Electrolytes, electrochemical devices and electronic devices

Abstract

This invention discloses an electrolyte, an electrochemical device, and an electronic device, comprising additives including fluoroethylene carbonate and an alkoxydisiloxane compound. Based on the mass of the electrolyte, the mass of the fluoroethylene carbonate is A%, and the mass of the alkoxydisiloxane compound is B%. The value of A / B ranges from 2.5 to 50, and the value of A+B ranges from 3.5 to 15. The electrolyte of this invention can optimize the film-forming characteristics of the negative electrode surface, resulting in a longer cycle life for the electrochemical device, while reducing the volume expansion problem during high-temperature storage.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and more particularly to an electrolyte, an electrochemical device, and an electronic device. Background Technology

[0002] Because lithium-ion batteries have significant advantages such as high voltage and high capacity, as well as excellent characteristics such as long cycle life and good safety performance, they have broad application prospects in many fields such as portable electronic devices, electric vehicles, space technology and defense industry. In particular, electric vehicles powered by lithium-ion batteries have been rapidly developed and popularized in recent years.

[0003] To alleviate range anxiety and improve the driving range of electric vehicles, lithium-ion batteries have been continuously developing towards higher energy densities. Compared to conventional graphite anodes, silicon-carbon anode materials are increasingly being used in power batteries due to their higher specific capacity. However, in practical applications, the significant volume expansion and contraction during charging and discharging of silicon-carbon anode materials leads to a substantial decrease in battery cycle life. To improve the cycle stability of silicon-carbon anode materials, those skilled in the art have turned their attention to electrolytes.

[0004] Electrolyte, the "blood" of lithium-ion batteries, is one of the four key raw materials. It acts as a carrier for ion transport, conducting lithium ions between the positive and negative electrodes. It significantly impacts the energy density, specific capacity, operating temperature range, cycle life, and safety performance of lithium-ion batteries. Currently, the main technical approach for adapting electrolytes is to introduce a high content of fluoroethylene carbonate to continuously repair the solid electrolyte interphase (SEI) film on the negative electrode surface. However, the presence of a high content of fluoroethylene carbonate can exacerbate side reactions and decomposition of the electrolyte during high-temperature storage, leading to severe gas generation and volume expansion problems in the battery. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte, an electrochemical device, and an electronic device. The electrolyte of the present invention can improve the film-forming stability on the negative electrode surface, reduce the proportion of fluoroethylene carbonate in the optimized electrolyte, thereby enabling the electrochemical device to have good cycle stability, while reducing volume expansion during high-temperature storage.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides an electrolyte comprising an additive, the additive comprising fluoroethylene carbonate and an alkoxydisiloxane compound, wherein, based on the mass of the electrolyte, the mass of the fluoroethylene carbonate is A%, the mass of the alkoxydisiloxane compound is B%, the value of A / B ranges from 2.5 to 50, and the value of A+B ranges from 3.5 to 15.

[0008] A second aspect of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, a membrane, and an electrolyte as described in the first aspect.

[0009] A third aspect of the present invention provides an electronic device comprising the electrochemical device as described in the second aspect.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] According to the electrolyte of the present invention, the introduction of cyanoalkylalkoxysilane compounds can improve the film-forming stability of the negative electrode surface, reduce and optimize the content of fluoroethylene carbonate in the electrolyte, so that the electrochemical device has good cycle stability, while reducing the volume expansion during high-temperature storage, and thus can be better adapted to electrochemical devices containing silicon-carbon negative electrodes. Detailed Implementation

[0012] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0013] The present invention provides an electrolyte comprising solvents such as ethylene carbonate, ethyl methyl carbonate, propylene carbonate, fluoroethylene carbonate, and cyanoalkylalkoxysilane compounds.

[0014] Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is A, and the mass percentage of the cyanoalkylalkoxysilane compound is B, satisfying that: the value of A / B ranges from 2.5 to 50, and the value of A+B ranges from 3.5 to 15.

[0015] According to the electrolyte of the present invention, by introducing cyanoalkylalkoxysilane compounds, the alkoxy groups react with the hydroxyl groups on the surface of silicon suboxide to form stronger chemical bond connection sites, thereby improving the adhesion strength of the SEI film. Simultaneously, the introduction of cyano functional groups can complex free transition metal ions dissolved in the high-nickel cathode material, reducing their reduction and precipitation catalytic decomposition effect on the organic components of the SEI film, improving the overall stability of the SEI film, thereby reducing the content of fluoroethylene carbonate and better balancing the cycle stability and high-temperature storage performance of the battery.

[0016] In this invention, the value range of A / B is 4 to 16, and the value range of A+B is 6 to 11.

[0017] It should be noted that if the content of A is too high, it will lead to severe gas generation during high-temperature storage of the battery; if the content of A is too low, it will lead to a decrease in the cycle life of the battery. If the content of B is too low, it will not be able to enhance the stability of film formation and the improvement in cycle life will not be significant; if the content of B is too high, the battery impedance will increase significantly.

[0018] The cyanoalkylalkoxysilane compound is the compound shown in formula (I):

[0019]

[0020] R1 and R2 are selected from C 1-12 Saturated alkyl groups; R3, R4, R5, and R6 are each independently selected from C10. 1-6 Alkyl, alkenyl or alkoxy groups.

[0021] The electrolyte contains disiloxane compounds, specifically those of formula (I):

[0022]

[0023] Among them, R1 and R2 are each independently selected from C. 1-12 Saturated alkyl groups; R3, R4, R5, and R6 are each independently selected from C10. 1-6 Alkyl, alkenyl, or alkoxy groups. The compounds represented by formula (I) include at least one of the compounds shown in formulas I-1 to I-7:

[0024]

[0025] The electrolyte also contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC). Based on the mass of the electrolyte, the mass percentages of EC and PC are 10% and 6%, respectively. The EMC content is within the range of 30% to 60%, and the DEC content is within the range of 10% to 30%. Excessive DEC content will increase electrolyte viscosity and battery impedance, while insufficient DEC content will reduce the electrolyte's antioxidant capacity, worsening high-temperature storage gas generation and high-temperature cycling performance.

[0026] Preferably, the mass percentage of DEC is 15% to 25%.

[0027] The present invention also provides an electrochemical device, comprising a positive electrode, a negative electrode, a diaphragm, and the electrolyte described above.

[0028] The electrochemical device includes any device in which an electrochemical reaction occurs, and specific examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0029] In some embodiments, the electrochemical device of this application is an electrochemical device having a positive electrode having a positive electrode active material capable of adsorbing and releasing metal ions and a negative electrode active material capable of adsorbing and releasing metal ions.

[0030] The positive electrode comprises a positive electrode active material, which is a lithium-nickel transition metal composite oxide. The general formula of the lithium-nickel transition metal composite oxide is Li. 1+a Ni x Co y Mn z M b O 2-e X e In the general formula, -0.2 < a < 0.2, 0.7 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.3, 0.05 ≤ z ≤ 0.3, 0 ≤ b ≤ 0.05, 0 ≤ e ≤ 0.1, M is selected from any one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, and Mn, and X is selected from F and / or Cl. It should be noted that the above general chemical formula of the lithium-nickel transition metal composite oxide is the chemical formula when the battery SOC (State of Charge) is 0%.

[0031] The negative electrode includes a negative electrode active material layer and a current collector. The negative electrode active material layer includes a negative electrode active material, which includes graphite and silicon suboxide. Based on the mass of the negative electrode active material layer, the mass percentage of the silicon suboxide is 5% to 15%.

[0032] The negative electrode includes a negative electrode active material and a current collector, wherein the negative electrode active material includes graphite or silicon-carbon negative electrode active material.

[0033] The silicon-carbon anode active material is selected from any one or a mixture of two of silicon and silicon oxides, with a total mass percentage ranging from 5% to 15%.

[0034] The negative electrode also includes a carbon material, which is selected from any one or a mixture of two or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes and Ketjen black.

[0035] The present invention also provides an electronic device comprising the electrochemical device described above.

[0036] The electronic devices include, but are not limited to, the following types: laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0037] By using the electrolyte of the present invention, it is possible to better adapt it to electrochemical devices containing silicon-carbon anodes. Specifically, by introducing cyanoalkylalkoxysilane compounds into the electrolyte, the film-forming stability on the anode surface can be improved, and the content of fluoroethylene carbonate in the electrolyte can be reduced and optimized. This results in electrochemical devices using the electrolyte having better cycle stability, while reducing volume expansion during high-temperature storage.

[0038] The preparation method of the battery using this electrolyte and specific embodiments thereof are described below. Unless otherwise specified, all raw materials of this invention are commercially available or prepared according to conventional methods in the art.

[0039] (1) NCM (LiNi 0.9 Co 0.05 Mn 0.05 Preparation of O2 positive electrode

[0040] The positive electrode active material (LiNi) 0.9 Co 0.05 Mn 0.05 O2), polyvinylidene fluoride as a binder, and Super P as a conductive agent are mixed in a weight ratio of 97:2:1. N-methylpyrrolidone (NMP) is then added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil. The aluminum foil is dried at room temperature and then transferred to an oven for drying. Finally, it is cold-pressed and slit to obtain the positive electrode (electrode sheet).

[0041] (2) Preparation of silicon-carbon anode

[0042] Artificial graphite and silicon suboxide were used as negative electrode active materials, Super P as a conductive agent, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and styrene-butadiene rubber (SBR) as a binder. They were mixed in a mass percentage ratio of 86:10:1:1:2, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil current collector. The copper foil was dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode (electrode sheet) was obtained.

[0043] (3) Preparation of electrolyte

[0044] In an argon-atmosphere glove box with a water content of <10 ppm, battery-grade ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in the specified proportions to form an organic solvent. Other components were then quantitatively added according to the electrolyte composition described in the table below, and the mixture was thoroughly mixed to obtain the electrolyte. The content of each component in the table is a weight percentage calculated based on the total weight of the electrolyte. PS is 1,3-propanesulfonyl lactone, and VC is vinylene carbonate.

[0045] (4) Secondary battery

[0046] Using a 12μm thick polypropylene (PP) film as a separator, the prepared positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film was wrapped around the separator, and the mixture was dried in a vacuum oven at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the mixture was sealed and liquefied to obtain a ternary soft-pack battery (i.e., a lithium-ion battery) with a capacity of 1Ah. The electrolyte injection ratio of this lithium-ion battery is 3 g / Ah, the cell capacity is 1Ah, and the electrolyte mass is 3 g.

[0047] Next, the electrolyte in the prepared battery needs to be formed. The specific steps and conditions for the formation are as follows.

[0048] After the electrolyte is injected, it is kept in a hot-pressure environment of 0.1 MPa and charged at 0.02C for 17 minutes at 45°C in a static state. After standing for 5 minutes, it is charged to 0.3Ah at 0.02C. Then the gas bag is removed and vacuum sealed. It is left to stand at room temperature for 48 hours to complete the formation of the electrolyte.

[0049] In the embodiments of the present invention, the compounds represented by formula (I) are the following five types: Compound 1 used in Examples 1-18 is 1,3-divinyl-1,1,3,3-tetramethoxydisiloxane, while other different types of compounds represented by formula (I) are used in Examples 19-22, specifically: Compound 2 is tetraethoxydivinyldisiloxane, Compound 3 is 1,3-dimethoxy-1,3-dimethyl-1,3-divinyldisiloxane, Compound 4 is 1,1,3,3-tetramethoxy-1,3-dimethyldisiloxane, and Compound 5 is 1,3-dimethoxy-1,1,3,3-tetramethyldisiloxane.

[0050] The secondary battery of the present invention can be tested by the following method:

[0051] (1) Secondary battery cycle test

[0052] In an oven at a specified temperature (room temperature 25℃ or high temperature 45℃), the battery is cyclically charged and discharged within a specified potential range at a current of 1C. The discharge capacity of each cycle is recorded, and the test ends when the battery capacity reaches 80% of the capacity of the first cycle.

[0053] (2) DC resistance (DCR) test of secondary battery

[0054] At a specified temperature, when the battery is discharged to 50% SOC (State of Charge, reflecting the battery's remaining capacity) at a 1C current, the current is increased to 4C and maintained for 30 seconds. The difference between the updated stable voltage and the original platform voltage is measured, and the ratio of this difference to the 3C current value is the battery's DC resistance. The DCR test result performed after the battery's first full charge is the battery's initial DCR.

[0055] (3) High-temperature storage volume expansion rate test of secondary batteries

[0056] After fully charging the secondary battery, the initial volume V0 of the cell is measured by the water displacement method. Then, it is placed in a constant temperature chamber at 60°C. After 60 days, it is taken out and cooled to room temperature. The final volume V1 is then measured by the water displacement method. The volume expansion rate of the cell during high-temperature storage is calculated by (V1-V0) / V0.

[0057] Specifically, the cutoff voltage for charging and discharging ranges from 2.5V to 4.2V.

[0058] The electrolyte compositions of Examples 1 to 9 and Comparative Examples 1 to 4 of the present invention are shown in Table 1-1. Based on the components in Table 1-1, lithium-ion batteries were prepared using the above preparation method and their performance was tested. The test results are shown in Table 1-2. The compound shown in Formula I in Table 1 is the compound shown in Formula I-1.

[0059] Table 1-1

[0060]

[0061] Note: "-" indicates that it has not been added, and the same applies below.

[0062] Table 1-2

[0063]

[0064] As shown in Table 1-2, the range of values ​​for A+B determines the range of the total amount of additives used in the negative electrode film formation. When A+B is in the range of 3.5-15, the number of 80% cycles at room temperature and 80% cycles at high temperature are both maintained at a relatively high value of over 400, while the volume expansion rate after 60 days of storage at 60℃ is maintained at around 20% or less. In other words, when A+B is 3.5-15, it can simultaneously ensure good cycle life and low gas production. This is because Compound 1 can form stronger chemical bonds with the hydroxyl groups on the surface of the silicon-carbon negative electrode through the reaction of alkoxy groups, improving the mechanical strength and stability of the SEI film on the negative electrode surface, thus showing good effects in improving cycle life and gas production. Compared with the case without Compound 1 in Comparative Example 1, the combined performance of the above two aspects of the embodiment is better than that of simply using FEC. Although the higher the FEC content in the silicon-oxygen electrolyte formulation, the higher the cycle life, the more significantly gas production deteriorates during high-temperature storage. The introduction of Compound 1 can significantly improve cycle and gas production performance, and also improve battery impedance. Therefore, by controlling A+B and A / B within a suitable range, the battery cycle and high-temperature storage performance can be improved by introducing compound 1. This can reduce the FEC content, maintain and improve the overall cycle performance of the battery, further improve the gas generation performance during high-temperature storage, and at the same time control the battery impedance within a suitable range.

[0065] Furthermore, it can be seen that when the value of A+B is in the range of 6 to 11 and the value of A / B is in the range of 3 to 10, the stability of the negative electrode film formation can be more effectively guaranteed to balance the cycle performance and the battery impedance.

[0066] The electrolyte composition of Examples 10 to 13 of the present invention is shown in Table 2-1. By further adjusting the amount of compound 1 added, the A+B values ​​of each example are adjusted to be different from those of Example 8 while maintaining the same A+B value. Examples 10 to 13 also use the above preparation method to prepare lithium-ion batteries and test their performance. The test results are shown in Table 2-2. The compound used is shown in Formula I-1.

[0067] Table 2-1

[0068]

[0069]

[0070] Table 2-2

[0071]

[0072] Tables 2-1 and 2-2 are based on Example 7, with further adjustments to the A / B values ​​for testing. By making A+B the same for Examples 10-13 and Example 7, and then adjusting A / B for testing, it can be seen that under the same A+B conditions, the smaller the A / B, the smaller the gas production, and the larger the A / B, the larger the gas production.

[0073] The electrolyte compositions of Examples 14 to 17 are shown in Table 3-1. Examples 14 to 17 are based on Example 7, with adjustments made to the content of EMC and DEC in the solvent components. The lithium-ion batteries were prepared using the same preparation method described above, and their performance was tested. The test results are shown in Table 3-2. The compound used was shown in Formula I-1.

[0074] Table 3-1

[0075]

[0076] Table 3-2

[0077]

[0078]

[0079] As can be seen from the data in Table 3-2, under the optimal content and ratio of FEC and disiloxane compounds determined in this invention, the battery performance can also be locally adjusted by controlling the content ratio of EMC and DEC. It can be seen that increasing the DEC content improves the overall antioxidant properties of the solvent and improves the performance of high-temperature storage and high-temperature cycling. However, the increase in viscosity will significantly worsen the battery impedance. Conversely, the battery impedance decreases, but the overall high-temperature performance degrades. The preferred DEC content ratio is 15%-25%.

[0080] The electrolyte composition of Examples 18 to 21 differs from that of Example 8 in that the types of compounds shown in Formula (I) are different. Example 8 uses the compound shown in Formula I-1, Example 19 uses the compound shown in Formula I-2, Example 20 uses the compound shown in Formula I-3, Example 21 uses the compound shown in Formula I-4, and Example 22 uses the compound shown in Formula I-5. All other components are the same as those of Example 8.

[0081] Lithium-ion batteries were prepared using the above method, and their performance was tested. The test results are shown in Table 4.

[0082] Table 4

[0083]

[0084] As shown in Table 4, Examples 7, 18 to 21 used different types of compounds represented by formula (I). Compared with Comparative Example 2, all of them improved the room temperature and high temperature cycling performance of the battery and suppressed gas generation during high temperature storage. This result further verifies that adding the compound represented by formula (I) can improve the cycling and high temperature storage performance. Furthermore, by comparing the examples in Table 4, it can be seen that since the number of alkoxy groups and unsaturated bonds in the compounds 1-5 added in Examples 8, 18-21 decreases sequentially, the number of cycles also decreases accordingly. Therefore, it can be seen that increasing the number of alkoxy groups and unsaturated bonds can improve the strength and stability of the negative electrode interface film, thereby improving the cycling and high temperature storage performance. Although this may worsen the battery impedance, the addition of these compounds can significantly reduce the FEC content, so the overall battery resistance can still be optimized to varying degrees.

[0085] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

[0086] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0087] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0088] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. An electrolyte comprising an additive, characterized in that, The additives include fluoroethylene carbonate and alkoxydisiloxane compounds; Based on the mass of the electrolyte, the mass of the fluoroethylene carbonate is A%, the mass of the alkoxydisiloxane compound is B%, the value of A / B ranges from 4 to 7.5, and the value of A+B ranges from 6 to 8.

5.

2. The electrolyte according to claim 1, characterized in that, The alkoxydisiloxane compound is the compound shown in formula (I): Among them, R1 and R2 are each independently selected from C 1-12 Saturated alkyl groups; R3, R4, R5, and R6 are each independently selected from C10. 1-6 Alkyl, alkenyl or alkoxy groups.

3. The electrolyte according to claim 1, characterized in that, The compound represented by formula (I) includes at least one of the compounds represented by formula I-1 to formula I-7:

4. The electrolyte according to claim 1, characterized in that, The electrolyte also contains diethyl carbonate, wherein the mass percentage of diethyl carbonate in the electrolyte is C%, where C is 10 to 30.

5. The electrolyte according to claim 1, characterized in that, The electrolyte further comprises methyl ethyl carbonate, ethylene carbonate, and propylene carbonate, wherein the mass percentages of ethylene carbonate and propylene carbonate in the electrolyte are 10% and 6%, respectively, and the mass percentage of methyl ethyl carbonate is 30% to 60%.

6. An electrochemical device, characterized in that, It comprises a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1 to 5.

7. The electrochemical device according to claim 6, characterized in that, The positive electrode comprises a positive electrode active material, which comprises a lithium-nickel transition metal composite oxide, wherein the molar percentage of nickel in the transition metal element of the lithium-nickel transition metal composite oxide is more than 70%.

8. The electrochemical device according to claim 6 or 7, characterized in that, The negative electrode includes a negative electrode active material layer and a current collector. The negative electrode active material layer includes a negative electrode active material, which includes graphite or silicon suboxide material. Based on the mass of the negative electrode active material layer, the mass percentage of the silicon suboxide material is 5% to 15%.

9. An electronic device, characterized in that, The electrochemical device comprising any one of claims 6 to 8.

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