Novel additive, electrolyte, and lithium ion battery

Abstract

A novel additive, an electrolyte, and a lithium ion battery, relating to the technical field of lithium ion batteries. The electrolyte comprises a lithium salt and a non-aqueous solvent for dissolving the lithium salt, the electrolyte further comprises an electrolyte additive, the electrolyte additive comprises a positive electrode film-forming additive and a negative electrode film-forming additive, and the electrolyte additive further comprises a fluoro isocyanate-based pyridazine organic compound. The additive can absorb moisture and hydrofluoric acid in the electrolyte, reduce the dissolution of transition metals, improve the thermal stability of lithium hexafluorophosphate, and maintains the stability of a ternary material under high voltage; a sulfuric acid group on the novel additive can be oxidized by oxygen at a positive electrode, so that the oxygen generated when an LFO lithium supplementing agent is activated is absorbed, the capacity exertion, high temperature cycle and high temperature storage of the LFO lithium supplementing agent are significantly improved, and the DCIR of the battery will not obviously increase, thereby improving the stability of the battery.

Description

A novel additive, electrolyte and lithium ion battery thereof Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a novel additive, an electrolyte and a lithium-ion battery thereof for lithium-supplemented lithium-ion batteries. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in electric vehicles and energy storage due to their high energy density and long life. While LIBs have a high energy density, their energy density per unit mass is lower than that of traditional fuels, and this energy density still cannot fully address the range anxiety of electric vehicles. Current methods for improving the energy density of LIBs include: 1. increasing the voltage per unit mass of the battery cell; 2. increasing the capacity per unit mass of the battery cell. Increasing cell capacity primarily involves using silicon-based anodes with higher energy density. While silicon-based anodes have a high energy density, they experience significant volume expansion and contraction during charge and discharge, resulting in low initial charge and discharge efficiency. Adding cathode film-forming additives to silicon-based LIBs can significantly improve the battery's coulombic efficiency during initial charge and discharge. Common cathode film-forming additives include lithium-rich ferrite (LFO) and lithium-rich nickel oxide (LNO). LNO has a lower discharge capacity than LFO and exhibits a certain amount of reversible capacity, making it less commonly used in silicon-based LIBs. LFO, on the other hand, has a higher discharge capacity and is therefore suitable for use in silicon-based LIBs. The full potential of the LFO lithium supplement requires a higher voltage. High-voltage charging can lead to decomposition of the electrolyte. At the same time, oxygen is produced during the oxidation of the LFO lithium supplement, further accelerating the decomposition of the electrolyte. To address the decomposition of the electrolyte, patent CN114975917A introduces a method of coating the negative electrode surface with an aluminum layer to absorb the oxygen produced by LFO. Specifically, aluminum powder, a lithium supplement, and ethanol are mixed, then ball-milled to form a composite material. Using the composite material as a reaction source, it is deposited on a graphite surface using atomic vapor deposition. The aluminum powder absorbs the oxygen produced by the lithium supplement, significantly reducing the decomposition of the electrolyte and improving the cycle performance. Patent CN114725392A introduces the addition of a sulfur-containing interfacial film-forming additive to the electrolyte to improve the initial performance, high-temperature cycling, and high-temperature storage of lithium-ion batteries after lithium supplementation. The addition of sulfur-containing additives is conducive to the formation of an interfacial film, reducing direct contact between the electrolyte and the electrode, and reducing the decomposition of the electrolyte.

[0003] Silicon-based anodes have high specific capacity but low initial efficiency. The addition of a lithium supplement can address this low initial efficiency issue. Given that existing production processes remain unchanged, the commonly used lithium supplement is a positive electrode supplement, which can be added directly to the positive electrode slurry. However, the capacity of positive electrode supplements requires increasing the charging voltage, which leads to oxygen evolution and electrolyte decomposition, impairing high-temperature storage and the specific capacity of the supplement. There are two approaches to addressing oxygen evolution and accelerated electrolyte decomposition in positive electrode supplements under high pressure. One approach is to adjust the electrode formulation by adding substances that absorb oxygen and inhibit electrolyte decomposition, such as aluminum powder. Another approach is to modify the electrolyte formulation by adding film-forming additives that absorb oxygen or inhibit electrolyte decomposition, such as 1,3-propane sultone. Adding aluminum powder, which absorbs oxygen and inhibits electrolyte decomposition, to the electrode reduces the amount of active material added, which in turn reduces the battery capacity. Furthermore, the resulting product is generally insulating material, and the addition of aluminum powder increases the DCIR of the battery cell. The addition of metal powder increases the risk of separator puncture and internal short circuits. Adding additives directly to the electrolyte is the most convenient and direct method, but currently, high-impedance additives such as PS and PST are commonly used. These additions significantly increase the DCIR of the battery cell, causing the DC internal resistance to fall below standard and even worsening room-temperature cycling performance. It is essential to select an electrolyte additive with low impedance and in small quantities to replace commonly used additives in order to increase the discharge capacity of the lithium supplement and the initial efficiency of the battery. Summary of the Invention

[0004] In order to solve the problems of poor capacity utilization and electrolyte decomposition of LFO lithium supplement agents in the prior art, the present application provides a new additive, electrolyte and lithium-ion battery thereof. Because the new additive contains pyrazine functional groups and isocyanate functional groups, it can significantly improve the capacity utilization, high-temperature cycling and high-temperature storage of LFO lithium supplement agents under the condition of low addition amount, and will not significantly increase the DCIR of the battery, thereby improving the stability of the battery.

[0005] In order to solve the above problems, this application provides a technical solution:

[0006] In the first aspect, the present application provides a novel additive having a compound represented by formula I,

[0007] Formula I:

[0008] In formula I, R is selected from hydrogen, halogen, substituted or unsubstituted alkane, alkene, alkyne, aromatic group, phosphate, sulfonate, sulfate, borate, and siloxy.

[0009] Preferably, R in Formula I is selected from one or more of phosphate group, sulfonyl group, sulfate group, borate group and siloxy group.

[0010] In the second aspect, the present application provides an electrolyte comprising a lithium salt and a non-aqueous solvent for dissolving the lithium salt. The electrolyte also comprises an electrolyte additive, the electrolyte additive comprises a film-forming additive, the film-forming additive comprises a positive electrode film-forming additive and a negative electrode film-forming additive, wherein the electrolyte additive also comprises the novel additive provided in any embodiment of the present application.

[0011] Preferably, the novel additive is a fluoroisocyanate-based pyridazine organic compound, and the electrolyte contains 0.01%-0.1% of the novel additive by mass.

[0012] Preferably, the electrolyte contains 0.01%-0.05% of the new additive by mass percentage.

[0013] Preferably, the electrolyte salt, non-aqueous solvent and additives in the electrolyte are in the following proportions by mass: 8%-20%: 70%-90%: 0.01%-10%.

[0014] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium perchlorate, lithium hexafluoroarsenate, lithium bisoxalatoborate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate; the non-aqueous solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, and propyl propionate; the positive electrode film-forming additive is one or more of propane sultone, vinyl sulfate, methylene methanedisulfonate, vinyl sulfite, propylene sultone, TMSP, propylene sulfate, TMSB, lithium bisoxalatoborate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorooxalatophosphate; the negative electrode film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, lithium difluorooxalatophosphate, and vinyl sulfate.

[0015] Preferably, the film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, methylene methanesulfonate, 1,3-propane sultone, vinyl sulfate, TMSP, lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0016] Further preferably, the film-forming additives selected in the embodiments of the present application include vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, lithium difluorophosphate and fluoroisocyanate-based pyridazine organic compounds. Specifically, by mass fraction, the film-forming additives in the electrolyte are as follows: the amount of vinylene carbonate added is between 0.1-1%, the amount of fluoroethylene carbonate added is between 3%-10%, the amount of vinyl sulfate added is between 0.5-2%, the amount of 1,3-propane sultone added is between 0.5%-2%, the amount of lithium difluorophosphate added is between 0.3%-1.2%, and the amount of fluoroisocyanate-based pyridazine organic compounds added is between 0.01%-0.1%.

[0017] In a third aspect, the present application provides a lithium-ion battery, which is a lithium-ion battery having a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the electrolyte being the electrolyte provided in any embodiment of the present application, the positive electrode sheet being composed of aluminum foil, a positive electrode active material, a conductive agent, a binder, and a lithium supplement agent, the negative electrode sheet being composed of copper foil, a negative electrode active material, a conductive agent, and a binder, the separator including one or more of a PP separator, a PE separator, a ceramic separator, and a coated separator; the positive electrode active material including one or more of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, lithium iron phosphate, rich lithium manganese oxide, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel oxide; the lithium supplement agent mainly including one or more of lithium-rich lithium nickel oxide, lithium-rich lithium iron oxide, lithium oxide, lithium fluoride, and lithium nitride; the negative electrode active material including one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon, silicon carbon, and silicon oxide.

[0018] In a fourth aspect, the present application also provides a method for preparing a lithium-ion battery, comprising the following steps:

[0019] S1: Preparation of the positive electrode sheet: Select one or more of the above positive electrode active materials, lithium-rich lithium ferrite, a conductive agent, and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:2.5:2:2.5, disperse them in an appropriate amount of N-methylpyrrolidone, and then thoroughly stir them according to the homogenization process. The evenly dispersed positive electrode slurry is evenly coated on aluminum foil. The positive electrode sheet is obtained through baking, roller pressing, slitting, and punching.

[0020] S2: Preparation of the negative electrode sheet: One or more negative electrode active materials, a conductive agent, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are selected and placed into a Xingxing mixing tank at a mass ratio of 96:1:2:1. A uniformly dispersed negative electrode slurry is prepared according to the slurry preparation process. The negative electrode slurry is then evenly coated on copper foil. After baking, rolling, slitting, and punching, the negative electrode sheet is obtained.

[0021] S3: Preparation of lithium-ion batteries: After punching the positive and negative electrodes, bake the positive electrode in an oven at 110-140°C and the negative electrode in an oven at 90-100°C for 20-30 hours. When the electrode moisture content meets the requirements, the positive and negative electrodes and separator are placed in a laminating machine to form a bare cell, which is then encapsulated in a stamped aluminum-plastic film bag. After the packaged dry battery cells are dried at 80-95°C for 8-15h, the electrolyte of the present invention is injected into the dry battery cells. After the battery cells are shelved, formed, shelved at high temperature, evacuated and sealed, and capacity divided, a lithium-ion battery is obtained. The embodiments of the present application do not strictly limit the range of choice of the diaphragm. Commonly used diaphragms meet the requirements of the present invention, such as: polypropylene diaphragm (PP), polyethylene diaphragm (PE), polyethylene / polypropylene double-layer composite film, polyimide electrospun diaphragm (PI), polypropylene / polyethylene / polypropylene three-layer composite diaphragm (PP / PE / PP), ceramic diaphragm, PVDF coated diaphragm, etc.

[0022] Beneficial effects: The present application provides a new additive suitable for high-voltage LFO lithium supplements. The isocyanate group on the additive can absorb moisture and hydrofluoric acid in the electrolyte, reduce the dissolution of transition metals, and improve the thermal stability of lithium hexafluorophosphate. The pyrazine group on the additive can not only absorb moisture and hydrofluoric acid, but also complex with the nickel of the positive electrode material, thereby stabilizing the stability of the ternary material under high pressure. The sulfate group on the new additive can be oxidized by oxygen at the positive electrode, absorbing the oxygen generated when the LFO lithium supplement is activated, significantly improving the capacity utilization, high-temperature cycling and high-temperature storage of the LFO lithium supplement, without significantly increasing the DCIR of the battery, thereby improving the stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a flow chart of a method for preparing a lithium-ion battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The present application is further described below in conjunction with the examples. The technical terms involved in the following examples and comparative examples have the same meanings as the concepts involved in the field of sodium ion batteries. The chemical reagents used in the following examples and comparative examples are all conventional chemical reagents unless otherwise specified; the experimental methods used in this application are all conventional methods. In addition, the specific descriptions in the following examples and comparative examples do not constitute any limitation to this application, and any limited modifications made within the claims of this application are still within the scope of the claims of this application.

[0025] The English abbreviations and their Chinese meanings appearing in the embodiments of this application

[0026] VC: vinylene carbonate; FEC: fluoroethylene carbonate; PS: propane sultone; DTD: vinyl sulfate;

[0027] MMDS: dimethyl methanesulfonate; TMSP: tris(trimethyl)silyl phosphate; LiDFOB: lithium difluorooxalatoborate;

[0028] LiDFOP: lithium difluorobis(oxalatophosphate); LiDFP: lithium difluorophosphate; EC: ethylene carbonate; PC: propylene carbonate; DMC: dimethyl carbonate; DEC: diethyl carbonate; EMC: ethyl methyl carbonate; LiPF6: lithium hexafluorophosphate;

[0029] LiFSI: lithium bis(fluorosulfonyl)imide; LiTFSI: lithium bis(trifluoromethylsulfonyl)imide; LFO: lithium-rich lithium ferrite; LNO: lithium-rich lithium nickelate; Li2O: lithium oxide; DCIR: direct current internal resistance.

[0030] In the first aspect, the embodiments of the present application provide a novel additive, which has a compound represented by Formula I,

[0031] Formula I:

[0032] In formula I, R is selected from hydrogen, halogen, substituted or unsubstituted alkane, alkene, alkyne, aromatic group, phosphate, sulfonate, sulfate, borate, and siloxy.

[0033] In an optional embodiment, R in Formula I is selected from one or more of phosphate group, sulfonyl group, sulfate group, borate group, and siloxy group. Specifically, Formula 1 of the present invention is selected from one of T1-T6.

[0034]

[0035] In this embodiment, the novel additive provided by the present application can partially replace the positive and negative electrode film-forming additives, but it is also necessary to add the positive and negative electrode film-forming additives to further improve the stability of the SEI film. The film-forming additives involved are one or more of carbon-based additives, sulfur-based additives, phosphorus-based additives, boron-based additives, nitrogen-based additives, and silicon-based additives. Adding commonly used film-forming additives to the electrolyte containing fluoroisocyanate-based pyridazine compounds can further optimize the performance of lithium-ion batteries, especially improve the cycle life and rate performance of lithium-ion batteries. This is mainly because the addition of commonly used film-forming additives can form CEI films and SEI films at the positive and negative electrodes before the decomposition of the novel additives occurs, which further enhances the stability of the interface film and further improves the cycle performance.

[0036] In an optional embodiment, the film-forming additive is one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), methylene methanesulfonate (MMDS), 1,3-propane sultone (PS), diethylene sulfate (DTD), tris(trimethyl)silyl phosphate (TMSP), lithium tetrafluorooxalatophosphate (LiDFOP), lithium difluorooxalatoborate (LiDFOB), and lithium difluorophosphate (LiDFP).

[0037] Another optional embodiment, the embodiment of the present application selects VC, FEC, PS, DTD, LiDFP and fluoroisocyanate pyridazine organic compounds as film-forming additives. Specifically, by mass fraction, in the electrolyte, the amount of VC added is between 0.1-1%, the amount of FEC added is between 3%-10%, the amount of DTD added is between 0.5-2%, the amount of PS added is between 0.5%-2%, the amount of LiDFP added is between 0.3%-1.2%, and the amount of fluoroisocyanate pyridazine organic compounds added is between 0.01%-0.1%.

[0038] The present invention uses one or more commonly used carbonates and carboxylates to prepare the electrolyte, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), and propyl propionate (PP). The solvent used in the present invention includes two or more of the above solvents, and the ratio between the solvents is not limited. The lithium salt used in the present invention includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate. The present invention does not impose any restrictions on the lithium salt content and ratio; the examples herein do not specifically limit the mass fractions of lithium salt and solvent in the electrolyte. These limits may be based on commonly used mass fractions of lithium salt and solvent in lithium-ion battery electrolytes, or determined based on factors such as the lithium-ion battery positive electrode material, negative electrode material, separator, cell design, and development requirements. In specific embodiments of the present invention, the lithium salt content is controlled between 8% and 17%.

[0039] The electrolytes in the embodiments and comparative examples of this application are prepared by the following steps: controlling the moisture content in the glove box to be less than 10 ppm and controlling the moisture content of the solvent to be less than 10 ppm. Use a pipette to accurately transfer ethylene carbonate and ethyl methyl carbonate in the glove box in a ratio of 3:7, then pour them into an aluminum bottle, stir them thoroughly and place them in a constant temperature box at 0°C and freeze for 1 hour. Then, lithium hexafluorophosphate is added to the mixed solvent at a concentration of 1.2 mol / L while stirring. Finally, add one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, lithium difluorophosphate, and fluoroisocyanate pyridazine organic compounds.

[0040] The positive electrode active material of the lithium-ion battery used in the examples and comparative examples of the present application is a nickel-cobalt-manganese 811 ternary material and an LFO lithium supplement, the negative electrode active material is artificial graphite and silicon oxide, and the diaphragm is a polypropylene / polyethylene / polypropylene three-layer composite ceramic diaphragm.

[0041] This application illustrates the effect of the electrolyte additive of the present invention on the electrochemical performance of lithium-ion batteries by comparing the test data of the examples and comparative examples. For the specific preparation of the lithium-ion battery, please refer to Figure 1. This application provides a preferred embodiment, a method for preparing a lithium-ion battery, comprising the following steps:

[0042] S1: Prepare the positive electrode sheet: Select one or more of the above positive electrode active materials, lithium-rich lithium ferrite, a conductive agent, and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:2.5:2:2.5, disperse them in an appropriate amount of N-methylpyrrolidone, and then thoroughly stir them according to the homogenization process. The evenly dispersed positive electrode slurry is evenly coated on aluminum foil. The positive electrode sheet is obtained through baking, roller pressing, slitting, and punching.

[0043] S2: Prepare the negative electrode sheet: Select one or more negative electrode active materials, a conductive agent, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC). Place all raw materials in a Xingxing mixing tank at a mass ratio of 96:1:2:1. Follow the slurrying process to create a uniformly dispersed negative electrode slurry. The negative electrode slurry is then evenly coated on copper foil. After baking, rolling, slitting, and punching, the negative electrode sheet is obtained.

[0044] S3: Preparation of lithium-ion batteries: After punching the positive and negative electrodes, place the positive electrode in an oven at 110-140°C and the negative electrode in an oven at 90-100°C for 20-30 hours. When the moisture content of the electrode sheets meets the requirements, place the positive electrode sheets, negative electrode sheets and diaphragms in a laminating machine, stack them into bare cells, and then encapsulate the bare cells into stamped aluminum-plastic film bags. After the encapsulated dry cells are dried at 80-95°C for 8-15 hours, the electrolyte of the present invention is injected into the dry cells. After the cells are shelved, formed, shelved at high temperature, evacuated and sealed, and capacity divided, a lithium-ion battery is obtained. Example

[0045] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T1 additive is added to this, and the amount of T1 added accounts for 0.05% by mass of the electrolyte. Example

[0046] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T2 additive is added to this, and the amount of T2 added accounts for 0.05% of the mass fraction of the electrolyte. Example

[0047] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T3 additive is added to this, and the amount of T3 added accounts for 0.05% of the mass fraction of the electrolyte. Example

[0048] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T4 additive is added to this, and the amount of T4 added accounts for 0.05% by mass of the electrolyte. Example

[0049] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T5 additive is added to this, and the amount of T5 added accounts for 0.05% by mass of the electrolyte. Example

[0050] The common film-forming additives used in this embodiment are 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate. T6 additive is added to this, and the amount of T6 added accounts for 0.05% by mass of the electrolyte. Example

[0051] In this embodiment, conventional film-forming additives are not used, and only T1 additive is added. The amount of T1 added accounts for 0.05% by mass of the electrolyte. Example

[0052] In this embodiment, conventional film-forming additives are not used, and only T2 additive is added. The amount of T2 added accounts for 0.05% by mass of the electrolyte. Example

[0053] In this embodiment, conventional film-forming additives are not used, and only T3 additive is added. The amount of T3 added accounts for 0.05% of the mass fraction of the electrolyte. Example

[0054] In this embodiment, conventional film-forming additives are not used, and only T4 additive is added. The amount of T4 added accounts for 0.05% by mass of the electrolyte. Example

[0055] In this embodiment, conventional film-forming additives are not used, and only T5 additive is added. The amount of T5 added accounts for 0.05% by mass of the electrolyte. Example

[0056] In this embodiment, conventional film-forming additives are not used, and only T6 additive is added. The amount of T6 added accounts for 0.05% by mass of the electrolyte.

[0057] Comparative Example 1

[0058] This comparative example does not add any conventional positive and negative electrode film-forming additives and fluoroisocyanate-based pyridazine organic compounds;

[0059] Comparative Example 2

[0060] In this comparative example, only commonly used film-forming additives were added, namely 0.5% vinylene carbonate, 5% fluoroethylene carbonate, 1.5% 1,3-propane sultone, 1% vinyl sulfate, and 0.8% lithium difluorophosphate, without adding fluoroisocyanate-based pyridazine organic compounds.

[0061] The electrolytes and lithium-ion batteries of the examples and comparative examples were tested and their performances compared using the following methods:

[0062] (1) LFO lithium supplement capacity utilization

[0063] The present application determines the extent to which the electrolytes of the examples and comparative examples utilize the capacity of the LFO lithium supplement by measuring the actual gram capacity of the LFO lithium supplement. The actual gram capacity of the LFO lithium supplement is mainly obtained by calculating the charging capacity of the LFO lithium supplement charged at a constant current of 0.1C between 3.8V-4.4V and dividing it by the total amount of the LFO lithium supplement inside the lithium-ion battery. The equipment for measuring the actual gram capacity of the LFO lithium supplement is a commonly used lithium-ion battery test cabinet. The test steps for the capacity utilization of the LFO lithium supplement are mainly as follows: place the lithium-ion battery in a constant temperature test cabinet at 25°C, and connect the connecting wires of the battery test cabinet to the positive and negative poles of the battery cell respectively. Let it stand for 1 hour, and then set the charge and discharge steps. First charge to 3.8V with a constant current and constant voltage of 1C, and then charge to 4.4V with a constant current of 0.1C to obtain the charging capacity C1. A batch of lithium-ion batteries containing the same mass of positive active material were trial-produced and charged according to the same charging steps to obtain C2. The charge capacity of LFO lithium supplement is equal to C1-C2. According to the weight of LFO lithium supplement in the lithium-ion battery, the charge capacity of LFO lithium supplement is further calculated. The specific test data is shown in Table 1.

[0064] (2) Lithium-ion battery 45°C cycle test

[0065] The embodiments and comparative examples in this patent are subjected to a 45°C cycle test on lithium-ion batteries according to the following steps. The detailed steps are: take a lithium-ion battery that has been fixed in capacity and place it in a constant temperature box at 45°C. In order to fully reduce the temperature of the battery, control the shelf time of the battery to ensure that it is more than 1 hour. Then charge it with a constant current and constant voltage of 1C, with a cut-off voltage of 4.4V and a cut-off current of 0.05C. Then discharge it to 2.8V with a constant current of 1C. Perform charge and discharge cycles on the battery according to the above steps, and record the discharge capacity retention rate after 1000 and 2000 cycles. The discharge capacity retention rate of the battery after 400 and 800 cycles is calculated by dividing the discharge capacity of the battery after 400 and 800 cycles by the discharge capacity of the battery in the first cycle. Specific test data are shown in Table 2.

[0066] (3) Lithium-ion battery storage test at 60°C

[0067] The steps for testing the high-temperature storage performance of the battery cells in the embodiments and comparative examples of this patent are as follows: discharge the fixed-capacity battery cells to 2.8V at a constant current of 1C, set aside for 5 minutes, and then charge to 4.4V at a constant current and constant voltage of 1C, with a cut-off current of 0.05C. Place the battery in a constant temperature box at 60°C and store for 30 days, 60 days, 90 days, 120 days, and 150 days respectively. After the battery reaches the specified storage date, take out the battery cells, connect them to the battery test cabinet, discharge to 2.8V at a constant current of 1C, and then charge at a constant current and constant voltage of 1C. Repeat the process of 1C constant current discharge 3 times. Finally, the discharge capacity recovery rate of the battery cell is obtained, and the relevant test results are shown in Table 3.

[0068] (4) DCIR test of lithium-ion battery at 25°C and 50% SOC

[0069] The battery cells in the embodiments and comparative examples of this patent are tested for DCIR at 50% SOC at 25°C according to the following steps. First, the battery is constant-capacity and discharge capacity is determined by 1C constant-current constant-voltage charging and 1C constant-current discharging. Then, the discharge time at 50% SOC is calculated based on the discharge capacity, and the capacity of the battery is adjusted to 50% SOC. After standing for one hour, the battery cell is charged and discharged for 20 seconds with a 3C pulse current. Based on the change in voltage, the DCIR of the battery is calculated. The relevant test results are shown in Table 4.

[0070] Table 1

[0071] Group LFO charging capacity / mAh.g -1 Group LFO charging capacity / mAh.g-1 Example 1475 Example 8285 Example 2496 Example 9325 Example 3512 Example 10348 Example 4521 Example 11319 Example 5519 Example 12305 Example 6489 Comparative Example 1254 Example 7296 Comparative Example 2438

[0072] The LFO charge capacity data in Table 1 demonstrates that the addition of commonly used positive and negative electrode film-forming additives significantly improves the LFO lithium supplement's charge capacity. This is primarily because these additives form a stable interfacial film at the positive and negative electrode interfaces, reducing the LFO's capacity loss and the battery's DCIR. Adding fluoroisocyanate-based pyridazines to electrolytes with or without positive and negative electrode film-forming additives significantly improves the LFO's charge capacity, particularly those containing sulfate groups. Among the 12 examples, Example 4 exhibits the highest LFO charge capacity.

[0073]

[0074] Table 2

[0075]

[0076] Table 2 shows the discharge capacity retention of different battery cells after 400 and 800 cycles in a high-temperature environment at 45°C. When common positive and negative electrode film-forming additives are not added to the electrolyte, the discharge capacity retention of the lithium-ion battery after 400 and 800 cycles is relatively low. However, the addition of common positive and negative electrode film-forming additives and the novel film-forming additive significantly improves the discharge capacity retention of the lithium-ion battery after 400 and 800 cycles. This is because common additives form an interfacial film at the positive and negative electrode interface, significantly improving the stability of the interface, reducing electrolyte decomposition, and extending the battery's cycle life. The addition of the novel additive not only forms a stable interfacial film at the positive and negative electrode interface but also absorbs moisture from the electrolyte and complexes with the positive electrode transition metal, further stabilizing the interface. Comparing all examples and comparative examples, the addition of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, lithium difluorophosphate, and T3 to the electrolyte significantly improves the battery's cycle life.

[0077] Table 3

[0078]

[0079] Table 3 shows the capacity recovery rate of batteries filled with different electrolytes at different storage times. Compared with lithium-ion batteries without conventional electrolyte additives, the high-temperature storage performance of lithium-ion batteries is significantly improved after adding vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, and lithium difluorophosphate to the battery. After adding T1-T6 electrolyte additives on the basis of conventional electrolyte additives, the high-temperature storage capacity recovery rate of lithium-ion batteries is further improved, especially the addition of T3 electrolyte additive. Comparing the high-temperature storage data of the embodiments and comparative examples, the degree of improvement of the high-temperature storage of the battery by T3 electrolyte additive is higher than that of T1, T2, T4, T5, and T6.

[0080] Table 4

[0081] Group DCIR / Ω Group DCIR / Ω Group DCIR / Ω Example 1 0.829 Example 6 0.844 Example 1 1 0.946 Example 2 0.841 Example 7 0.935 Example 1 2 0.948 Example 3 0.848 Example 8 0.953 Comparative Example 1 1.051 Example 4 0.837 Example 9 0.958 Comparative Example 2 0.832 Example 5 0.834 Example 10 0.949

[0082] Table 4 lists the DCIR of the batteries from the examples and comparative examples. When no film-forming additives were added to the electrolyte, the DCIR increased significantly, primarily due to the formation of thick interfacial films on the positive and negative electrode surfaces. Adding conventional film-forming additives or fluoroisocyanate-based pyridazine organic compounds to the additive-free electrolyte significantly reduced the DCIR of the battery. Furthermore, adding fluoroisocyanate-based pyridazine organic compounds to the electrolyte containing conventional film-forming additives significantly reduced the DCIR of the battery.

[0083] In summary, the novel electrolyte additive proposed in this application, because it contains pyrazine functional groups and isocyanate functional groups, can significantly improve the capacity, high-temperature cycling and high-temperature storage of the LFO lithium supplement under the condition of low addition amount, without significantly increasing the DCIR of the battery.

Claims

1. A novel additive, characterized in that, The novel additive has a compound shown in Formula I. Formula Ⅰ:

2. In Formula I, R is selected from hydrogen, halogen, substituted or unsubstituted alkane, alkene, alkyne, aromatic group, phosphate ester, sulfonate group, sulfate ester group, borate ester group, and siloxy group.

3. A novel additive according to claim 1, characterized in that, In Formula I, R is selected from one or more of phosphate ester group, sulfonyl ester group, sulfate ester group, borate ester group, and siloxy group.

4. An electrolyte, characterized in that, It includes a lithium salt and a non-aqueous solvent for dissolving the lithium salt. The electrolyte further includes an electrolyte additive, and the electrolyte additive includes a film-forming additive. The film-forming additive includes a positive electrode film-forming additive and a negative electrode film-forming additive. Among them, the electrolyte additive further includes the novel additive described in any one of claims 1-2.

5. An electrolyte according to claim 3, wherein, The novel additive is a fluoro-isocyanate-based pyridazine organic compound. By mass percentage, 0.01%-0.1% of the novel additive is contained in the electrolyte.

6. An electrolyte according to claim 4, characterized in that, By mass percentage, 0.01%-0.05% of the novel additive is contained in the electrolyte.

7. An electrolyte according to claim 3, wherein In the electrolyte, the mass ratio of the electrolyte salt, non-aqueous solvent, and additive is 8%-20%: 70%-90%: 0.01%-10%.

8. An electrolyte according to claim 6, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium difluorophosphate. The non-aqueous solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, and propyl propionate. The positive electrode film-forming additive is one or more of propane sultone, vinylene sulfate, methylene methanedisulfonate, vinylene sulfite, propene sulfonic acid lactone, TMSP, propylene sulfate, TMSB, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate, and lithium difluoro(oxalato)phosphate. The negative electrode film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, ethylene ethyl carbonate, lithium difluoro(oxalato)phosphate, and vinylene sulfate.

9. An electrolyte according to claim 3, wherein The film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, methylene methanesulfonate, 1,3-propane sultone, vinylene sulfate, TMSP, lithium tetrafluoro(oxalato)phosphate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.

10. An electrolyte according to claim 8, characterized in that, The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinylene sulfate, lithium difluorophosphate, and a fluoro-isocyanate-based pyridazine organic compound. Specifically, by mass fraction percentage, in the electrolyte, the addition amount of vinylene carbonate is between 0.1% and 1%, the addition amount of fluoroethylene carbonate is between 3% and 10%, the addition amount of vinylene sulfate is between 0.5% and 2%, the addition amount of 1,3-propane sultone is between 0.5% and 2%, the addition amount of lithium difluorophosphate is between 0.3% and 1.2%, and the addition amount of the fluoro-isocyanate-based pyridazine organic compound is between 0.01% and 0.1%.

11. A lithium-ion battery, characterized in that, It is a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The electrolyte is the electrolyte described in any one of claims 3-8. The positive electrode sheet is composed of an aluminum foil, a positive electrode active material, a conductive agent, a binder, and a lithium supplement agent. The negative electrode sheet is composed of a copper foil, a negative electrode active material, a conductive agent, and a binder. The separator includes one or more of a PP separator, a PE separator, a ceramic separator, and a coated separator. The positive electrode active material includes one or more of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium-rich manganese oxide, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel oxide. The lithium supplement agent mainly includes one or more of lithium-rich lithium nickel oxide, lithium-rich lithium iron oxide, lithium oxide, lithium fluoride, and lithium nitride. The negative electrode active material is one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon, silicon carbon, and silicon oxide.

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