Electrolytes and energy storage devices

Abstract

The application provides an electrolyte and an energy storage device, the electrolyte comprising an additive A, the structural formula of the additive A comprising a naphthyl group, an acid anhydride and a nitro group, the structure of the naphthyl group being shown in chemical formula 1, the acid anhydride being a substituent represented by chemical formula 2, and the nitro group being a substituent represented by chemical formula 3; chemical formula 1: ; chemical formula 2: ; and chemical formula 3: ; wherein R1, R2 and R3 are each independently selected from any one carbon atom in positions 1-8 in the naphthyl group. The electrolyte provided by the application can improve the capacity retention rate of the energy storage device after cycling, thereby improving the cycle life of the energy storage device.

Description

Technical Field

[0001] This application relates to the field of energy storage device technology, and more particularly to an electrolyte and an energy storage device. Background Technology

[0002] With the widespread application of energy storage devices such as lithium-ion batteries in new energy vehicles, mobile communications, and other fields, higher demands are being placed on the cycle life of these devices. Currently, the main methods for improving the cycle life of lithium-ion batteries include optimizing the composition and structure of electrode materials, optimizing the composition of the electrolyte, and optimizing the battery manufacturing process. Although existing technologies can improve the cycle life of lithium-ion batteries to some extent, some problems and limitations still exist. How to develop lithium-ion batteries with long cycle life remains an urgent problem to be solved. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and an energy storage device. Using this electrolyte can improve the capacity retention rate of the energy storage device after cycling, thereby improving the cycle life of the energy storage device.

[0004] This application provides an electrolyte comprising additive A. The additive A has a structure that includes a naphthyl group, an acid anhydride, and a nitro group. The structure of the naphthyl group is shown in chemical formula 1. The acid anhydride is a substituent represented by chemical formula 2, and the nitro group is a substituent represented by chemical formula 3. Chemical Formula 1: Chemical formula 2: Chemical formula 3: ; R1, R2, and R3 are each independently selected from any carbon atom at positions 1 to 8 of the naphthyl group.

[0005] In the electrolyte provided in this application embodiment, the added additive A contains functional groups of naphthyl, acid anhydride, and nitro groups. During the operation of the energy storage device assembled from the electrolyte, the nitro functional group in additive A can undergo a reduction reaction to generate Li3N and LiN. x O yInorganic SEI (Solid Electrolyte Interphase) membranes can be formed by reacting the anhydride functional groups to generate organic SEI membranes containing RCO2Li. Furthermore, the naphthyl functional group can promote electron cloud conjugation of additive A, increasing the reduction potential of additive A molecules. Simultaneously, the rigid structure of the naphthyl group enhances the stability of the SEI membrane structure. The electrolyte formed using additive A can generate an SEI membrane structure with an inner inorganic layer and an outer organic layer. This SEI membrane structure exhibits high stability, which is beneficial for stabilizing the interface of the negative electrode, reducing side reactions, and thus improving the cycle stability and capacity retention of the energy storage device. This, in turn, helps to extend the cycle life of the energy storage device and facilitates the construction of long-life energy storage devices.

[0006] Furthermore, the nitro group in the structural formula of additive A can generate an SEI film containing lithium nitride. Since lithium nitride has relatively high conductivity, the resulting SEI film has a relatively low interfacial impedance, leading to less polarization in the battery assembled with the electrolyte containing additive A. This, in turn, improves the performance of the energy storage device, such as cycle performance and energy efficiency. In contrast, replacing the naphthyl group with other functional groups, such as fluorine functional groups, generates an SEI film containing lithium fluoride. Lithium fluoride has relatively low conductivity, resulting in a higher interfacial impedance in the SEI film, which reduces the performance of the assembled energy storage device.

[0007] In one possible implementation, R1 is selected from the carbon atom at position 1 of the naphthyl group, and R2 is selected from the carbon atom at position 8 of the naphthyl group. In the structure of additive A, the anhydride functional group is simultaneously connected to the two benzene rings of the naphthyl group, which makes the electron conjugation degree of additive A high, which is beneficial to improving the reduction and decomposition ability of additive A, thereby making the SEI film formed by the energy storage device during operation more stable.

[0008] In one possible implementation, additive A is selected from at least one of structural formulas (I-1) to (I-12): (I-1) (I-2) (I-3) (I-4) (I-5) (I-6) (I-7) (I-8) (I-9) (I-10) (I-11) (I-12).

[0009] In one possible implementation, the electrolyte further includes a cyclic carbonate solvent. The anhydride group is also a reducing functional group; while one part of the anhydride functional group forms the organic SEI component RCO2Li, another part of the anhydride functional group can undergo a reduction reaction to generate O. - It can react with C· free radicals and initiate the ring-opening polymerization of cyclic carbonate solvents such as ethylene carbonate (EC) to generate polycarbonate-based SEI components, which can further improve the stability of the SEI film, improve the stability of the interface of the negative electrode, reduce side reactions, thereby improving the cycle stability and capacity retention of the energy storage device, and thus improving the cycle life of the energy storage device, which is conducive to the construction of long-life energy storage devices.

[0010] In one possible implementation, the cyclic carbonate solvent is selected from at least one of ethylene carbonate and propylene carbonate.

[0011] In one possible implementation, the mass fraction of additive A, based on the mass of the electrolyte, is 0.01% to 5%. If the content of additive A in the electrolyte is too low, its effect is not significant, and its optimization effect on improving the stability of the SEI membrane is not obvious. If the content of additive A in the electrolyte is too high, it will increase the interfacial impedance of the SEI membrane, thus not significantly contributing to the performance improvement of the energy storage device. By controlling the mass fraction of additive A to 0.01% to 5%, it is beneficial to ensure that the assembled energy storage device has a high cycle life.

[0012] In one possible implementation, the mass fraction of additive A is 0.2% to 1%.

[0013] This application embodiment also provides an energy storage device, which includes a negative electrode sheet and an electrolyte as described above, wherein the electrolyte wets at least a portion of the negative electrode sheet.

[0014] In one possible implementation, the negative electrode sheet includes a negative electrode active material, which includes any one of artificial graphite, natural graphite, soft carbon, hard carbon, lithium metal, sodium metal, silicon, silicon-carbon, or silicon-oxygen materials.

[0015] In one possible implementation, the energy storage device includes either a lithium-ion battery or a sodium-ion battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The dQ / dV curves are for lithium-graphite button batteries assembled using the electrolytes of Comparative Example 1 and Example 1. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] This application provides an energy storage device, which, for example, includes, but is not limited to, any one of lithium-ion batteries and sodium-ion batteries. The lithium-ion battery can be a lithium-ion hard-case battery, a lithium-ion soft-pack battery, or a lithium-ion button cell battery.

[0020] Taking an energy storage device comprising a casing, a battery cell, and an electrolyte as an example. Specifically, the battery cell is installed inside the casing, and the electrolyte is injected into the inside of the casing and wets the battery cell.

[0021] A battery cell includes a positive electrode, a separator, a negative electrode, a positive tab, and a negative tab. The separator is located between the positive and negative electrode, the positive tab is electrically connected to the positive electrode, and the negative tab is electrically connected to the negative electrode. For example, the positive electrode, separator, and negative electrode can be stacked sequentially, wound to form a bare battery cell, and then the positive and negative tabs can be soldered to obtain the battery cell.

[0022] The positive electrode sheet includes a positive current collector and a positive active layer covering the surface of the positive current collector. For example, the positive current collector is aluminum foil. The positive electrode material layer includes a positive active material and additives. For example, the positive active material is lithium iron phosphate. The additives in the positive electrode material layer include conductive agents and binders. For example, the conductive agent is conductive carbon black SP (Super P), and the binder is polyvinylidene fluoride (PVDF).

[0023] The separator can be an existing battery separator; for example, a polypropylene (PP) membrane. The negative electrode includes a negative current collector and a negative active layer covering the surface of the current collector. For example, the negative current collector is copper foil. The negative active layer includes materials such as a negative active material and additives. For example, the negative active material includes any one of artificial graphite, natural graphite, soft carbon, hard carbon, lithium metal, sodium metal, silicon, silicon-carbon, or silicon-oxygen materials. The additives in the negative active layer include materials such as conductive agents, thickeners, and binders. For example, the conductive agent is conductive carbon black SP (SuperP), the thickener is carboxymethyl cellulose (CMC), and the binder is polymerized styrene-butadiene rubber (SBR) or asphalt.

[0024] The electrolyte wets at least a portion of the negative electrode and at least a portion of the positive electrode to achieve electrolyte-wetted battery cell. The electrolyte includes a solvent, a lithium salt, and additive A. Exemplarily, the solvent includes a cyclic carbonate solvent. Exemplarily, the cyclic carbonate solvent is selected from at least one of ethylene carbonate (EC) and propylene carbonate (PC). It is understood that the solvent may also include other types of solvents such as chain carbonate solvents. Exemplarily, the chain carbonate solvent may be ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. Exemplarily, the lithium salt may be lithium hexafluorophosphate (LiPF6).

[0025] Among them, the structural formula of additive A contains naphthyl, acid anhydride and nitro. The structure of naphthyl is shown in chemical formula 1, acid anhydride is a substituent represented by chemical formula 2, and nitro is a substituent represented by chemical formula 3. Chemical Formula 1: Chemical formula 2: Chemical formula 3: ; R1, R2, and R3 are each independently selected from any carbon atom at positions 1 to 8 of the naphthyl group.

[0026] The structure of additive A contains functional groups of naphthyl, acid anhydride, and nitro. During the operation of the energy storage device assembled with the electrolyte, the nitro functional group in additive A is a reducing functional group and can undergo a reduction reaction to generate Li3N and LiN. x O yIn an inorganic SEI membrane, the anhydride functional group can react to generate an organic SEI membrane with RCO2Li. Furthermore, the naphthyl functional group can promote electron cloud conjugation of additive A, increasing the reduction potential of additive A molecules. Simultaneously, the rigid structure of the naphthyl group can improve the stability of the SEI membrane structure. The electrolyte formed using additive A can generate an SEI membrane structure with an inner inorganic layer and an outer organic layer. This SEI membrane structure has high stability, which is beneficial for stabilizing the interface of the negative electrode, reducing side reactions, and thus improving the cycle stability and capacity retention of the energy storage device. This, in turn, helps to extend the cycle life of the energy storage device and facilitates the construction of long-life energy storage devices.

[0027] The process by which the acid anhydride functional group reacts to generate the RCO2Li organic component is as follows: .

[0028] Furthermore, the nitro group in the structural formula of additive A can generate an SEI film containing lithium nitride. Since lithium nitride has relatively high conductivity, the resulting SEI film has a relatively low interfacial impedance, leading to less polarization in the battery assembled with the electrolyte containing additive A. This, in turn, improves the performance of the energy storage device, such as cycle performance and energy efficiency. In contrast, replacing the naphthyl group with other functional groups, such as fluorine functional groups, generates an SEI film containing lithium fluoride. Lithium fluoride has relatively low conductivity, resulting in a higher interfacial impedance in the SEI film, which reduces the performance of the assembled energy storage device.

[0029] Furthermore, the acid anhydride group is also a reducing functional group. When a portion of the acid anhydride functional group forms the organic SEI component RCO2Li, another portion of the acid anhydride functional group can undergo a reduction reaction to generate O. - It can react with C· free radicals and initiate the ring-opening polymerization of cyclic carbonate solvents such as ethylene carbonate (EC) to generate polycarbonate-based SEI components, which can further improve the stability of the SEI film, improve the stability of the interface of the negative electrode, reduce side reactions, thereby improving the cycle stability and capacity retention of the energy storage device, and thus improving the cycle life of the energy storage device, which is conducive to the construction of long-life energy storage devices.

[0030] For example, additive A is selected from at least one of structural formulas (I-1) to (I-12): (I-1) (I-2) (I-3) (I-4) (I-5) (I-6) (I-7) (I-8) (I-9) (I-10) (I-11) (I-12).

[0031] For example, R1 is selected from the carbon atom at position 1 of the naphthyl group, R2 is selected from the carbon atom at position 8 of the naphthyl group, and R3 can be selected from the carbon atom at position 5 (or position 4) of the naphthyl group. In this case, the structural formula of additive A is the above structural formula (I-1). R1 ​​is selected from the carbon atom at position 1 of the naphthyl group, and R2 is selected from the carbon atom at position 6 (or position 3) of the naphthyl group. In this case, the structural formula of additive A is the above structural formula (I-2). R1 ​​is selected from the carbon atom at position 1 of the naphthyl group, and R2 is selected from the carbon atom at position 7 (or position 2) of the naphthyl group. In this case, the structural formula of additive A is the above structural formula (I-3).

[0032] In the above-mentioned structural formula of additive A, when R1 is selected from the carbon atom at position 1 of the naphthyl group and R2 is selected from the carbon atom at position 8 of the naphthyl group, the anhydride functional group in the structure of additive A is simultaneously connected to the two benzene rings of the naphthyl group, which makes the electron conjugation degree in the structure of additive A high, which is conducive to improving the reduction and decomposition ability of additive A, thereby making the formation of SEI (Solid Electrolyte Interphase) film in the energy storage device more stable during operation.

[0033] For example, when R1 is selected from the carbon atom at position 7 of the naphthyl group, R2 is selected from the carbon atom at position 8 of the naphthyl group, and R3 is selected from the carbon atom at positions 6, 5, 4, 3, 2, and 1 of the naphthyl group, additive A is formed corresponding to the above structural formulas (Ⅰ-4), (Ⅰ-5), (Ⅰ-6), (Ⅰ-7), (Ⅰ-8), and (Ⅰ-9), respectively.

[0034] For example, when R1 is selected from the carbon atom at position 6 of the naphthyl group, R2 is selected from the carbon atom at position 7 of the naphthyl group, and R3 is selected from the carbon atom at position 5 (or position 8), position 4 (or position 1), and position 3 (or position 2) of the naphthyl group, additive A is formed corresponding to the above structural formulas (Ⅰ-10), (Ⅰ-11), and (Ⅰ-12), respectively.

[0035] For example, the mass fraction of additive A, based on the mass of the electrolyte, is 0.01% to 5%, meaning that additive A accounts for 0.01% to 5% of the electrolyte's mass. Specifically, the mass fraction of additive A can be 0.01%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value between these values. If the content of additive A in the electrolyte is too low, its effect is not significant, and its optimization effect on improving the stability of the SEI membrane is not obvious. If the content of additive A in the electrolyte is too high, it will increase the interfacial impedance of the SEI membrane, thus not significantly improving the performance of the energy storage device. By controlling the mass fraction of additive A to 0.01% to 5%, it is beneficial to ensure that the assembled energy storage device has a high cycle life. In some other embodiments, the mass fraction of additive A, based on the mass of the electrolyte, is 0.2% to 1%.

[0036] The following uses additive A of structural formula (I-1) as an example to test the reduction potential of additive A of structural formula (I-1). The specific test method is as follows: lithium-ion button batteries are assembled using the electrolyte of Comparative Example 1 without additive A and the electrolyte of Example 1 containing additive A. Then, the lithium-ion button batteries are subjected to constant current discharge at 25°C with a current of 0.05mA to obtain the differential capacity (dQ / dV) curve during the discharge process. The reduction potential of additive A of structural formula (I-1) is identified based on this dQ / dV curve.

[0037] The lithium-ion button cell battery is prepared according to the following steps: Preparation of electrolyte: First, lithium hexafluorophosphate (LiPF6) electrolyte was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) to obtain 100g of basic electrolyte. The mass ratio of EC, EMC, and DMC in the mixed solvent was 1:1:2. The electrolyte of Comparative Example 1 was used as the basic electrolyte. Additive A was added at 0.2% to the basic electrolyte to obtain the electrolyte of Example 1.

[0038] Preparation of the negative electrode sheet: Graphite (negative electrode active material), conductive carbon (SP), thickener (CMC), binder (SBR), and asphalt were dispersed in deionized water according to the specified ratio and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was then coated onto the copper foil of the negative electrode current collector. The coating weight of the negative electrode slurry was 144 mg / 1540.25 mm. 2 After drying, cold pressing, slitting, and cutting, the negative electrode sheet is obtained. The negative electrode slurry coating forms the negative electrode active layer.

[0039] Preparation of the diaphragm: A 16μm thick polypropylene (PP) membrane was used as the diaphragm.

[0040] Preparation of lithium-ion button batteries: Lithium-graphite button batteries are assembled using graphite negative electrode sheets, separators, lithium metal discs, and electrolytes.

[0041] The dQ / dV curves of the lithium-graphite button batteries assembled with the electrolytes of Comparative Example 1 and Example 1 are shown below. Figure 1 As shown. Figure 1 The dQ / dV curves shown indicate that additive A in the electrolyte of Example 1 undergoes a multi-step reduction reaction at a potential of 2.62V vs. Li / Li + When the temperature is around 100°C, the nitro functional groups in additive A are reduced to form Li3N and LiN. x O y SEI films with equal inorganic components, at a potential of 2.27 V vs. Li / Li + When the anhydride functional group in additive A is reduced, it generates O- and C· radicals, which initiate the ring-opening polymerization of the cyclic carbonate solvent ethylene carbonate (EC) to form an organic SEI film. Additionally, the anhydride group can also react to generate an organic SEI film of RCO2Li. Therefore, by using additive A, which contains both nitro and anhydride functional groups, an SEI structure with an inner inorganic layer and an outer organic layer can be formed, exhibiting high stability. Furthermore, the naphthyl functional group in additive A can promote electron cloud conjugation, increasing the reduction potential of the molecule, while the rigid structure of naphthalene can enhance the stability of the SEI structure. Experimental results show that, in the embodiments of this application, by adding additive A to the electrolyte, a highly stable SEI structure can be formed, which helps stabilize the graphite anode interface, reduce side reactions, and effectively improve the cycle stability and capacity retention of the assembled battery, thereby achieving the construction of a long-life lithium-ion battery.

[0042] The performance of the energy storage device assembled with an electrolyte containing additive A is investigated below through specific Examples 1-36 and Comparative Example 1. Examples 1-36 and Comparative Example 1 both provide an energy storage device, using a lithium-ion battery as an example. The positive electrode in the energy storage device is a lithium iron phosphate positive electrode, and the negative electrode is a graphite negative electrode, prepared according to the following steps: Preparation of the positive electrode: Lithium iron phosphate (LiFePO4), conductive carbon black (SP), and PVDF binder were dispersed in a mass ratio of 90:5:5 in NMP (N-Methylpyrrolidone) solvent and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was then coated onto a positive electrode current collector aluminum foil, with a coating weight of 300 mg / 1540.25 mm². 2After drying, cold pressing, slitting, and cutting, the positive electrode sheet is obtained. Among them, the positive electrode slurry coating forms the positive electrode active layer.

[0043] Preparation of the negative electrode sheet: Graphite (negative electrode active material), SP (conductive carbon), CMC (thickening agent), and SBR (binder) were dispersed in deionized water at a mass ratio of 96:1:1.5:1.5 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was then coated onto the copper foil of the negative electrode current collector. The coating weight of the negative electrode slurry was 144 mg / 1540.25 mm. 2 After drying, cold pressing, slitting, and cutting, the negative electrode sheet is obtained. The negative electrode slurry coating forms the negative electrode active layer.

[0044] Preparation of electrolyte: First, lithium hexafluorophosphate (LiPF6) electrolyte was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) to obtain 100g of basic electrolyte. The mass ratio of EC, EMC, and DMC in the mixed solvent was 1:1:2. The electrolyte of Comparative Example 1 was used as the basic electrolyte. Different amounts of additive A were added to the basic electrolyte to obtain the electrolytes of Examples 1-40.

[0045] Preparation of the diaphragm: A 16μm thick polypropylene (PP) membrane was used as the diaphragm.

[0046] Preparation of lithium-ion pouch batteries: The prepared lithium iron phosphate positive electrode, separator, and graphite negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to separate them. After winding, a bare cell is obtained. After welding tabs, the cell is assembled into a casing. After injecting the prepared electrolyte, the cell is packaged, left to stand, formed, shaped, and its capacity is tested, and finally, a lithium-ion battery is prepared.

[0047] The types and contents of additive A in the electrolyte of the lithium-ion batteries in Examples 1-40 and Comparative Example 1 are shown in Table 1. The capacity retention rates of the lithium-ion batteries from Examples 1-40 and Comparative Example 1 were measured after 1000 cycles at 25°C and 0.5P constant power, and after 1000 cycles at 45°C and 1P constant power, respectively. The results are shown in Table 1.

[0048] Capacity retention test at 25℃ and 0.5P for 1000 cycles: The test temperature was 25℃. The lithium-ion battery was charged at a constant power of 0.5P until the charging cutoff voltage of the lithium-ion battery was 3.65V. The initial charging capacity was recorded. The lithium-ion battery was then left to stand for 10 minutes and discharged at a constant power of 0.5P until the discharge cutoff voltage of the lithium-ion battery was 2.5V. The discharge capacity of the lithium-ion battery was recorded. Capacity retention rate after 1000 cycles at 25℃ = (Discharge capacity after the 1000th cycle / Discharge capacity of the first cycle) × 100%.

[0049] Capacity retention test at 45℃ and 1P for 1000 cycles: The test temperature was 45℃. The lithium-ion battery was charged at a constant power of 1P until the charging cutoff voltage of 3.65V. The initial charging capacity was recorded. The lithium-ion battery was then left to stand for 10 minutes and discharged at a constant power of 1P until the discharging cutoff voltage of 2.5V. The discharge capacity was recorded. Capacity retention rate after 1000 cycles at 45℃ = (Discharge capacity after the 1000th cycle / Discharge capacity of the first cycle) × 100%.

[0050] Wherein, P refers to the rated charging or discharging power of the battery, which is the nominal voltage U of the battery multiplied by the current density of 1C. The nominal voltage of the iron phosphate battery is 3.2V, and 0.5P refers to 0.5 times the rated power.

[0051] Table 1. Types, contents, and lithium-ion battery performance of additive A in Examples 1-40 and Comparative Example 1

[0052] As shown in Table 1, the electrolyte of Comparative Example 1 does not contain additive A and is only a simple carbonate mixed solvent system. The capacity retention rate of the assembled lithium-ion battery after 1000 cycles at room temperature (25°C) is 61%, and the capacity retention rate after 1000 cycles at high temperature (45°C) is 55%. The capacity retention rate of the lithium-ion battery of Comparative Example 1 is low after both 25°C and 45°C cycles, indicating a lower cycle life. By comparing Examples 1-40 and Comparative Example 1, additive A was added to the electrolytes of Examples 1-40 of this application. The capacity retention rate of the lithium-ion batteries assembled from the electrolytes of Examples 1-36 is approximately 65%~94% after 1000 cycles at room temperature (25°C) and approximately 60%~90% after 1000 cycles at high temperature (45°C). The cycle performance of the lithium-ion batteries of Examples 1-40 is improved at both 25°C and 45°C. Experimental results show that by adding additive A to the electrolyte, the capacity retention rate of the assembled lithium-ion battery after cycling at room temperature and high temperature can be effectively improved, thereby helping to improve the cycle life of the lithium-ion battery.

[0053] Furthermore, by comparing Examples 3-7 and Examples 1-2, as the content of additive A increases, the capacity retention of the energy storage devices in Examples 1-7 after cycling initially increases gradually, then gradually decreases. Specifically, the electrolyte in Example 1 has a lower content of additive A, resulting in a slightly improved cycle performance of the assembled energy storage device compared to Comparative Example 1. In Example 2, the electrolyte has an excessively high content of additive A, leading to a slightly improved cycle performance of the assembled energy storage device compared to Comparative Example 1. Extensive experimental research in this application has shown that controlling the mass fraction of additive A in the electrolyte between 0.01% and 5% can significantly improve the capacity retention rate of lithium-ion batteries after cycling at room temperature and high temperature, thereby contributing to improved cycle life. Furthermore, controlling the mass fraction of additive A in the electrolyte between 0.2% and 1% results in a higher capacity retention rate of the assembled lithium-ion battery after cycling at both room temperature and high temperature, leading to a longer cycle life.

[0054] By comparing Examples 5-13 and Examples 14-40, taking an electrolyte additive A mass fraction of 0.2% as an example, lithium-ion batteries assembled with electrolytes containing additives A of structural formulas (I-1) to (I-3) (Examples 5, 8, and 11) exhibited a capacity retention of approximately 87% to 89% after 1000 cycles at room temperature (25°C) and approximately 79% to 81% after 1000 cycles at a high temperature (45°C). In contrast, lithium-ion batteries assembled with electrolytes containing additives A of structural formulas (I-4) to (I-12) exhibited a capacity retention of approximately 79% to 83% after 1000 cycles at room temperature (25°C) and approximately 71% to 76% after 1000 cycles at a high temperature (45°C), which is lower than that of lithium-ion batteries assembled with electrolytes containing additives A of structural formulas (I-1) to (I-3).

[0055] Experimental results show that, with the same content of additive A in the electrolyte, the lithium-ion batteries assembled in Examples 5-13 with additive A of structural formulas (I-1) to (I-3) exhibited better capacity retention after cycling at both room temperature (25°C) and high temperature (45°C) than the lithium-ion batteries in Examples 14-40. This is because in additive A of structural formulas (I-1) to (I-3), the anhydride functional group and the two benzene rings of the naphthyl group are simultaneously connected, resulting in a high degree of electron conjugation in the structure of additive A and a stronger reductive decomposition ability. This leads to a more stable SEI film formation, which in turn further improves the capacity retention of the assembled battery after cycling, thus facilitating the improvement of the cycle life of the lithium-ion battery.

[0056] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte includes additive A, the structural formula of which simultaneously contains naphthyl, acid anhydride and nitro, the structure of which is shown in chemical formula 1, the acid anhydride is a substituent represented by chemical formula 2, and the nitro is a substituent represented by chemical formula 3. Chemical Formula 1: Chemical formula 2: Chemical formula 3: ; R1, R2, and R3 are each independently selected from any carbon atom at positions 1 to 8 of the naphthyl group.

2. The electrolyte according to claim 1, characterized in that, R1 is selected from the carbon atom at position 1 of the naphthyl group, and R2 is selected from the carbon atom at position 8 of the naphthyl group.

3. The electrolyte according to claim 1, characterized in that, The additive A is selected from at least one of structural formulas (I-1) to (I-12): (I-1)、 (I-2)、 (I-3)、 (I-4)、 (I-5)、 (I-6)、 (I-7)、 (I-8)、 (I-9)、 (I-10)、 (I-11)、 (I-12)。 4. The electrolyte according to any one of claims 1 to 3, characterized in that, The electrolyte also includes a cyclic carbonate solvent.

5. The electrolyte according to claim 4, characterized in that, The cyclic carbonate solvent is selected from at least one of ethylene carbonate and propylene carbonate.

6. The electrolyte according to any one of claims 1 to 3, characterized in that, The mass fraction of additive A is 0.01% to 5% based on the mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that, The mass fraction of additive A is 0.2% to 1% based on the mass of the electrolyte.

8. An energy storage device, characterized in that, The energy storage device includes a negative electrode and an electrolyte as described in any one of claims 1 to 7, wherein the electrolyte wets at least a portion of the negative electrode.

9. The energy storage device according to claim 8, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes any one of artificial graphite, natural graphite, soft carbon, hard carbon, lithium metal, sodium metal, silicon, silicon-carbon, or silicon-oxygen materials.

10. The energy storage device according to claim 8, characterized in that, The energy storage device includes any one of lithium-ion batteries and sodium-ion batteries.

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