A long-cycle lithium-ion battery

Abstract

This application relates to the field of lithium batteries, and more particularly to a long-cycle lithium-ion battery. The negative electrode material of this battery is natural graphite with a surface coated with fast ion conductors, and is directionally modified in conjunction with a corresponding electrolyte. The lithium battery prepared by this application can effectively suppress the solvation co-intercalation phenomenon of natural graphite, thereby significantly improving the cycle performance of natural graphite batteries.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and in particular to a long-cycle lithium-ion battery. Background Technology

[0002] Artificial graphite, with its advantages of high specific capacity, high rate performance, high temperature resistance, and long cycle life, is currently the mainstream anode material for lithium batteries. However, artificial graphite requires a long-term high-temperature graphitization process (the industry standard graphitization time is 21 days), resulting in significant energy consumption and environmental pollution. Natural graphite, on the other hand, does not require graphitization and possesses a higher specific capacity than artificial graphite, making it a more promising material for applications.

[0003] However, when natural graphite is used as a negative electrode material for lithium-ion batteries, there is a problem that the graphite layer is easily peeled off due to solvation co-intercalation, which leads to a decrease in the cycle performance of lithium-ion batteries. Summary of the Invention

[0004] This application provides a long-cycle lithium-ion battery that uses natural graphite as the negative electrode material and can effectively reduce the probability of solvation co-intercalation of graphite, thereby significantly improving the cycle performance of the lithium-ion battery.

[0005] This application provides a long-cycle lithium-ion battery, which adopts the following technical solution:

[0006] A long-cycle lithium-ion battery, wherein the negative electrode material is natural graphite with a surface coated with fast ion conductors.

[0007] The structure of natural graphite causes significant volume changes in lithium ions during insertion and extraction, especially in Li. + The co-intercalation of solvents makes it easier to damage the graphite layer structure, leading to easy exfoliation of the graphite layers and resulting in irreversible capacity loss and decreased cycling performance. In the above technical solution, coating the surface of natural graphite with fast ion conductors can act as a buffer, effectively reducing Li... + - The probability of solvent co-intercalation into the layered structure of natural graphite. Simultaneously, the fast ion conductor possesses lithium-ion diffusion channels, enabling rapid transfer of lithium ions to the natural graphite layers for storage, ensuring the proper intercalation of lithium ions within the natural graphite.

[0008] This application utilizes natural graphite instead of artificial graphite, which facilitates lithium-ion insertion and extraction. It reduces the likelihood of lithium-ion deposition and dendrite formation during battery charging and discharging, thus ensuring battery capacity and improving cycle performance. Furthermore, the surface-coated fast-ion conductor can provide some lithium ions to the battery, further enhancing its cycle performance.

[0009] Preferably, the fast ion conductor includes a sodium superion conductor, a lithium superion conductor, a garnet-type ion conductor, a perovskite-type lithium lanthanum titanate, and Li7P3S. 11 One or more of them.

[0010] The aforementioned fast ion conductors can effectively coat and modify natural graphite, providing good buffering protection and lithium-ion transfer.

[0011] Typical, but not limiting, sodium superionic conductors are NaFe₂PO₄(MoO₄)₂; lithium superionic conductors are LATP, i.e., Li₂. 1+x Al x Ti 2-x (PO4)3 (2≥x≥0); Garnet-type ionic conductor is Li 7-x La 3+x Zr2O 12 (0.5≥x≥0.1), Li2S-P2S5, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Perovskite-type lithium lanthanum titanate is Li 3x La 2 / 3-x TiO3 (0.5 ≥ x ≥ 0.1).

[0012] Preferably, the coating thickness of the fast ion conductor is 5–300 nm.

[0013] By adopting the above technical solution, the thickness of the fast ion conductor needs to play a buffering and protective role on the one hand, and a role in rapidly transferring lithium ions on the other hand. Therefore, its thickness should be controlled within the above-mentioned suitable range.

[0014] Preferably, the D50 of the natural graphite is 15-20 μm.

[0015] When the surface is coated with a fast ion conductor, the aforementioned limited range of natural graphite particle size helps to reduce the van der Waals forces that need to be overcome during lithium ion insertion, increase the number of lithium ion diffusion channels, reduce the probability of lithium dendrite formation, and help ensure the cycle performance of the battery.

[0016] Typical, but not limiting, natural graphite has a D50 of 17 ± 2 μm.

[0017] Preferably, the negative electrode material of the lithium-ion battery is obtained by ball milling.

[0018] The aforementioned ball milling refers to the process of repeatedly extruding and deforming natural graphite particles and fast ion conductor particles under high kinetic energy through ball milling, followed by fracture welding to form a coating structure.

[0019] Typically, but not limitingly, the amount of fast ion conductor used in ball milling is 1 to 10% of the graphite mass.

[0020] Preferably, the electrolyte solvent of the lithium-ion battery is a combination of two or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0021] The electrolyte solvent obtained by combining the above technical solutions has, on the one hand, good compatibility with fast ion conductors and is not prone to electrolyte decomposition, thereby suppressing the generation of solvation co-intercalation; on the other hand, this combined solvent can reduce Li + Interaction with the solvent, thereby reducing Li + - Solvent co-intercalation.

[0022] Preferably, the electrolyte of the lithium-ion battery contains an additive, wherein the additive is at least two of the following: vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, and methane disulfonate.

[0023] By adopting the above technical solution, the addition of the above additives can promote the improvement of the cycle life and storage stability of lithium-ion batteries. In particular, the addition of fluoroethylene carbonate and difluoroethylene carbonate can promote the repair of the interface of the natural graphite inner layer after co-generation and reduce the probability of natural graphite layer peeling off.

[0024] Preferably, the lithium salt used in the electrolyte of the lithium-ion battery is one or more of LiPF6, LiTFSI, LiFSI, LiPF2O2, LiBOB, and LiDFOB.

[0025] By adopting the above technical solution, the lithium salt provides a sufficient lithium-ion reserve for the electrolyte, ensuring the charge and discharge performance of the lithium battery.

[0026] In summary, this application has the following beneficial effects:

[0027] 1. In this application, by coating and modifying the surface of natural graphite with fast ion conductors, the problem of graphite layer peeling caused by solvation co-intercalation can be effectively alleviated, thereby effectively improving the cycle performance of lithium-ion batteries.

[0028] 2. The electrolyte of the lithium battery in this application, by employing a composition of specific solvents, can effectively suppress Li... + - The formation of solvent structures and the reduction of solvation co-intercalation. Detailed Implementation

[0029] Example of negative electrode material preparation

[0030] Preparation Example 1: A negative electrode material with a D50 of 17 ± 2 micrometers and a specific surface area of ​​2.5 ± 0.5 μm. 2 1 kg of natural graphite with a closing capacity ≥360 mAh / g was added to a ball mill, and then 0.03 kg of Li was weighed out. 1.3 Al 0.3 Ti 1.7 (PO4)3 (lithium superionic conductor). Using small balls with a diameter of 5 mm and a ball-to-material ratio of 10:1, the material was ball-milled at a speed of 300 r / min for 2 h to obtain natural graphite with a surface coating of fast ion conductors, and the coating thickness of the fast ion conductors was 100 nm.

[0031] Preparation Example 2: A negative electrode material with a D50 of 17 ± 2 micrometers and a specific surface area of ​​2.5 ± 0.5 μm. 2 Add 1 kg of natural graphite with a closing capacity ≥360 mAh / g to a ball mill, and then weigh out 0.1 kg of Li. 7-x La 3+x Zr2O 12 (0.5≥x≥0.1)(Garnet-type ionic conductor). Using small balls with a diameter of 8 mm and a ball-to-material ratio of 15:1, the material was ball-milled at a speed of 400 r / min for 2 h to obtain natural graphite with a surface coating of fast ionic conductors, and the coating thickness of the fast ionic conductors was 300 nm.

[0032] Preparation Example 3: A negative electrode material with a D50 of 17 ± 2 micrometers and a specific surface area of ​​2.5 ± 0.5 μm. 2 Add 1 kg of natural graphite with a closing capacity ≥360 mAh / g to a ball mill, and then weigh out 0.05 kg of Li. 3x La 2 / 3-x TiO3 (0.5≥x≥0.1) (perovskite type lanthanum lithium titanate). Using small balls with a diameter of 5 mm and a ball-to-material ratio of 10:1, the mixture was ball-milled at 260 r / min for 3 h to obtain natural graphite with a surface coating of fast ion conductors, and the coating thickness of the fast ion conductors was 150 nm.

[0033] Preparation Example 4: A negative electrode material with a D50 of 17 ± 2 micrometers and a specific surface area of ​​2.5 ± 0.5 μm. 2 1 kg of natural graphite with a closing capacity ≥360 mAh / g was added to a ball mill, and then 0.01 kg of Li was weighed out. 1.3 Al 0.3 Ti 1.7 (PO4)3 (lithium superionic conductor). Using small balls with a diameter of 10 mm and a ball-to-material ratio of 10:1, the material was ball-milled at a speed of 300 r / min for 1 h to obtain natural graphite with a surface coating of fast ion conductors, and the coating thickness of the fast ion conductors was 5 nm.

[0034] Preparation Example 5, an anode material, differs from Preparation Example 1 in that an equal amount of NaFe2PO4(MoO4)2 (sodium superionic conductor) is used instead of lithium superionic conductor.

[0035] Preparation Example 6, an anode material, differs from Preparation Example 1 in that it uses an equal amount of Li7P3S. 11 Replacement for lithium superion conductors.

[0036] Example

[0037] Example 1: A long-cycle lithium battery using lithium iron phosphate as the positive electrode material, with a positive electrode slurry ratio of LFP:PVDF:SP = 96:2.0:2.0 and a positive electrode areal density of 500±6 g / m³. 2 Compacted density 2.2 g / cm³ -3 Using the fast ion conductor-coated natural graphite obtained in Example 1 as the negative electrode material, the negative electrode slurry ratio was C:CMC:SP:SBR = 95.8:1.4:1.0:1.8; the negative electrode surface density was 220±5 g / m³. 2 Compacted density 1.65 g / cm³ -3 The separator is a 25-micron dry-process double-stretched separator, and the electrolyte formula is shown in Table 1. Then, a 100Ah square aluminum-shell cell is made by stacking the separator, negative electrode, separator, positive electrode, and separator in that order.

[0038] Example 2: A long-cycle lithium battery using lithium iron phosphate as the positive electrode material, with a positive electrode slurry ratio of LFP:PVDF:SP = 95:3.5:1.5 and a positive electrode areal density of 400±6 g / m³. 2 Compacted density 2.25 g / cm³ -3 Using the fast ion conductor-coated natural graphite obtained in Example 2 as the negative electrode material, the negative electrode slurry ratio was C:CMC:SP:SBR = 94.8:2.0:1.2:2; the negative electrode areal density was 176±5 g / m³. 2 Compacted density 1.6 g / cm³ -3 The separator is a 25-micron dry-process double-stretched separator, and the electrolyte formula is shown in Table 1. Then, a 100Ah square aluminum-shell cell is made by stacking the separator, negative electrode, separator, positive electrode, and separator in that order.

[0039] Example 3: A long-cycle lithium battery using lithium iron phosphate as the positive electrode material, with a positive electrode slurry ratio of LFP:PVDF:SP = 95:3.5:1.5 and a positive electrode areal density of 360±6 g / m³. 2 Compacted density 2.5 g / cm³ -3Using the fast ion conductor-coated natural graphite obtained in Example 3 as the negative electrode material, the negative electrode slurry ratio was C:CMC:SP:SBR = 94.8:2.0:1.2:2; the negative electrode areal density was 176±5 g / m³. 2 Compacted density 1.6 g / cm³ -3 The separator is a 25-micron dry-process double-stretched separator, and the electrolyte formula is shown in Table 1. Then, a 100Ah square aluminum-shell cell is made by stacking the separator, negative electrode, separator, positive electrode, and separator in that order.

[0040] Example 4, a long-cycle lithium battery, differs from Example 1 in that an equal amount of natural graphite coated with the fast-ion conductor obtained in Example 4 is used as the negative electrode material.

[0041] Example 5, a long-cycle lithium battery, differs from Example 1 in that an equal amount of natural graphite coated with the fast-ion conductor obtained in Example 5 is used as the negative electrode material.

[0042] Example 6, a long-cycle lithium battery, differs from Example 1 in that an equal amount of natural graphite coated with the fast-ion conductor obtained in Example 6 is used as the negative electrode material.

[0043] Examples 7-12 are long-cycle lithium batteries, which differ from Example 1 in that the electrolyte ratios are different and are shown in Table 1.

[0044] Table 1. Lithium-ion battery electrolyte ratio (kg)

[0045]

[0046] Comparative Example

[0047] Comparative Example 1, a long-cycle lithium battery, differs from Example 8 in that it uses natural graphite with a surface uncoated for fast ion conductors.

[0048] Performance testing

[0049] Lithium battery cycle performance test

[0050] Test subjects: Lithium batteries obtained in the above embodiments and comparative examples.

[0051] Test method: At 60℃, charge and discharge cycles were performed using a charge / discharge rate of 0.5C / 0.5C. The resting time between charge and discharge was 30 minutes. The cycle termination condition was 80% of the initial battery capacity. The number of battery cycles was recorded. The test results are shown in Table 2.

[0052] Table 2. Results of lithium battery cycle performance test

[0053]

[0054] Analysis of experimental results:

[0055] (1) As can be seen from Examples 1-12 and Comparative Example 1, and in conjunction with Table 2, compared to Comparative Example 1, the embodiments of this application effectively improve the cycle performance of lithium batteries by using fast-ion conductors to coat and modify natural graphite and using it as a negative electrode material for lithium batteries. Under high-temperature charge-discharge cycles, when the battery capacity decays to 80%, the lithium battery using fast-ion coated natural graphite has approximately 300% more cycles than a conventional natural graphite battery.

[0056] The reason for the above phenomenon may be that the fast ion conductor coating modification on the surface of natural graphite can play a buffering and protective role, effectively reducing Li. + - The solvent co-intercalates into the layered structure of natural graphite, thereby reducing the shedding of natural graphite and ensuring battery capacity. Simultaneously, the fast ion conductor contains lithium-ion diffusion channels, enabling rapid transfer of lithium ions to the natural graphite layers for storage, ensuring proper lithium-ion intercalation within the natural graphite.

[0057] (2) Combining Examples 1 and 9 with Table 2, it can be seen that, compared with Example 9, the electrolyte in Example 1 uses at least two specific solvents to form a compound, which makes it more compatible with natural graphite and weakens the interaction between the solvent and lithium ions, thereby further reducing the solvation co-intercalation phenomenon. This effectively ensures the cycle performance of the battery.

[0058] (3) Combining Examples 1, 10, 11 and Examples 8, 12 and Table 2, it can be seen that, compared with Examples 8 and 12, the electrolytes used in Examples 1, 10, and 11 are fluoroethylene carbonate, difluoroethylene carbonate, or a combination of both. These electrolytes can promote the repair of the interface of the natural graphite inner layer after co-intercalation, reduce the probability of natural graphite layer peeling off, and thus help improve the cycle performance of lithium batteries.

[0059] This specific embodiment is merely an explanation of this application and is not intended to limit it. Those skilled in the art can make modifications to this embodiment without contributing any inventive step after reading this specification.

Claims

1. A lithium-ion battery, wherein the battery cells are stacked in the order of separator, negative electrode, separator, positive electrode, and separator, characterized in that, The negative electrode material of the lithium-ion battery is natural graphite with a fast ion conductor coated on its surface. Fast ionic conductors include sodium superionic conductors, lithium superionic conductors, garnet-type ionic conductors, perovskite-type lithium lanthanum titanate and Li7P3S. 11 One or more of them; The negative electrode material of the battery is prepared by ball milling, and the amount of fast ion conductor used in the ball milling is 1 to 10% of the graphite mass; The electrolyte solvent of the battery uses at least two of the following: ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate. Additives are added to the electrolyte of the battery, and the additives are one or more of the following: vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, and methane disulfonate. The D50 of natural graphite is 15–20 μm; The coating thickness of fast ion conductors is 5–300 nm; The ball milling refers to the process of repeatedly extruding and deforming natural graphite particles and fast ion conductor particles under high kinetic energy through ball milling, followed by fracture welding to form a coating structure.

2. A lithium-ion battery according to claim 1, characterized in that, The electrolyte of the lithium-ion battery uses one or more of the following lithium salts: LiPF6, LiTFSI, LiFSI, LiPF2O2, LiBOB, and LiDFOB.

Images