A lithium ion battery electrolyte containing tris(2-cyanoethyl)phosphite and a lithium ion battery

Abstract

The present invention provides a lithium ion battery electrolyte, including an organic solvent, a lithium salt and an additive; the additive includes a first additive and a second additive; the first additive includes tris (2-cyanoethyl) phosphite; the second additive includes a fluorine-containing lithium phosphate salt compound; the fluorine-containing lithium phosphate salt compound has a structure as shown in formula (I). The present invention is creative using tris (2-cyanoethyl) phosphite as the first electrolyte additive and using a fluorine-containing lithium phosphate salt compound as the second additive; the two additives are used together, cooperate with each other, and act synergistically to generate inorganic lithium salt components such as "LiF" and "Li3PO4", and functional groups such as "P-O" and "-CN", which can suppress the precipitation of transition metal ions and the decomposition of the electrolyte, promote lithium ion conduction, thereby improving the comprehensive performance of the battery such as high voltage performance, high temperature performance and cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery electrolytes and relates to a lithium ion battery electrolyte and a lithium ion battery, and in particular to a lithium ion battery electrolyte and a lithium ion battery containing tris(2-cyanoethyl)phosphite. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in digital products, power generation, and energy storage. With the advancement of lithium-ion battery technology, especially with new energy vehicles placing higher demands on driving range, developing higher energy density has become a research hotspot in the lithium-ion battery industry. The solution proposed in the materials field is to develop high-nickel or high-voltage cathode materials in combination with silicon-carbon anode materials. However, these new battery systems face several challenges, such as the precipitation of high-valent transition metal ions, electrochemical polymerization at high voltages, and thermal decomposition of electrochemically charged ions (FEC), posing greater challenges to electrolyte performance.

[0003] The cyanide group of nitrile additives has a strong electronegativity and has a strong coordination effect with transition metal ions, which can inhibit the dissolution of metal ions. At the same time, it preferentially captures H protons when oxidation side reactions occur in the electrolyte, inhibiting the decomposition of LiPF6 and FEC. Among them, 1,3,6-hexanetricarbonitrile (HTCN) is recognized as the nitrile additive with the best application performance. However, like other commonly used nitrile additives, it does not participate in the formation of positive electrode films, and its stabilization effect on transition metal ions is limited. In addition, its main chain structure is composed of C atoms, which conducts Li + LiPO2F2 forms a film at the cathode interface, significantly improving the electrochemical performance of the battery, but its low solubility limits its further application.

[0004] Therefore, how to find a more suitable way to solve the above-mentioned problems of existing nitrile additives has become one of the focuses of widespread attention of many researchers and R&D companies in the industry. Summary of the Invention

[0005] In light of this, the present invention provides a lithium-ion battery electrolyte and a lithium-ion battery, particularly a lithium-ion battery electrolyte containing tris(2-cyanoethyl)phosphite. The present invention provides an additive containing tris(2-cyanoethyl)phosphite and a fluorine-containing lithium phosphate salt compound, which synergistically enhance the high-voltage, high-temperature, and cycle performance of the lithium-ion battery.

[0006] The present invention provides a lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive;

[0007] The additives include a first additive and a second additive;

[0008] The first additive includes tris(2-cyanoethyl)phosphite;

[0009] The second additive includes a fluorine-containing lithium phosphate compound;

[0010] The fluorine-containing lithium phosphate compound has a structure as shown in formula (I):

[0011]

[0012] Wherein, R is selected from one of Li, alkyl, hydrocarbon, cyano and fluorinated alkyl.

[0013] Preferably, the amount of tris(2-cyanoethyl)phosphite added is 0.1% to 5% of the total mass of the electrolyte;

[0014] The number of carbon atoms in the alkyl group, hydrocarbon group, cyano group or fluorinated alkyl group is less than or equal to 3;

[0015] The tris(2-cyanoethyl)phosphite has a structure as shown in formula (II):

[0016]

[0017] Preferably, the fluorine-containing lithium phosphate compound comprises a structure as shown in any one or more of formulas (1) to (14):

[0018]

[0019]

[0020] Preferably, the amount of the second additive added accounts for 0.1% to 3% of the total mass of the electrolyte;

[0021] The organic solvent comprises two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, propyl propionate and ethyl propionate;

[0022] The added amount of the organic solvent accounts for 50% to 75% of the total mass of the electrolyte.

[0023] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorophosphate;

[0024] The amount of lithium salt added accounts for 12% to 20% of the total mass of the electrolyte;

[0025] The additives further include a third additive.

[0026] Preferably, the third additive includes one or more of tris(trimethylsilane)phosphate, tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, tris(2-cyanoethyl)borate, tris(2-cyanoethyl)phosphite, tris(2-cyanoethyl)phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, fluoroethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid and methylene methanedisulfonate;

[0027] The amount of the third additive added accounts for 0.1% to 20% of the total mass of the electrolyte.

[0028] Preferably, the tris(2-cyanoethyl)phosphite is obtained by using 3-hydroxypropionitrile and phosphorus trichloride as raw materials through a substitution reaction.

[0029] Preferably, the preparation method of tris(2-cyanoethyl)phosphite comprises the following steps:

[0030] 1) mixing 3-hydroxypropionitrile, a hydrogen chloride chelating agent, and an organic alkali metal salt to obtain a mixture;

[0031] 2) Under protective gas conditions, at a first temperature, adding a phosphorus trichloride organic solution to the system solution obtained in the above step to react, and continuing the reaction at a second temperature to obtain a cyanophosphite.

[0032] Preferably, after the continued reaction, a purification step is further included;

[0033] The purification comprises the following steps:

[0034] The crude product obtained after the reaction is further reacted is added with an organic solvent and filtered, and then an alkali solution is added to separate the organic phase, and then the organic solvent is removed to obtain cyanophosphite.

[0035] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode and the electrolyte described in any one of the above technical solutions.

[0036] The present invention provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and an additive; the additive comprises a first additive and a second additive; the first additive comprises tris(2-cyanoethyl)phosphite; the second additive comprises a fluorine-containing lithium phosphate salt compound; the fluorine-containing lithium phosphate salt compound has a structure as shown in formula (I). Compared with the prior art, the present invention addresses the problems existing in existing lithium-ion electrolyte additives, especially nitrile additives. The present invention studies and believes that, taking 1,3,6-hexanetrinitrile (HTCN) as an example, its main chain structure is all C atoms, which greatly limits the Li + The present invention creatively uses tris(2-cyanoethyl)phosphite as the first electrolyte additive and fluorine-containing lithium phosphate compounds as the second additive. The two additives are used together, cooperate with each other, and act synergistically to generate inorganic lithium salt components such as "LiF" and "Li3PO4", and functional groups such as "PO" and "-CN", which can inhibit the precipitation of transition metal ions and the decomposition of the electrolyte, promote lithium ion conduction, and thus improve the overall performance of the battery.

[0037] Compared with traditional nitrile additives, the present invention uses tris(2-cyanoethyl)phosphite to participate in positive electrode film formation, solving the problem of unstable passivation films formed by adsorption of traditional nitrile additives and enhancing the effect of inhibiting transition metal precipitation. The "PO" in the skeleton structure improves lithium ion conductivity, solving the problem of increased battery impedance caused by traditional nitrile additives. Fluorine-containing lithium phosphate salt compounds are structurally similar to LiPO2F2, circumventing the problem of LiPO2F2's low solubility in the electrolyte. After participating in film formation, they generate inorganic lithium salt components such as "LiF" and "Li3PO4", improving lithium ion conductivity and inhibiting the decomposition of LiPF6. The present invention uses the first additive and the second additive to synergize, further improving the battery's comprehensive performance, including high voltage performance, high temperature performance, and cycle performance.

[0038] The present invention also provides a method for synthesizing tris(2-cyanoethyl)phosphite, which has simple process, mild conditions, strong operability, and is more conducive to industrial production and application.

[0039] Experimental results show that the rate performance, high temperature performance and cycle performance of the lithium ion battery prepared by the present invention using tris(2-cyanoethyl)phosphite and fluorine-containing lithium phosphate compound electrolyte are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the C NMR spectrum of tris(2-cyanoethyl)phosphite prepared in the present invention;

[0041] Figure 2This is the H NMR spectrum of tris(2-cyanoethyl)phosphite prepared in the present invention;

[0042] Figure 3 This is the NMR P spectrum of tris(2-cyanoethyl)phosphite prepared by the present invention;

[0043] Figure 4 1 and 2 are LSV curves of the embodiments of the present invention and the comparative example. DETAILED DESCRIPTION

[0044] To further understand the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0046] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials of conventional purity in the field of lithium-ion battery electrolytes.

[0047] The present invention provides a lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive;

[0048] The additives include a first additive and a second additive;

[0049] The first additive includes tris(2-cyanoethyl)phosphite;

[0050] The second additive includes a fluorine-containing lithium phosphate compound;

[0051] The fluorine-containing lithium phosphate compound has a structure as shown in formula (I):

[0052]

[0053] Wherein, R is selected from one of Li, alkyl, hydrocarbon, cyano and fluorinated alkyl.

[0054] In the present invention, the amount of tris(2-cyanoethyl)phosphite added is preferably 0.1% to 5% of the total mass of the electrolyte, more preferably 1% to 4%, and even more preferably 2% to 3%.

[0055] In the present invention, the number of carbon atoms in the alkyl group, hydrocarbon group, cyano group or fluorine-containing alkyl group is less than or equal to 3, more preferably less than or equal to 2, or equal to 1.

[0056] In the present invention, the tris(2-cyanoethyl)phosphite has a structure as shown in formula (II):

[0057]

[0058] Specifically, the fluorine-containing lithium phosphate compound preferably includes a structure as shown in any one or more of formulas (1) to (14), and more preferably a structure as shown in any one of formulas (1) to (14):

[0059]

[0060]

[0061] The present invention has no particular limitation on the specific preparation method of the fluorine-containing lithium phosphate compound having a structure represented by formula (I) or the fluorine-containing lithium phosphate compound having a structure represented by any one of formulas (1) to (14). The fluorine-containing lithium phosphate compound can be prepared by a preparation method well known to those skilled in the art, or by adapting and improving a preparation method of a similar structure.

[0062] In the present invention, the amount of the second additive added is preferably 0.1% to 3% of the total mass of the electrolyte, more preferably 0.5% to 2.5%, and even more preferably 1% to 2%.

[0063] In the present invention, the organic solvent preferably includes two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, propyl propionate and ethyl propionate, and more preferably includes two of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, propyl propionate and ethyl propionate.

[0064] In the present invention, the amount of the organic solvent added is preferably 50% to 75% of the total mass of the electrolyte, more preferably 55% to 70%, and even more preferably 60% to 65%.

[0065] In the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide and lithium difluorophosphate, more preferably lithium hexafluorophosphate, lithium bisfluorosulfonyl imide or lithium difluorophosphate.

[0066] In the present invention, the amount of the lithium salt added is preferably 12% to 20% of the total mass of the electrolyte, more preferably 13% to 19%, more preferably 14% to 18%, and more preferably 15% to 17%.

[0067] In the present invention, the additives preferably further include a third additive.

[0068] In the present invention, the third additive preferably includes tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, tris(trimethylsilane) borate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, tris(2-cyanoethyl)borate, tris(2-cyanoethyl)phosphite, tris(2-cyanoethyl)phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, fluoroethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid and methanedisulfonic acid ester. One or more of the methyl esters, more preferably tris(trimethylsilane)phosphate, tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, tris(2-cyanoethyl)borate, tris(2-cyanoethyl)phosphite, tris(2-cyanoethyl)phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, fluoroethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylenesulfonic acid or methylene methanedisulfonate.

[0069] In the present invention, the amount of the third additive added is preferably 0.1% to 20% of the total mass of the electrolyte, more preferably 1% to 15%, and even more preferably 5% to 10%.

[0070] In the present invention, the tris(2-cyanoethyl)phosphite is preferably obtained by using 3-hydroxypropionitrile and phosphorus trichloride as raw materials through a substitution reaction.

[0071] In the present invention, the preparation method of tris(2-cyanoethyl)phosphite preferably comprises the following steps:

[0072] 1) mixing 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution;

[0073] 2) adding a phosphorus trichloride organic solution to the system solution obtained in the above step to carry out a low-temperature reaction. After the dropwise addition is completed, an organic metal base is added under the reaction temperature conditions of stage II, and the reaction is continued under the same temperature conditions to obtain tris(2-cyanoethyl)phosphite.

[0074] The invention first mixes 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution.

[0075] The present invention further adds a phosphorus trichloride organic solution to the system solution obtained in the above step to carry out a low-temperature reaction. After the dropwise addition is completed, an organic metal base is added under the reaction temperature conditions of stage II, and the reaction is continued under the temperature conditions to obtain tris(2-cyanoethyl)phosphite.

[0076] In the present invention, after the continued reaction, a purification step is preferably included.

[0077] In the present invention, the purification preferably comprises the following steps:

[0078] The crude product obtained after the reaction is further reacted is added with an organic solvent and filtered, and then an alkali solution is added to separate the organic phase, and then the organic solvent is removed to obtain cyanophosphite.

[0079] The present invention is a complete and detailed overall technical solution to better improve the effect of lithium-ion battery electrolyte. The lithium-ion battery electrolyte can specifically be the following:

[0080] A lithium-ion battery electrolyte comprising an organic solvent, a lithium salt and an additive;

[0081] The additives include a first additive and a second additive;

[0082] The first additive includes tris(2-cyanoethyl)phosphite;

[0083] The second additive includes a fluorine-containing lithium phosphate compound.

[0084] Specifically, the amount of tris(2-cyanoethyl)phosphite added accounts for 0.1% to 5% of the total mass of the electrolyte.

[0085] Specifically, the tris(2-cyanoethyl)phosphite has a structure as shown in formula (II):

[0086]

[0087] Specifically, the fluorine-containing lithium phosphate compound has a structure as shown in formula (I):

[0088]

[0089] Wherein, R is Li, or one of an alkyl group, a hydrocarbon group, a cyano group, and a fluorinated alkyl group, and the number of carbon atoms is ≤ 3. The specific structural formula of the second additive fluorinated lithium phosphate salt compound includes the following:

[0090]

[0091] Specifically, the amount of the second additive added accounts for 0.1% to 3% of the total mass of the electrolyte.

[0092] Specifically, the organic solvent includes two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, propyl propionate and ethyl propionate.

[0093] Specifically, the amount of the organic solvent added accounts for 50% to 75% of the total mass of the electrolyte.

[0094] Specifically, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorophosphate.

[0095] Specifically, the amount of the lithium salt added accounts for 12% to 20% of the total mass of the electrolyte.

[0096] Specifically, the additives further include a third additive.

[0097] Specifically, the third additive includes one or more of tris(trimethylsilane)phosphate, tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, tris(2-cyanoethyl)borate, tris(2-cyanoethyl)phosphite, tris(2-cyanoethyl)phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, fluoroethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid and methylene methanedisulfonate.

[0098] Specifically, the amount of the third additive added accounts for 0.1% to 20% of the total mass of the electrolyte.

[0099] Specifically, the tris(2-cyanoethyl)phosphite is obtained by using 3-hydroxypropionitrile and phosphorus trichloride as raw materials through a substitution reaction.

[0100] Specifically, the preparation method of tris(2-cyanoethyl)phosphite comprises the following steps:

[0101] 1) mixing 3-hydroxypropionitrile and a hydrogen chloride chelating agent to obtain a system solution;

[0102] 2) adding a phosphorus trichloride organic solution to the system solution obtained in the above step to carry out a low-temperature reaction, and after the dropwise addition is completed, adding an organic metal base under the reaction temperature conditions of stage II, and continuing the reaction under the same temperature conditions to obtain tris(2-cyanoethyl)phosphite;

[0103] The preparation method further comprises a purification step.

[0104] Specifically, the method for purifying tris(2-cyanoethyl)phosphite comprises the following steps:

[0105] The crude product obtained after the reaction is further reacted is added with an organic solvent and filtered, and then an alkali solution is added to separate the organic phase, and then the organic solvent is removed to obtain cyanophosphite.

[0106] Furthermore, the tris(2-cyanoethyl)phosphite may also include a fine purification method comprising the following steps:

[0107] 1) adding a crude tris(2-cyanoethyl)phosphite product to an organic solvent, filtering the mixture, adding an alkali solution, mixing the mixture, and separating the organic phase to obtain an organic phase solution;

[0108] 2) The organic phase solution and the stabilizer obtained in the above step are subjected to reduced pressure distillation to obtain purified tris(2-cyanoethyl)phosphite.

[0109] The present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode and the electrolyte described in any one of the above technical solutions.

[0110] The present invention provides a lithium-ion battery electrolyte and a lithium-ion battery containing tris(2-cyanoethyl)phosphite. The present invention uses tris(2-cyanoethyl)phosphite as a first electrolyte additive and a fluorine-containing lithium phosphate compound as a second additive. The two additives are used together, interacting synergistically to generate inorganic lithium salt components such as "LiF" and "Li3PO4" and functional groups such as "PO" and "-CN." These components inhibit transition metal ion precipitation and electrolyte decomposition, promote lithium ion conduction, and thus enhance the overall battery performance.

[0111] Compared with traditional nitrile additives, the present invention uses tris(2-cyanoethyl)phosphite to participate in positive electrode film formation, solving the problem of unstable passivation films formed by adsorption of traditional nitrile additives and enhancing the effect of inhibiting transition metal precipitation. The "PO" in the skeleton structure improves lithium ion conductivity, solving the problem of increased battery impedance caused by traditional nitrile additives. Fluorine-containing lithium phosphate salt compounds are structurally similar to LiPO2F2, circumventing the problem of LiPO2F2's low solubility in the electrolyte. After participating in film formation, they generate inorganic lithium salt components such as "LiF" and "Li3PO4", improving lithium ion conductivity and inhibiting the decomposition of LiPF6. The present invention uses the first additive and the second additive to synergize, further improving the battery's comprehensive performance, including high voltage performance, high temperature performance, and cycle performance.

[0112] The present invention also provides a method for synthesizing tris(2-cyanoethyl)phosphite, which has simple process, mild conditions, strong operability, and is more conducive to industrial production and application.

[0113] Experimental results show that the rate performance, high temperature performance and cycle performance of the lithium ion battery prepared by the present invention using tris(2-cyanoethyl)phosphite and fluorine-containing lithium phosphate compound electrolyte are significantly improved.

[0114] To further illustrate the present invention, a lithium-ion battery electrolyte and a lithium-ion battery provided by the present invention are described in detail below in conjunction with examples. However, it should be understood that these examples are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operating processes are provided only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The scope of protection of the present invention is not limited to the following examples.

[0115] The reagents used in the following examples of the present invention are all commercially available products.

[0116] Preparation Example

[0117]

[0118] (1) Add 0.4 mol of anhydrous 3-hydroxypropionitrile, 0.3 mol of anhydrous triethylamine, and 0.303 g of a mixed solution of sodium ethoxide to a four-necked flask, and control the reaction temperature to below -30°C;

[0119] (2) Mix 13.73 g of 0.1 mol of phosphorus trichloride and 100 ml of dichloromethane and place them in a constant pressure dropping funnel;

[0120] (3) Under nitrogen protection, the mixed solution of step (2) was added dropwise to the mixed solution of step (1) at a rate of 10 ml / h; after the addition was completed, the mixture was transferred to 65° C. and reacted for 15 h to obtain a crude product, and then dichloromethane was added to filter out triethylamine hydrochloride.

[0121] (4) A 3% NaOH aqueous solution was added to the filtered filtrate, stirred for 30 minutes, and then allowed to stand for separation. After rotary separation, dichloromethane was removed from the organic phase solution to obtain pure tris(2-cyanoethyl)phosphite with a yield of 81.75%. The product content was measured by gas chromatography to be 97.3%.

[0122] The tris(2-cyanoethyl)phosphite prepared by the present invention was characterized.

[0123] See also Figure 1 , Figure 1 This is the C NMR spectrum of tris(2-cyanoethyl)phosphite prepared in the present invention.

[0124] See also Figure 2 , Figure 2 This is the H NMR spectrum of tris(2-cyanoethyl)phosphite prepared in the present invention.

[0125] See also Figure 3 , Figure 3 This is the NMR P spectrum of tris(2-cyanoethyl)phosphite prepared in the present invention.

[0126] Example

[0127] (1) Preparation of electrolyte: In an argon-filled glove box, the corresponding solvents were mixed uniformly in a predetermined ratio and stirred continuously. A predetermined amount of electrolyte lithium salt and additives were slowly added to the mixed solvent to obtain Examples 1 to 8 and Comparative Examples 1 to 6. The electrolyte formulations are shown in Table 1. Table 1 shows the electrolyte formulations in the Examples and Comparative Examples of the present invention.

[0128] Table 1

[0129]

[0130] (2) LSV test: The three-electrode test method was used to test the LSV curves of the electrolytes of Comparative Example 1, Comparative Example 2, and Example 1.

[0131] See also Figure 4 , Figure 4 1 and 2 are LSV curves of the embodiments of the present invention and the comparative example.

[0132] (3) Preparation of positive electrode sheets: Polyvinylidene fluoride (PVDF), conductive agent and high voltage ternary material (NCM622) are added to N-methylpyrrolidone (NMP) in a mass ratio of 1.5%:1.5%:97%, stirred and mixed thoroughly, and the slurry is coated on an aluminum foil current collector, dried, cold pressed and punched to obtain positive electrode sheets.

[0133] (4) Preparation of negative electrode sheets: Sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), conductive agent and graphite are added to deionized water in a mass ratio of 1.2%: 2%: 1%: 96.8% in sequence, and the mixture is thoroughly stirred and evenly mixed. The slurry is coated on a copper foil current collector, dried, cold pressed and punched to obtain a negative electrode sheet.

[0134] (5) Preparation of lithium batteries: The separator, positive electrode sheets, and negative electrode sheets are stacked in a "Z" shape to obtain a bare cell to be filled with liquid, and then the cell to be filled with liquid is packaged with aluminum-plastic film. After baking, the electrolyte is injected at an addition amount of 2.8g / Ah to obtain a lithium-ion battery with a nominal capacity of 5Ah to be tested.

[0135] (6) Testing of lithium-ion batteries:

[0136] DCR test: Charge the battery to 4.0V with constant current and constant voltage, let it sit for 6 hours, and then test the battery's DC internal resistance.

[0137] Rate discharge performance test: Charge to 4.4V at 0.2C, discharge to 3.0V at 0.2C, 1C, and 5C, and calculate the ratio of discharge capacity at different rates to the 0.2C discharge capacity.

[0138] Rate charging performance test: Discharge to 3.0V at 0.2C, charge to 4.4V at 0.2C, 1C, and 5C, and calculate the ratio of cross-current charging capacity to total charging capacity at different charging rates;

[0139] Cycling performance test: Test the capacity retention rate at different times of 1C charge and discharge cycles at different temperatures, with a charge and discharge cut-off voltage of 3.0V to 4.4V;

[0140] High-temperature storage performance test: The fully charged battery is stored at 60°C for 7 days to test the capacity retention rate and capacity recovery rate.

[0141] Referring to Table 2 and Table 3, Table 2 shows the performance test results of batteries of different embodiments of the present invention and comparative examples, and Table 3 shows the performance test results of batteries of different embodiments of the present invention and comparative examples.

[0142] Table 2

[0143]

[0144] Table 3

[0145]

[0146] Result analysis:

[0147] Figures 1 to 3 The invention provides a nuclear magnetic spectrum of tris(2-cyanoethyl)phosphate, which proves that the invention synthesizes tris(2-cyanoethyl)phosphate, and the purity of the crude product can reach more than 97%, and can reach more than 99% after fine purification.

[0148] Figure 4 The LSV curves of the electrolytes of Comparative Example 1, Comparative Example 2 and Example 1 are provided. It can be seen from the LSV curve of the electrolyte of Comparative Example 1 that the electrolyte undergoes a significant oxidation reaction at around 4.5V, which is mainly due to the film-forming reaction of LiPO2F2. Compared with Comparative Example 1, the antioxidant performance of the electrolyte of Comparative Example 2 is improved, mainly because the first additive tris(2-cyanoethyl)phosphite participates in the oxidation reaction. The integral area of ​​the film-forming reaction of the LSV curve of the electrolyte of Example 1 is the lowest and the antioxidant potential is the highest, which confirms that with the joint participation of the first additive, the second additive and LiPO2F2, the three have a good synergistic effect, which is fed back to the battery, and it is easy to form a thin and dense CEI film, which greatly improves the high voltage performance of the battery.

[0149] Combined with the battery test results analysis in Table 2 and Table 3:

[0150] Comparison of the test results of Comparative Examples 2 to 4 with those of Comparative Example 1 shows that the addition of the first additive tris(2-cyanoethyl)phosphite and the second additive fluorinated lithium phosphate compound alone can improve the overall performance of the battery, of which the first additive is more effective in improving the high-temperature storage and cycle performance of the battery, and the second additive is mainly effective in improving the DC internal resistance and rate performance of the battery. Compared with other comparative examples, the battery performance of Examples 1 to 2 and Comparative Examples 5 to 6 is more excellent, which reflects that the nitrile additives and the fluorinated lithium phosphate compound additives have good compatibility and synergy in electrolyte applications. The battery performance of the embodiment is better because the same amount of tris(2-cyanoethyl)phosphite replaces HTCN, which can greatly reduce the DC internal resistance of the battery, and the overall performance of the battery is also greatly improved, and tris(2-cyanoethyl)phosphite can participate in the positive electrode film formation, which is more advantageous than traditional nitrile additives in improving the electrochemical performance of the battery.

[0151] The above describes in detail a lithium-ion battery electrolyte and lithium-ion battery containing tris(2-cyanoethyl)phosphite provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above examples is intended only to facilitate understanding of the methods and core concepts of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be noted that, without departing from the principles of the present invention, a person skilled in the art may make various improvements and modifications to the present invention, and such improvements and modifications fall within the scope of protection of the claims of the present invention. The scope of patent protection for the present invention is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those described in the claims, or if they include equivalent structural elements that are not substantially different from the claims, then these other embodiments are also intended to be included within the scope of the claims.

Claims

1. A lithium ion battery electrolyte, characterized in that including organic solvents, lithium salts and additives; The additives include a first additive and a second additive; The first additive includes tris(2-cyanoethyl)phosphite; The second additive includes a fluorine-containing lithium phosphate compound; The fluorine-containing lithium phosphate compound has a structure as shown in formula (I): Wherein, R is selected from one of Li, alkyl, hydrocarbon, cyano and fluorinated alkyl.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The amount of tris(2-cyanoethyl)phosphite added is 0.1% to 5% of the total mass of the electrolyte; The number of carbon atoms in the alkyl group, hydrocarbon group, cyano group or fluorinated alkyl group is less than or equal to 3; The tris(2-cyanoethyl)phosphite has a structure as shown in formula (II):

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The fluorine-containing lithium phosphate compound includes a structure represented by any one or more of formulas (1) to (14):

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The amount of the second additive added accounts for 0.1% to 3% of the total mass of the electrolyte; The organic solvent comprises two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, propyl propionate and ethyl propionate; The added amount of the organic solvent accounts for 50% to 75% of the total mass of the electrolyte.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorophosphate; The amount of lithium salt added accounts for 12% to 20% of the total mass of the electrolyte; The additives further include a third additive.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that The third additive includes one or more of tris(trimethylsilane)phosphate, tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, tris(2-cyanoethyl)borate, tris(2-cyanoethyl)phosphite, tris(2-cyanoethyl)phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, fluoroethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylenesulfonic acid and methylene methanedisulfonate; The amount of the third additive added accounts for 0.1% to 20% of the total mass of the electrolyte.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that The tris(2-cyanoethyl)phosphite is obtained by using 3-hydroxypropionitrile and phosphorus trichloride as raw materials through a substitution reaction.

8. The lithium-ion battery electrolyte according to claim 7, characterized in that The preparation method of the tris(2-cyanoethyl)phosphite comprises the following steps: 1) mixing 3-hydroxypropionitrile, a hydrogen chloride chelating agent, and an organic alkali metal salt to obtain a mixture; 2) Under protective gas conditions, at a first temperature, adding a phosphorus trichloride organic solution to the system solution obtained in the above step to react, and continuing the reaction at a second temperature to obtain a cyanophosphite.

9. The lithium-ion battery electrolyte according to claim 8, characterized in that After the continued reaction, a purification step is also included; The purification comprises the following steps: The crude product obtained after the reaction is further reacted is added with an organic solvent and filtered, and then an alkali solution is added to separate the organic phase, and then the organic solvent is removed to obtain cyanophosphite.

10. A lithium ion battery, characterized in that: The electrolyte comprises a positive electrode, a negative electrode and the electrolyte according to any one of claims 1 to 9.

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