Low-concentration safe lithium ion battery electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a low-concentration safe lithium ion battery electrolyte and a lithium ion battery, the electrolyte is composed of a lithium salt, a carbonic ester main solvent, a diluent and a fluorinated phosphite additive; wherein the total concentration of the lithium salt is 0.5 mol / L to 0.8 mol / L, the proportion of the carbonic ester main solvent is 50 percent to 70 percent, the proportion of the diluent is 15 percent to 20 percent, and the proportion of the fluorinated phosphite ester additive is 10 percent to 15 percent. By introducing the fluorinated phosphite ester additive, the stability of an electrolyte system can still be maintained while the consumption of the lithium salt is reduced, so that the cost of the lithium salt is effectively reduced; the cycling stability of the lithium ion battery is favorably improved; and the lithium ion battery has relatively high voltage stability and can stably operate in a high-nickel positive electrode system, so that the energy density of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a low-concentration, safe lithium-ion battery electrolyte and a lithium-ion battery. Background Technology

[0002] Electrolytes play a crucial role in ion transport and internal circuit conduction in lithium-ion batteries. Low cost and high safety are the two core design dimensions in electrolyte development. Traditional commercial lithium-ion battery electrolytes typically need to maintain an overall salt concentration of at least 1 mol / L to ensure sufficient ionic conductivity for satisfactory electrochemical performance. However, in such traditional systems, although the electrolyte accounts for approximately 7% of the electrolyte cost, using low-concentration electrolytes (LCEs) can significantly reduce costs and offer advantages such as a wider operating temperature range. Nevertheless, low-concentration electrolytes also face significant technical bottlenecks.

[0003] Specifically, a decrease in salt concentration not only directly leads to a decrease in ionic conductivity, but also triggers a solvent-dominated solvation structure. This structure is not conducive to the construction of a stable interfacial film rich in inorganic components, and easily causes the solvent to decompose on the surface of the negative electrode (especially the graphite negative electrode), thereby forming a loose and unstable solid electrolyte interfacial film, resulting in a significant decrease in the cycle stability and rate performance of the battery.

[0004] Furthermore, traditional electrolyte systems are prone to oxidative decomposition under high voltage conditions, further exacerbating interfacial instability. The flammable nature of the electrolyte itself also poses safety hazards. To improve safety, flame-retardant additives, such as phosphorus compounds, are typically introduced. However, existing phosphate ester additives, due to their strong lithium-ion solvation ability, can enhance the interaction between lithium ions and the solvent, making it more difficult for lithium ions to desolvate and thus affecting their transport process at the electrode interface.

[0005] On the other hand, combustion generates reactive species such as hydrogen radicals (H) or hydroxyl radicals (OH), which further promote the combustion chain reaction. Although some additives can inhibit combustion to a certain extent, they often have an adverse effect on electrochemical performance.

[0006] Therefore, existing technologies present a difficult-to-reconcile contradiction between cost, safety, and electrochemical performance. On the one hand, it is necessary to reduce salt concentration to lower costs and broaden the applicable temperature range; on the other hand, it is essential to avoid the resulting decrease in conductivity, interfacial instability, and safety issues. How to maintain a low salt concentration to reduce costs while simultaneously suppressing the flammability of the electrolyte and improving interfacial stability and kinetic performance, thereby achieving a low-concentration electrolyte system with high safety and long cycle life, remains a crucial technical problem that urgently needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-concentration, safe lithium-ion battery electrolyte and a lithium-ion battery.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A low-concentration, safe lithium-ion battery electrolyte, comprising lithium salt, carbonate-based main solvent, diluent, and fluorinated phosphite additive; wherein the total concentration of lithium salt is 0.5~0.8 mol / L, the carbonate-based main solvent accounts for 50~70%, the diluent accounts for 15~20%, and the fluorinated phosphite additive accounts for 10~15%.

[0010] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium trifluoromethanesulfonylimide, lithium bis(oxalato)borate, and lithium difluorooxalato)borate.

[0011] Preferably, the carbonate primary solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, fluoroethylene carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

[0012] Preferably, the diluent comprises at least one selected from 1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorobenzene, 3-fluorotoluene, and 1,3,5-trifluorobenzene.

[0013] Preferably, the fluorinated phosphite additive includes at least one of tris(2,2,2-trifluoroethyl) phosphite, tris(1,1,1,3,3,3-hexafluoroisopropyl) phosphite, tris(2,2,3,3-tetrafluoropropyl) phosphite, and tris(2,2,3,3,3-pentafluoropropyl) phosphite.

[0014] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the aforementioned low-concentration safe lithium-ion battery electrolyte, wherein the positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material.

[0015] Preferably, the positive electrode active material includes at least one selected from lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary lithium materials, wherein the ternary lithium material includes LiNi. 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi0.5 Mn 0.3 Co 0.2 O2 and LiNi 0.3 Mn 0.3 Co 0.3 At least one of O2.

[0016] Preferably, the negative electrode active material includes at least one of natural graphite, mesophase carbon microspheres, KS-6, KS-4, and lithium metal negative electrode.

[0017] The beneficial effects of this invention are as follows:

[0018] The low-concentration safe lithium-ion battery electrolyte of the present invention, by introducing fluorinated phosphite additives, can maintain the stability of the electrolyte system while reducing the amount of lithium salt used, thereby effectively reducing the cost of lithium salt.

[0019] The low-concentration safe lithium-ion battery electrolyte can form an interface film rich in inorganic components at the electrode interface, including a solid-liquid interface layer rich in lithium fluoride (LiF) and lithium carbonate (Li2CO3), which is beneficial to improving the cycle stability of lithium-ion batteries.

[0020] The low-concentration, safe lithium-ion battery electrolyte of this invention has high voltage stability and can operate stably in a high-nickel cathode system, thereby improving the energy density of lithium-ion batteries.

[0021] Furthermore, the low-concentration safe lithium-ion battery electrolyte can form a stable interface film on the negative electrode surface, improving the stability of the negative electrode interface and enabling it to operate stably in commercial graphite negative electrode systems, thus demonstrating good commercialization potential.

[0022] The low-concentration, safe lithium-ion battery electrolyte of this invention has excellent flame-retardant properties and can effectively suppress combustion reactions during thermal runaway, thereby significantly improving battery safety.

[0023] Furthermore, the low-concentration safe lithium-ion battery electrolyte can achieve stable operation in actual battery systems, especially exhibiting good cycle performance in the NMC811||graphite system, thus showing good commercial application prospects.

[0024] Because the PO group in the fluorinated phosphite additive has weak polarity and the F element has an electron-withdrawing effect, its solvation ability for lithium ions is relatively weak. However, through the interaction with carbonate-based main solvents, an anion-rich lithium ion solvation structure can be formed, thereby accelerating the desolvation process and facilitating the construction of a solid-liquid interface film rich in inorganic components, thus improving the transport efficiency of lithium ions at the electrode interface.

[0025] Meanwhile, fluorinated phosphite additives can capture free radicals and block the combustion chain reaction during combustion, thereby significantly improving the thermal stability and safety performance of the electrolyte and ensuring the safe and stable operation of lithium-ion batteries in practical applications. Attached Figure Description

[0026] Figure 1 The diagram shows the voltage windows for Example 1, Comparative Example 1, and Comparative Example 2.

[0027] Figure 2 The images show the nuclear magnetic resonance (NMR) Li elemental spectra of Example 1, Comparative Example 1, and Comparative Example 3.

[0028] Figure 3 The rate performance curves of Li||NMC811 half-cells of Examples 1, 3 and Comparative Example 2 at room temperature (25 °C) are shown.

[0029] Figure 4 The cycling performance curves of the Li||NMC811 half-cells of Examples 1, 2 and Comparative Example 1 at 0.5 C rate at room temperature (25 °C) are shown.

[0030] Figure 5 The cycling performance curves of the Li||Gr half-cells of Example 1, Example 2 and Comparative Example 1 at 0.5 C rate at room temperature (25 °C) are shown.

[0031] Figure 6 The cycling performance curves of NMC811|| graphite pouch cells with a capacity of 1 Ah in Examples 1, Comparative Examples 1 and 2 at 1 C rate at room temperature (25 °C) are shown.

[0032] Figure 7 The cycling performance curves of NMC811|| graphite pouch cells with a capacity of 1 Ah in Examples 1, Comparative Examples 1 and 2 at a rate of 0.1 C at low temperature (-20 °C) are shown.

[0033] Figure 8 The cycling performance curves of the 1 Ah NMC811|| graphite pouch cells of Examples 1, Comparative Examples 1 and 2 at 1 C rate at high temperature (55 °C) are shown.

[0034] Figure 9 Self-extinguishing time tests for Example 1 and Comparative Example 1. Detailed Implementation

[0035] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention is described in detail below, but this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the methods used in this invention are conventional methods in this technical field. In this invention, materials, reagents, or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0036] In one embodiment, the present invention provides a low-concentration safe lithium-ion battery electrolyte, comprising a lithium salt, a carbonate-based main solvent, a diluent, and a fluorinated phosphite additive; wherein the total concentration of the lithium salt is 0.5~0.8 mol / L, the carbonate-based main solvent accounts for 50~70%, the diluent accounts for 15~20%, and the fluorinated phosphite additive accounts for 10~15%.

[0037] In a preferred embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium trifluoromethylsulfonylimide, lithium bis(oxalate-borate) and lithium difluorooxalate-borate.

[0038] In a preferred embodiment of the present invention, the carbonate main solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, fluoroethylene carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

[0039] In a preferred embodiment of the present invention, the diluent includes at least one selected from 1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorobenzene, 3-fluorotoluene, and 1,3,5-trifluorobenzene.

[0040] In a preferred embodiment of the present invention, the fluorinated phosphite additive includes at least one of tris(2,2,2-trifluoroethyl) phosphite, tris(1,1,1,3,3,3-hexafluoroisopropyl) phosphite, tris(2,2,3,3-tetrafluoropropyl) phosphite, and tris(2,2,3,3,3-pentafluoropropyl) phosphite.

[0041] In this invention, the introduced fluorinated phosphite molecules can capture hydrogen radicals from the battery's thermal decomposition and combustion chain reaction during thermal runaway, thereby blocking the combustion chain reaction and improving the battery's flame retardancy and safety. Simultaneously, the PO groups in the fluorinated phosphite molecules can coordinate with lithium ions, weakening the binding strength between lithium ions and the solvent, making it easier for lithium ions to form an initial solvation structure, thus preventing destructive decomposition on the negative electrode surface.

[0042] Furthermore, fluorinated phosphites can form dipole coupling interactions with carbonate-based main solvents. Combined with diluents, this further weakens the solvent's coordination ability for lithium ions, thereby promoting the conversion of lithium ions from solvent-separated ion pairs (SSIP) to aggregated ion pairs (AGG), allowing more anions to participate in the construction of the solvation structure. This anion-rich solvation structure facilitates reduction / oxidation reactions at the positive and negative electrode interfaces, generating an interfacial film rich in inorganic components.

[0043] A solid electrolyte interphase (SEI) film rich in inorganic components such as lithium fluoride (LiF) can be formed on the negative electrode surface, and a corresponding cathode electrolyte interphase (CEI) film can be formed on the positive electrode surface. These interfacial films have good stability and density, can effectively suppress interfacial side reactions, reduce interfacial impedance, and thus improve the rate performance and cycle life of lithium-ion batteries.

[0044] In one embodiment, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the aforementioned low-concentration safe lithium-ion battery electrolyte.

[0045] In a preferred embodiment of the present invention, the positive electrode active material includes at least one selected from lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary lithium materials, wherein the ternary lithium material includes LiNi. 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2 and LiNi 0.3 Mn 0.3 Co 0.3 At least one of O2.

[0046] In a preferred embodiment of the present invention, the negative electrode active material includes at least one of natural graphite, mesophase carbon microspheres, KS-6, KS-4 and lithium metal negative electrode.

[0047] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0048] Example 1: The electrolyte preparation process was carried out in a glove box filled with high-purity argon gas (>99.9999%), where the moisture and oxygen content were below 0.1 ppm. First, methyl ethyl carbonate, fluoroethylene carbonate, m-fluorotoluene, and tris(2,2,2-trifluoroethyl) phosphite were mixed and stirred at a volume ratio of 4.75:2.125:2.125:1. Then, appropriate amounts of lithium hexafluorophosphate and lithium difluorooxalate borate were added to make the concentrations of the two lithium salts in the electrolyte 0.7 mol / L and 0.05 mol / L, respectively. The mixture was stirred evenly to obtain the low-concentration safe lithium-ion battery electrolyte of Example 1.

[0049] Example 2: The difference from Example 1 lies in the composition of the lithium salt. The concentration of lithium hexafluorophosphate is 0.7 mol / L, and the concentration of lithium difluorooxalate borate is 0.1 mol / L. The remaining solvent system is the same as in Example 1, namely, methyl ethyl carbonate, fluoroethylene carbonate, m-fluorotoluene, and tris(2,2,2-trifluoroethyl) phosphite are prepared in a volume ratio of 4.5:2.125:2.125:1.

[0050] Example 3: The difference from Example 1 is the solvent ratio. The concentration of lithium hexafluorophosphate is 0.7 mol / L, the concentration of lithium difluorooxalate borate is 0.05 mol / L, and the volume ratio of methyl ethyl carbonate, fluoroethylene carbonate, m-fluorotoluene and tris(2,2,2-trifluoroethyl) phosphite in the solvent system is 4:2:3:1.

[0051] Comparative Example 1: The difference from Example 1 is that the solvent system does not contain tris(2,2,2-trifluoroethyl) phosphite. The solvent consists of ethyl methyl carbonate, fluoroethylene carbonate and m-fluorotoluene in a volume ratio of 4.5:2.125:2.125. The lithium salts are lithium hexafluorophosphate 0.7 mol / L and lithium difluorooxalate borate 0.05 mol / L.

[0052] Comparative Example 2: The difference from Example 1 is that the lithium salt and solvent system are different. Only lithium hexafluorophosphate is used as the lithium salt with a concentration of 1.2 mol / L. The solvent system is ethylene carbonate and methyl ethyl carbonate with a volume ratio of 3:7.

[0053] Comparative Example 3: The difference from Example 1 is that the solvent system does not contain m-fluorotoluene and tris(2,2,2-trifluoroethyl) phosphite, the solvent is composed of ethyl methyl carbonate and fluoroethylene carbonate in a volume ratio of 4.5:2.125, and the lithium salt is lithium hexafluorophosphate 0.7 mol / L and lithium difluorooxalate borate 0.05 mol / L.

[0054] After obtaining the low-concentration safe lithium-ion battery electrolytes described in Examples 1-3 and Comparative Examples 1-3, the following tests and battery assembly were performed on them.

[0055] First, the electrolyte voltage window was tested. CR2032 coin cells (316 stainless steel) with aluminum foil separator lithium sheets filled with the above electrolyte were assembled in a glove box. Then, an electrochemical workstation (Chenhua, CHI760E) was used to perform a linear voltammetric scan to test the voltage window of the electrolyte. The voltage range of the linear scan was 3~5 V, and the scan rate was 0.1 mV / s.

[0056] Further assembly and testing of lithium-ion batteries were conducted. In the assembly of the positive electrode half-cell, 0.9 g of the positive electrode active material LiNi was first... 0.8 Mn 0.1 Co 0.1 O2 (NMC811), 0.05 g of binder polyvinylidene fluoride (PVDF), and 0.05 g of conductive agent carbon black (Super P) were dissolved in 1.45 g of N-methylpyrrolidone (NMP) and stirred for 4 h to obtain a uniform black positive electrode slurry. The positive electrode slurry was then uniformly coated onto aluminum foil and dried in a vacuum oven at 80 ℃ for 12 h. The dried positive electrode sheet was cut into positive electrode discs with a diameter of 12 mm, and assembled with a lithium metal sheet (15 mm × 0.5 mm), a separator (Celgard 2320), and the electrolyte prepared above to form a CR2032 coin cell. The Land CT3002A battery testing system was used to test the cycle performance and rate performance of lithium-ion batteries. For cycle performance testing, the batteries were first activated at 0.1 C for 3 cycles, followed by 200 cycles at 0.5 C. For rate performance testing, the batteries were cycled 5 times each at 0.1 C, 0.3 C, 0.5 C, 1 C, and 2 C rates. The charge / discharge cutoff voltage for cycle performance testing was 2.8–4.3 V.

[0057] In the assembly of the negative electrode half-cell, 0.16 g of negative electrode active material graphite (Gr), 0.02 g of binder PVDF, and 0.02 g of conductive agent Super P were first dissolved in 0.7 g of NMP and stirred for 4 h to obtain a uniform black positive electrode slurry. The negative electrode slurry was then uniformly coated onto copper foil and dried in a vacuum oven at 80 ℃ for 12 h. The dried negative electrode sheet was cut into 12 mm diameter negative electrode discs, which were then assembled with a lithium metal sheet (15 mm × 0.5 mm), a separator (Celgard 2320), and the electrolyte prepared above to form a CR2032 coin cell. The lithium-ion battery was cycle-tested using a Land CT3002A battery testing system. The cycle performance test involved activation at 0.1 C rate for 3 cycles, followed by 200 cycles at 0.5 C rate. The charge / discharge cutoff voltage for the cycle performance test was 0–2 V.

[0058] In the assembly of the full cell, 16 g of negative electrode active material NMC811 (Gr), 2 g of binder PVDF and 2 g of conductive agent Super P were first dissolved in 7 g of NMP and stirred for 4 h to obtain a uniform black slurry. Then, the positive (negative) electrode slurries were mixed at a ratio of 2.9 (3.4) mAh·cm⁻¹. -2 The loading capacity was uniformly coated onto aluminum (copper) foil and dried in a vacuum oven at 80 ℃ for 12 h. After electrode preparation, the two types of electrodes were cut into rectangular electrodes with an N / P ratio of 1.2, and then combined with tabs, a separator, an aluminum-plastic film, and the above-mentioned electrolyte (3 g Ah). -1 The cells were assembled into a 1 Ah pouch cell at 0.1 C rate at room temperature. The full cell was cycle-tested using a Land CT3002K battery testing system. The cells were first activated at 0.1 C rate for 5 cycles, then cycled at 1 C rate (0.1 C at low temperature) for 200 cycles (50 cycles at low and high temperatures). The charge / discharge cutoff voltage was 3~4.2 V.

[0059] Voltage window tests were performed on the electrolytes of Example 1, Comparative Example 1, and Comparative Example 2. The test results are as follows: Figure 1 As shown, from Figure 1 The data shows that, compared with Comparative Example 1 and Comparative Example 2, Example 1 has a higher voltage window (4.75 V), which indicates that the introduction of an appropriate amount of fluorinated phosphite greatly improves the upper limit of the electrochemical window of the electrolyte.

[0060] The electrolytes of Example 1, Comparative Example 1, and Comparative Example 3 were tested using nuclear magnetic resonance (NMR) technology. The test results are as follows: Figure 2 As shown, from Figure 2The data shows that the 7Li peak of Example 1 shifts to a lower field compared to Comparative Examples 1 and 3. This indicates that the introduction of an appropriate amount of fluorinated phosphite can weaken the shielding effect of the solvent on lithium ions, promote more anions to enter the first solvation sheath, and convert the solvent-separated ion pair (SSIP) into more ion aggregates (AGG).

[0061] The Li||NMC811 half-cells of Examples 1, 3, and Comparative Example 2 were subjected to rate performance tests at room temperature (25 °C). The test results are as follows: Figure 3 And Table 1, from Figure 3 As shown in Table 1, compared with Comparative Example 2, Examples 1 and 3 exhibit superior rate performance, with a capacity retention of >78% at a charge / discharge rate of 2 C. This indicates that introducing appropriate proportions of diluent and fluorinated phosphite can ensure the ionic conductivity of the low-concentration electrolyte. Table 1 shows the specific capacity and capacity retention of the Li||NMC811 half-cells of Examples 1, 3, and Comparative Example 2 at different rates at room temperature (25 °C).

[0062] Table 1

[0063] magnification Remaining capacity Example 1 Example 3 Comparative Example 2 0.1 C <![CDATA[Capacity / mAh g -1 (Capacity retention rate)]]> 203.0（100%） 202.0（100%） 202.4（100%） 0.3 C <![CDATA[Capacity / mAh g -1 (Capacity retention rate)]]> 192.6（94.9%） 190.3（94.2%） 190.7（94.2%） 0.5 C <![CDATA[Capacity / mAh g -1 (Capacity retention rate)]]> 184.1（90.7%） 183.0（90.6%） 185.3（91.6%） 1 C <![CDATA[Capacity / mAh g -1 (Capacity retention rate)]]> 180.1（88.7%） 174.6（86.4%） 170.8（84.4%） 2 C <![CDATA[Capacity / mAh g -1 (Capacity retention rate)]]> 166.3（81.9%） 159.1（78.8%） 139.3（68.8%）

[0064] The Li||NMC811 half-cells of Examples 1, 2, and Comparative Example 1 were subjected to 200 cycles at 0.5 C at room temperature (25 °C). The test results are as follows: Figure 4 ,from Figure 4 The data shows that the capacity retention rates of both Examples 1 and 2 after 200 cycles are >98%. This indicates that introducing an appropriate proportion of fluorinated phosphite can significantly improve the cycling stability of the electrolyte in low-concentration electrolyte systems.

[0065] The Li||Gr half-cells of Examples 1, 2, and Comparative Example 1 were subjected to 200 cycles at 0.5C at room temperature (25 °C). The test results are shown in [Figure number missing]. Figure 5 ,from Figure 5 The data shows that the capacity of Examples 1 and 2 hardly decreased after 200 cycles. This indicates that introducing an appropriate proportion of fluorinated phosphite can significantly improve the cycle stability of Li||Gr batteries in low-concentration electrolyte systems.

[0066] The NMC811||Gr pouch cells of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to 200 cycles of 1C cycling performance testing at room temperature (25 °C). The test results are shown in [Figure Number]. Figure 6 ,from Figure 6The data shows that the capacity retention rate of Example 1 after 200 cycles is >93%. This indicates that the low-concentration lithium-ion battery electrolyte described in this invention has excellent cycling performance at room temperature.

[0067] The NMC811||Gr pouch cells of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to 50 cycles at 0.1 C at a low temperature (-20 °C). The test results are shown in [Figure number missing]. Figure 7 ,from Figure 7 The data shows that the capacity retention rate of Example 1 after 50 cycles is >98%. This indicates that the low-concentration lithium-ion battery electrolyte described in this invention has excellent cycle performance in low-temperature environments.

[0068] The NMC811||Gr pouch cells of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to 50 cycles of 1C cycling performance testing at a high temperature (55 °C). The test results are shown in [Figure Number]. Figure 8 ,from Figure 8 The data shows that the capacity retention rate of Example 1 after 200 cycles is >98%. This indicates that the low-concentration lithium-ion battery electrolyte described in this invention has excellent cycle performance in high-temperature environments.

[0069] Self-extinguishing time tests were conducted on Example 1 and Comparative Example 2, and the test results are shown in [the table below]. Figure 9 ,from Figure 9 As can be seen from the images, the electrolyte in Example 1 produced only a small amount of white smoke after ignition, while the electrolyte in Comparative Example 2 ignited immediately upon contact with the flame and burned violently, with the flame continuing to burn during the bath combustion stage. Meanwhile, the self-extinguishing times (SET) of Example 1 and Comparative Example 2 were 82 and 0 s·g, respectively. -1 This indicates that the electrolyte containing fluorinated phosphite is non-flammable, greatly improving battery safety.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-concentration, safe lithium-ion battery electrolyte, characterized in that, The electrolyte is composed of lithium salt, carbonate main solvent, diluent and fluorinated phosphite additive; wherein the total concentration of lithium salt is 0.5~0.8 mol / L, the carbonate main solvent accounts for 50~70%, the diluent accounts for 15~20%, and the fluorinated phosphite additive accounts for 10~15%.

2. The low-concentration safe lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethylsulfonyl)imide, lithium bis(oxalate-borate) and lithium di(fluorooxalate-borate).

3. The low-concentration safe lithium-ion battery electrolyte according to claim 1, characterized in that, The carbonate primary solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, fluoroethylene carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

4. The low-concentration safe lithium-ion battery electrolyte according to claim 1, characterized in that, The diluent includes at least one selected from 1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorobenzene, 3-fluorotoluene, and 1,3,5-trifluorobenzene.

5. The low-concentration safe lithium-ion battery electrolyte according to claim 1, characterized in that, The fluorinated phosphite additive includes at least one of tris(2,2,2-trifluoroethyl) phosphite, tris(1,1,1,3,3,3-hexafluoroisopropyl) phosphite, tris(2,2,3,3-tetrafluoropropyl) phosphite, and tris(2,2,3,3,3-pentafluoropropyl) phosphite.

6. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the low-concentration safe lithium-ion battery electrolyte as described in any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, characterized in that, The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary lithium materials, wherein the ternary lithium material includes LiNi. 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2 and LiNi 0.3 Mn 0.3 Co 0.3 At least one of O2.

8. The lithium-ion battery according to claim 6, characterized in that, The negative electrode active material includes at least one of natural graphite, mesophase carbon microspheres, KS-6, KS-4, and lithium metal negative electrode.

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