Additive containing acetal structure, magnesium secondary battery electrolyte and preparation method thereof, and magnesium secondary battery

Abstract

The invention discloses an acetal structure-containing additive, a magnesium secondary battery electrolyte and a preparation method thereof, and a magnesium secondary battery, and relates to the technical field of magnesium secondary batteries. The additive comprises the following compounds: R1-Lm-C (R2) (OR3) (OR4), and the additive containing the acetal structure improves the interface stability and the cation mobility of the electrolyte and remarkably improves the long cycle stability; the raw materials do not contain chlorine elements, so that corrosion to the current collector is avoided; the magnesium deposition-dissolution efficiency is high, the overpotential is low, the oxidation stability is high, and the cycling stability is good; the preparation method is simple, reaction only needs to be carried out at normal temperature, reaction conditions are mild, raw materials are low in price, and industrialization is facilitated. The coulombic efficiency of the magnesium secondary battery is close to 100%, the long cycle stability is high, the magnesium secondary battery can be matched with different positive electrode materials, and the electrochemical performance is excellent.

Description

Technical Field

[0001] This invention relates to the field of magnesium secondary battery technology, and more specifically, to additives containing acetal structures, magnesium secondary battery electrolytes and their preparation methods, and magnesium secondary batteries. Background Technology

[0002] Among numerous magnesium battery electrolyte systems, ether-based electrolytes based on magnesium trifluoromethanesulfonate (Mg(OTf)2) are considered one of the most promising systems due to their wide electrochemical window, good reduction stability, and simple preparation process. However, this system faces significant challenges in practical applications: First, ether-based electrolytes of Mg(OTf)₂ suffer from poor solubility, and their magnesium deposition and dissolution processes exhibit abnormally high overpotentials, severely impacting battery energy efficiency and exacerbating side reactions. Second, this electrolyte system is extremely sensitive to impurities such as water and oxygen, making its electrochemical performance heavily dependent on the purity and source of the raw materials. Although subsequent studies have modified Mg(OTf)₂-based electrolytes by introducing organic amine additives, improving their solubility and interfacial behavior to some extent, these improvements have not addressed the fundamental obstacles to the system.

[0003] The specific solvation structure formed by magnesium ions, ether solvents, and anions readily decomposes on the magnesium anode surface, generating an inorganic passivation layer with extremely low ionic conductivity (mainly containing MgO, Mg(OH)2, etc.). This passivation layer severely hinders the reversible deposition, dissolution, and transport of magnesium ions, preventing the magnesium deposition / dissolution reaction from proceeding, resulting in extremely high overpotentials and complete cell failure. The fundamental reason is that the coordination ability of conventional ether solvents (such as DME, G2) is insufficient to completely break down [Mg(OTf)]. + The stable presence of contact ion pairs (CIP) and aggregates (AGG) leads to the preferential electron gain and decomposition of these anion-rich structures at the low potential of the magnesium anode, generating ion-insulating products that severely hinder the cross-interface transport of magnesium ions. This makes it difficult for the magnesium deposition / dissolution reaction to continue, ultimately resulting in extremely high polarization voltage and rapid battery failure.

[0004] Chinese patent CN202211343791 discloses a halogen-free rechargeable magnesium battery electrolyte, its preparation method, and its application. The electrolyte system consists of magnesium trifluoromethanesulfonate, specific alkyl nitroxide chelating agents (such as 2-methoxyethylamine, 2-ethoxyethylamine, etc.), and ether solvents (such as ethylene glycol dimethyl ether / diethylene glycol dimethyl ether). This scheme achieves halogen-free operation and high oxidation stability (>3.4 V vs. Mg / Mg) by regulating the magnesium ion solvation structure through chelating agents. 2+This system exhibits reversible magnesium deposition / dissolution (with a coulombic efficiency of 97%) and boasts advantages such as simple preparation and low cost. However, it still relies on alkyl nitrile chelating agents, which presents significant limitations: First, the overpotential retention rate of magnesium deposition / dissolution is poor during long-term cycling, with the overpotential increasing to 0.1V after 800 hours, affecting the battery's energy consumption and efficiency; second, when matched with Mo6S8 cathode material, the capacity retention after 200 cycles is only 54 mAh / g, indicating that its overall electrochemical performance, especially capacity utilization and long-term cycling stability, remains insufficient.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide additives containing acetal structures, magnesium secondary battery electrolytes and their preparation methods, and magnesium secondary batteries, so as to solve or improve the above-mentioned technical problems.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides an additive containing an acetal structure, the additive comprising a compound represented by formula (I): R1-L m -C(R2)(OR3)(OR4) (I; Where R1 is not hydrogen, and formula (I) does not contain chlorine atoms; R1 is selected from at least one of amino, halogen, cyano, nitro, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, C2-C6 alkenyl, C2-C6 alkynyl, C2-C6 acyloxy, C2-C12 dialkylamino, C6-C10 aryl, C6-C10 aryloxy, and 5-10 heteroaryl. L is selected from at least one of C1-C10 alkylene, C2-C10 alkenylene, C2-C10 ynynylene, C6-C10 aryleneene, and 5-10 heteroarylene. m is 0 or 1; R2 is selected from hydrogen or C1-C6 alkyl; R3 and R4 are each independently at least one of C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl and C6-C10 aryl; or, R3 and R4 together with the oxygen atom to which they are attached and the acetal carbon form a 5-8 membered ring.

[0008] In a second aspect, the present invention provides a magnesium secondary battery electrolyte, comprising an additive, a conductive magnesium salt, and an organic solvent as described in any of the foregoing embodiments.

[0009] Thirdly, the present invention provides a method for preparing a magnesium secondary battery electrolyte as described in any of the foregoing embodiments, comprising the following steps: The additives, conductive magnesium salts, and organic solvents are mixed in proportion and reacted at room temperature for 24-48 hours to obtain the magnesium secondary battery electrolyte.

[0010] Fourthly, the present invention provides a magnesium secondary battery, comprising an additive as described in any of the foregoing embodiments, a magnesium secondary battery electrolyte as described in any of the foregoing embodiments, or a magnesium secondary battery electrolyte prepared by the preparation method described in the foregoing embodiments.

[0011] The present invention has the following beneficial effects: The acetal-containing additive provided in this embodiment of the invention, while having advantages such as being halogen-free and having high voltage, further improves the interfacial stability and cation mobility of the electrolyte, significantly enhances long-cycle stability, and can still maintain an overpotential of less than 0.1V after 4000 hours of cycling. It also achieves higher capacity and better long-cycle stability when matched with positive electrodes such as Mo6S8 and CuS, demonstrating a comprehensive performance improvement.

[0012] The magnesium secondary battery electrolyte provided by this invention uses magnesium trifluoromethanesulfonate as raw material, does not contain halogen elements, and avoids corrosion of the current collector; moreover, it has high magnesium deposition-dissolution efficiency, low overpotential, high oxidation stability, and good cycle stability.

[0013] The method for preparing the magnesium secondary battery electrolyte provided by this invention is simple, requiring only the reaction to be carried out at room temperature. The reaction conditions are mild, the raw materials are inexpensive, and this method is conducive to industrialization.

[0014] The magnesium secondary battery provided by this invention has a coulombic efficiency close to 100%, high long-cycle stability, can be matched with different cathode materials, and has excellent electrochemical performance. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The results are the constant current charge-discharge cycle performance test results of the symmetrical battery prepared in Example 1; Figure 2 The results are the reversible magnesium deposition / dissolution cycle curve and coulombic efficiency test results for Example 1; Figure 3 The results of charge / discharge rate performance tests under different current densities in Example 1 are shown. Figure 4 The cyclic voltammetry curves for Example 1 using stainless steel foil as the working electrode are shown below. Figure 5 The linear sweep voltammetry curve for Example 1 using stainless steel foil as the working electrode; Figure 6 Test results of the Mo6S8||Mg full cell prepared in Example 1: (a) charge-discharge curves, (b) capacity and coulombic efficiency curves; Figure 7 Test results of the CuS||Mg full cell prepared in Example 1: (a) charge-discharge curves, (b) capacity and coulombic efficiency curves; Figure 8 The results of constant current charge-discharge cycle performance tests for symmetrical batteries in Examples 6-8 are as follows; Figure 9 The results are the reversible magnesium deposition / dissolution cycle curves and coulombic efficiency test results for Examples 6-8. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The acetal-containing additive introduced in this invention, while offering advantages such as halogen-free and high voltage, further enhances the interfacial stability and cation mobility of the electrolyte, significantly improving long-cycle stability. Even after 4000 hours of cycling, it maintains an overpotential of less than 0.1V and achieves higher capacity and superior long-cycle stability when matched with cathodes such as Mo6S8 and CuS, demonstrating a comprehensive performance improvement. Specific implementation methods are as follows: In a first aspect, the present invention provides an additive containing an acetal structure, the additive comprising a compound represented by formula (I): R1-L m -C(R2)(OR3)(OR4) (I; Where R1 is not hydrogen, and formula (I) does not contain chlorine atoms; R1 is selected from at least one of amino, halogen, cyano, nitro, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, C2-C6 alkenyl, C2-C6 alkynyl, C2-C6 acyloxy, C2-C12 dialkylamino, C6-C10 aryl, C6-C10 aryloxy, and 5-10 heteroaryl. L is selected from at least one of C1-C10 alkylene, C2-C10 alkenylene, C2-C10 ynynylene, C6-C10 aryleneene, and 5-10 heteroarylene. m is 0 or 1; R2 is selected from hydrogen or C1-C6 alkyl; R3 and R4 are each independently at least one of C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl and C6-C10 aryl; or, R3 and R4 together with the oxygen atom to which they are attached and the acetal carbon form a 5-8 membered ring.

[0019] This invention utilizes the unique electronic structure and coordination ability of the acetal functional group (-OCO-) to competitively enter the solvation sheath of magnesium ions, replacing some solvent molecules and anions, thereby altering the interfacial reaction priority. During charge and discharge, this additive preferentially reduces on the magnesium anode surface, forming a dense, stable electrolyte interfacial film rich in organic ethers. This interfacial film efficiently conducts magnesium ions while effectively inhibiting the continuous decomposition of electrolyte components, thus simultaneously achieving low overpotential, high coulombic efficiency, a wide electrochemical window, and excellent cycle stability.

[0020] In an optional implementation, when m is 0, R1 is directly connected to the acetal carbon; And / or, R1 is selected from at least one of amino, methylamino, halogen and phenyl.

[0021] In an optional embodiment, in L, the alkylene, alkenylene, ynylene, or heteroarylene group is optionally substituted with one or more substituents; Preferably, L is a C1-C4 alkylene or phenylene; the substituent is selected from at least one of halogen, amino, C1-C6 alkyl, C1-C6 alkoxy and heteroatom; the heteroatom is selected from at least one of O, S and N.

[0022] In an optional embodiment, R3 and R4 are independently selected from methyl or ethyl, or R3 and R4 together with the oxygen atom to which they are attached and the central carbon atom form a 1,3-dioxolane ring.

[0023] In optional embodiments, the additive includes at least one selected from aminoacetaldehyde dimethyl acetal, diethanolaminoacetaldehyde, 4-aminobutyraldehyde dimethyl acetal, methylaminoacetaldehyde dimethyl acetal, (dimethylamino)acetaldehyde dimethyl acetal, N,N-dimethylformamide dimethyl acetal, 1-bromo-3,3-dimethoxypropene, 1-bromo-4-(dimethoxymethyl)benzene, 2-bromo-1,1-dimethoxyethane, 3-bromopropyl methyl ether, and 2,2-dimethoxyethyl(methyl)thion.

[0024] In a second aspect, the present invention provides a magnesium secondary battery electrolyte, comprising an additive, a conductive magnesium salt, and an organic solvent as described in any of the foregoing embodiments.

[0025] It should be noted that in the magnesium secondary battery electrolyte provided by this invention, the additives, conductive magnesium salts, and solvents work together to produce a significant synergistic effect, effectively promoting the reversible deposition and stripping of magnesium, thereby solving the problems of high overpotential and poor performance repeatability. The magnesium secondary battery electrolyte has good affinity with the magnesium metal anode, high interfacial stability, and exhibits a small reaction overpotential and high magnesium deposition / stripping coulombic efficiency.

[0026] In an optional embodiment, the concentration of the conductive magnesium salt in the organic solvent is 0.2 mol / L-1.0 mol / L, and the volume of the additive is 0.1%-30% of the volume of the organic solvent.

[0027] For example, the concentration of the conductive magnesium salt in the organic solvent can be selected from any one of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, and 1.0 mol / L, or other values ​​within the range of 0.2 mol / L to 1.0 mol / L; based on the volume of the organic solvent, the volume of the additive is any one of 0.1%, 1%, 5%, 8%, 10%, 12%, 16%, 18%, 20%, 25%, 28%, and 30%, or any one of 0.1% to 30%.

[0028] In an optional embodiment, the organic solvent is an organic ether solvent, selected from at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The conductive magnesium salt is selected from magnesium trifluoromethanesulfonate or magnesium bis(trifluoromethanesulfonyl)imide.

[0029] For example, the organic ethers can be selected from at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; for the combination form, it can be a combination of two substances, such as a combination of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, a combination of tetrahydrofuran and ethylene glycol dimethyl ether, or a combination of ethylene glycol dimethyl ether or triethylene glycol dimethyl ether, etc.; it can also be a combination of three substances, such as a combination of tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether, a combination of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether, or a combination of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, etc.; of course, it can also be a combination of more than three substances, such as four or five substances, etc. The specific quantity and types of substances in the combination are reasonably selected according to actual needs.

[0030] Thirdly, the present invention provides a method for preparing a magnesium secondary battery electrolyte as described in any of the foregoing embodiments, comprising the following steps: The additives, conductive magnesium salts, and organic solvents are mixed in proportion and reacted at room temperature for 24-48 hours to obtain the magnesium secondary battery electrolyte.

[0031] The preparation method provided by this invention only requires mixing and stirring the components at room temperature to complete the in-situ preparation in one step, without the need for complex equipment or harsh conditions. This process has outstanding advantages such as fewer steps, simple operation, low cost, and easy scale-up production, providing a reliable technical path for the large-scale promotion of rechargeable magnesium batteries.

[0032] Fourthly, the present invention provides a magnesium secondary battery, comprising an additive as described in any of the foregoing embodiments, a magnesium secondary battery electrolyte as described in any of the foregoing embodiments, or a magnesium secondary battery electrolyte prepared by the preparation method described in the foregoing embodiments.

[0033] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0034] Example 1 This embodiment provides a magnesium secondary battery electrolyte, which is prepared using the following steps: In an argon glove box with both water and oxygen content below 0.1 ppm, an organic ether solvent (4 mL of ethylene glycol dimethyl ether and 4 mL of diethylene glycol dimethyl ether) was added to a reagent bottle. 1.3 g of conductive magnesium salt, magnesium trifluoromethanesulfonate, was weighed and added to the above mixed solvent. Then, 2 mL of the additive aminoacetaldehyde dimethyl acetal was added, and the mixture was stirred for 35 h to obtain the magnesium secondary battery electrolyte, in which the magnesium ion concentration was 0.4 mol·L⁻¹. -1 The volume of the additive is 25% of the volume of the organic solvent.

[0035] Examples 2-8 This embodiment provides a magnesium secondary battery electrolyte, and the preparation steps are the same as in Example 1, with the only difference being: Example 2: The organic ether solvent was 8 mL of ethylene glycol dimethyl ether, and the conductive magnesium salt was 2.338 g of bis(trifluoromethylsulfonyl)imide magnesium.

[0036] Example 3: The additive was 2 mL of diethanolamine acetaldehyde.

[0037] Example 4: The additive was 2 mL of 1-bromo-4-(dimethoxymethyl)benzene.

[0038] Example 5: The additive was 2 mL of 3-bromopropyl methyl ether.

[0039] Example 6: The organic ether solvents were 4.5 mL of ethylene glycol dimethyl ether and 4.5 mL of diethylene glycol dimethyl ether, and the additive was 1 mL of 1-bromo-3,3-dimethoxypropylene (the volume of the additive was 10% of the volume of the organic solvent).

[0040] Example 7: The organic ether solvents were 4 mL of ethylene glycol dimethyl ether and 4 mL of diethylene glycol dimethyl ether, and the additive was 2 mL of 1-bromo-3,3-dimethoxypropylene (the volume of the additive was 20% of the volume of the organic solvent).

[0041] Example 8: The organic ether solvents were 3.5 mL of ethylene glycol dimethyl ether and 3.5 mL of diethylene glycol dimethyl ether, and the additive was 3 mL of 1-bromo-3,3-dimethoxypropylene (the volume of the additive was 30% of the volume of the organic solvent).

[0042] Comparative Example 1 This comparative example provides a magnesium secondary battery electrolyte, which is prepared using the following steps: In an argon glove box with both water and oxygen content below 0.1 ppm, an organic ether solvent (5 mL of ethylene glycol dimethyl ether and 5 mL of diethylene glycol dimethyl ether) was added to a reagent bottle. 1.3 g of conductive magnesium salt, magnesium trifluoromethanesulfonate, was then added to the mixed solvent. After stirring for 35 hours, a magnesium secondary battery electrolyte was obtained, in which the concentration of magnesium ions was 0.4 mol·L⁻¹. -1 .

[0043] Test Example 1 This test example examines the magnesium secondary battery electrolytes prepared in Examples 1-8 and Comparative Example 1, and tests the following performance parameters: The test items and corresponding results are as follows: (1) Charge-discharge cycle performance test: The charge-discharge cycle performance was tested using a constant current charge-discharge test. Using 14 mm diameter magnesium sheets as electrodes, the magnesium metal electrodes, along with the magnesium secondary battery electrolyte and separator prepared according to the embodiments of this invention, were assembled into CR2032 type coin cells, i.e., Mg||Mg symmetrical cells, using conventional methods. The test used a Xinwei charge-discharge testing system with a current density of 0.1 mA·cm⁻¹. -2 The surface capacity is 0.1 mAh·cm³. -2 The relevant data on overpotential and cycle stability are summarized in Table 1; specific test results are presented in images using Examples 1 and 6-8 as examples. The constant current charge-discharge cycle performance test results for Example 1 are shown in […]. Figure 1 The constant current charge-discharge cycle performance test results of Examples 6-8 are shown in [the original text]. Figure 8 .

[0044] from Figure 1 As can be seen, long-term cycling tests verified the excellent stability of the electrolyte in Example 1 at 0.1 mAcm⁻¹. -2 It maintains stable charge-discharge cycle performance under current density, and the overpotential is still less than 0.1V after 4000h.

[0045] from Figure 8It can be seen that Example 7 is the optimal ratio among Examples 6-8. The optimal ratio still maintains an overpotential of less than 0.1V after 1000h.

[0046] (2) Reversible magnesium deposition / dissolution cycle curves and coulombic efficiency tests: The reversible deposition / dissolution behavior of magnesium was evaluated by constant current charge-discharge tests. The test cells used a 12mm stainless steel working electrode and a 14mm magnesium sheet as the counter and reference electrodes. The magnesium secondary battery electrolyte prepared according to this embodiment was used as the electrolyte to assemble CR2032 coin-type asymmetric cells. The tests used a Xinwei charge-discharge testing system with a current density of 0.1 mA·cm⁻¹. -2 The relevant data on coulombic efficiency are summarized in Table 1; specific test results are presented in images using Examples 1 and 6-8 as examples. The reversible magnesium deposition / dissolution cycle curve and coulombic efficiency test results for Example 1 are shown in [reference needed]. Figure 2 The reversible magnesium deposition / dissolution cycle curves and coulombic efficiencies of Examples 6-8 are shown in [reference needed]. Figure 9 .

[0047] from Figure 2 It can be seen that the electrolyte in Example 1 of the constant current test was at 0.1 mAcm -2 It achieves a coulombic efficiency of up to 97% at current density and maintains stable cycling for over 500 hours.

[0048] from Figure 9 It can be seen that Example 7 is the optimal ratio among Examples 6-8. The optimal ratio can achieve a theoretical efficiency of more than 98% and maintain a stable cycle of more than 700 times.

[0049] (3) Charge / discharge rate performance test: The charge / discharge rate performance was tested using a constant current charge / discharge method. A CR2032 coin cell was constructed using a 14 mm diameter magnesium sheet as the electrode, and assembled with the magnesium secondary battery electrolyte and separator prepared according to conventional methods. The test was conducted using a Xinwei charge / discharge testing system, with the current density set to 0.1 mA·cm⁻¹. -2 0.25 mA·cm -2 0.5 mA·cm -2 0.75 mA·cm -2 1 mA·cm -2 1.5 mA·cm -2 2 mA·cm -2 2.5 mA·cm -2 3 mA·cm -2 3.5 mA·cm -2 4 mA·cm -2 4.5 mA·cm -2 5 mA·cm -2and 0.1 mA·cm -2 The surface capacity is 0.1 mAh·cm³. -2 The test results are presented in images using Example 1 as an example; see details below. Figure 3 .

[0050] from Figure 3 It can be seen that the magnesium secondary battery electrolyte prepared in Example 1 of the symmetrical battery test exhibits good polarization characteristics at different current densities, with a regular voltage response and good symmetry, and can achieve a voltage response of 5 mA·cm⁻¹. -2 Stable charging and discharging under high current density.

[0051] (4) Magnesium Deposition / Dissolution Reversibility Test: Cyclic voltammetry was used to evaluate the reversibility of magnesium deposition / dissolution. The deposition and dissolution performance of the electrolyte was tested on a DHMultiElec electrochemical workstation. A 12 mm diameter stainless steel sheet was used as the working electrode, and a 14 mm diameter magnesium sheet was used as the counter electrode and reference electrode. The magnesium secondary battery electrolyte prepared according to the embodiments of the present invention was used as the electrolyte to assemble CR2032 coin cells. The scanning potential range was -0.8 V to 2 V, and the scanning rate was set to 1 mV / s. The test results are presented in images using Example 1 as an example. See [link to example]. Figure 4 .

[0052] from Figure 4 As can be seen from the cyclic voltammetry curves using stainless steel foil as the working electrode, the electrolyte of Example 1 exhibits excellent magnesium deposition / dissolution reversibility. The peak current density stabilizes after 20 cycles, indicating that a stable SEI film has been formed at this point, ensuring the reversible stability of subsequent magnesium deposition / dissolution. (5) Electrochemical oxidation stability test: The oxidation stability of the electrolyte was determined by linear sweep voltammetry. The test system was a DHMultiElec electrochemical workstation. A 12 mm diameter stainless steel foil was used as the working electrode, and a 14 mm diameter magnesium sheet was used as the counter electrode and reference electrode. The magnesium secondary battery electrolyte prepared according to the embodiments of this invention was used as the electrolyte. The scan range was from the open circuit potential to 5 V, and the scan rate was 1 mV / s. The test results are presented in the image of Example 1 as an example. See [link to example]. Figure 5 .

[0053] from Figure 5 As can be seen, the test on the stainless steel current collector further confirms that the electrolyte of Example 1 has excellent oxidation stability, with a stable potential of 3.5 V.

[0054] (6) Ionic conductivity test: Ionic conductivity was measured using electrochemical impedance spectroscopy. The magnesium secondary battery electrolyte prepared according to the embodiments of this invention was used as the electrolyte, and a symmetrical cell was assembled using stainless steel foil as the blocking electrode. The EIS results were obtained using a Swagelok battery test. The test was conducted at open circuit potential (OCP) with an amplitude of 10 mV and a frequency range of 1 MHz to 0.01 Hz. Ionic conductivity (σ, mS / cm) was calculated according to the following formula. Where L (0.2 cm) and S (0.5026 cm) are... 2 The numbers and represent the thickness of the gasket (cm) and the contact area between the electrolyte and the electrode (cm²), respectively. 2 Rs is the bulk impedance (Ω) of the electrolyte. The results related to ionic conductivity are summarized in Table 1.

[0055]

[0056] (7) Full cell performance test: Using a 14 mm diameter magnesium sheet electrode as the counter electrode and reference electrode, and Mo6S8 and CuS as the positive electrode respectively, a CR2032 coin cell was assembled using the magnesium secondary battery electrolyte prepared in this embodiment of the invention as the electrolyte for testing, with a current density of 1C. Specific test results are presented using Example 1 as an example. The test results for the Mo6S8||Mg full cell are shown below. Figure 6 (a) Charge-discharge curves, (b) Capacity and coulombic efficiency curves; Test results of CuS||Mg full cells. Figure 7 (a) Charge-discharge curves, (b) Capacity and coulombic efficiency curves.

[0057] from Figure 6 As can be seen, the full cell assembled with Mo6S8 electrolyte in Example 1 exhibits a coulombic efficiency close to 100% at a current density of 1C, and maintains a capacity of 60 mAh·g after 1000 cycles. -2 .

[0058] from Figure 7 As can be seen, the full cell assembled with CuS as the positive electrode in Example 1 exhibits a coulombic efficiency close to 100% at a current density of 1C, and a specific capacity as high as 500 mAh·g in the early stages of cycling. -2 .

[0059] Table 1 Performance Test Results

[0060] As can be seen from the data in Table 1, compared with Comparative Example 1, Examples 1-8, which incorporated acetal-containing additives, showed significant improvements in long-cycle stability and coulombic efficiency. This indicates that the addition of the additives enabled reversible magnesium deposition / dissolution in the magnesium secondary battery electrolyte and significantly improved the ionic conductivity of the electrolyte. Examples 6-8 investigated the effect of additive content on electrolyte performance. Figure 8-9 It can be seen that the addition of additives significantly improves the performance of the electrolyte, and the best stability is exhibited when the additive content is 20% (v:v).

[0061] In summary, the acetal-containing additive introduced in this invention, while possessing advantages such as halogen-free and high voltage, further improves the interfacial stability and cation mobility of the electrolyte, significantly enhances long-cycle stability, and can still maintain an overpotential of less than 0.1V after 4000 hours of cycling. It also achieves higher capacity and better long-cycle stability when matched with cathodes such as Mo6S8 and CuS, demonstrating a comprehensive performance improvement.

[0062] Furthermore, the unique electronic structure and coordination ability of the acetal functional group (-OCO-) competitively enter the solvation sheath of magnesium ions, replacing some solvent molecules and anions, thereby altering the interfacial reaction priority. During charge and discharge, this additive preferentially reduces on the magnesium anode surface, forming a dense, stable electrolyte interfacial film rich in organic ethers. This interfacial film efficiently conducts magnesium ions while effectively inhibiting the continuous decomposition of electrolyte components, thus simultaneously achieving low overpotential, high coulombic efficiency, a wide electrochemical window, and excellent cycle stability.

[0063] In the provided magnesium secondary battery electrolyte, the additives, conductive magnesium salts, and solvents work together to produce a significant synergistic effect, effectively promoting reversible magnesium deposition and stripping, thus solving the problems of high overpotential and poor performance repeatability. The magnesium secondary battery electrolyte exhibits good affinity with the magnesium metal anode, high interfacial stability, and demonstrates a small reaction overpotential and high magnesium deposition / stripping coulombic efficiency.

[0064] The preparation method only requires mixing and stirring the components at room temperature to complete the in-situ preparation in one step, without the need for complex equipment or harsh conditions. This process has outstanding advantages such as fewer steps, simple operation, low cost, and easy scale-up production, providing a reliable technical path for the large-scale promotion of rechargeable magnesium batteries.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An acetal group-containing additive characterized by, The additive includes a compound represented by Formula (I): R1-L m -C(R2)(OR3)(OR4) (I); wherein R1 is not hydrogen, and formula (I) does not contain a chlorine atom; R1 is selected from at least one of amino, halogen, cyano, nitro, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, C2-C6 alkenyl, C2-C6 alkynyl, C2-C12 dialkylamino, C6-C10 aryl, C6-C10 aryloxy, and 5-10 membered heteroaryl; L is selected from at least one of C1-C10 alkylene, C2-C10 alkenylene, C2-C10 alkynylene, C6-C10 arylene, and 5-10 membered heteroarylene; m is 0 or 1; R2 is selected from hydrogen or C1-C6 alkyl; R3 and R4 are each independently at least one of C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, and C6-C10 aryl; or R3 and R4, together with the oxygen atom and the acetal carbon to which they are attached, form a 5-8 membered ring.

2. The additive of claim 1, wherein When m is 0, R1 is directly attached to the acetal carbon; R1 is selected from at least one of amino, methylamino, halogen, and phenyl.

3. The additive of claim 1, wherein In L, the alkylene, alkenylene, alkynylene, or heteroarylene is optionally substituted with one or more substituents; Preferably, L is C1-C4 alkylene or phenylene; the substituents are selected from at least one of halogen, amino, C1-C6 alkyl, C1-C6 alkoxy, and a heteroatom selected from at least one of O, S, and N.

4. The additive of claim 1, wherein R3 and R4 are each independently selected from methyl or ethyl, or R3 and R4, together with the oxygen atom and the central carbon atom to which they are attached, form a 1,3-dioxolane ring.

5. The additive according to any one of claims 1 to 4, characterized in that, The additive includes at least one of aminoacetaldehyde dimethyl acetal, diethylamino acetaldehyde, 4-aminobutyraldehyde dimethyl acetal, methylamino acetaldehyde dimethyl acetal, (dimethylamino) acetaldehyde dimethyl acetal, N,N-dimethylformamide dimethyl acetal, 1-bromo 3,3-dimethoxy propene, 1-bromo-4-(dimethoxymethyl) benzene, 2-bromo-1,1-dimethoxy ethane, 3-bromopropyl methyl ether, and 2,2-dimethoxyethyl) (methyl) sulfane.

6. A magnesium secondary battery electrolyte, characterized by, The additive, the conductive magnesium salt, and the organic solvent are as claimed in any one of claims 1-5.

7. The magnesium secondary battery electrolyte according to claim 6, characterized in that, The concentration of the conductive magnesium salt in the organic solvent is 0.2 mol / L-1.0 mol / L, and the volume of the additive is 0.1%-30% of the volume of the organic solvent.

8. The magnesium secondary battery electrolyte according to claim 6, characterized in that, The organic solvent is an organic ether solvent selected from at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; The conductive magnesium salt is selected from magnesium triflate or magnesium bis(trifluoromethylsulfonyl)imide.

9. A method for preparing a magnesium secondary battery electrolyte as claimed in any one of claims 6 to 8, characterized in that, The method comprises the following steps: The additive, the conductive magnesium salt, and the organic solvent are mixed in proportion, and the magnesium secondary battery electrolyte is prepared after reacting at room temperature for 24-48 hours.

10. A magnesium secondary battery, characterized by comprising: The magnesium secondary battery electrolyte is prepared by using the additive as claimed in any one of claims 1-5 or the magnesium secondary battery electrolyte as claimed in any one of claims 6-8 or the preparation method as claimed in claim 9.

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