Sulfate-aluminum composite electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a sulfate-aluminum composite electrolyte and a preparation method and application thereof. The sulfate-aluminum composite electrolyte comprises an electrolyte solute, a non-aqueous solvent and an electrolyte additive, the electrolyte additive comprises an aluminum alcohol additive and a sulfate additive; according to the invention, aluminum alkoxide and a sulfate compound are introduced into the electrolyte as a bifunctional additive, so that the cycling stability and the capacity retention rate of the lithium secondary battery in a high-temperature environment can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a sulfate-aluminum composite electrolyte, its preparation method, and its application. Background Technology

[0002] With the widespread application of rechargeable lithium batteries (RLBs) in electric vehicles, wearable electronic devices, and large-scale energy storage systems, the stable operation of batteries under complex conditions such as high temperatures is receiving increasing attention. Especially in applications such as energy storage power stations operating in high-temperature regions and electric vehicles undergoing long-term high-power discharge, battery systems must possess good thermal stability and safety to ensure their reliability and lifespan.

[0003] High-temperature environments not only accelerate the decomposition of electrolyte solvents and lithium salts, but also exacerbate side reactions at the positive and negative electrode interfaces, leading to a series of irreversible changes such as interfacial film damage and electrode structure degradation. Ultimately, this results in rapid capacity decay and shortened cycle life. Therefore, optimizing the high-temperature stability of electrolytes to improve the overall performance of RLBs under high-temperature conditions has become an important topic in current battery research.

[0004] To address this issue, researchers have proposed various optimization strategies. Among them, electrolyte additives, as the most convenient and cost-effective method, have shown great potential in improving the high-temperature performance of batteries. Additives suppress lithium dendrite growth by regulating solvation structure, promoting the formation of stable solid electrolyte interface (SEI) or cathode electrolyte interface (CEI), and enhancing interfacial ion migration kinetics, thereby significantly improving the charge-discharge performance and cycle stability of batteries under high-temperature conditions. As research progresses, it has become increasingly clear that single additives often struggle to simultaneously address multiple performance requirements across a wide temperature range, including conductivity, interfacial stability, and dendrite growth suppression. Their effectiveness is limited and cannot comprehensively solve the complex problems of batteries in extreme environments. Therefore, the use of multi-additive synergistic strategies has become an important research direction in recent years. By synergistically designing two or more additives with complementary functions, it is possible to improve high-temperature stability while simultaneously addressing other performance requirements, achieving comprehensive optimization of the electrolyte system in high-temperature conditions.

[0005] For example, patent CN113793985A discloses a battery electrolyte, its preparation method, and its application. The battery electrolyte contains aluminum alkoxide nanowires and organic carbonates, wherein the organic carbonates include at least one of fluoroethylene carbonate and vinylene carbonate. This invention uses aluminum alkoxide nanowires and fluoroethylene carbonate (or vinylene carbonate) as additives in lithium metal battery electrolytes. The aluminum alkoxide nanowires and fluoroethylene carbonate (or vinylene carbonate) react on the surfaces of the positive and negative electrodes to form a hard aluminum-based solid film with high ionic conductivity. This aluminum-based solid film not only inhibits stress corrosion and structural decay of the lithium metal battery positive electrode but also prevents dendrite formation on the lithium metal negative electrode, greatly improving the long-cycle performance and rate performance of lithium metal batteries. This invention develops a low-cost, efficient, and environmentally friendly dual-additive system, which is of great significance for the large-scale application of high-performance lithium metal batteries. However, the cycle performance of the battery under high-temperature conditions still needs improvement.

[0006] Therefore, developing a composite additive electrolyte system that can significantly improve battery cycle performance under high temperature conditions is of great significance for improving the stability and lifespan of batteries in high-temperature environments and can meet the needs of RLBs in different application scenarios. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a sulfate-aluminum composite electrolyte, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a sulfate-aluminum composite electrolyte, comprising an electrolyte solute, a non-aqueous solvent, and an electrolyte additive; The electrolyte additives include aluminum alcohol additives and sulfate ester additives; The sulfate ester electrolyte additive is a compound represented by general formula 2 or general formula 3; In general formula 2, m is selected from integers from 0 to 3, and R4 is selected from... , R5 is selected from one of oxygen atoms, saturated alkylene groups or unsaturated alkylene groups of C1-C5, and R6 is selected from one of hydrogen atoms, halogen atoms, and alkyl groups of C1-C5.

[0009]

[0010] General Formula 2 For general formula 3, R7 and R9 are each independently a C1-C5 saturated alkylene or unsaturated hydrocarbon group, and R8 is selected from... , , , , , , One of them;

[0011] General Formula 3.

[0012] Preferably, the aluminum alkoxide has the structure shown in general formula 1, where R1, R2, and R3 are alkyl groups containing 1-8 carbons;

[0013] General Formula 1.

[0014] Preferably, the electrolyte solute is selected from one or more of LiPF6, LiFSI, LiTFSI, LiBOB, LiDFOB, LiClO4, LiPO2F2, and LiBF4.

[0015] More preferably, the electrolyte solute is LiPF6.

[0016] Preferably, the non-aqueous solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0017] More preferably, the non-aqueous solvent is a mixture of ethylene carbonate and diethyl carbonate, with a volume ratio of 0.5-2:1, and more preferably 1:1.

[0018] Preferably, the aluminum alkoxide additive is selected from one or more of aluminum triethanolamine, aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, and aluminum isoamyl alcohol.

[0019] Preferably, the sulfate ester additive is selected from one or more of 1,3-propanesulfonyl lactone (PS), propylene sulfite (PRS), 1,4-butanesulfonyl lactone (BS), dimethyl sulfite (DMS), ethylene sulfite (ES), 1,3-propenesulfonyl lactone (PST), and vinyl sulfate (DTD).

[0020] Preferably, the amount of aluminum alkoxide additive added is 0.1-2% of the total mass of the composite electrolyte.

[0021] More preferably, the amount of aluminum alkoxide additive added is 0.5% of the total mass of the composite electrolyte.

[0022] Preferably, the amount of the sulfate ester additive added is 0.5-15% of the total mass of the composite electrolyte.

[0023] More preferably, the amount of the sulfate ester additive added is 1% of the total mass of the composite electrolyte.

[0024] Preferably, the amount of electrolyte solute added is 0.5-1.5M.

[0025] More preferably, the amount of electrolyte solute added is 1M.

[0026] Preferably, the amount of the non-aqueous solvent added is 0.5-3 mL.

[0027] More preferably, the amount of the non-aqueous solvent added is 1 mL.

[0028] This invention employs aluminum alkoxide and sulfate ester compounds as bifunctional additives in the electrolyte. These two additives synergistically exert a regulatory effect, significantly improving the interfacial stability and electrochemical performance of the battery under high-temperature conditions. Aluminum alkoxide, as a Lewis acidic additive, participates in the initial film-forming reaction at the negative electrode interface, inducing the formation of a stable inorganic enriched layer with Al-O bonds as its framework, enhancing the thermal stability and mechanical strength of the SEI film. Sulfate ester compounds, on the other hand, possess excellent electrochemical reducing properties and thermal stability, preferentially decomposing under high-temperature conditions to generate an organic-inorganic composite film rich in Li₂S, ROSO₃Li, etc., effectively suppressing side reactions between the electrolyte and electrode materials, mitigating polarization, and enhancing the integrity and ion conductivity of the interfacial film. Under the synergistic effect of the two additives, a composite SEI / CEI film consisting of inorganic components such as Li₂S and Al₂O₃ and organic polymer components can be constructed in situ on the electrode surface, significantly improving the structural stability and interfacial kinetics of the electrode interface, thereby achieving excellent cycle stability of the battery under high-temperature conditions.

[0029] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps: dissolving the electrolyte solute, aluminum alkoxide additive, and sulfate ester additive in a non-aqueous solvent to obtain the electrolyte.

[0030] Thirdly, the present invention provides a battery prepared from the above-mentioned electrolyte.

[0031] Preferably, the battery includes the electrolyte, separator, positive electrode material, and negative electrode material described above.

[0032] Preferably, the cathode material is selected from one of graphite, lithium metal, silicon carbide, and silicon.

[0033] Preferably, the negative electrode material is selected from lithium nickel cobalt manganese oxide (LiNi). x Co y Mn 1-x-y O2), lithium iron phosphate (LiFePO4), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-yO2), lithium cobalt oxide (LiCoO2), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), lithium-rich manganese-based cathode materials (Li 1+x [NiMnCo] 1-x One of the types of O2.

[0034] The present invention has the following beneficial effects: (1) This invention significantly improves the cycle stability and capacity retention of lithium secondary batteries under high-temperature conditions by introducing aluminum alkoxide and sulfate ester compounds as bifunctional additives into the electrolyte. The composite additive system synergistically regulates the solvation structure of lithium ions and the film formation process at the electrode interface, thereby improving the compatibility and interfacial structure stability between the electrolyte and the electrode.

[0035] (2) Under high temperature conditions, the electrolyte of this invention can effectively suppress the occurrence of side reactions and enhance the integrity and thermal stability of the interfacial film. At the same time, the system can accelerate the charge transfer rate and significantly improve the interfacial reaction kinetics, thereby improving the high-temperature cycle performance of the battery and demonstrating excellent high-temperature applicability and engineering application prospects. Detailed Implementation

[0036] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0037] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0038] The preparation of aluminum triethanolamine can refer to existing techniques [Lei, D. et al. Transformation of bulk alloys to oxide nanowires. Science. 355: 267]. [271 (2017)] prepared nanowires with a diameter of 20-200 nm. The specific preparation method is as follows: Lithium powder and aluminum powder were used as materials for synthesizing LiAl alloy. 0.085 g of Li and 0.3 g of Al were added to a graphite crucible lined with graphite paper. After heating at 800 °C for 30 min, the graphite crucible was removed from the muffle furnace, and the graphite plunger was immediately pressed down to obtain the LiAl alloy. 0.115 g of the synthesized LiAl alloy was placed in 20 mL of anhydrous ethanol and placed at 60 °C for 30 h. Homogeneous aluminum triethanolamine was obtained by chemical desalting.

[0039] Preparation of the positive electrode: The positive electrode active material LiNi was mixed in a mass ratio of 94:3:3. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are added to N-methyl-2-pyrrolidone (NMP) and stirred evenly to form a positive electrode slurry. The positive electrode slurry is then evenly coated onto the current collector aluminum foil, and after baking, rolling, and cutting, a positive electrode sheet is obtained.

[0040] The negative electrode uses lithium sheets produced by Tianjin Zhongneng Lithium Industry Co., Ltd.

[0041] Example 1: A method for preparing a sulfate-aluminum composite electrolyte Specifically as follows: Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed evenly in a volume ratio of 1:1 to serve as the electrolyte solvent; LiPF6 is added to a concentration of 1M and mixed evenly; 0.5% of aluminum triethanolamine and 1% of ethylene sulfate (DTD) additives are added to the total mass of the composite electrolyte and mixed evenly to obtain the final product.

[0042] Example 2 The difference from Example 1 is that the additives are 0.5% aluminum triethanolamine and 1% 1,3-propanesulfonyl lactone (PS) by the total mass of the composite electrolyte, while the rest are the same as in Example 1.

[0043] Example 3 The difference from Example 1 is that the additives are 0.5% aluminum triethanolamine and 1% dimethyl sulfite (DMS) by mass of the composite electrolyte, while the rest are the same as in Example 1.

[0044] Example 4 The difference from Example 1 is that the additives are 0.5% aluminum triethanolamine and 1% propylene sulfite (PRS) by mass of the total electrolyte, while the rest are the same as in Example 1.

[0045] Example 5 The difference from Example 1 is that the additives are aluminum triethanolamine (0.5% by weight of the total mass of the composite electrolyte) and ethylene sulfite (ES) (1% by weight of the total mass of the electrolyte), while the rest are the same as in Example 1.

[0046] Example 6 The difference from Example 1 is that the additives are aluminum triethanolamine (0.5% by weight of the total mass of the composite electrolyte) and 1% 1,4-butanolactone (BS), while the rest are the same as in Example 1.

[0047] Example 7 The difference from Example 1 is that the additives are aluminum triethanolamine at 0.5% of the total mass of the composite electrolyte and 1% of 1,3-propenesulfonate lactone (PST), while the rest are the same as in Example 1.

[0048] Example 8 The difference from Example 1 is that the additives are aluminum triethanolamine (0.1% by weight of total electrolyte) and vinyl sulfate (DTD) (0.5% by weight of total electrolyte), while the rest are the same as in Example 1.

[0049] Example 9 The difference from Example 1 is that the additives are aluminum triethanolamine (2% by mass of electrolyte) and vinyl sulfate (DTD) (15% by mass of electrolyte), while the rest are the same as in Example 1.

[0050] Comparative Example 1 The difference from Example 1 is that no electrolyte additive is added.

[0051] Comparative Example 2 The difference from Example 1 is that the electrolyte additive is aluminum triethanolamine, which accounts for 0.5% of the total mass of the electrolyte.

[0052] Comparative Example 3 The difference from Example 1 is that the electrolyte additive is vinyl sulfate (DTD) accounting for 1% of the total mass of the electrolyte.

[0053] Comparative Example 4 The difference from Example 1 is that the electrolyte additive is aluminum triethanolamine, which accounts for 1.5% of the total mass of the electrolyte.

[0054] Comparative Example 5 The difference from Example 1 is that the electrolyte additive is vinyl sulfate (DTD) accounting for 1.5% of the total mass of the electrolyte.

[0055] Detection example The above embodiments and comparative examples were subjected to the following performance tests: Assembly and testing of the full battery: The coin cell was assembled in the following order: negative electrode shell, negative electrode sheet, 15 μL electrolyte, separator, 15 μL electrolyte, positive electrode sheet, gasket, spring contact, and positive electrode shell. High-temperature testing: The battery was left to stand at 30 ℃ for 6 hours, and then activated for 3 cycles at a current of 0.1 C. It was then charged to 4.4 V at 45 ℃ at 1 C and discharged to 3.0 V for cycling to obtain the first-cycle discharge specific capacity and first coulombic efficiency at 1 C. The battery was cycled 50 times under the above conditions to obtain the discharge specific capacity at the 50th cycle, and the 50-cycle capacity retention rate was calculated: 50-cycle capacity retention rate = 50th-cycle discharge specific capacity / first-cycle discharge specific capacity.

[0056] Tafel Testing: The assembled coin cells were placed in a 45°C constant temperature chamber and allowed to stabilize for 1 hour to ensure uniform temperature. Subsequently, Tafel polarization testing of the electrodes was performed using an electrochemical workstation. The test used the battery charge / discharge potential as the reference potential, with the scan potential range set to ±100 mV and the scan rate at 1 mV / s. By measuring the polarization current of the electrodes within this potential range, the Tafel polarization curves of the battery at 45°C were obtained. Based on the Tafel curve fitting results, the charge transfer kinetics of the electrode interface were analyzed.

[0057] The results are shown in Table 1.

[0058] Table 1

[0059] As shown in Table 1, without electrolyte additives (Comparative Example 1), the battery's capacity retention after 50 cycles at 45°C was poor, at only 62.37%, indicating significant capacity decay. When only 0.5% aluminum triethanolamine (Comparative Example 2) or only 1% ethylene sulfate (DTD, Comparative Example 3) was added to the electrolyte, the former showed a slight decrease in performance, while the latter only showed a slight improvement, still unsatisfactory, indicating that a single additive has limited effect on improving high-temperature long-cycle performance. In contrast, the embodiments of this invention, by employing specific combinations of additive systems, exhibited significant advantages in high-temperature cycling performance. All embodiments showed higher capacity retention after 50 cycles than the comparative examples, especially Example 1, which retained 91% of its capacity after 50 cycles, far exceeding the comparative example. Simultaneously, the initial discharge specific capacity and initial coulombic efficiency of the embodiments generally remained at a high level, demonstrating good overall electrochemical performance. Furthermore, the exchange current density data showed higher values ​​in the embodiments, reflecting superior interfacial reaction kinetics, which helps improve the battery's cycle stability. The relatively low exchange current density of the comparative sample indicates poor electrode interface conductivity, consistent with the decline in cycle performance. In summary, the additive combination provided by this invention can effectively improve battery cycle life and interfacial reactivity under high-temperature conditions, exhibiting a significant synergistic enhancement effect.

[0060] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A sulfate-aluminum composite electrolyte, characterized in that, Includes electrolyte solute, non-aqueous solvent, and electrolyte additives; The electrolyte additives include aluminum alcohol additives and sulfate ester additives; The sulfate ester electrolyte additive is a compound represented by general formula 2 or general formula 3; In general formula 2, m is selected from integers from 0 to 3, and R4 is selected from... , R5 is selected from one of oxygen atoms, saturated alkylene groups or unsaturated alkylene groups of C1-C5, and R6 is selected from one of hydrogen atoms, halogen atoms, and alkyl groups of C1-C5. General Formula 2 For general formula 3, R7 and R9 are each independently a C1-C5 saturated alkylene or unsaturated hydrocarbon group, and R8 is selected from... , , , , , , One of them; General Formula 3.

2. The electrolyte according to claim 1, characterized in that, The structure of the aluminum alkoxide is shown in general formula 1, where R1, R2, and R3 are alkyl groups containing 1 to 8 carbons; General Formula 1.

3. The electrolyte according to claim 1, characterized in that, The electrolyte solute is selected from one or more of LiPF6, LiFSI, LiTFSI, LiBOB, LiDFOB, LiClO4, LiPO2F2, and LiBF4.

4. The electrolyte according to claim 1, characterized in that, The non-aqueous solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

5. The electrolyte according to claim 2, characterized in that, The aluminum alkoxide additive is selected from one or more of aluminum triethanolamine, aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, and aluminum isoamyl alcohol.

6. The electrolyte according to claim 1, characterized in that, The sulfate ester additives are selected from one or more of 1,3-propanesulfonyl lactone, propylene sulfite, 1,4-butanesulfonyl lactone, dimethyl sulfite, ethylene sulfite, 1,3-propenesulfonyl lactone, and vinyl sulfate.

7. The electrolyte according to claim 1, characterized in that, The amount of aluminum alkoxide additive added is 0.1-2% of the total mass of the composite electrolyte; the amount of sulfate ester additive added is 0.5-15% of the total mass of the composite electrolyte.

8. The method for preparing the electrolyte according to any one of claims 1-7, characterized in that, Includes the following steps: The electrolyte is prepared by dissolving the electrolyte solute, aluminum alkoxide additive, and sulfate ester additive in a non-aqueous solvent.

9. The application of the electrolyte according to any one of claims 1-7 or the electrolyte prepared by the preparation method according to claim 8 in the preparation of lithium-ion secondary batteries.

10. The application according to claim 9, characterized in that, The battery comprises the electrolyte, separator, positive electrode material, and negative electrode material as described in any one of claims 1-7.

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