Lithium-rich manganese-based lithium ion battery

Abstract

The invention relates to a lithium-rich manganese-based lithium ion battery. In order to solve the problem of battery cycle performance when a traditional carbonate solvent is matched with a lithium-rich manganese-based high-voltage positive electrode material in the prior art, the invention provides a lithium-rich manganese-based lithium ion battery, the lithium-rich manganese-based lithium ion battery comprises a positive electrode, a negative electrode, an isolating membrane and an electrolyte, an active substance in the material of the positive electrode is lithium-rich manganese-based xLi2MnO3. (1-x) LiMO2, x is more than 0 and less than 1, and x is more than 0 and less than 1. M is one or more of Ni, Co, Mn and Al; the electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent is a phosphate ester solvent, a fluoro-ether solvent and a chain ester solvent, and the mass fraction of the phosphate ester solvent in the non-aqueous organic solvent is less than or equal to 30%; and the material of the positive electrode also contains LiNO3. According to the electrolyte for the lithium-rich manganese-based lithium ion battery, the normal-temperature and high-temperature cycle performance of the battery can be remarkably improved, and bulging of the battery in the high-temperature shelving process is inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium-rich manganese-based lithium ion battery. Background Art

[0002] In order to achieve the dual carbon goals as soon as possible, the vigorous popularization of new energy vehicles and the widespread implementation of energy storage technology have become one of the feasible solutions. However, the current energy density of lithium batteries is low, and the cycle performance cannot meet the existing needs, which brings endurance anxiety to people's lives and travel. Lithium-rich manganese-based positive electrode materials have become one of the preferred options for further improving battery energy density due to their advantages of high voltage (4.8V), high gram capacity (~300mAh / g), and low cost. However, conventional carbonate solvents will strongly decompose and produce gas in lithium-rich manganese-based high-voltage systems due to narrow voltage windows and insufficient oxidation resistance, causing lithium-rich manganese-based batteries to suffer from voltage and capacity decay too fast. Therefore, a new electrolyte system is urgently needed to match lithium-rich manganese-based batteries to meet their long cycle performance requirements.

[0003] The introduction of F elements can change the charge density distribution of the substance itself, reduce the HOMO orbit of the substance, and improve the oxidation resistance of the substance, thereby widening the voltage window. Xia Lan et al. introduced 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether into the electrolyte to increase the voltage window to above 5V, so that the electrolyte can be cycled in high-voltage nickel-manganese batteries for 200 weeks with a retention rate of 98% (Physicochemical and Electrochemical Properties of 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl Ether as a Co-Solvent for High-Voltage Lithium-Ion Electrolytes, ChemElectroChem, 2019, 6, 3747-3755). However, the introduction of fluorinated solvents will inevitably cause the viscosity of the electrolyte to increase and the conductivity to decrease, which is not conducive to the realization of a long cycle life of the battery.

[0004] In addition, the lithium-rich manganese-based high-voltage positive electrode material is a layered metal oxide, which undergoes a crystal transformation during the charging process, transforming into a spinel oxide, while releasing oxygen in the lattice, causing the decomposition of the electrolyte and reducing the battery's cycle performance. Adding positive electrode film-forming additives to the electrolyte is a simple and effective measure to inhibit the decomposition of the electrolyte. Li3N has a high ionic conductivity (10 -3S / cm) has become an ideal solid interface film component, and lithium nitrate (LiNO3) as a precursor for constructing Li3N can be widely used in high-voltage battery electrolytes. However, the solubility of LiNO3 in organic solvents is extremely low and it cannot effectively play its due value. Therefore, it is necessary to develop new strategies to convert NO3 - Dissolved in solvents with high voltage windows, further improving the battery's cycle performance. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium-rich manganese-based battery to alleviate the problem of electrolyte decomposition caused by high voltage, increase the solubility of LiNO3 in the electrolyte, increase the cycle life of the battery, and reduce the internal resistance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A lithium-manganese-rich lithium-ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte. The active substance in the material of the positive electrode is a lithium-manganese-rich xLi2MnO3·(1-x)LiMO2, wherein 0<x<1, and M is one or more of Ni, Co, Mn and Al; the electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive. The non-aqueous organic solvent is a phosphate solvent, a fluoroether solvent and a chain ester solvent, and the mass fraction of the phosphate solvent in the non-aqueous organic solvent is ≤30%; the material of the positive electrode also contains LiNO3.

[0008] Preferably, the mass fraction of the phosphate ester solvent in the non-aqueous organic solvent is ≤20%, such as 5%, 10%, 15%, 20%, etc.; more preferably, it is 8% to 13%.

[0009] Preferably, the mass fraction of the fluoroether solvent in the non-aqueous organic solvent is ≤40%; preferably ≤30%, for example 5%, 10%, 15%, 20%, 25%, 30%, etc.; further preferably 18% to 23%.

[0010] According to some specific and preferred embodiments, the mass ratio of the phosphate ester solvent, the fluoroether solvent and the chain ester solvent is 1:(0.3-3):(1.6-7).

[0011] Furthermore, the mass ratio of the phosphate solvent, the fluoroether solvent and the chain ester solvent is 1:(0.5-3):(2.5-7), for example, 1:1:3, 1:1:4, 1:1:4.5, 1:1:5, 1:1:5.5, 1:1:6.5, 1:2:3, 1:2:4, 1:2:4.5, 1:2:5, 1:2:5.5, 1:2:6.5, 1:2.5:3, 1:2.5:4, 1:2.5:4.5, 1:2.5:5, 1:2.5:5.5, 1:2.5:6.5, etc.

[0012] Furthermore, the mass ratio of the phosphate solvent, the fluoroether solvent and the chain ester solvent is 1:(2-3):(6-7).

[0013] Furthermore, the mass ratio of the phosphate ester solvent, the fluoroether solvent and the chain ester solvent is 1:(2-2.5):(6.5-7).

[0014] Preferably, the phosphate ester solvent is selected from trimethyl phosphate (TMP) and / or triethyl phosphate (TEP).

[0015] Preferably, the fluoroether solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, perfluoro-3.5-dioxahexyl methyl ether, and perfluoro-3-oxabutyl methyl ether.

[0016] Preferably, the chain ester solvent is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl formate (MF), ethyl acetate (EA), methyl butyrate, and methyl acrylate (MA).

[0017] According to some specific and preferred embodiments, the non-aqueous organic solvent is TMP, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and DMC.

[0018] Preferably, the molar concentration of the lithium salt in the electrolyte is 0.6M to 1.5M; preferably 0.8M to 1.3M.

[0019] Preferably, the lithium salt is selected from one or more of lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium sulfite (Li2SO3), lithium nitrate (LiNO3), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), and lithium difluorobis(oxalyl)phosphate (LiDFOP).

[0020] Furthermore, the lithium salt is selected from one or more of LiPF6, LiFSI, and LiTFSI.

[0021] Furthermore, the lithium salt includes LiPF6.

[0022] According to some specific and preferred embodiments, the lithium salt is LiPF6 and LiFSI.

[0023] Preferably, the molar concentration ratio of LiPF6 and LiFSI is (0.5-1):(0.1-0.5); preferably (0.8-1):(0.2-0.3).

[0024] According to other specific and preferred embodiments, the lithium salt is LiPF6 and LiTFSI.

[0025] Preferably, the molar concentration ratio of LiPF6 and LiTFSI is (0.5-1):(0.1-0.5); preferably (0.8-1):(0.2-0.3).

[0026] Preferably, the mass percentage of the additive in the electrolyte is 0.05% to 10%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, etc.

[0027] Furthermore, the mass percentage of the additive in the electrolyte is 3% to 10%.

[0028] Furthermore, the mass percentage of the additive in the electrolyte is 4.5% to 8.5%.

[0029] Furthermore, the mass percentage of the additive in the electrolyte is 6% to 7%.

[0030] Preferably, the additive includes one or more of lithium difluorooxalatoborate (LiDFOB), lithium difluorobisoxalatophosphate (LiDFOP), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), maleic anhydride (MA), glutaric anhydride (GA), triallyl isocyanurate (TAIC), tetravinylsilane, fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate (DFEC), and lithium difluorophosphate (LiPO2F2).

[0031] Furthermore, the additive includes one or more of LiDFOB, LiDFOP, TMSP, GA, DFEC, and LiPO2F2.

[0032] Furthermore, the additive includes one or more of LiDFOB, TMSP, DFEC, and LiPO2F2.

[0033] According to some specific and preferred embodiments, the additives are LiDFOB, TMSP, DFEC and LiPO2F2.

[0034] Preferably, the mass ratio of LiDFOB, TMSP, DFEC and LiPO2F2 is (1-3):1:(1-5):(0.1-0.5), for example: (1-3):1:(1-1.5):(0.1-0.5), (1-3):1:(1-2):(0.1-0.5), (1-3):1:(1-2.5):(0.1-0.5), (1-3):1:(1-3.5):(0.1-0.5), (1-3):1:(1-4):(0.1-0.5), (1-3):1:(1-4.5):(0.1-0.5), etc.

[0035] Furthermore, the mass ratio of LiDFOB, TMSP, DFEC and LiPO2F2 is (1.5-2.5):1:(3-5):(0.2-0.5).

[0036] Furthermore, the mass ratio of LiDFOB, TMSP, DFEC and LiPO2F2 is (1.5-2):1:(3-3.5):(0.4-0.5).

[0037] Preferably, the added mass of the LiNO3 accounts for 0.01% to 5% of the mass of the active material in the positive electrode material.

[0038] Furthermore, the added mass of the LiNO3 accounts for 0.5% to 5% of the mass of the active substance in the positive electrode material, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.

[0039] Furthermore, the added mass of the LiNO3 accounts for 3% to 5% of the mass of the active material in the positive electrode material.

[0040] Furthermore, the added mass of the LiNO3 accounts for 3% to 3.5% of the mass of the active material in the positive electrode material.

[0041] Preferably, the active substance in the negative electrode material is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon-carbon composites, lithium titanate, and metals that can form alloys with lithium.

[0042] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0043] In the present invention, by introducing phosphate solvents, fluoroether solvents and chain ester solvents into the electrolyte, the potential window of the electrolyte is greatly widened, providing the necessary conditions for the normal operation of the battery under high voltage conditions, and used in combination with lithium salts and additives, the mechanical strength of the interface film can be further increased, the interface impedance can be reduced, the normal temperature and high temperature cycle performance of the battery can be significantly improved, and the swelling of the battery during high temperature storage can be suppressed, thereby increasing the cycle life of the battery and reducing the internal resistance. In addition, adding LiNO3 to the positive electrode material and using it in combination with a non-aqueous organic solvent alleviates the problem of low solubility of LiNO3 in the electrolyte, and allows the positive electrode material to be used as a temporary storage device for LiNO3, slowing down the attenuation of the battery during the cycle, and further improving the cycle performance of the battery. DETAILED DESCRIPTION

[0044] All features disclosed in the present invention, or all steps in the methods or processes disclosed, except mutually exclusive features or steps, may be combined in any manner.

[0045] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0046] In order to find an electrolyte that matches a lithium-rich manganese-based battery, the inventors of the present invention conducted in-depth research and a large number of experiments, made minor adjustments to the lithium-rich manganese-based positive electrode material process, redesigned the components of the electrolyte, and finally proposed a lithium-rich manganese-based battery and its electrolyte.

[0047] The active material of the positive electrode in the lithium-rich manganese-based lithium-ion battery of the present invention is lithium-rich manganese-based, and LiNO3 is added to the positive electrode. At the same time, three types of substances, namely phosphates, fluoroethers and chain esters, are selected in the electrolyte as non-aqueous organic solvents, which work synergistically with lithium salts and additives, so that the obtained electrolyte can alleviate the problem of battery cycle performance when traditional carbonate solvents are matched with lithium-rich manganese-based high-voltage positive electrode materials, increase the solubility of LiNO3 in the electrolyte, and thus significantly improve the room temperature and high temperature cycle performance of the battery and inhibit the swelling of the battery during high-temperature storage.

[0048] Furthermore, by introducing phosphate ester solvents and fluoroether solvents into the electrolyte, the potential window of the electrolyte can be greatly broadened, providing the necessary conditions for the normal operation of the battery under high voltage conditions. However, due to their large viscosity and dielectric constant, the addition of both solvents to the electrolyte will cause the electrolyte conductivity to decrease and ion migration to be hindered. Therefore, a chain ester solvent with low viscosity and dielectric constant, such as DMC, is used to adjust the electrolyte, and the mass fraction of the phosphate ester solvent in the non-aqueous organic solvent is controlled to be ≤30%, and the mass fraction of the fluoroether solvent in the non-aqueous organic solvent is controlled to be ≤40%, so that the performance of the battery is greatly improved and the electrolyte has suitable conductivity and viscosity.

[0049] Furthermore, by combining the strategy of dual lithium salts and replacing part of LiPF6 with LiTFSI or LiFSI, which have a higher number of donors than LiPF6, the binding energy between lithium ions and the solvent can be increased, and the solvation of the electrolyte can be weakened, thereby allowing the electrolyte to obtain a higher conductivity, while alleviating the ion barrier caused by the increased viscosity of the electrolyte.

[0050] Furthermore, by adopting a combination strategy of multiple additives, especially selecting one or more of lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalatophosphate) (LiDFOP), tris(trimethylsilyl) phosphate (TMSP), glutaric anhydride (GA), 4,5-difluoroethylene carbonate (DFEC), lithium difluorophosphate (LiPO2F2), etc., a solid interface film rich in elements such as F, B, and P can be formed on the surface of the positive and negative electrodes, further increasing the mechanical strength of the interface film and reducing the interface impedance.

[0051] Furthermore, LiNO3 is added to the positive electrode material, and the solubility of LiNO3 in the electrolyte is improved by changing the solvation structure. First, it can be used as a positive electrode lithium supplement to improve the charge and discharge efficiency of the battery and slow down the attenuation of the battery during the cycle. It can also form a CEI film rich in Li3N / LixNOy in situ on the positive electrode surface, reduce the oxidative decomposition of the electrolyte, and reduce the battery impedance. Finally, when used in combination with a non-aqueous organic solvent, LiNO3 can be slowly dissolved into the electrolyte during the cycle, and move to the negative electrode surface under the action of the electric field for reduction and decomposition to form a SEI film, allowing the positive electrode material to serve as a temporary storage device for LiNO3, alleviating the problem of low solubility of LiNO3 in the electrolyte.

[0052] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0053] The experimental methods in the following examples are all conventional methods unless otherwise specified; the experimental materials used are all purchased from conventional biochemical reagent manufacturers unless otherwise specified.

[0054] It should be noted that HFE in the present invention refers to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; unless otherwise specified herein, "%" represents mass percentage.

[0055] Example 1

[0056] The present embodiment provides a lithium-rich manganese-based lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte.

[0057] Electrolyte: Trimethyl phosphate (TMP), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and dimethyl carbonate (DMC) were mixed in a mass ratio of 1:3:6, and LiPF6 and LiTFSI were fully dissolved so that the molar concentration of LiPF6 was 0.8M and the molar concentration of LiTFSI was 0.2M. LiDFOB, TMSP, DFEC, and LiPO2F2 were then added. The mass percentages of the four additives in the electrolyte were 2%, 1%, 3%, and 0.5%, respectively.

[0058] Preparation of the positive electrode: Add polyvinylidene fluoride (PVDF) to the N-methylpyrrolidone solvent system, stir thoroughly to dissolve, add LiNO3 accounting for 0.5% by mass of the active material in the positive electrode material, stir thoroughly, add the positive electrode active material lithium-rich manganese (Li-Rich) (Ningbo Fuli Battery Material Technology Co., Ltd., model LR-300) and conductive agent acetylene black, the mass ratio of lithium-rich manganese (Li-Rich), conductive agent acetylene black, and polyvinylidene fluoride (PVDF) is 95:3:2, continue to stir into a slurry, coat it on the positive electrode current collector Al foil, and obtain the positive electrode after drying and cold pressing, in which PVDF is used as a binder.

[0059] Preparation of the negative electrode: The active material graphite of the negative electrode, the conductive agent acetylene black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) are added to a deionized water solvent system at a mass ratio of 95:2:2:1, and after being fully stirred and mixed, they are coated on the negative electrode current collector Cu foil, and then dried and cold pressed to obtain the negative electrode, in which SBR is used as a binder and CMC-Na is used as a thickener.

[0060] Preparation of isolation membrane: PE porous polymer film is used as isolation membrane.

[0061] Preparation of lithium-ion battery: stack the prepared positive electrode, separator and negative electrode in order, so that the separator is between the positive and negative electrodes to play an isolating role, and then wind them to obtain a bare cell. Place the bare cell in an outer package, inject the above-prepared electrolyte, and package to obtain a lithium-ion battery. The obtained lithium-ion battery has a designed capacity of 1000mAh, and the battery's charge and discharge range is 3.0V to 4.6V.

[0062] Example 2

[0063] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=1 / 2 / 7.

[0064] Example 3

[0065] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=2 / 3 / 5.

[0066] Example 4

[0067] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=3 / 2 / 5.

[0068] Example 5

[0069] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=3 / 1 / 6.

[0070] Example 6

[0071] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=2 / 1 / 7.

[0072] Example 7

[0073] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the mass of each solvent in the electrolyte of this example was TMP / HFE / DMC=2 / 4 / 4.

[0074] Example 8

[0075] The electrolyte and lithium ion battery were prepared in the same manner as in Example 2, except that LiNO3 in this example accounted for 1% of the mass of the active material in the positive electrode material.

[0076] Example 9

[0077] The electrolyte and lithium ion battery were prepared in the same manner as in Example 2, except that LiNO3 in this example accounted for 3% of the mass of the active material in the positive electrode material.

[0078] Example 10

[0079] The electrolyte and lithium ion battery were prepared in the same manner as in Example 2, except that LiNO3 in this example accounted for 5% of the mass of the active material in the positive electrode material.

[0080] Embodiment 11

[0081] The electrolyte and the lithium ion battery were prepared in the same manner as in Example 1, except that the mass fraction of DFEC in the electrolyte of this example was 1%.

[0082] Example 12

[0083] The electrolyte and the lithium ion battery were prepared in the same manner as in Example 1, except that the mass fraction of DFEC in the electrolyte of this example was 5%.

[0084] Example 13

[0085] An electrolyte and a lithium-ion battery were prepared in the same manner as in Example 1, except that the lithium salt in the electrolyte of this example was 0.8M LiPF6 and 0.2M LiFSI.

[0086] Comparative Example 1

[0087] The electrolyte and lithium ion battery were prepared in the same manner as in Example 2, except that the positive electrode material of this example did not contain LiNO 3 .

[0088] Comparative Example 2

[0089] The electrolyte and lithium-ion battery were prepared in the same manner as in Comparative Example 1, except that the lithium salt used in the electrolyte of this embodiment was 1M LiPF6.

[0090] Comparative Example 3

[0091] The electrolyte and lithium ion battery were prepared in the same manner as in Comparative Example 1, except that the solvent in the electrolyte of this comparative example was a conventional carbonate solvent, specifically DEC / EC / EMC=2 / 3 / 5 (EC is ethylene carbonate).

[0092] Comparative Example 4

[0093] The electrolyte and lithium-ion battery were prepared in the same manner as in Comparative Example 3, except that the lithium salt used in the electrolyte of this comparative example was 1M LiPF6.

[0094] Comparative Example 5

[0095] The electrolyte and lithium ion battery were prepared in the same manner as in Comparative Example 3, except that the LiNO3 in this comparative example accounted for 3% of the mass percentage of the active material in the positive electrode material.

[0096] The fine adjustment of the positive electrode material and the proportion of each substance in the electrolyte are shown in Table 1.

[0097] Table 1 Proportions of positive electrode materials and electrolytes in the batteries obtained in the examples and comparative examples

[0098]

[0099]

[0100] Performance Testing

[0101] The normal temperature and high temperature cycle performance and the swelling rate during high temperature storage of the batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 5 were tested according to the following method.

[0102] (1) Normal temperature cycle performance test

[0103] At 25°C, the battery was tested for 300 cycles of charge and discharge at 1C / 1C. The charge and discharge voltage range was 3.0V to 4.6V. The discharge capacities of the first week and the 300th week were recorded respectively, and the capacity retention rate of the 300th week was calculated. The formula is: Capacity retention rate of the 300th week (%) = discharge capacity of the 300th week / discharge capacity of the first week*100%. The calculation results are shown in Table 2.

[0104] (2) High temperature cycle test

[0105] At 45°C, the battery was tested for 200 cycles of charge and discharge at 1C / 1C, with a charge and discharge voltage range of 3.0V to 4.6V, and the discharge capacity of the first week and the 200th week was recorded respectively. The capacity retention rate of the 200th week was calculated as follows: Capacity retention rate of the 200th week (%) = discharge capacity of the 200th week / discharge capacity of the first week*100%. The calculation results are shown in Table 2.

[0106] (3) High temperature expansion test

[0107] First, the formed battery is charged and discharged three times at 1C at room temperature, with a charge and discharge voltage range of 3.0V to 4.6V. The battery is then charged to 4.6V at 1C with a constant current and constant voltage, with a cut-off current of 0.05C. The initial thickness of the battery is measured and recorded as t1. The battery is then stored at 60°C for 7 days and the battery is completely cooled. The battery thickness is measured again and recorded as t2. The thickness change rate is calculated, and the formula is: thickness change rate = (t2-t1) / t1*100%. The calculation results are shown in Table 2.

[0108] Table 2 Test results of the embodiments and comparative examples at room temperature and high temperature

[0109]

[0110]

[0111] It can be seen from Comparative Examples 3 to 5 in Table 2 that the change of the solvent system has a significant effect on improving the cycle performance of the battery and inhibiting high-temperature swelling. The reason is that when a conventional carbonate solvent is used in a lithium-rich manganese-based system, the lithium-rich manganese-based positive electrode material undergoes a crystal transformation during the charging process, thereby releasing active oxygen in the crystal lattice, causing oxidative decomposition of the electrolyte and aggravating the gas production behavior of the battery. At the same time, due to the continuous decomposition of the electrolyte, the CEI film on the surface of the positive electrode material gradually thickens, causing the internal resistance of the battery to increase, which is not conducive to the cycle of the battery.

[0112] From Examples 1 to 7 and Example 13, it can be seen that although the introduction of TMP and HFE has greatly improved the performance of the battery, the ratio between the internal solvents is also particularly important. From the final results, it can be seen that the electrolyte has a relatively high performance when the ratio of TMP / HFE / DMC=1 / 2 / 7, so this ratio is used for subsequent experiments. In order to alleviate the ion barrier caused by the increase in electrolyte viscosity, LiTFSI and LiFSI with a higher number of ion donors are used to replace part of LiPF6, and the results are also significantly improved.

[0113] It can be seen from Example 2, Examples 8 to 10, and Comparative Examples 1 to 2 that, relative to the case without adding LiNO3, the performance of the battery is improved to varying degrees after adding different contents of LiNO3 to the positive electrode material; at the same time, due to the addition of different contents of LiNO3, the performance of the battery shows a trend of first increasing and then decreasing, and reaches the highest at 3%. This may be because when there is too much LiNO3 in the positive electrode, the migration resistance of ions in the material caused by the thickening of the battery pole piece is greater than the positive effect that LiNO3 can contribute.

[0114] It can be seen from Examples 11 and 12 that the combined use of four additives, LiDFOB, TMSP, DFEC and LiPO2F2, can form a solid interface film rich in elements such as F, B, and P on the surfaces of the positive and negative electrodes, further increasing the mechanical strength of the interface film and reducing the interface impedance.

[0115] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes made according to the spirit of the present invention.

Claims

1. A lithium-rich manganese-based lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, a separator and an electrolyte. The active material in the positive electrode material is a lithium-rich manganese-based xLi2MnO3·(1-x)LiMO2, wherein 0<x<1, and M is one or more of Ni, Co, Mn, and Al; the electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent is a phosphate solvent, a fluoroether solvent and a chain ester solvent, and the mass fraction of the phosphate solvent in the non-aqueous organic solvent is ≤30%; the positive electrode material also contains LiNO3.

2. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The mass fraction of the fluoroether solvent in the non-aqueous organic solvent is ≤40%.

3. The lithium-rich manganese-based lithium-ion battery according to claim 2, characterized in that: The mass ratio of the phosphate solvent, the fluoroether solvent and the chain ester solvent is 1:(0.3-3):(1.6-7).

4. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The added mass of the LiNO3 accounts for 0.01% to 5% of the mass of the active material in the positive electrode material.

5. The lithium-rich manganese-based lithium-ion battery according to claim 4, characterized in that: The added mass of the LiNO3 accounts for 0.5% to 5% of the mass of the active material in the positive electrode material.

6. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The phosphate ester solvent is selected from trimethyl phosphate and / or triethyl phosphate; and / or the fluoroether solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, perfluoro-3.5-dioxahexyl methyl ether, and perfluoro-3-oxabutyl methyl ether; and / or the chain ester solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl butyrate, and methyl acrylate.

7. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, and lithium difluorobis(oxalyl)phosphate; and / or the molar concentration of the lithium salt in the electrolyte is 0.6M to 1.5M.

8. The lithium-rich manganese-based lithium-ion battery according to claim 7, characterized in that: The lithium salt is lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide. Alternatively, the lithium salt is lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide.

9. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The additive includes one or more of lithium difluorooxalatoborate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, maleic anhydride, glutaric anhydride, triallyl isocyanurate, tetravinylsilane, fluoroethylene carbonate, and 4,5-difluoroethylene carbonate; and / or the mass percentage of the additive in the electrolyte is 0.05% to 10%.

10. The lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The active material in the negative electrode material is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon-oxygen compounds, silicon-carbon composites, lithium titanate, and metals that can form alloys with lithium.

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