An electrolyte additive, an electrolyte, and a lithium-ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to an electrolyte additive, an electrolyte, and a lithium-ion battery. The electrolyte additive comprises a compound having the structure shown in Formula I, where A1, A2, A3, and A4 are each independently selected from one of C0-10 alkylene, alkoxide, haloalkylene, or haloalkoxide groups. The electrolyte additive of this invention includes three cyano groups, which can form stable coordination compounds with high-valence metal ions in the cathode material, suppressing the occurrence of side reactions at the cathode interface and improving the oxidation stability of the electrolyte under high voltage; it also possesses the high Li- content of ether-like substances. + Solvency. The lithium battery electrolyte of this invention can suppress the reduction and destruction of positive electrode metal ions at the negative electrode, significantly improving the cycle performance, high-temperature performance, and rate performance of lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] In recent years, with the widespread application of portable electronic devices and electric vehicles, people have increasingly higher requirements for the energy density and lifespan of lithium-ion batteries. Currently, increasing the battery operating voltage is an important means to improve battery energy density. However, when the battery operating voltage exceeds 4.2V, the accompanying problems gradually become apparent. Under high voltage, the oxidation activity of the positive electrode active material is high, and its reactivity with the electrolyte increases, exacerbating the oxidation and decomposition reaction of the electrolyte. The oxidation and decomposition products of the electrolyte continuously deposit on the surface of the positive electrode, increasing the battery's internal resistance and thickness. In addition, under high voltage, lithium salts in the electrolyte are very easy to decompose to produce HF. HF corrodes the positive electrode, causing the lithium cobalt oxide material to undergo an incompletely reversible structural phase transition, accompanied by volume changes that lead to structural damage. At the same time, the corrosion phenomenon causes Co ions to dissolve from the lithium cobalt oxide material in the positive electrode and deposit on the negative electrode, increasing the number of side reactions at the solid-liquid interface. Meanwhile, lattice oxygen participates in charge compensation, causing oxygen to be generated in the positive electrode, further oxidizing the electrolyte and reducing the battery's performance and safety.

[0003] Using electrolyte additives is one of the economical and effective methods to circumvent the aforementioned problems and improve the performance of lithium-ion batteries. Nitrile additives such as SN, ADN, and HTCN, due to the good antioxidant properties of the cyano group and its ability to form stable complexes with Co ions, can effectively suppress the occurrence of side reactions at the positive electrode interface and are now widely used in 4.4V lithium batteries. However, for higher voltage systems (4.45V and above), the cycle performance and high-temperature performance of lithium batteries remain challenging. Polycyano additives, with their more flexible coordination capabilities, have attracted widespread attention from researchers. For example, Chinese invention patents CN113013489A, CN112467219A, and CN114006045A mention polycyano additives. However, their improvement on the cycle performance, high-temperature performance, and rate performance of lithium batteries is still insufficient, making it difficult to meet the high energy density requirements of batteries in smartphones, tablets, and other electronic digital products. Summary of the Invention

[0004] In view of this, it is necessary to provide an electrolyte additive, an electrolyte, and a lithium-ion battery to address the above-mentioned problems, thereby improving the cycle performance, high-temperature performance, and rate performance of lithium batteries.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an electrolyte additive comprising a compound having the structure shown in Formula I:

[0007]

[0008] In structural formula I, A1, A2, A3, and A4 are each independently selected from one of the following: alkylene, alkoxy, haloalkylene, or haloalkoxy groups with a C0-10 group.

[0009] Furthermore, structural formula I is any one of the following compounds:

[0010]

[0011]

[0012] In a second aspect, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, and additives, wherein the additives include the above-mentioned electrolyte additives and conventional additives.

[0013] Furthermore, the organic solvent accounts for 60% to 80% of the total mass of the electrolyte.

[0014] Furthermore, the organic solvent includes any one or a combination of two or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), ethyl butyrate (EB), γ-butyrolactone (GBL), γ-valerolactone (GVL), and δ-valerolactone (DVL).

[0015] More preferably, the organic solvent is a combination of three or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP).

[0016] Furthermore, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

[0017] Furthermore, the lithium salt includes lithium hexafluorophosphate (LiPF6).

[0018] Furthermore, the lithium salt also includes any one or a combination of two or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate borate) (LiBOB), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0019] More preferably, the lithium salt includes a combination of at least two of LiPF6, LiPO2F2, and LiODFB.

[0020] Furthermore, the mass of the additive is 8% to 20% of the total mass of the electrolyte.

[0021] Furthermore, the mass of the electrolyte additive is 1% to 5% of the total mass of the electrolyte.

[0022] Furthermore, the conventional additives include any one or a combination of two or more of the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), adiponitrile (ADN), succinate (SN), ethylene glycol dipropionitrile ether (DENE), 1,3,6-hexanetrionitrile (HTCN), vinylene carbonate (VC), vinyl sulfate (DTD), ethylene ethylene carbonate (VEC), 1,3-sulfonate lactone (PST), fluorobenzene (FB), tris(trimethylsilane)borate (TMSB), and methane disulfonate methylene (MMDS).

[0023] Thirdly, the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned electrolyte.

[0024] Furthermore, the lithium-ion battery also includes a positive electrode, a negative electrode, and a separator.

[0025] Furthermore, the active material in the positive electrode includes LiCO2, LiMn2O4, LiFePO4, and LiNi. x Co y Mn z M 1-x-y- z O2 or LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one or more of Co, Ni, Mn, Mg, Al, Mo, B, Zr, Ga, Cr, V and Ti, and x+y+z≤1.

[0026] Furthermore, the active material in the negative electrode includes one or more of natural graphite, artificial graphite, silicon-carbon composite material, and lithium titanate.

[0027] Furthermore, the operating voltage of the lithium-ion battery is 4.45V to 4.50V.

[0028] Beneficial effects

[0029] 1. The electrolyte additive in this invention contains three cyano groups, which can form stable coordination compounds with high-valence metal ions in the cathode material, inhibit the occurrence of side reactions at the cathode interface, and improve the oxidation stability of the electrolyte under high voltage. At the same time, nitriles can react with water under acidic conditions to generate non-electrochemically active amides, which have the function of removing water and acid.

[0030] 2. The electrolyte additive in this invention is a nitrile ether compound, which not only possesses the excellent antioxidant properties of cyano groups but also exhibits the high Li content of ether compounds. + Solvability; furthermore, fluorination reduces the Li- content of the ether compared to the chain-like nitrile ether structure. + The solubilization capability of the electrolyte additive of this invention is that it has a cyclic chain structure, and the O in the linear ether segment and the O in the cyclic portion after fluorination still maintain a high Li content. + Solvation ability.

[0031] 3. The electrolyte additive in this invention contains a -CF3 group, which improves the electrochemical stability of the electrolyte additive. Furthermore, it interacts with the ether bonds in the compound, reducing the electron density on the -O- atom, thereby regulating the Li... + The solvation structure retains the high Li content of the ether. + Solvation ability.

[0032] 4. The synergistic effect of various nitrile additives, negative electrode film-forming additives, and compounds provided by this invention in the lithium battery electrolyte can optimize the SEI film structure, forming a more uniform and dense SEI film at the negative electrode, thereby inhibiting the reduction and destruction of positive electrode metal ions at the negative electrode, and significantly improving the cycle performance, high temperature performance, and rate performance of lithium batteries. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described clearly and completely below in conjunction with the embodiments of this invention. It should be noted that the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0034] This invention provides an electrolyte additive, an electrolyte, and a lithium-ion battery.

[0035] The electrolyte additive includes compounds having the structure shown in Formula I:

[0036]

[0037] In structural formula I, A1, A2, A3, and A4 are each independently selected from one of the C0-10 alkylene, alkoxide, haloalkylene, or haloalkoxide groups. When A1, A2, A3, and A4 are each independently selected from the C0 alkylene, alkoxide, haloalkylene, or haloalkoxide groups, it indicates that A1 and / or A2 and / or A3 and / or A4 are not present.

[0038] Preferably, structural formula I is any one of the following compounds:

[0039]

[0040]

[0041] In the embodiments of the present invention, compounds 1 and 2 are prepared by reacting a derivative of 2-chloro-1,1,1-triethoxyethane with a derivative of 1,1,1-trifluoro-2,3-propanediol under acid catalysis. The reaction temperature is controlled at 100-150℃ and the reaction time is 1-8h.

[0042] In the embodiments of the present invention, compounds 3 and 4 are prepared by reacting a derivative of the original tetraethyl carbonate compound with a derivative of the 1,1,1-trifluoro-2,3-propanediol compound under acid catalysis. The reaction temperature is controlled at 100-150℃ and the reaction time is 1-8h.

[0043] In the embodiments of the present invention, compounds 5 and 6 are prepared by reacting a derivative of the original tetraethyl carbonate compound with a derivative of 1,1,1-trifluoro-3,4-butanediol under acid catalysis. The reaction temperature is controlled at 100-150℃ and the reaction time is 1-8h.

[0044] The preparation methods of compounds 7, 8, 9, and 10 in the embodiments of the present invention are as follows: under acid catalysis, they are obtained by a condensation reaction of a derivative of 2-chloro-1,1,1-triethoxyethane and a derivative of 1,1,1-trifluoro-3,4-butanediol. The reaction temperature is controlled at 100-150℃ and the reaction time is 1-8h.

[0045] It should be noted that the preparation method described in this invention is not intended to limit the compounds of this invention. Other conventional chemical methods can also be used to synthesize the compounds of this invention, as long as they conform to the structure of the compounds of this invention.

[0046] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0047] Example 1

[0048] 1. Preparation of electrolyte

[0049] Ethylene carbonate (EC), propyl propionate (PP), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:PP:DEC = 1:2:5:2. After mixing, conventional additives and electrolyte additives were added sequentially. The conventional additives were 8.0 wt% FEC, 3.0 wt% PS, 1.5 wt% SN, 1 wt% ADN, and 2 wt% HTCN. The electrolyte additive was 1 wt% Compound 1. Then, 0.5 wt% LiPO₂F₂ and 15 wt% LiPF₆ were added, and the mixture was thoroughly mixed and dissolved before use. The mass fractions refer to the ratio of each additive to the total mass of the electrolyte.

[0050] 2. Preparation of the positive electrode

[0051] The positive electrode active material LiCO2, conductive carbon black (Super-P), carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.9:0.8:0.8:1.5, and then dispersed in N-methyl-2-pyrrolidone (NMP). After thorough stirring, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated onto the positive electrode current collector Al foil, dried at 110°C, rolled and slit, and then the tabs were welded and adhesive was applied to form a positive electrode sheet that met the requirements.

[0052] 3. Preparation of the negative electrode

[0053] Artificial graphite (anode active material), conductive carbon black (Super-P), styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 94:1:2.5:2.5 and then dispersed in deionized water to obtain anode slurry. The anode slurry was uniformly coated onto Cu foil (anode current collector), dried at 98°C, rolled and slit, and then tabs were welded to produce anode sheets that met the requirements.

[0054] 4. Preparation of lithium-ion batteries

[0055] The positive and negative electrode sheets prepared by the above method are wound together with the separator and packaged to form a lithium-ion battery with a thickness of 4.8 mm, a length of 86 mm, and a width of 66 mm. The battery cells are then vacuum baked at 80°C for 24 h to obtain the cells to be injected with electrolyte. The prepared electrolyte is injected into the cells in a glove box with the dew point controlled below -40°C. After standing at high temperature and room temperature for 24 h respectively, the cells are formed, sealed again, and tested for capacity to complete the battery manufacturing process.

[0056] Example 2

[0057] The difference from Example 1 is that the electrolyte additive in the additive is 3 wt% of compound 1, and the rest are the same.

[0058] Example 3

[0059] The difference from Example 1 is that the electrolyte additive in the additive is 5 wt% of Compound 1, and the rest are the same.

[0060] Example 4

[0061] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 2, and the rest are the same.

[0062] Example 5

[0063] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 3, and the rest are the same.

[0064] Example 6

[0065] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 4, and the rest are the same.

[0066] Example 7

[0067] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 5, and the rest are the same.

[0068] Example 8

[0069] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 6, and the rest are the same.

[0070] Example 9

[0071] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 7, and the rest are the same.

[0072] Example 10

[0073] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 8, and the rest are the same.

[0074] Example 11

[0075] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 9, and the rest are the same.

[0076] Example 12

[0077] The difference from Example 1 is that the electrolyte additive in the additive is 1 wt% of compound 10, and the rest are the same.

[0078] Example 13

[0079] The difference from Example 1 is that the conventional additives also include 0.5 wt% VC, and the rest are the same.

[0080] Example 14

[0081] The difference from Example 1 is that the lithium salt also includes 1 wt% LiODFB, otherwise it is the same.

[0082] Example 15

[0083] The difference from Example 1 is that the conventional additives also include 0.5 wt% VC, and the lithium salt also includes 1 wt% LiODFB, with the rest being the same.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that this comparative electrolyte additive does not contain 1 wt% of compound 1, but all other aspects are the same.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that this comparative electrolyte additive does not contain 1 wt% of compound 1, but contains 1 wt% of EGBE, and the rest are the same.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that this comparative electrolyte additive contains 10 wt% of compound 1, and the rest are the same.

[0090] Lithium-ion battery performance testing

[0091] The high-voltage lithium-ion batteries prepared in Comparative Examples 1-2 and Examples 1-11 were subjected to performance tests.

[0092] 1) Room temperature cycling performance test: At 25℃, charge to 4.5V with constant current and constant voltage at 0.7C, cut off current at 0.05C, and then discharge to 3.0V with constant current at 1.0C. Record the initial discharge capacity as C0. Repeat the charge and discharge cycle 500 times and record the discharge capacity on the 500th cycle as C1. Calculate the capacity retention rate of room temperature cycling according to the following formula: Capacity retention rate = C1 / C0*100%.

[0093] 2) High-temperature cycling performance test: In a 45℃ constant temperature chamber, charge to 4.5V with a constant current and constant voltage of 0.7C and cut off current of 0.05C. Then discharge to 3.0V with a constant current of 1.0C. Record the initial discharge capacity as C0. Repeat the charge and discharge cycle 500 times and record the discharge capacity on the 500th cycle as C1. Calculate the capacity retention rate of the high-temperature cycle according to the following formula: Capacity retention rate = C1 / C0*100%.

[0094] 3) Performance test after 4 hours of storage at 85℃: At 25℃, charge to 4.5V with a constant current and constant voltage of 0.7C, cutoff current 0.05C, then discharge to 3.0V with a constant current of 0.2C, recording the initial discharge capacity as C0. At 25℃, charge to 4.5V with a constant current and constant voltage of 0.7C, cutoff current 0.05C, and test the battery thickness at room temperature after full charge. Then transfer the fully charged battery to 85℃ and leave it for 4 hours. After storage, test the hot thickness. Then leave it at 25℃ for 2 hours, and discharge to 3.0V with a constant current of 0.2C, recording the discharge capacity as C1. The capacity retention rate after 4 hours of storage at 85℃ = C1 / C0*100%.

[0095] 4) Rate Discharge Test: At 25℃, charge to 4.5V with a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C, and then discharge to 3.0V with a constant current of XC (where X = 0.2, 0.5, 1). Record the discharge capacities at 0.2C, 0.5C, and 1C as C0, C1, and C2, respectively. The discharge ratio at 0.5C = C1 / C0, and the discharge ratio at 1C = C2 / C0.

[0096] The test data is shown in Table 1.

[0097] Table 1. Lithium Battery Performance Test Results

[0098]

[0099]

[0100] As can be seen from Comparative Example 1 and Examples 1-12, adding compounds 1-10 to the electrolyte can significantly improve the cycle performance, high-temperature performance and rate performance of lithium batteries.

[0101] As can be seen from Comparative Example 2 and Examples 1-12, adding EGBE to the electrolyte can also improve the overall performance of the battery. However, compounds 1-10 have a more significant effect on improving the cycle performance, high-temperature performance, and rate performance of lithium batteries. One reason is that compounds 1-10 all contain three cyano groups, which have a stronger and more flexible coordination ability with high-valence metal ions of the cathode, and can more effectively slow down the dissolution of cathode metal ions. Another reason is that compounds 1-10 all contain a cyclic chain structure and a -CF3 group, which has higher oxidation stability and adjustable Li+ solvation ability.

[0102] As can be seen from Comparative Example 3 and Examples 1-3, the addition of Compound 1 significantly improves the cycle performance, high-temperature performance and rate performance of lithium batteries within the scope of this application. This is because the more nitrile compounds there are, the better the protection effect on the positive electrode. However, when too many nitrile compounds are added, it will lead to an increase in impedance, thereby deteriorating the cell performance.

[0103] As shown in Examples 1 and 13-15, the addition of VC and LiODFB to the electrolyte, in addition to Compound 1, resulted in improved cycle performance, high-temperature performance, and rate performance of the lithium-ion battery. This is because Compound 1 can slow down the dissolution of Co ions at the positive electrode, while VC and LiODFB can optimize the SEI film structure, forming a more uniform and dense SEI film at the negative electrode. This effectively suppresses the damage of positive electrode byproducts to the negative electrode, and the synergistic effect of the three compounds more effectively protects the stability of the system.

[0104] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An electrolyte, characterized in that, It includes an organic solvent, a lithium salt, and an additive, said additive having a compound as shown in structural formula I: In structural formula I, A1, A2, A3, and A4 are each independently selected from one of the following: alkylene, alkoxy, haloalkylene, or haloalkoxy groups with a C0-10 group.

2. The electrolyte according to claim 1, characterized in that, The structural formula I is any one of the following compounds:

3. The electrolyte according to claim 1 or 2, characterized in that, The additives also include conventional additives; the conventional additives include any one or a combination of two or more of the following: fluoroethylene carbonate, 1,3-propanesulfonate lactone, adiponitrile, succinate, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, vinylene carbonate, vinyl sulfate, ethylene ethylene carbonate, 1,3-sulfonate lactone, fluorobenzene, tris(trimethylsilane)borate, and methane disulfonate.

4. The electrolyte according to claim 3, characterized in that, The organic solvent accounts for 60% to 80% of the total mass of the electrolyte; the organic solvent includes any one or a combination of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

5. The electrolyte according to claim 3, characterized in that, The lithium salt accounts for 10% to 20% of the total mass of the electrolyte; the lithium salt includes lithium hexafluorophosphate.

6. The electrolyte according to claim 3, characterized in that, The mass of the additive is 8% to 20% of the total mass of the electrolyte; the mass of the electrolyte additive is 1% to 5% of the total mass of the electrolyte.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that, The lithium-ion battery also includes a positive electrode, a negative electrode, and a separator.

9. The lithium-ion battery according to claim 8, characterized in that, The active materials in the positive electrode include LiCO2, LiMn2O4, LiFePO4, and LiNi. x Co y Mn z M 1-x-y-z O2 or LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one or more of Co, Ni, Mn, Mg, Al, Mo, B, Zr, Ga, Cr, V and Ti, and x+y+z≤1; the active material in the negative electrode includes one or more of natural graphite, artificial graphite, silicon-carbon composite material and lithium titanate.

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