A non-aqueous calcium battery electrolyte and a non-aqueous calcium battery comprising the same

Abstract

The application relates to a non-aqueous calcium battery electrolyte and a non-aqueous calcium battery containing the electrolyte, and belongs to the technical field of batteries. The electrolyte comprises an electrolyte calcium salt, an amine organic solvent and a nitrile additive; wherein the concentration of the electrolyte calcium salt in the amine organic solvent is 0.05-5 mol / L, and the addition amount of the nitrile additive is 0.01-10 wt% of the total mass of the electrolyte calcium salt and the amine organic solvent. The nitrile additive is any one or a combination of 3,3-oxydipropionitrile, hexanetricarbonitrile, ethoxymethylenemalononitrile, adiponitrile, butanedinitrile, maleonitrile, 3-methoxypropionitrile, 4,4-dimethoxybutyronitrile and 1,2,3-tris(2-cyanoethyloxy)propane. Compared with the prior art, the non-aqueous calcium battery electrolyte of the application can construct an interface with stability and ionic conductivity when applied to a calcium battery negative electrode, so that the calcium battery exhibits excellent cycle performance and rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a non-aqueous calcium battery electrolyte and a non-aqueous calcium battery containing the electrolyte. Background Technology

[0002] Rechargeable batteries, represented by lithium-ion batteries (LIBs), have now permeated all aspects of our daily lives. However, the energy density of LIBs is currently approaching 300 Wh kg. -1 This figure is close to the theoretical energy density of lithium-ion batteries. Furthermore, the availability of Li and its potential cost fluctuations have been topics of discussion, prompting the exploration of alternative technologies utilizing other resources.

[0003] Compared to monovalent lithium-ion batteries, various battery systems under research, including those based on multivalent metals such as zinc (Zn), magnesium (Mg), and calcium (Ca), are attracting significant attention due to their potential commercial viability. In contrast, calcium (Ca) is extremely abundant in the Earth's crust, with reserves approximately 1000 times higher than that of lithium (Li). Furthermore, Ca exhibits a low potential (-2.87 V vs. SHE), and its energy density is comparable to that of lithium-ion batteries. Calcium metal batteries (CMBs) technology is not only an efficient energy storage method but also possesses high safety due to the absence of harmful heavy metals, making it a promising area for development. For example, CN116830339A discloses an electrolyte composition for a calcium battery, an electrolyte for a calcium battery, and a calcium battery that utilizes a cage-like calcium salt composition combined with DME and THF as solvents to form a high-concentration electrolyte. This ensures high Ca ion conductivity, stable dissolution and release reactions, and a wide potential window, while avoiding fluoride formation.

[0004] However, using Ca anodes in practical applications is not easy. Due to Ca's low reduction potential, various solvents, electrolyte salts, or impurities are easily reduced on the Ca surface, and the resulting passivation layer cannot effectively transport Ca. 2+ The interaction with the isolation of electrons makes Ca 2+ The deposition and dissolution of Ca are difficult to proceed smoothly, resulting in a large overpotential, which limits the electrochemical activity of Ca. Furthermore, due to the fact that Ca... 2+ It is a divalent ion, with a charge relative to Li + Larger diameters mean slower migration in the electrolyte and slower desolvation at the interface, severely hindering the rate performance of calcium batteries.

[0005] To address the aforementioned issues, the use of additives is often an effective means of improving battery performance. Additives do not affect the main components of the electrolyte, nor do they significantly increase electrolyte costs. However, how to select electrolyte additives for use in the negative electrode of calcium batteries to construct an interface that simultaneously possesses stability and ionic conductivity, thereby enabling calcium batteries to exhibit excellent cycle performance and rate performance, still requires further research. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing calcium batteries in terms of cycle stability and rate performance, and to provide a non-aqueous calcium battery electrolyte and a non-aqueous calcium battery containing the electrolyte.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] This invention first provides a non-aqueous calcium battery electrolyte, the electrolyte comprising an electrolyte calcium salt, an amine organic solvent, and a nitrile additive;

[0009] The concentration of the electrolyte calcium salt in the amine organic solvent is 0.05~5 mol / L, and the amount of nitrile additive added is 0.01~10 wt% of the total mass of the electrolyte calcium salt and the amine organic solvent.

[0010] The nitrile additive is any one or a combination of 3,3-oxadipropionitrile, hexanetrionitrile, ethoxymethylene malononitrile, adiponitrile, butadionitrile, transbutenedionitrile, 3-methoxypropionitrile, 4,4-dimethoxybutadionitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0011] Furthermore, the amount of the nitrile additive added is 0.5 to 2 wt% of the total mass of the electrolyte calcium salt and the amine organic solvent.

[0012] Furthermore, the electrolyte calcium salt is any one or a combination of calcium bis(trifluoromethanesulfonyl)imide, calcium trifluoromethanesulfonate, and calcium hexafluorophosphate.

[0013] Further, the amine organic solvent is any one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, dimethylacrylamide, 2-thiophenesulfonamide, p-toluenesulfonamide, 2-methoxyethylamine, 2-methoxypropylamine, and trifluoroethylamine.

[0014] Furthermore, the water content in the amine organic solvent is not higher than 50 ppm.

[0015] Furthermore, the LUMO energy level of the nitrile additive is lower than that of the amine organic solvent, and the nitrile additive preferentially adsorbs onto the negative electrode of the calcium battery and undergoes reduction decomposition compared to the amine organic solvent.

[0016] The present invention also provides a method for preparing a non-aqueous calcium battery electrolyte, the method comprising the following steps: adding an electrolyte calcium salt to an amine organic solvent at room temperature to obtain a raw material electrolyte; adding a nitrile additive to the raw material electrolyte and dissolving it to obtain the non-aqueous calcium battery electrolyte.

[0017] The present invention also provides a non-aqueous calcium battery, which is assembled from a non-aqueous calcium battery electrolyte, a positive electrode, a negative electrode, and a separator. The non-aqueous calcium battery electrolyte is any one of the non-aqueous calcium battery electrolytes described above.

[0018] Furthermore, the positive electrode is made of metallic calcium.

[0019] Furthermore, the negative electrode is made of metallic calcium.

[0020] Furthermore, the diaphragm is made of any one of glass fiber, glass ceramic, polyethylene, polypropylene, and cellulose.

[0021] Furthermore, the assembly of the non-aqueous calcium battery is carried out in an inert gas atmosphere.

[0022] Furthermore, the calcium battery is a rechargeable secondary battery, and the structure of the calcium battery is any one of button type, coin type, cylindrical type, square type, or laminated type.

[0023] In lithium-ion electrolytes, the primary function of adding nitrile additives is to improve the structural stability and high-voltage performance of the cathode material (e.g., CN113972396A). The cyano group in the nitrile additive can effectively complex transition metal ions (especially Co) in the cathode material. 2+ Firstly, nitrile additives lower the valence state of transition metals, thereby inhibiting their dissolution and enhancing the structural stability of the cathode material. Secondly, nitrile additives typically possess high highest occupied molecular orbital (HOMO) energy levels, exhibiting high oxidation stability. Their adsorption on the cathode surface effectively isolates the cathode material from the electrolyte, inhibiting the oxidative decomposition of the electrolyte under high voltage and improving the high-voltage stability of the cathode material.

[0024] In comparison, this invention innovatively incorporates nitrile additives into the calcium battery electrolyte, and these additives exhibit stronger reducing activity compared to solvent molecules. This is significantly different from the application of nitrile additives in lithium-ion batteries. During operation and resting, nitrile additives preferentially adsorb onto the calcium metal anode surface to form a monolayer, rather than solvent molecules. Due to the lower lowest unoccupied molecular orbital (LUMO) energy level of the nitrile additives compared to the solvent, they undergo preferential reduction on the calcium metal surface, generating a nitride-rich SEI (solid electrolyte interface film). This effectively isolates electrons and facilitates calcium ion transport, improving the battery's cycle stability and rate performance.

[0025] Compared with the prior art, the present invention has the following technical advantages:

[0026] (1) This invention innovatively introduces nitrile additives into the electrolyte of calcium batteries. Compared with amine solvent molecules, they have stronger reducing activity and can preferentially adsorb on the surface of calcium metal anode to form a monolayer. They are preferentially reduced on the surface of calcium metal to generate a solid electrolyte interface film rich in nitrides, which can effectively isolate electrons and transport calcium ions, ultimately improving the cycle stability and rate performance of calcium batteries.

[0027] (2) The calcium battery electrolyte of the present invention only needs to add a small amount of nitrile additives to achieve effective improvement in cycle stability and rate performance, without affecting the main components of the calcium battery electrolyte, and without significantly increasing the cost of the electrolyte.

[0028] (3) After adding nitrile additives, the calcium battery electrolyte of the present invention was unexpectedly found to have a significant improvement in gas production, especially the content of ethylene gas with strong reducing properties was greatly reduced, which will effectively improve the safety performance of the calcium battery.

[0029] (4) The nitrile additives and amine solvents of the present invention are diverse and can be combined in various ways while satisfying the priority of reducing properties, making them suitable for various calcium battery electrolytes. Attached Figure Description

[0030] Figure 1 This is a comparison chart of the cycle performance of Example 1 and Comparative Example 1.

[0031] Figure 2 This is a comparison chart of the cycle performance of Example 2 and Comparative Example 1.

[0032] Figure 3 This is a comparison chart of the cycle performance of Example 3 and Comparative Example 1.

[0033] Figure 4 This is a comparison chart of the cycle performance of Example 4 and Comparative Example 1.

[0034] Figure 5 This is a comparison chart of the cycle performance of Example 5 and Comparative Example 1.

[0035] Figure 6 This is a comparison chart of the cycle performance of Example 6 and Comparative Example 1.

[0036] Figure 7 This is a comparison chart of the cycle performance of Example 7 and Comparative Example 1.

[0037] Figure 8 This is a comparison chart of the cycle performance of Example 8 and Comparative Example 1.

[0038] Figure 9This is a comparison chart of the rate performance of Example 1 and Comparative Example 1.

[0039] Figure 10 This is a comparison chart of the cyclic performance of Comparative Example 2 and Comparative Example 1.

[0040] Figure 11 This is a comparison chart of the cyclic performance of Comparative Example 3 and Comparative Example 1.

[0041] Figure 12 This is a comparison chart of the gas production performance of the calcium batteries in Example 1 and Comparative Example 1.

[0042] Figure 13 The diagram shows the LUMO energy levels for different molecules.

[0043] Figure 14 A comparison diagram showing the binding energies of different molecules with the Ca(110) crystal plane. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0045] The first aspect of this invention provides a non-aqueous calcium battery electrolyte, the electrolyte comprising an electrolyte calcium salt, an amine organic solvent, and a nitrile additive; wherein the concentration of the electrolyte calcium salt in the amine organic solvent is 0.05~5 mol / L, and the amount of the nitrile additive added is 0.01~10 wt% of the total mass of the electrolyte calcium salt and the amine organic solvent. The nitrile additive is any one or a combination of 3,3-oxodipropionitrile, hexanetrionitrile, ethoxymethylene malononitrile, adiponitrile, butadionitrile, trans-butenedionitrile, 3-methoxypropionitrile, 4,4-dimethoxybutadienenitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0046] In some specific embodiments, the amount of nitrile additive added is preferably 0.5 to 2 wt% of the total mass of the electrolyte calcium salt and amine organic solvent. If the amount of nitrile additive added is too small, the content of its derived effective components will be insufficient, resulting in an incomplete solid electrolyte interface film and thus continuous decomposition of the electrode material. If the amount of nitrile additive added is too large, it will lead to an excessively thick solid electrolyte interface film, excessive interfacial impedance, hindering ion migration and reducing the rate performance of the battery.

[0047] In some specific embodiments, the electrolyte calcium salt is any one or a combination of calcium bis(trifluoromethanesulfonyl)imide, calcium trifluoromethanesulfonate, and calcium hexafluorophosphate.

[0048] In some specific embodiments, the amine organic solvent is any one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, dimethylacrylamide, 2-thiophenesulfonamide, p-methylbenzenesulfonamide, 2-methoxyethylamine, 2-methoxypropylamine, and trifluoroethylamine, preferably 2-methoxyethylamine.

[0049] In some specific embodiments, the water content in the amine organic solvent is not higher than 50 ppm.

[0050] In some specific embodiments, the LUMO energy level of the nitrile additive is lower than that of the amine organic solvent. The nitrile additive preferentially adsorbs onto the negative electrode of the calcium battery and undergoes reduction decomposition compared to the amine organic solvent. The nitrile additive of this invention contains multiple cyano groups, enabling it to preferentially adsorb onto the calcium metal surface. Furthermore, the nitrile additive has a strong electron-withdrawing effect and stronger reducing activity compared to solvent molecules. After adsorption onto the calcium metal surface, it preferentially undergoes reduction decomposition to form a nitride-rich SEI (solid electrolyte interphase), which effectively reduces the diffusion barrier of ions through the SEI, thereby effectively reducing the battery overpotential and improving the battery's rate performance.

[0051] The second aspect of the present invention provides a method for preparing a non-aqueous calcium battery electrolyte, the method comprising the following steps: adding an electrolyte calcium salt to an amine organic solvent at room temperature to obtain a raw material electrolyte; adding a nitrile additive to the raw material electrolyte and dissolving it to obtain the non-aqueous calcium battery electrolyte.

[0052] In some specific embodiments, the amine organic solvent is pre-purified by removing impurities and dehydrating with molecular sieves.

[0053] A third aspect of the present invention provides a non-aqueous calcium battery, wherein the non-aqueous calcium battery is assembled from a non-aqueous calcium battery electrolyte, a positive electrode, a negative electrode, and a separator. The non-aqueous calcium battery electrolyte is any one of the non-aqueous calcium battery electrolytes described above.

[0054] In some specific embodiments, the positive electrode material is metallic calcium.

[0055] In some specific embodiments, the negative electrode is made of metallic calcium.

[0056] In some specific embodiments, the diaphragm is made of any one of glass fiber, glass ceramic, polyethylene, polypropylene, and cellulose, preferably glass fiber.

[0057] In some specific embodiments, the assembly of the non-aqueous calcium battery is carried out in an inert gas atmosphere.

[0058] In some specific embodiments, the calcium battery is a rechargeable secondary battery, and the calcium battery has any one of the following structures: button type, coin type, cylindrical type, square type, and laminated type.

[0059] The non-aqueous calcium battery of this invention has significant advantages over aqueous calcium batteries in terms of voltage platform, interface stability, ion transport, and energy density, making it more suitable as a next-generation high-energy-density energy storage technology. Specifically, the reasons are as follows: organic electrolytes have a wider electrochemical window (>2.0 V) than water (~1.23 V), supporting higher voltage systems; calcium metal is sensitive to moisture, easily leading to side reactions and passivation problems; compared to the stable hydrated shell structure in aqueous systems, organic solvents participate in the Ca... 2+ The solvation structure has a low desolvation energy barrier, which can improve ion mobility and reaction kinetics; the organic system can be paired with high-voltage cathode materials, and its theoretical energy density is much higher than that of the aqueous system.

[0060] The calcium battery of this invention uses calcium as both the positive and negative electrodes, which has the following advantages: the only reaction involved is Ca. Ca 2+ The capacity decay of the battery can only be attributed to the reversibility of the metal and the interface chemistry, eliminating interference from "dissolution of the cathode material, phase change, stress cracking" and other factors. The electrolyte and SEI can be judged by the polarization curve in a short time, eliminating the need for full cycle testing of the battery.

[0061] Each of the above embodiments can be implemented individually, or in any combination of two or more. The following detailed description of specific examples will further illustrate these embodiments.

[0062] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0063] Example 1:

[0064] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery, specifically including the following steps:

[0065] (1) Preparation of non-aqueous calcium battery electrolyte:

[0066] After removing impurities from 2-methoxyethylamine (hereinafter referred to as M3) and purifying it with a molecular sieve to remove water, 0.1 mol of bis(trifluoromethanesulfonyl)imide calcium was added to the solvent at room temperature as the electrolyte calcium salt to form a 0.1 mol / L electrolyte solution.

[0067] After the calcium electrolyte salt is completely dissolved, 2-methoxyethylamine and 1 wt% of hexanetrionitrile (HTCN) of the total mass of the calcium electrolyte salt are added to obtain a non-aqueous calcium battery electrolyte.

[0068] (2) Preparation of non-aqueous calcium batteries:

[0069] Using calcium metal as the positive and negative electrodes respectively, and glass fiber membrane as the separator, a CR2032 type button cell (hereinafter referred to as Ca / / Ca symmetric button cell) was assembled in a high-purity argon glove box, and about 100 μL of non-aqueous calcium battery electrolyte was injected into each cell.

[0070] Example 2:

[0071] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is 3,3-oxodiapropionitrile (DOPN).

[0072] Example 3:

[0073] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is ethoxymethylene malononitrile (EOMMN).

[0074] Example 4:

[0075] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is succinic anionyl nitrile (SN).

[0076] Example 5:

[0077] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is adiponitrile (ADN).

[0078] Example 6:

[0079] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is trans-butenedionitrile (FN).

[0080] Example 7:

[0081] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is 3-methoxypropionitrile (MOPN).

[0082] Example 8:

[0083] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the nitrile additive used in the non-aqueous calcium battery electrolyte of this embodiment is dimethoxybutyronitrile (DMBN).

[0084] Example 9:

[0085] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Example 1 is that the amount of hexanetrionitrile added in this embodiment is 0.1 wt% of the total mass of 2-methoxyethylamine and the calcium electrolyte salt.

[0086] Example 10:

[0087] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the amount of hexanetrionitrile added in this embodiment is 5 wt% of the total mass of 2-methoxyethylamine and the calcium electrolyte salt.

[0088] Example 11:

[0089] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Example 1 is that the amine organic solvent in this embodiment is N,N-dimethylformamide.

[0090] Example 12:

[0091] This embodiment provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Embodiment 1 is that the amine organic solvent in this embodiment is dimethylacrylamide.

[0092] Comparative Example 1:

[0093] This comparative example provides a preparation of a non-aqueous calcium battery electrolyte and an assembly of a non-aqueous calcium battery. The difference from Example 1 is that no nitrile additives are added in this comparative example.

[0094] Comparative Example 2:

[0095] This comparative example provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Example 1 is that nitrile additives are not used in this comparative example; instead, ether additives, represented by dimethyl ethylene glycol (DME), are used.

[0096] Comparative Example 3:

[0097] This comparative example provides a method for preparing a non-aqueous calcium battery electrolyte and assembling a non-aqueous calcium battery. The difference from Example 1 is that nitrile additives are not used in this comparative example; instead, ester additives, represented by vinyl sulfite (ES), are used.

[0098] The present invention performs the following performance tests on the non-aqueous calcium batteries assembled in the above embodiments and comparative examples:

[0099] (1) Electrochemical testing procedure:

[0100] At room temperature, the Ca / / Ca symmetrical coin cell was subjected to constant current charge / discharge test using the Newway test system.

[0101] For cycle performance testing, the applied current density and energy density to the Ca / / Ca coin cell were 0.02 mA·cm⁻¹. -2 With 0.02 mA·h·cm -2 .

[0102] Rate performance testing was conducted at 0.5 C (1 C = 0.02 mA·cm). -2 After 5 cycles of the multiplier, it is then charged / discharged 5 times each at 1 C, 3 C, 5 C, 7 C, 10 C, and 20 C before returning to 1 C charge / discharge.

[0103] (2) Gas production test:

[0104] In the gas detection step, the three-electrode assembly step is as follows: assemble a three-way battery, in which two of the two channels are the working electrode and the participating / counter electrode, which are copper foil and calcium metal sheet respectively. The upper side is sealed with a rubber stopper to form a closed cavity to store the gas generated during the electrochemical process.

[0105] The electrochemical testing procedure is as follows: Connect the three electrodes to the EC-Lab workstation and perform cyclic voltammetry (CV) tests in the voltage range of -1.5 to 2 V at a scan rate of 5 mV·s. -1 After five scans, discharge at a constant voltage of 0.05 V for 2 hours.

[0106] The gas detection procedure is as follows: An electrochemical-gas chromatography / mass spectrometry (GC / MS) platform is set up. After running the three-way battery for 5 cycles of CV testing and 2 hours of constant voltage discharge at 0.05V, gas is extracted from the chamber using a gas sampling needle and injected into the GC / MS instrument. The gas species are determined based on the peak time and retention time. The content of each gas is qualitatively analyzed based on the peak area.

[0107] (3) Molecular simulation:

[0108] The LUMO energy levels of each molecule were calculated: molecular structure optimization was performed using the Gaussian 16 software package, and the B3LYP functional of density functional theory (DFT) was employed. A polarized continuum model based on the dielectric constants of each molecule was used.

[0109] Calculate the adsorption energy of each molecule on the Ca(110) crystal plane: Model using Materials Studio software, where the metal crystal plane is selected as the Ca(110) crystal plane.

[0110] Figures 1-8 The graphs show a comparison of the cycle performance of the calcium batteries prepared in Examples 1-8 and Comparative Example 1. Taking Example 1 as an example, after introducing nitrile additives into the electrolyte, the overpotential of the battery was significantly reduced to 0.25V, and the cycle stability improved from 20 h to over 200 h of stable cycling. In Examples 2-8, after changing to different nitrile additives, the overpotential of the batteries remained stable below 0.3V, indicating that nitrile additives have similar mechanisms of action and performance-enhancing effects. The SEI derived from nitrile additives can effectively reduce the calcium content of the calcium batteries. 2+ The diffusion energy barrier.

[0111] Figure 9 To compare the rate performance of Example 1 and Example 1, the figure shows that the rate performance of the battery is significantly improved after adding the nitrile additive. Even after increasing the current density to 10 C, the battery overpotential remains stable at a low level of 0.67 V. Even when the current density is increased to 20 C, the battery still maintains a low overpotential. When the current density returns to 1 C, the overpotential is even lower than before the rate test (0.23 V), indicating that the SEI derived from the nitrile additive not only has fast ion transport capabilities but also high stability.

[0112] Furthermore, this invention also applies two commonly used lithium metal battery additives, ether-based additives (ethylene glycol dimethyl ether, DME) and ester-based additives (ethylene sulfite, ES), to calcium battery electrolytes to investigate the differences in the evolution of the lithium metal anode interface and the calcium metal anode interface. Figure 10 It is evident that adding DME additives to the calcium metal system not only failed to improve the performance of the calcium battery but also worsened its cycle performance. This indicates a significant difference in the evolutionary behavior of the calcium metal anode interface compared to the lithium metal interface. Furthermore, the deteriorated cycle stability suggests that the ether-derived SEI has insufficient electronic insulation, leading to continuous reductive decomposition at the interface and accelerating battery failure. The addition of ether additives increased the overpotential of the calcium battery, indicating that the ether-derived decomposition components react with the Ca... 2+ It has a strong binding ability and will hinder the migration of ions.

[0113] Depend on Figure 11It is evident that while the addition of ES additives to the calcium metal battery system slightly improves the cycle stability, it also significantly increases the overpotential, which is detrimental to the practical application of calcium batteries. This is because the ES additives are derived from CaS or Ca. x (SO3) y The low ionic conductivity hinders ion migration. Furthermore, the overpotential of the battery gradually increases with increasing cycle count, indicating that the ES-derived interface film provides insufficient protection for the calcium metal anode.

[0114] Figure 12 This figure compares the gas production performance of the calcium batteries in Comparative Example 1 and Example 1. The gray bars represent the gas content test results after 5 cycles of CV testing, and the black bars represent the gas content test results after 5 cycles of CV testing and 2 hours of constant voltage discharge at 0.05 V. As can be seen from the figure, ethylene (C2H4) gas has the highest proportion in Comparative Example 1. Analysis of the solvent and additive molecular structures indicates that this gas mainly originates from solvent M3, suggesting severe decomposition of the solvent molecules. The adsorption of its derived gaseous products on the electrode surface can isolate the electrode from the separator, leading to a battery open circuit. The addition of nitrile additives significantly improves gas production, especially by drastically reducing the content of highly reducing ethylene gas, which will effectively improve the safety performance of the calcium battery.

[0115] Furthermore, this invention has also conducted molecular simulation calculations to explore the mechanism of action of nitrile additives in greater depth. Figure 13 This is a LUMO energy level diagram of different molecules after molecular simulation. The more negative the LUMO energy level, the lower the lowest unoccupied molecular orbital, indicating that the molecule is more likely to gain electrons and undergo reductive decomposition. As can be seen from the figure, the LUMO energy levels of nitrile additives are generally lower than those of M3, indicating that nitrile additives are more likely to undergo reductive decomposition and participate in the construction of SEI compared to amine organic solvents (M3). Figure 14 The binding energy represents the binding energy between different molecules and the Ca(110) crystal plane. A negative binding energy indicates a tendency for molecules to spontaneously adsorb onto Ca(110). The more negative the binding energy, the easier it is for molecules to adsorb onto the metal surface. Calculations show that nitrile additives adsorb onto metal surfaces more easily than solvent molecules. Combined with the higher reducing activity of nitrile additives, the mechanism of action is that they preferentially adsorb onto the Ca anode surface, then undergo preferential reduction and decomposition to generate effective components such as nitrides, which participate in the construction of the SEI (Sediment-Insulation), improving battery cycle and rate performance.

[0116] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A non-aqueous calcium battery electrolyte, characterized in that, The electrolyte comprises an electrolyte calcium salt, an amine organic solvent, and a nitrile additive; The concentration of the electrolyte calcium salt in the amine organic solvent is 0.05~5 mol / L, and the amount of nitrile additive added is 0.5~2wt% of the total mass of the electrolyte calcium salt and the amine organic solvent. The electrolyte calcium salt is bis(trifluoromethylsulfonyl)imide calcium; The nitrile additive is any one or a combination of 3,3-oxodipropionitrile, hexanetrionitrile, ethoxymethylene malononitrile, adiponitrile, butadionitrile, transbutenedionitrile, 3-methoxypropionitrile, 4,4-dimethoxybutadionitrile, and 1,2,3-tris(2-cyanoethoxy)propane. The LUMO energy level of the nitrile additive is lower than that of the amine organic solvent. The nitrile additive preferentially adsorbs onto the calcium metal anode and undergoes reduction decomposition to generate a solid electrolyte interface film rich in nitrides.

2. The non-aqueous calcium battery electrolyte according to claim 1, characterized in that, The amine organic solvent is any one or a combination of N,N-dimethylformamide, dimethylacrylamide, 2-thiophenesulfonamide, p-methylbenzenesulfonamide, 2-methoxyethylamine, 2-methoxypropylamine, and trifluoroethylamine.

3. The non-aqueous calcium battery electrolyte according to claim 1, characterized in that, The water content in the amine organic solvent is not higher than 50 ppm.

4. A method for preparing the non-aqueous calcium battery electrolyte according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: At room temperature, the calcium salt of electrolyte is added to an amine organic solvent to obtain the raw material electrolyte; Nitrile additives are added to the raw electrolyte, and the non-aqueous calcium battery electrolyte is obtained after dissolution.

5. A non-aqueous calcium battery, characterized in that, It is assembled from a non-aqueous calcium battery electrolyte, a positive electrode, a negative electrode, and a separator; wherein the non-aqueous calcium battery electrolyte is the non-aqueous calcium battery electrolyte according to any one of claims 1-3.

6. A non-aqueous calcium battery according to claim 5, characterized in that, The positive electrode is made of metallic calcium. The negative electrode is made of metallic calcium. The diaphragm is made of any one of glass fiber, glass ceramic, polyethylene, polypropylene, or cellulose.

7. A non-aqueous calcium battery according to claim 5, characterized in that, The assembly of the non-aqueous calcium battery is carried out in an inert gas atmosphere.

Images