the compaction density of negative electrode, and synergistically optimize the parameters of positive and negative electrodes, so as to provide a lithium-ion battery with high energy density, high first-time efficiency and long cycle life, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The main objective of this invention is to provide a lithium-ion battery and its application to solve the problem that existing lithium-ion batteries are difficult to achieve simultaneously with high energy density, high initial efficiency, and long cycle life.

[0008] To achieve the above objectives, a first aspect of the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The positive active layer includes a positive active material and a lithium replenishing agent, with the weight ratio of the positive active material to the lithium replenishing agent denoted as a. The negative active layer includes a silicon-carbon composite material and graphite, with the weight ratio of the silicon-carbon composite material to the graphite denoted as b. The compaction density of the negative active layer is denoted as c. a, b, and c satisfy: 100 ≤ a × c / b ≤ 3000.

[0009] Furthermore, a, b, and c satisfy: 150≤a×c / b≤2500, preferably 200≤a×c / b≤700.

[0010] Furthermore, a satisfies: 5≤a≤60, preferably 11.5≤a≤49, and more preferably 15≤a≤35.

[0011] Further, the positive electrode active material is selected from one or more of lithium manganese iron phosphate, lithium iron phosphate, and ternary positive electrode materials, preferably lithium manganese iron phosphate; and / or, the lithium supplement is selected from one or more of lithium nickel oxide, Li5FeO4, and lithium manganese oxide, preferably lithium nickel oxide; preferably, the D50 of the positive electrode active material is 1 μm to 8 μm; and / or, the D50 of the lithium supplement is 3 μm to 15 μm; more preferably, the ratio of the D50 of the positive electrode active material to the lithium supplement is 1:(1 to 6).

[0012] Furthermore, b satisfies: 0.02≤b≤0.20, preferably 0.03≤b≤0.17, and more preferably 0.08≤b≤0.12.

[0013] Further, the D50 of graphite is 8 μm to 25 μm; and / or, the D50 of silicon-carbon composite material is 3 μm to 15 μm; preferably, the silicon content of silicon-carbon composite material is 3 wt% to 15 wt%.

[0014] Furthermore, c satisfies: 1.4≤c≤1.8, preferably 1.45≤c≤1.75, and more preferably 1.55≤c≤1.65.

[0015] Further, the thickness of the positive electrode active layer is 70 μm to 120 μm; and / or, the thickness of the negative electrode active layer is 60 μm to 100 μm; preferably, the ratio of the thickness of the positive electrode active layer to the thickness of the negative electrode active layer is 1:(0.8 to 1.0).

[0016] Furthermore, the electrolyte includes LiPF6, LiFSI, and additives; and the concentration of LiPF6 is 1±0.05M, the concentration of LiFSI is 0.2±0.01M; the additives include fluoroethylene carbonate and vinylene carbonate; preferably, based on the total weight of the electrolyte (100%), the content of fluoroethylene carbonate is 5wt% to 8wt%, and the content of vinylene carbonate is 1wt% to 3wt%.

[0017] A second aspect of the present invention provides an application of the above-mentioned lithium-ion battery as an energy storage device in the field of electric vehicles or energy storage.

[0018] By applying the technical solution of this invention, a mathematical relationship model is established between the weight ratio a of the positive electrode active material and the lithium replenishing agent, the weight ratio b of the negative electrode silicon-carbon composite material and graphite, and the compaction density c of the negative electrode active layer in the lithium-ion battery system. This provides a lithium-ion battery with superior performance and greater safety and reliability, effectively finding the optimal balance between improving energy density, first-time efficiency, and cycle life. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] As described in the background section, existing lithium-ion batteries suffer from the problem of simultaneously achieving high energy density, high initial efficiency, and long cycle life. To address these technical problems, a first aspect of the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The positive active layer comprises a positive active material and a lithium replenishing agent, with the weight ratio of the positive active material to the lithium replenishing agent denoted as a. The negative active layer comprises a silicon-carbon composite material and graphite, with the weight ratio of the silicon-carbon composite material to the graphite denoted as b. The compaction density of the negative active layer is denoted as c. a, b, and c satisfy: 100 ≤ a × c / b ≤ 3000.

[0021] In the lithium-ion battery system, this invention establishes a mathematical relationship model between the weight ratio a of the positive electrode active material and the lithium replenishing agent, the weight ratio b of the negative electrode silicon-carbon composite material and graphite, and the compaction density c of the negative electrode active layer.

[0022] In the above formula, regarding a: In the positive electrode active layer, the positive electrode active material is responsible for the lithium-ion insertion and extraction process during charging and discharging, while the lithium replenishment agent aims to compensate for lithium loss during the first charge and discharge process, enhancing the first coulombic efficiency. The value of a reflects the relative amount between the positive electrode active material and the lithium replenishment agent, which directly affects the battery's first efficiency and energy density. Regarding b: The negative electrode active layer provided by this invention is composed of silicon-carbon composite material and graphite. The high theoretical capacity of silicon-based materials is key to improving battery energy density, but its volume expansion during charging and discharging poses a threat to battery structural stability and cycle performance. Although graphite has a lower capacity, it has a stable structure and is not easily expanded. Therefore, the value of b reflects the ratio between silicon-carbon composite material and graphite, requiring a balance between high capacity and structural stability. The compaction density c refers to the state of the negative electrode active layer when compressed to a specific density. A higher compaction density allows more active material to fill a limited space, increasing energy density, while reducing the contact area between the electrode and the electrolyte, lowering interfacial impedance, and improving the battery's rate performance. However, excessively high compaction density increases the stress in silicon-carbon composites, exacerbates volume expansion, and reduces cycle stability.

[0023] In other words, by limiting the upper limit of the 'a' value in the above formula, excessive addition of lithium additive can be avoided, thereby reducing the risk of electrolyte oxidation and gas generation, and enhancing battery safety. A reasonable 'a' value ensures the effective conduct of the lithium addition process while preventing side reactions that may harm battery stability. Appropriate 'b' and 'c' values ​​not only improve the battery's energy density and cycle life but also enhance the battery's structural stability during charge and discharge, reducing electrode pulverization caused by volume expansion, thus lowering the risk of internal short circuits and further enhancing safety.

[0024] Based on this, by adjusting the relationship between the three parameters a, b, and c as described above, the lithium replenishment efficiency of the positive electrode and the volume expansion management of the negative electrode can be coordinated. This coordination helps maintain the structural integrity of the battery during cycling, reduces capacity decay, and thus ensures that the battery maintains a high capacity retention rate even after long-term use. In summary, by establishing a mathematical model relating the weight ratio 'a' of the positive electrode active material to the lithium replenishment agent, the weight ratio 'b' of the negative electrode silicon-carbon composite material to graphite, and the compaction density 'c' of the negative electrode active layer, effective matching between the positive and negative electrode materials is achieved, thereby significantly optimizing the overall performance of the resulting lithium-ion battery.

[0025] Furthermore, a, b, and c satisfy the following condition: 150 ≤ a × c / b ≤ 2500, preferably 200 ≤ a × c / b ≤ 700. These two more preferred numerical ranges allow for better coordination between the lithium replenishment efficiency of the positive electrode and the volume expansion management of the negative electrode, achieving refined control of the resulting battery performance. Therefore, in the pursuit of high energy density in lithium-ion batteries, cycle stability and safety can be better maintained.

[0026] Regarding the value of 'a' (i.e., the weight ratio of positive electrode active material to lithium replenisher), it is preferred to satisfy: 5≤a≤60, more preferably 11.5≤a≤49, and even more preferably 15≤a≤35, so that the lithium replenisher can more significantly replenish lithium ion loss, while more effectively reducing the excessive oxidation of electrolyte and the decrease in structural stability caused by excessive addition, thereby further improving the stability and safety of the resulting lithium-ion battery throughout its entire life cycle.

[0027] In several preferred embodiments, the positive electrode active material is selected from one or more of lithium manganese iron phosphate, lithium iron phosphate, and ternary positive electrode materials (specifically, NCM111, NCM523, etc.). Among these, lithium manganese iron phosphate is preferred due to its higher safety and lower cost characteristics. The lithium supplementer is selected from one or more of lithium nickel oxide, Li5FeO4, and lithium manganese oxide. To better match and optimize the α value and obtain a battery system with higher energy density, lithium nickel oxide is preferred as the specific type of lithium supplementer.

[0028] Meanwhile, in the positive electrode active layer, in order to more effectively shorten the diffusion path of lithium ions, improve the electrochemical reaction rate, and thus significantly enhance the power density of the battery, the D50 of the positive electrode active material is preferably 1 μm to 8 μm, more preferably 2 μm to 5 μm; and / or, the D50 of the lithium replenishing agent is preferably 3 μm to 15 μm, more preferably 5 μm to 12 μm. Based on this, the D50 ratio of the positive electrode active material to the lithium replenishing agent is preferably 1:(1 to 6), more preferably 1:(2.5 to 3), so as to optimize the interaction between the positive electrode material and the lithium replenishing agent at the microscopic level, thereby further reducing interfacial impedance and promoting a higher energy density in the resulting lithium-ion battery.

[0029] Regarding the b-value (i.e., the weight ratio of silicon-carbon composite material to graphite), it is preferably satisfied that: 0.02 ≤ b ≤ 0.20, more preferably 0.03 ≤ b ≤ 0.17, and even more preferably 0.08 ≤ b ≤ 0.12. As mentioned above, silicon-carbon composite materials are used to improve energy density due to their high theoretical capacity, but their significant volume expansion needs to be balanced by the ratio with graphite. Therefore, this invention improves energy density while more significantly suppressing the volume expansion problem by progressively optimizing the b-value representing the weight ratio of silicon-carbon composite material to graphite, ultimately enabling the resulting lithium-ion battery to maintain better cycle performance.

[0030] Furthermore, in the negative electrode active layer, to more effectively promote lithium-ion diffusion and better facilitate a more uniform distribution of the negative electrode active material, thereby reducing stress concentration within the electrode, the D50 of graphite is preferably 8 μm to 25 μm, more preferably 15 μm to 20 μm; and / or, the D50 of the silicon-carbon composite material is 3 μm to 15 μm, more preferably 8 μm to 10 μm. Based on this, the D50 ratio of graphite to silicon-carbon composite material is further preferably (1.5 to 2.5):1, to better integrate with the adjustment of the b-value, thereby better managing the volume expansion of the negative electrode material, reducing electrode pulverization, and ultimately improving the stability of the resulting lithium-ion battery at high energy densities.

[0031] Furthermore, in order to further mitigate the volume expansion problem and achieve a better balance between increasing energy density and maintaining structural stability, the silicon content of the silicon-carbon composite material is preferably 3wt% to 15wt%.

[0032] In several preferred embodiments, c satisfies: 1.4 ≤ c ≤ 1.8, preferably 1.45 ≤ c ≤ 1.75, and more preferably 1.55 ≤ c ≤ 1.65. As mentioned earlier, higher compaction density means that more active material can be loaded into the same volume of electrode, theoretically significantly improving energy density. However, excessively high compaction density increases internal stress in the electrode, especially when the b value is high, which exacerbates the volume expansion of the silicon-carbon composite material, leading to damage to the electrode structure. Based on this, the present invention improves energy density while more effectively reducing the cycle performance degradation caused by excessively high compaction density by gradually optimizing the range of c values. Simultaneously, the gradually optimized c values ​​can be coordinated with the adjustment of parameters a and b to more efficiently balance battery capacity, structural stability, and energy density, maximizing the overall performance of the battery.

[0033] To achieve a better balance between improving battery energy density and optimizing lithium-ion transport speed, the thickness of the positive electrode active layer is further preferably 70 μm to 120 μm, more preferably 80 μm to 100 μm; and / or, the thickness of the negative electrode active layer is 60 μm to 100 μm, more preferably 70 μm to 90 μm. Furthermore, the ratio of the thickness of the positive electrode active layer to the thickness of the negative electrode active layer is further preferably 1:(0.8 to 1.0), in order to complement the optimizations in a, b, and c above and more significantly enhance the overall performance of the resulting lithium-ion battery.

[0034] Furthermore, the electrolyte comprises LiPF6, LiFSI, and additives; the concentration of LiPF6 is 1 ± 0.05 M, and the concentration of LiFSI is 0.2 ± 0.01 M; the additives include fluoroethylene carbonate and vinylene carbonate; preferably, based on 100% of the total weight of the electrolyte, the content of fluoroethylene carbonate is 5 wt% to 8 wt%, and the content of vinylene carbonate is 1 wt% to 3 wt%. In particular, the addition of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) at specific concentrations can synergistically work with the α value in the positive electrode to reduce lithium loss during the first charge and discharge cycle, thereby further improving the initial efficiency and cycle stability of the resulting lithium-ion battery.

[0035] A second aspect of the present invention provides an application of the above-mentioned lithium-ion battery as an energy storage device in the fields of electric vehicles or energy storage. Because the lithium-ion battery obtained by the present invention can balance high energy density, high initial efficiency, and long cycle life, its performance is particularly superior, and its safety is also more reliable, providing strong technical support and application prospects for the fields of electric vehicles and energy storage.

[0036] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Example 1

[0039] A type of lithium-ion battery:

[0040] (1) Preparation of positive electrode sheet: Lithium manganese iron phosphate (LMFP) with a D50 of 2.5 μm and lithium nickel oxide (LNO) with a D50 of 7 μm were weighed and mixed at a weight ratio of LMFP:LNO = 24 (i.e., a) to obtain a composite positive electrode active material. The obtained composite positive electrode active material was dispersed in NMP with a conductive agent and a binder at a weight ratio of 97.1%:0.9%:2% and stirred evenly to obtain a positive electrode active slurry. The obtained positive electrode active slurry was coated on a positive electrode current collector and then dried and cold-pressed to obtain a positive electrode sheet with a positive electrode active layer thickness of 86 μm.

[0041] (2) Preparation of negative electrode sheet: Weigh graphite with a D50 of 16 μm and silicon-carbon composite material (model HD-1111-443-007A, with a silicon content of 10 wt%) with a D50 of 8.5 μm, and mix them according to the weight ratio of graphite:silicon-carbon composite material = 0.1 (i.e., b) to obtain a composite negative electrode active material. Disperse the obtained composite negative electrode active material with conductive agent and binder in NMP at a weight ratio of 95.9%:1.4%:2.7%, and stir evenly to obtain a negative electrode active slurry. Coat the obtained negative electrode active slurry onto the negative electrode current collector, and obtain a negative electrode sheet through drying, cold pressing and other processes. The thickness of the negative electrode active layer on the sheet is 82 μm, and the compaction density c is 1.60 g / cm³. 3 .

[0042] (3) Preparation of electrolyte: a. Under argon protection, EC, EMC, and DMC (volume ratio 3:5:2) are added to a dry reactor and stirred for 30 minutes (25°C); b. LiPF6 (controlling the final concentration to 1M) and LiFSI (controlling the final concentration to 0.2M) are slowly added and stirred for 2 hours until completely dissolved (avoiding excessively high local concentrations); c. FEC (5wt%), VC (2wt%), LiDFOB (1wt%), DTD (0.5wt%), and TMSPi (0.3wt%) are added sequentially, stirring for 15 minutes after each addition; d. The solution is filtered through a 0.2μm polytetrafluoroethylene (PTFE) membrane, and the moisture content (<20ppm) and free acid content (<50ppm) are measured; e. The solution is sealed with argon gas and stored in an environment below 25°C in the dark. It should be used within 48 hours.

[0043] (4) Assembly of lithium-ion batteries: The above positive and negative electrode sheets and polyethylene separator with a thickness of 25μm after vacuum drying are cut and die-cut, and then injected with the electrolyte obtained above to assemble a lithium-ion square battery, wherein a, b and c satisfy the following: a×c / b=384.

[0044] For ease of comparison, the values ​​of a, b, c, silicon content of silicon-carbon composite materials, and the value of a×c / b are shown in Table 1.

[0045] Example 2

[0046] A type of lithium-ion battery:

[0047] (1) Preparation of positive electrode sheet: Lithium manganese iron phosphate (LMFP) with a D50 of 4 μm and lithium nickel oxide (LNO) with a D50 of 11 μm were weighed and mixed at a weight ratio of LMFP:LNO = 32 (i.e., a) to obtain a composite positive electrode active material. The obtained composite positive electrode active material was dispersed in NMP with a conductive agent and a binder at a weight ratio of 97.1%:0.9%:2% and stirred evenly to obtain a positive electrode active slurry. The obtained positive electrode active slurry was coated on a positive electrode current collector and then dried and cold-pressed to obtain a positive electrode sheet with a positive electrode active layer thickness of 94 μm.

[0048] (2) Preparation of negative electrode sheet: Graphite with a D50 of 19 μm and silicon-carbon composite material (model HD-1111-443-007A, with a silicon content of 8 wt%) with a D50 of 9.5 μm were weighed and mixed according to the weight ratio of graphite:silicon-carbon composite material = 0.08 (i.e., b) to obtain a composite negative electrode active material. The obtained composite negative electrode active material, conductive agent, and binder were dispersed in NMP at a weight ratio of 95.9%:1.4%:2.7% and stirred evenly to obtain a negative electrode active slurry. The obtained negative electrode active slurry was coated on a negative electrode current collector, and the negative electrode sheet was obtained through drying, cold pressing, and other processes. The thickness of the negative electrode active layer on the sheet was 90 μm, and the compaction density c was 1.55 g / cm³. 3 .

[0049] (3) a. Under argon protection, add EC, EMC, and DMC (volume ratio 3:5:2) to the dry reactor and stir for 30 minutes (25°C); b. Slowly add LiPF6 (control the final concentration to 1M) and LiFSI (control the final concentration to 0.2M) and stir for 2 hours until completely dissolved (avoid local high concentration); c. Add FEC (5wt%), VC (2wt%), LiDFOB (1wt%), DTD (0.5wt%), and TMSPi (0.3wt%) in sequence, stirring for 15 minutes after each addition; d. Filter through a 0.2μm polytetrafluoroethylene (PTFE) membrane and test for moisture (<20ppm) and free acid (<50ppm); e. Seal with argon gas and store in an environment below 25°C, protected from light, and use within 48 hours.

[0050] (4) Assembly of lithium-ion batteries: The above positive and negative electrode sheets and polyethylene separator with a thickness of 25μm after vacuum drying are cut and die-cut, and then injected with the electrolyte obtained above to assemble a lithium-ion square battery, wherein a, b and c satisfy the following: a×c / b=620.

[0051] For ease of comparison, the values ​​of a, b, c, silicon content of silicon-carbon composite materials, and the value of a×c / b are shown in Table 1.

[0052] Examples 3 to 5

[0053] The differences between Examples 3 to 5 and Example 1 are only in the values ​​of a, b, c, silicon content of the silicon-carbon composite material, and the value of a×c / b, as detailed in Table 1.

[0054] Example 6

[0055] A type of lithium-ion battery:

[0056] The only difference between this embodiment and Embodiment 1 is that in step (1), the D50 of lithium manganese iron phosphate is changed to 2 μm, and the D50 of lithium nickel oxide lithium supplement is changed to 12 μm.

[0057] At this point, the D50 ratio of lithium manganese iron phosphate to lithium nickel oxide lithium supplement is changed to 1:6.

[0058] Example 7

[0059] A type of lithium-ion battery:

[0060] The only difference between this embodiment and Embodiment 1 is that the D50 of both lithium manganese iron phosphate and lithium nickel oxide lithium supplementer is changed to 8 μm in step (1).

[0061] At this point, the D50 ratio of lithium manganese iron phosphate to lithium nickel oxide lithium supplement is changed to 1:1.

[0062] Example 8

[0063] A type of lithium-ion battery:

[0064] The only difference between this embodiment and Embodiment 1 is that in step (2), the D50 of graphite is changed to 25 μm and the D50 of silicon-carbon composite material is changed to 5 μm.

[0065] At this point, the D50 ratio of the graphite to silicon-carbon composite material changes to 5:1.

[0066] Example 9

[0067] A type of lithium-ion battery:

[0068] The only difference between this embodiment and Embodiment 1 is that in step (2), the D50 of graphite is changed to 8 μm and the D50 of silicon-carbon composite material is changed to 15 μm.

[0069] At this point, the D50 ratio of the graphite to silicon-carbon composite material changes to 0.53:1.

[0070] Example 10

[0071] A type of lithium-ion battery:

[0072] The only difference between this embodiment and Embodiment 1 is that the thickness of the obtained positive electrode active layer is changed to 70 μm in step (1), and the thickness of the obtained negative electrode active layer is changed to 100 μm in step (2).

[0073] At this point, the thickness ratio of the positive electrode active layer to the negative electrode active layer changes to 1:1.39.

[0074] Example 11

[0075] A type of lithium-ion battery:

[0076] The only difference between this embodiment and Embodiment 1 is that the thickness of the obtained positive electrode active layer is changed to 120 μm in step (1), and the thickness of the obtained negative electrode active layer is changed to 60 μm in step (2).

[0077] At this point, the thickness ratio of the positive electrode active layer to the negative electrode active layer changes to 1:0.5.

[0078] Example 12

[0079] A type of lithium-ion battery:

[0080] The only difference between this embodiment and Embodiment 1 is that FEC and VC were not added to the electrolyte system in step (3).

[0081] Comparative Examples 1 to 2

[0082] The only differences between Comparative Examples 1 and 2 and Example 1 are the values ​​of a, b, c, silicon content of the silicon-carbon composite material, and the value of a×c / b, as detailed in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] Examples and comparative examples not shown in the table, wherein the values ​​of a, b, c, silicon content of the silicon-carbon composite material, and a×c / b are the same as in Example 1.

[0087] Performance testing

[0088] (1) Initial Coulomb Efficiency Test: At 45℃, the device was charged with a small current of 0.2C and then divided at 0.5C at 25℃ to obtain the initial charge and discharge capacity data. The initial Coulomb efficiency was calculated, and the test results are shown in Table 2.

[0089] (2) Cyclic Performance Test: At 25℃, the battery samples obtained from each embodiment and comparative example were left to stand for 1 hour, then charged to 4.2V with a constant current and constant voltage of 1C, and the cutoff current was 0.05C; then left to stand for 30 minutes, and placed at 2.8V with a constant current of 1C; after 500 cycles, the stability of the material was evaluated by the cycle capacity retention rate. A HIOKI BT3562 instrument integrated in the capacity testing cabinet was used to monitor the thickness change during the charging and discharging process in real time, and the volume expansion was calculated. The test results are shown in Table 2. In the calculation, the volume expansion rate ≈ the thickness expansion rate, that is:

[0090]

[0091] Where ΔV is the increase in volume of the cell after 500 cycles, V0 is the initial volume of the cell, Δh is the increase in thickness of the cell after 500 cycles, and h0 is the initial thickness of the cell.

[0092] Table 2

[0093]

[0094]

[0095] As can be seen from the above description, compared with Comparative Example 1, which has low energy density, and Comparative Example 2, which has poor first-time efficiency and cycle life, the above embodiments of the present invention realize the preparation and assembly of a lithium-ion battery with superior overall performance. The resulting lithium-ion battery can have high energy density, high first-time efficiency, and long cycle life.

[0096] In each embodiment, comparing embodiments 1 to 5, it can be seen that by optimizing the values ​​of a, b, c, and a×c / b, the lithium replenishment efficiency of the positive electrode and the volume expansion management of the negative electrode can be better coordinated, thereby achieving fine control of the battery performance and ultimately significantly improving the various performance characteristics of the resulting lithium-ion battery, including energy density, cycle stability, and safety.

[0097] Comparing Examples 6 and 7 with Example 1, it can be seen that by optimizing the D50 ratio of the positive electrode active material to the lithium replenishing agent, the interfacial impedance in the positive electrode active layer can be further reduced, promoting the resulting lithium-ion battery to exhibit higher energy density.

[0098] Comparing Examples 8 and 9 with Example 1, it can be seen that by optimizing the D50 ratio of graphite to silicon-carbon composite material, the volume expansion of the negative electrode material can be better managed, electrode pulverization can be reduced, and the stability of the resulting lithium-ion battery under high energy density can be improved.

[0099] Comparing Examples 10 and 11 with Example 1, it can be seen that by optimizing the ratio of the thickness of the positive electrode active layer to the negative electrode active layer, it is possible to better coordinate with the optimization of the a value, b value, c value, and the relationship between the three, thereby significantly enhancing the overall performance of the obtained lithium-ion battery.

[0100] Comparing Example 12 with Example 1, it can be seen that in the electrolyte system, by optimizing the type and content of additives, they can work synergistically with the a value in the positive electrode to reduce lithium loss during the first charge and discharge process, thereby further improving the first efficiency and cycle stability of the obtained lithium-ion battery.

[0101] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, and the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, characterized in that, The positive electrode active layer includes a positive electrode active material and a lithium replenishing agent, and the weight ratio of the positive electrode active material to the lithium replenishing agent is denoted as a; The negative electrode active layer includes silicon-carbon composite material and graphite, and the weight ratio of the silicon-carbon composite material to the graphite is denoted as b. Let the compaction density of the negative electrode active layer be c; The conditions a, b, and c satisfy: 100 ≤ a × c / b ≤ 3000.

2. The lithium-ion battery according to claim 1, characterized in that, The conditions a, b, and c satisfy: 150 ≤ a × c / b ≤ 2500, preferably 200 ≤ a × c / b ≤ 700.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The condition 'a' satisfies: 5 ≤ a ≤ 60, preferably 11.5 ≤ a ≤ 49, and more preferably 15 ≤ a ≤ 35.

4. The lithium-ion battery according to claim 3, characterized in that, The positive electrode active material is selected from one or more of lithium manganese iron phosphate, lithium iron phosphate, and ternary positive electrode materials, preferably lithium manganese iron phosphate; and / or, The lithium supplement is selected from one or more of lithium nickel oxide, Li5FeO4 and lithium manganese oxide, preferably lithium nickel oxide; Preferably, the D50 of the positive electrode active material is 1 μm to 8 μm; and / or, the D50 of the lithium supplement is 3 μm to 15 μm; More preferably, the D50 ratio of the positive electrode active material to the lithium supplement is 1: (1～6)。 5. The lithium-ion battery according to any one of claims 1 to 4, characterized in that, The value of b satisfies: 0.02≤b≤0.20, preferably 0.03≤b≤0.17, and more preferably 0.08≤b≤0.

12.

6. The lithium-ion battery according to claim 5, characterized in that, The graphite has a D50 of 8 μm to 25 μm; and / or, The D50 of the silicon-carbon composite material is 3μm to 15μm; Preferably, the silicon content of the silicon-carbon composite material is 3wt% to 15wt%.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that, The c satisfies: 1.4≤c≤1.8, preferably 1.45≤c≤1.75, and more preferably 1.55≤c≤1.

65.

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that, The thickness of the positive electrode active layer is 70 μm to 120 μm; and / or, The thickness of the negative electrode active layer is 60μm to 100μm; Preferably, the thickness ratio of the positive electrode active layer to the negative electrode active layer is 1: (0.8～1.0)。 9. The lithium-ion battery according to any one of claims 1 to 8, characterized in that, The electrolyte includes LiPF6, LiFSI, and additives; and... The concentration of LiPF6 is 1 ± 0.05 M, and the concentration of LiFSI is 0.2 ± 0.01 M; The additives include fluoroethylene carbonate and vinylene carbonate; Preferably, based on the total weight of the electrolyte (100%), the content of fluoroethylene carbonate is 5 wt% to 8 wt%, and the content of vinylene carbonate is 1 wt% to 3 wt%.

10. The application of a lithium-ion battery as an energy storage device in the field of electric vehicles or energy storage, according to any one of claims 1 to 9.

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