Modified polymethyl hydrogen siloxane electrolyte additive, preparation method, electrolyte and application

Abstract

This invention discloses a modified polymethylhydrosiloxane electrolyte additive, its preparation method, electrolyte, and applications, belonging to the field of lithium metal batteries. The additive of this invention has a siloxane main chain, with at least one of carbonate and fluoroalkane substituents and an ether substituent introduced into the side chain. This allows the modified polymethylhydrosiloxane, when used as an electrolyte additive, to effectively reduce side reactions between lithium metal and the electrolyte, inhibit lithium dendrite growth, and maintain the crystal structure of the high-nickel cathode, reducing its disintegration and nickel ion deposition. When compounded with carbonate organic solvents as an electrolyte and applied to lithium metal batteries, it effectively improves the cycle stability and coulombic efficiency of lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal batteries and relates to a modified polymethylhydrosiloxane electrolyte additive, its preparation method, electrolyte, and its application. Background Technology

[0002] With the continuous growth in demand for high-energy-density energy storage, lithium metal batteries are considered an important development direction for next-generation battery systems due to their extremely high theoretical specific capacity and low electrochemical potential. However, lithium metal anodes are prone to problems such as dendrite growth, interfacial side reactions, and volume expansion during cycling, which seriously affect battery safety and cycle life. Meanwhile, high-energy-density NCM materials are the most commonly used cathode materials paired with lithium metal anodes, but NCM cathode particles often fail to maintain their crystal structure under high voltages, leading to a decline in lithium-ion storage capacity and nickel-ion dissolution. This results in a rapid drop in battery capacity using NCM cathodes. This vicious cycle of two behaviors leads to a continuous decrease in battery capacity and coulombic efficiency, severely hindering the development of lithium batteries.

[0003] However, traditional ester-based electrolyte systems often struggle to simultaneously stabilize both the lithium metal anode and cathode materials, leading to a rapid decline in overall battery performance. Therefore, developing a novel electrolyte additive capable of simultaneously stabilizing the lithium metal anode and cathode interface, suppressing harmful side reactions, and promoting uniform lithium deposition is crucial for improving the overall performance of lithium metal batteries. Chinese patent application CN116864808A discloses an electrolyte additive whose structural formula contains a thiosulfinate structure that can participate in the film formation of the CEI (Chemical Electrode Intake) and SEI (Sediment Electrode Intake) of both the cathode and anode, solving the problem of electrolyte poor oxidation resistance and effectively suppressing side reactions on the anode and cathode surfaces. However, this additive relies on reactive sites on the electrode surface; low reactivity makes it difficult to form a stable coating layer, while high reactivity leads to an increase in side reactions, thus affecting the coulombic efficiency of the battery. Furthermore, additives that rely on film formation through decomposition are gradually consumed during long-term cycling or high-voltage environments, resulting in the inability to maintain battery performance for extended periods. Summary of the Invention

[0004] To address the aforementioned technical problems, the first objective of this invention is to provide a modified polymethylhydrosiloxane electrolyte additive. This additive exhibits high lithium-ion conductivity and strong lithium affinity, as well as excellent wettability with the NCM cathode. The siloxane structure of the main chain possesses stable chemical properties and is not easily decomposed. The more reactive side chains (R1, R2) can simultaneously and stably protect both the lithium metal and the NCM cathode material by decomposing into a film.

[0005] The second objective of this invention is to provide a method for preparing modified polymethylhydrosiloxane electrolyte, which achieves modification through a single addition reaction, and has advantages such as high efficiency and simple process flow.

[0006] A third objective of this invention is to provide an electrolyte that, through the addition of modified polymethylhydrosiloxane electrolyte additives and synergistic effect with carbonate-based electrolyte base solutions, can effectively suppress harmful side reactions and promote uniform lithium deposition.

[0007] The fourth objective of this invention is to provide an application of an electrolyte in lithium metal batteries using NCM as the positive electrode active material. This electrolyte can maintain the crystal structure of NCM, stabilize the lithium metal positive and negative electrode interface, and effectively improve the long-term cycle stability and coulombic efficiency of lithium metal batteries.

[0008] To achieve the above technical objectives, the present invention provides a modified polymethylhydrosiloxane electrolyte additive, specifically with the following structural formula 1:

[0009] Formula 1;

[0010] Formula 2;

[0011] Formula 3;

[0012] In this structure, R1 and R2 are independently selected from substituents of Formula 2 or Formula 3, a is an integer from 2 to 6, such as 2, 3, 4, 5 or 6; x / (x+y+z) ranges from 0.5 to 0.75, and R3 is a C1 to C5 alkylene group, such as -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4- or -(CH2)5.

[0013] The modified polymethylhydrosiloxane electrolyte additive of this invention can regulate the positive and negative electrode interfaces of high-voltage lithium metal batteries, while simultaneously exhibiting high lithium-ion conductivity and strong lithiophilicity. It also demonstrates excellent wettability with the NCM positive electrode and provides stable protection for lithium metal. The key to the synergistic effect of the structural units lies in the interaction of these additives with the NCM material. Specifically, at the positive electrode, due to the stable chemical properties of the Si-O units on the additive's main chain, which are not easily decomposed and possess high bond energy and oxygen-donating capacity, these polymers preferentially interact with the oxygen-deficient sites on the NCM811 particles. This results in a stronger adsorption capacity at the positive electrode compared to traditional carbonate solvents, achieving excellent wettability. The formed CEI layer helps Li... +Rapid and uniform embedding / precipitation prevents drastic volume changes in the crystal structure that could lead to disintegration. At the negative electrode, the carbonate and fluoroalkane structures in the branched chains exhibit strong reactivity with lithium metal, generating robust inorganic SEI components such as Li₂O and LiF through decomposition and film formation reactions. Simultaneously, the flexible organic segments of the polymer adsorb onto the negative electrode surface, forming an organic-inorganic composite SEI. This organic-inorganic composite SEI provides abundant reaction sites, inducing Li… + Uniform deposition / stripping, on the other hand, resists the formation of cracks and excessive dead lithium caused by volume changes on the negative electrode surface.

[0014] Within the range of x, y, and z values ​​selected in this invention, the modified polymethylhydrosiloxane electrolyte additive of this invention can comprehensively regulate the ionic conductivity of the additive and suppress the side reactions of the positive and negative electrodes by adjusting different side chain ratios.

[0015] As a preferred embodiment, when R1 is selected from the substituent of Formula 2 and R2 is selected from the substituent of Formula 3, the value of y / (x+y+z) ranges from 0.21 to 0.4, and the value of z / (x+y+z) ranges from 0.04 to 0.1. Experiments have shown that when the side chain substituents simultaneously contain both Formula 2 and Formula 3 structures, the resulting modified polymethylhydrosiloxane electrolyte additive exhibits better overall performance.

[0016] As a preferred embodiment, 'a' is 4 or 5, and R3 is methylene or ethylene. Further preferred values ​​for the substituents and 'a' can yield modified polymethylhydrosiloxane electrolyte additives with superior overall performance.

[0017] The present invention also provides a method for preparing a modified polymethylhydrosiloxane electrolyte additive, which involves reacting polymethylhydrosiloxane with a monomer containing a double bond via an addition reaction; wherein the monomer containing the double bond is selected from at least one olefin having a structure of formula 6 and formula 5 and an olefin having a structure of formula 4.

[0018] Equation 4;

[0019] Formula 5;

[0020] Formula 6;

[0021] Where a is an integer from 2 to 6, and R3 is a C1 to C5 alkylene group.

[0022] The polymethylhydrosiloxane in this invention has the following structural formula (Formula 7):

[0023] Formula 7;

[0024] Where m = x + y + z.

[0025] The addition reaction of this invention mainly utilizes the addition of active H on polymethylhydrosiloxane to double bonds on monomers, thereby achieving modification of polymethylhydrosiloxane.

[0026] As a preferred embodiment, the conditions for the addition reaction are: using a platinum catalyst, a temperature of 60-80°C, and a molar ratio of polymethylhydrosiloxane to the monomer containing double bonds of 1:(1-1.2). The content of substituents in the resulting modified polymethylhydrosiloxane electrolyte additive can be adjusted by controlling the molar ratio of polymethylhydrosiloxane to the monomer containing double bonds.

[0027] Furthermore, the double-bonded monomer is composed of monomers having structural formulas 4, 5 and 6, wherein the molar ratio of monomers of formulas 4, 5 and 6 is (0.5~0.9):(0.25~0.4):(0.05~0.1).

[0028] As a preferred embodiment, the addition reaction is carried out using at least one organic solvent selected from toluene and 1,2-dichloroethane. The choice of organic solvent ensures that the dissolution of the polymethylhydrosiloxane with the double-bonded monomer promotes the reaction.

[0029] As a preferred embodiment, after the addition reaction is completed, the organic solvent is removed by evaporation under vacuum, and then purified by washing, column chromatography, and other methods to obtain high-purity modified polymethylhydrosiloxane. Further, the solvent used for washing is n-pentane.

[0030] The present invention also provides an electrolyte comprising the above-mentioned modified polymethylhydrosiloxane electrolyte additive, a carbonate organic solvent, and a lithium salt. The electrolyte combination of the present invention can effectively suppress harmful side reactions and promote uniform lithium deposition.

[0031] The electrolyte of this invention uses carbonate-based organic solvents as the base solution. This effectively dissolves lithium salts and additives, and leverages their high conductivity and energy density. However, when used alone, these organic solvents can cause severe side reactions in lithium metal, often failing to sustain long-term or high-voltage cycling. This invention addresses this by adding a small amount of modified polymethylhydrosiloxane additive to the carbonate-based organic solvent. This not only solves the side reaction problem between the carbonate-based electrolyte and lithium metal but also improves the nickel dissolution problem in the nickel-cobalt-manganese cathode under high voltage, achieving a good synergistic effect.

[0032] As a preferred embodiment, the amount of modified polymethylhydrosiloxane electrolyte additive in the electrolyte is 0.5~3wt%. When the amount of additive is too low, the film-forming ability is insufficient, and the performance improvement is not significant, only manifested as a decrease in impedance and a reduction in polarization voltage. Conversely, when the amount of additive is too high, the film-forming effect is significantly improved, and the system impedance is significantly reduced. However, excessive non-conductive polymer additive will lead to a decrease in the overall ionic conductivity of the electrolyte, thereby causing a decline in both battery cycle performance and rate performance. More preferably, the amount of modified polymethylhydrosiloxane electrolyte additive in the electrolyte is 1~1.5wt%, within which a better film-forming ability and maximum retention of the high ionic conductivity of ester electrolytes can be achieved.

[0033] As a preferred embodiment, the carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate.

[0034] As a preferred embodiment, the carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and propylene carbonate, along with ethylene carbonate (EC), wherein the volume percentage of ethylene carbonate is 20-30%.

[0035] As a preferred embodiment, the total amount of the carbonate organic solvent used is 80 microliters per coin cell.

[0036] As a preferred embodiment, the lithium salt is LiPF6, and the amount used is 1~1.2 mol / L.

[0037] As a preferred embodiment, the electrolyte is prepared by dissolving the modified polymethylhydrosiloxane electrolyte additive and lithium salt in a carbonate-based organic solvent. Alternatively, this invention can directly use a commercially available electrolyte containing carbonate-based electrolytes as the base solution, combined with the modified polymethylhydrosiloxane electrolyte additive.

[0038] Finally, this invention also provides an application of the electrolyte in lithium metal batteries using NCM as the positive electrode active material. The main-chain siloxane in the electrolyte additive of this invention exhibits excellent adsorption properties with NCM, maintaining the crystal structure of the high-nickel positive electrode, inducing uniform lithium-ion deposition while preventing the disintegration of the positive electrode NCM particles, stabilizing the lithium metal positive and negative electrode interface, and inhibiting the dissolution of nickel ions from the positive electrode and the rapid degradation of the battery. This effectively improves the long-term cycle stability and coulombic efficiency of lithium metal batteries.

[0039] As a preferred embodiment, the negative electrode active material of the lithium metal battery is pure lithium metal or a lithium-boron alloy.

[0040] As a preferred embodiment, the lithium-boron alloy includes one of 84Li-B alloy, Li-B-Mg alloy, Li-B-Al alloy, Li-B-Mg-Al alloy, and Li-B-In alloy.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The modified polymethylhydrosiloxane electrolyte additive provided by this invention can change the properties of polymethylhydrosiloxane by introducing different substituents into the side chain of the polymethylsiloxane. Its siloxane backbone exhibits excellent adsorption properties with NCM cathode materials, while the ether, carbonate, and fluoroalkane structures introduced into the side chain can synergistically construct an organic-inorganic composite SEI on the negative electrode surface. Therefore, the modified polymethylhydrosiloxane electrolyte additive of this invention can simultaneously protect lithium metal and NCM cathode materials.

[0043] (2) The modified polymethylhydrosiloxane electrolyte additive provided by the present invention has high lithium-ion conductivity, strong lithium affinity and good positive electrode wettability. While inducing uniform deposition of lithium ions, it prevents the disintegration of positive electrode NCM particles, stabilizes the lithium metal positive and negative electrode interface, and inhibits the dissolution of positive electrode nickel ions and rapid battery degradation.

[0044] (3) The electrolyte of the present invention can solve the side reaction problem between carbonate electrolyte and lithium metal by adding modified polymethylhydrosiloxane electrolyte additive to carbonate organic solvent base liquid, and at the same time improve the nickel dissolution problem of nickel cobalt manganese cathode under high voltage, thus achieving a good synergistic effect.

[0045] (4) When the electrolyte containing modified polymethylhydrosiloxane provided by this invention is applied to lithium metal batteries, the symmetrical battery achieves a speed of 1 mA / cm². 2 Current density, 1 mAh / cm 2 Under the given areal specific capacity conditions, it can achieve a long-term cycling time of 1000 hours while still maintaining a polarization voltage of less than 100 mV. The Li|NCM full cell formed by pairing with the NCM811 cathode has an initial charge-discharge specific capacity of 220 mAh / g at a 1C rate. After stable cycling to 250 cycles, the capacity retention rate is above 70%, and the coulombic efficiency remains at 100%, effectively improving the performance of lithium metal batteries. Attached Figure Description

[0046] Figure 1 The 1H NMR spectrum of the modified polymethylhydrosiloxane electrolyte additive prepared in Example 1 of this invention.

[0047] Figure 2 The infrared spectrum is shown for the modified polymethylhydrosiloxane electrolyte additive prepared in Example 1 of this invention.

[0048] Figure 3 The graph shows the performance test results of the electrolytes prepared in Example 1 and Comparative Example 2 of this invention and the commercial LB-005 electrolyte applied to a symmetric battery.

[0049] Figure 4 The graph shows the cycle performance test results of the electrolytes prepared in Example 1 and Comparative Example 2 of this invention and the commercial LB-005 electrolyte applied to a full battery at 1C.

[0050] Figure 5 The graph shows the cycle performance test of the electrolytes prepared in Example 1 and Comparative Example 2 of this invention and the commercial LB-005 electrolyte applied to a full battery at 3C.

[0051] Figure 6 The figures show the cycle test results of the electrolytes prepared in Example 1 and Comparative Example 2 of this invention and the commercial LB-005 electrolyte applied to full cells at a high voltage of 3.0~4.6V.

[0052] Figure 7 The coulombic efficiency test charts of the electrolyte prepared in Example 1 of this invention and the commercial LB-005 electrolyte applied to a full cell are shown.

[0053] Figure 8 This is a symmetrical cycling comparison diagram of the electrolyte prepared in Example 2 of the present invention and the commercial LB-005 electrolyte applied to a full cell.

[0054] Figure 9 The diagram shows the cycle performance test of the electrolyte prepared in Example 2 of this invention and the commercial LB-005 electrolyte applied to a full battery at 3C.

[0055] Figure 10 The graph shows the cycle performance test of the electrolyte prepared in Example 3 of this invention and the commercial LB-005 electrolyte applied to a full battery at 3C.

[0056] Figure 11 This is a symmetrical cycling comparison diagram of the electrolyte prepared in Example 4 of the present invention and the commercial LB-005 electrolyte applied to a full cell.

[0057] Figure 12 The graph shows the cycle performance test of the electrolyte prepared in Example 4 of this invention and the commercial LB-005 electrolyte applied to a full battery at 3C.

[0058] Figure 13 A symmetrical cycling comparison of the electrolyte prepared in Comparative Example 1 and the commercial LB-005 electrolyte applied to a full cell.

[0059] Figure 14The electrolyte prepared for Comparative Example 1 and the commercial LB-005 electrolyte are used in the cycle performance test of a full battery at 3C. Detailed Implementation

[0060] To more clearly illustrate the technical content of the present invention, it is described in detail here with reference to specific embodiments and accompanying drawings. Obviously, the listed embodiments are only preferred embodiments of the present technical solution, and other technical solutions that can be obviously derived by those skilled in the art based on the disclosed technical content still fall within the protection scope of the present invention.

[0061] In this embodiment of the invention, the chemical reagents used can be obtained by purchasing or by preparing them using existing methods, and the instruments and equipment used are conventional equipment in the prior art.

[0062] Example 1

[0063] A method for preparing a modified polymethylhydrosiloxane electrolyte additive, comprising the following steps:

[0064] 6 g (0.1 mol) of polymethylhydrosiloxane (purchased from Anaiji; E080709, CAS No. 63148-57-2), 2.85 g (0.025 mol) of ethylene ethylene carbonate, and 1.18 g (0.005 mol) of hexafluorobutyl acrylate were dissolved in 50 mL of toluene. 2 μL of platinum-diethylenetetramethyldisiloxane was added as a catalyst. After thorough mixing, the mixture was transferred to a single-necked flask, evacuated, and subjected to an addition reaction under argon as a protective gas. The mixture was stirred at room temperature. After 30 minutes, the mixture was transferred to an oil bath and heated to 70°C while stirring for 8 hours. Then, 18.36 g (0.09 mol) of 2,5,8,11-tetraoxatetradecene-13-ene was added using a syringe, and the reaction was allowed to proceed for 8 hours. The polymer obtained from the reaction was then removed by rotary evaporation to remove all toluene. After drying in a vacuum oven at 80°C for 24 hours, a viscous oily liquid was obtained. This liquid was washed five times with three times its volume of n-pentane and then dried in a vacuum oven at 80°C for 24 hours to obtain a modified polymethylhydrosiloxane electrolyte additive.

[0065] A method for preparing an electrolyte containing a modified polymethylhydrosiloxane additive: The modified polymethylhydrosiloxane electrolyte additive is added to LB005 commercial electrolyte (using a mixed organic solvent of EC and EMC with a volume ratio of 3:7 and 1 mol / L LiPF6) at a dosage of 1 wt% in a glove box and magnetically stirred for 2 hours to obtain the electrolyte.

[0066] Example 2

[0067] The only difference between this embodiment and Example 1 is that in the preparation method of the modified polymethylhydrosiloxane electrolyte additive, the molar ratio of polymethylhydrosiloxane, 2,5,8,11-tetraoxatetradecene-13-ene, ethylene carbonate, and hexafluorobutyl acrylate is changed to 1:0.5:0.4:0.1. All other steps and conditions are the same.

[0068] The electrolyte test results in this embodiment are as follows: Figure 8 and Figure 9 As shown, at 1mA / cm 2 Current density and 1mAh / cm 2 Under the condition of specific capacity, the symmetric battery can achieve a long cycle time of 600h, and the full battery cycle performance under 3C is significantly better than that of commercial electrolyte LB-005.

[0069] Example 3

[0070] The only difference between this embodiment and Example 1 is that hexafluorobutyl acrylate is not added in the preparation process of the modified polymethylhydrosiloxane electrolyte additive; all other steps and conditions are the same.

[0071] The electrolyte test results in this embodiment are as follows: Figure 10 As shown, the full battery cycle performance under 3C is significantly better than that of the commercial electrolyte LB-005, but the battery performance without the addition of hexafluorobutyl acrylate is worse than that of Example 1.

[0072] Example 4

[0073] The only difference between this embodiment and Example 1 is that the amount of modified polymethylhydrosiloxane electrolyte additive is replaced with 3wt% in the preparation process of the electrolyte containing the modified polymethylhydrosiloxane additive. All other steps and conditions are the same.

[0074] The electrolyte test results in this embodiment are as follows: Figure 11 and Figure 12 As shown, it can be seen that at 1mA / cm 2 Current density, 1 mAh / cm 2 Under the condition of specific area and capacity, symmetrical cells can achieve a long-term cycle time of over 500 hours.

[0075] Comparative Example 1

[0076] The only difference between this comparative example and Example 1 is that 2,5,8,11-tetraoxatetradecene-13-ene is not added during the preparation of the modified polymethylhydrosiloxane electrolyte additive; all other steps and conditions are the same.

[0077] The test results of this comparative example are as follows: Figure 13 and Figure 14As shown, the results indicate that polysiloxane additives lacking the 2,5,8,11-tetraoxatetradecene-13-ene structure do not significantly improve the cycle performance of the battery. This is because the 2,5,8,11-tetraoxatetradecene-13-ene structure plays an auxiliary role in the film formation of the electrolyte additive. + The role of rapid transportation, the lack of this structure leads to Li + The uneven and slow conduction at the positive and negative electrode interface caused the uneven deposition of lithium in the crystal structure of the positive electrode material to disintegrate.

[0078] Comparative Example 2

[0079] The only difference between this embodiment and Example 1 is that ethylene ethylene carbonate and hexafluorobutyl acrylate are not added during the preparation of the modified polymethylhydrosiloxane electrolyte additive; all other steps and conditions are the same.

[0080] The electrolyte test results for this comparative example are as follows: Figures 3-6 As shown, when neither ethylene carbonate nor hexafluorobutyl acrylate is added, the comparative example has a performance of 1 mA / cm². 2 Current density and 1mAh / cm 2 Under the condition of area specific capacity, the cycle performance of the symmetric battery decreased significantly from 1000h to less than 500h. At the same time, after 500 cycles of the full cell, the specific capacity decreased significantly from 82.97% to 71.51%. Moreover, under high voltage environment (3.0~4.6V), the capacity retention rate after 100 cycles decreased significantly to 18.43%.

[0081] Performance testing

[0082] The modified polymethylhydrosiloxane electrolyte additive (FPMHS) prepared in Example 1 was subjected to 1H NMR and IR spectroscopy, respectively. The results are as follows: Figure 1 and Figure 2 As shown in the figure, the target compound was successfully synthesized in this invention.

[0083] Electrochemical tests were conducted on Li|Li symmetric cells composed of the electrolyte containing modified polymethylhydrosiloxane additive obtained in Example 1 or the LB005 commercial electrolyte, respectively, and lithium metal was used. The test results are as follows: Figure 3 As shown. The results indicate that at 1 mA / cm 2 Current density, 1 mAh / cm 2 Under the condition of specific area and capacity, symmetrical cells can achieve a long cycle time of 1000 hours and still maintain a low polarization voltage (less than 100mV).

[0084] The electrolyte containing modified polymethylhydrosiloxane additive obtained in Example 1 or the LB005 commercial electrolyte were respectively used to form Li|NCM811 full cells with lithium metal and commercial NCM811 cathode material, and cycle tests were performed. The test results are as follows: Figure 4 As shown, the charge-discharge specific capacity at a 1C rate was initially 171 mAh / g, and after 500 stable cycles, the capacity retention rate was 82.97%, which is significantly better than the 48.40% retention rate of commercial electrolytes.

[0085] The electrolyte containing the modified polymethylhydrosiloxane additive or the LB005 commercial electrolyte obtained above were respectively used to form Li|NCM811 full cells with lithium metal and commercial NCM811 cathode material, and the rate performance was tested. The results are as follows: Figure 5 As shown in the figure. The results indicate that the specific capacity remained above 200 mAh / g throughout the low-current cycling process. After 500 stable cycles at 3 C, the capacity retention rate was 75.32%, and the coulombic efficiency remained at 100%, which is significantly better than the 29.26% retention rate of commercial electrolytes.

[0086] The electrolyte containing the modified polymethylhydrosiloxane additive or the LB005 commercial electrolyte obtained above were respectively used to form Li|NCM811 full cells with lithium metal and commercial NCM811 cathode material, and high-voltage performance tests were conducted. The results are as follows: Figure 6 As shown in the figure. The results show that after 200 stable cycles at 3.0~4.6V, the capacity retention rate is 66.30%, while the capacity retention rate of commercial electrolyte drops to 17.02% after only 100 cycles.

[0087] The above-described embodiments are merely preferred embodiments 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 technical scope of the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A modified polymethylhydrosiloxane electrolyte additive, characterized in that: It has the following structural formula as shown in Formula 1: Formula 1; Formula 2; Formula 3; Wherein, when R1 is selected from the substituents of Formula 2 and R2 is selected from the substituents of Formula 3, the value range of x / (x+y+z) is 0.5~0.75, the value range of y / (x+y+z) is 0.21~0.4, and the value range of z / (x+y+z) is 0.04~0.

1. Indicates the bonding site; a is 4 or 5, and R3 is methylene or ethylene; The modified polymethylhydrosiloxane electrolyte additive is used in the electrolyte in conjunction with carbonate organic solvents and lithium salts.

2. The preparation method of the modified polymethylhydrosiloxane electrolyte additive as described in claim 1, characterized in that: The polymethylhydrosiloxane is obtained by adding a monomer containing a double bond to it. The monomer containing double bonds is selected from alkenes having the structures of Formula 6 and Formula 5 and alkenes having the structure of Formula 4. Equation 4; Formula 5; Formula 6; Where a is 4 or 5, and R3 is methylene or ethylene.

3. The method for preparing a modified polymethylhydrosiloxane electrolyte additive according to claim 2, characterized in that: The conditions for the addition reaction are: using a platinum catalyst, a temperature of 60~80℃, and a molar ratio of polymethylhydrosiloxane to a monomer containing a double bond of 1:(1~1.2).

4. The method for preparing a modified polymethylhydrosiloxane electrolyte additive according to claim 2, characterized in that: The addition reaction is performed using at least one organic solvent selected from toluene and 1,2-dichloroethane.

5. An electrolyte, characterized in that: It comprises the modified polymethylhydrosiloxane electrolyte additive as described in claim 1, carbonate organic solvents, and lithium salts.

6. The electrolyte according to claim 5, characterized in that: The amount of modified polymethylhydrosiloxane electrolyte additive in the electrolyte is 0.5~3wt%.

7. The electrolyte according to claim 6, characterized in that: The carbonate organic solvents include at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate; Alternatively, the carbonate organic solvent may include at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate, in combination with ethylene carbonate.

8. The application of the electrolyte as described in any one of claims 5 to 7, characterized in that: It is applied to lithium metal batteries using NCM as the positive electrode active material.

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