Wide-working-voltage composite electrolyte for all-solid-state lithium-ion battery, preparation method therefor, and use thereof

Abstract

A wide-working-voltage composite electrolyte for an all-solid-state lithium-ion battery, a preparation method therefor, and a use thereof. By using a simple and efficient method, the voltage window and dendrite growth inhibition capability of a lithium borohydride-based solid electrolyte are comprehensively improved. The composite electrolyte can achieve a stable voltage window of 0-10 V at the maximum at room temperature, has the critical current density as high as 21.65mA·cm-2, can complete a continuous constant-voltage electroplating stripping test for 1000 h in a high-voltage interval of 10.0 V, and has extremely excellent electrochemical stability. The present invention has important significance for improving the working voltage and energy density of a lithium-ion battery and promoting large-scale commercialization of a solid electrolyte.

Description

A wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 16, 2023, with application number 202311029213.2, and invention name “A wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of all-solid-state lithium-ion batteries, and in particular to a wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries, and a preparation method and application thereof. Background Art

[0003] With the pursuit of high-energy-density energy storage devices, lithium-ion batteries have received unprecedented attention. However, traditional liquid lithium-ion batteries suffer from two key technical issues: low energy density and poor safety. Currently, replacing liquid electrolytes with all-solid-state electrolytes can solve these problems. In addition, all-solid-state electrolytes can simultaneously match high-voltage positive electrodes and lithium metal to achieve higher energy density. However, most inorganic all-solid-state electrolytes have a narrow voltage window, resulting in severe oxidative decomposition of all-solid-state lithium batteries at high voltages, causing serious performance degradation.

[0004] Lithium borohydride (LBH) is a solid electrolyte with the advantage of being thermodynamically stable relative to metallic lithium. When used in all-solid-state lithium-ion batteries, there is no need to consider interfacial reactions on the anode side. However, LBH solid electrolytes still have significant challenges. First, due to the high local electron density of borohydride ions, they are easily delocalized under external field excitation, leading to oxidation of the anions and a narrow thermodynamic oxidation window of only 2.8V. Second, the high electronic conductivity of the LBH electrolyte bulk phase can lead to severe dendrite growth.

[0005] Currently, the main approaches to improving the voltage window of lithium borohydride-based solid electrolytes include: 1. Introducing more electronegative anions to enhance the overall oxidative stability of the borohydride ion, such as lithium fluoride or lithium chloride. 2. Disrupting or replacing the borohydride anion structure, such as partially replacing lithium borohydride with a high boride or sulfide. Efforts to reduce electronic conductivity have primarily focused on introducing inert secondary phases with low electronic conductivity, such as aluminum oxide and silicon oxide, into lithium borohydride, as well as compounds that react to form ionic or covalent bonds, such as ammonia borane. However, systematic research on lithium borohydride-based solid electrolytes that can operate at high voltages and suppress dendrites has yet to be conducted, nor have modification methods been proposed, leaving lithium borohydride-based solid electrolytes still a significant distance from commercialization.

[0006] Therefore, it is extremely necessary to adopt a simple and efficient method to comprehensively improve the voltage window and the ability to inhibit dendrite growth of lithium borohydride-based solid electrolytes in order to achieve comprehensive improvement in the performance of solid electrolytes and large-scale commercial applications.

[0007] Summary of the Invention

[0008] In order to overcome the current shortcomings of lithium borohydride-based solid electrolytes that can serve and inhibit dendrites under high voltages, which have not yet been systematically studied and modification methods have not been proposed, resulting in a large gap between lithium borohydride-based solid electrolytes and true commercial use, the present application provides a simple and efficient method to comprehensively improve the voltage window and dendrite growth inhibition ability of lithium borohydride-based solid electrolytes. The resulting composite electrolyte can be matched with existing high-voltage lithium-ion batteries and can be adapted to positive electrode materials with higher operating voltages in the future, greatly widening the operating voltage window of lithium-ion batteries. This is of great significance for the large-scale commercial application of solid electrolytes and improving the energy density of lithium-ion batteries.

[0009] A wide operating voltage composite electrolyte for an all-solid-state lithium-ion battery, comprising a lithium borohydride-based solid electrolyte and a high molecular polymer coating layer coated on the surface of the lithium borohydride-based solid electrolyte, characterized in that:

[0010] The voltage window of the wide working voltage composite electrolyte is greater than or equal to 6V and is up to 10V;

[0011] The lithium borohydride-based solid electrolyte comprises lithium borohydride, aluminum oxide and lithium iodide;

[0012] The high molecular polymer coating layer is polymethyl methacrylate;

[0013] The lithium borohydride-based solid electrolyte accounts for 70 to 99 wt.% of the mass of the wide operating voltage composite electrolyte;

[0014] The mass proportion of the high molecular polymer coating layer to the wide operating voltage composite electrolyte is 1 to 30 wt.%.

[0015] Preferably, in the lithium borohydride-based solid electrolyte, based on the total molar amount of lithium borohydride, aluminum oxide and lithium iodide as 100%, the lithium borohydride accounts for 50-60% of the total molar amount, the aluminum oxide accounts for 20-25% of the total molar amount, and the lithium iodide accounts for 20-25% of the total molar amount.

[0016] Preferably, the thickness of the high molecular polymer coating layer is 1 to 100 nm.

[0017] Preferably, the degree of polymerization of the polymethyl methacrylate is 250 to 20,000.

[0018] Preferably, the high molecular polymer coating layer is an amorphous coating layer.

[0019] Preferably, the wide operating voltage composite electrolyte includes covalent (OCH3) x BH 4-x .

[0020] The present application also provides a method for preparing the wide operating voltage composite electrolyte described in the above technical solution, comprising:

[0021] Lithium borohydride, aluminum oxide, lithium iodide and polymethyl methacrylate are subjected to high-energy ball milling, and the obtained mixture powder is reacted at a certain temperature and a certain constant pressure in an in-situ melting reaction manner, and a sample is collected to obtain the wide operating voltage composite electrolyte.

[0022] Preferably, the high-energy ball milling time is 96 h and the ball milling speed is 530 rpm;

[0023] The ball milling medium of the high energy ball mill is agate, and the ball to material ratio of the high energy ball mill is 100 to 800:1;

[0024] The ball milling atmosphere of the high-energy ball mill is an argon atmosphere.

[0025] Preferably, the high-energy ball milling further includes screening.

[0026] Preferably, the temperature of the in-situ melting reaction is 130-180°C;

[0027] The in-situ melting reaction time is 1 to 5 hours;

[0028] The pressure of the in-situ melting reaction is 200-500 MPa.

[0029] The present application also provides the application of the wide operating voltage composite electrolyte described in the above technical solution or the wide operating voltage composite electrolyte prepared by the preparation method described in the above technical solution in an all-solid-state lithium-ion battery, wherein the all-solid-state lithium-ion battery includes a lithium-ion battery positive electrode, a negative electrode and the wide operating voltage composite electrolyte.

[0030] The present invention also provides an all-solid-state lithium-ion battery, comprising a positive electrode, a negative electrode and a wide operating voltage composite electrolyte;

[0031] The wide operating voltage composite electrolyte is the wide operating voltage composite electrolyte described in the above technical solution or the wide operating voltage composite electrolyte prepared by the preparation method described in the above technical solution.

[0032] Preferably, the material of the positive electrode comprises lithium cobalt oxide;

[0033] The material of the negative electrode includes lithium metal.

[0034] The present application has the following advantages: 1. The wide working voltage composite electrolyte described in the present application can achieve a stable voltage window of 0 to 10 V at room temperature, with a maximum operating voltage of 21.65 mA cm -2 It has a critical current density of 10.0V and can complete 1000h continuous constant voltage electroplating stripping test in the high voltage range of 10.0V, with extremely excellent electrochemical stability.

[0035] 2. When the wide operating voltage composite electrolyte described in this application is matched with a lithium cobalt oxide positive electrode and a lithium metal negative electrode to form an all-solid-state battery, a capacity retention rate of up to 100% can be achieved over 200 cycles within a voltage window of 3.0 to 4.2 V; and reversible and stable charge and discharge cycle performance can be achieved within a voltage window of 3.0 to 5.0 V.

[0036] 3. The preparation method of the wide working voltage composite electrolyte described in this application is a two-step process of conventional high-energy ball milling process supplemented by in-situ melting reaction. The preparation process induces polymethyl methacrylate to react with lithium borohydride-based solid electrolyte to form a covalent coordination compound (OCH3) x BH 4-x , thermodynamically improves BH4 - The oxidative stability of the anionic groups kinetically blocks electron transport at the electrolyte particle interface, ultimately achieving a wide voltage window and excellent dendrite suppression. This preparation process does not require additional electrolyte preparation steps or costs, is simple to operate, and offers highly controllable material preparation, making it fully suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a transmission electron micrograph of the wide operating voltage composite electrolyte prepared in Example 1;

[0038] FIG2 is an energy spectrum diagram of the wide operating voltage composite electrolyte prepared in Example 1;

[0039] Figure 3 is a wide working voltage composite electrolyte prepared in Example 1; wherein (a) is an X-ray photoelectron spectrum of oxygen, (b) is an X-ray photoelectron spectrum of boron, and (c) is 13 Solid-state NMR spectrum of carbon, (d) 11 Solid-state NMR spectrum of boron;

[0040] FIG4 shows the electronic conductivity and ionic conductivity of the wide operating voltage composite electrolyte prepared in Example 1 as a function of temperature from -30 to 150° C.;

[0041] FIG5 is a voltage window cyclic voltammetry curve of the wide working voltage composite electrolyte prepared in Example 1;

[0042] Figure 6 shows the lithium cobalt oxide half-cell assembled with the wide working voltage composite electrolyte prepared in Example 1 at 60 mA·g-1 Electrochemical performance at current density of 1000V; (a) is the first charge and discharge curve in the voltage window of 3.0-4.2V, (b) is the first charge and discharge curve in the voltage window of 12mA·g -1 (c) is the cycle performance curve under the current density of 3.0~5.0V;

[0043] FIG7 shows the critical current density of a lithium symmetric battery assembled with a wide operating voltage composite electrolyte prepared in Example 1 at room temperature (a) and the continuous lithium plating and stripping curve under an applied voltage of 10.0 V (b);

[0044] Figure 8 shows the wide working voltage composite electrolyte prepared in Example 2 13 Carbon solid NMR spectrum (a) and 11 Boron solid-state NMR spectrum (b);

[0045] FIG9 is a voltage window cyclic voltammetry curve of the wide working voltage composite electrolyte prepared in Example 2;

[0046] Figure 10 shows the lithium cobalt oxide half-cell assembled with the wide working voltage composite electrolyte prepared in Example 2 at 60 mA·g -1 Electrochemical performance at current density of 1000V; (a) is the first charge and discharge curve in the voltage window of 3.0-4.2V, (b) is the first charge and discharge curve in the voltage window of 12mA·g -1 (c) is the cycle performance curve under the current density of 3.0~5.0V;

[0047] FIG11 shows the critical current density of a lithium symmetric battery assembled with a wide operating voltage composite electrolyte prepared in Example 2 at room temperature (a) and the continuous lithium plating and stripping curve at an applied voltage of 10.0 V (b);

[0048] FIG12 is a voltage window cyclic voltammetry curve of the wide working voltage composite electrolyte prepared in Example 3;

[0049] FIG13 shows the lithium cobalt oxide half-cell assembled with the wide working voltage composite electrolyte prepared in Example 3 at 60 mA·g -1 Electrochemical performance at current density of 1000V; (a) is the first charge and discharge curve in the voltage window of 3.0-4.2V, (b) is the first charge and discharge curve in the voltage window of 12mA·g -1 (c) is the cycle performance curve under the current density of 3.0~5.0V;

[0050] FIG14 shows the critical current density of a lithium symmetric battery assembled with a wide operating voltage composite electrolyte prepared in Example 3 at room temperature (a) and the continuous lithium plating and stripping curve at an applied voltage of 10.0 V (b);

[0051] FIG15 is a voltage window cyclic voltammetry curve of the wide operating voltage composite solid electrolyte prepared in Example 4;

[0052] FIG16 shows the lithium cobalt oxide half-cell assembled with the wide working voltage composite electrolyte material prepared in Example 4 at 60 mA·g -1 Electrochemical performance at a current density of ; wherein, (a) is the first charge and discharge curve in the voltage window of 3.0~4.2V, and (b) is the cycle performance curve;

[0053] FIG17 is a voltage window cyclic voltammetry curve of the solid electrolyte prepared in Comparative Example 1;

[0054] FIG18 shows the lithium cobalt oxide half-cell assembled with the solid electrolyte prepared in Comparative Example 1 at 60 mA g -1 Electrochemical performance at a current density of ; wherein, (a) is the first charge and discharge curve in the voltage window of 3.0~4.2V, and (b) is the cycle performance curve;

[0055] FIG19 shows the critical current density of a lithium symmetric battery assembled with a solid electrolyte prepared in Comparative Example 1 at room temperature;

[0056] FIG20 is a voltage window cyclic voltammetry curve of the solid electrolyte prepared in Comparative Example 2;

[0057] Figure 21 shows the lithium cobalt oxide half-cell assembled with the solid electrolyte prepared in Comparative Example 2 at 60 mA g -1 Electrochemical performance at current density of ; wherein, (a) is the charge and discharge curve in the voltage window of 3.0~4.2V, and (b) is the cycle performance curve;

[0058] Figure 22 shows the critical current density of the lithium symmetric battery assembled with the solid electrolyte prepared in Comparative Example 2 at room temperature. DETAILED DESCRIPTION

[0059] The present application will be further described below with reference to specific examples, which are intended only to illustrate the present application and are not intended to limit the scope of the present application.

[0060] Example 1

[0061] A lithium borohydride-based solid electrolyte, composed of a molar ratio of 25% alumina, 25% lithium iodide, and 50% lithium borohydride, was ball-milled with polymethyl methacrylate (PMMA) with a degree of polymerization of 10,000. The mass ratio of lithium borohydride to PMMA was 95:5. The milled product was sieved to obtain a mixed powder. The powder sample was then subjected to an in-situ melt reaction to obtain the final composite electrolyte. The in-situ melt reaction process was performed at a temperature of 150°C, a reaction time of 1 hour, and a constant pressure of 300 MPa.

[0062] The electrochemical performance of the composite electrolyte prepared in this example was characterized using a solid-state battery test mold, assembled in an argon-filled glove box with water and oxygen concentrations less than 0.1 ppm. Lithium plating-stripping cycle testing was performed using a symmetrical lithium cell with lithium alloy as the electrode material on both sides. Voltage window testing was performed using a half-cell cyclic voltammetry test with lithium foil on one side and a lithium cobalt oxide cathode on the counter electrode. The electrochemical performance of the half-cell was tested using a constant current charge-discharge test.

[0063] The composite electrolyte prepared in this example was characterized for morphology. A high-resolution transmission electron microscopy photograph is shown in Figure 1. The image shows a uniform amorphous coating layer approximately 3 nm thick on the surface of the composite electrolyte. Further energy spectrum analysis of this layer (Figure 2) reveals that carbon, iodine, and aluminum are uniformly distributed on the surface of the electrolyte's secondary particles. The carbon is derived from polymethyl methacrylate, indicating that polymethyl methacrylate is coated on the surface of the lithium borohydride-based solid electrolyte.

[0064] In Figure 3, (a) is the X-ray photoelectron spectrum of O1s of the composite electrolyte, and (b) is its X-ray photoelectron spectrum of B1s. The XPS results show that the sample after the in-situ melting reaction has a new phase composition, (OCH3) x BH 4-x (c) is a composite electrolyte 13 The results of carbon solid NMR spectrum show that 13 There is a shielding effect on carbon, corresponding to (OCH3) x BH 4-x The middle part is composed of covalent BO bonds. (d) is the composite electrolyte 11 In the solid-state NMR spectrum of B, two regions corresponding to (OCH3)4B and (OCH3) can be observed. x BH 4-x The above test conclusions indicate that the composite electrolyte sample obtained after high-energy ball milling and in-situ melting reaction produces covalent (OCH3) x BH 4-x .

[0065] Figure 4 shows the temperature-dependent electronic and ionic conductivities of the composite electrolyte of this embodiment from -30 to 150°C. The results show that at room temperature, the electronic conductivity of the composite electrolyte is only 4×10 -10 S cm -2 , the ionic conductivity is 5.1×10 -4 S cm -2 More importantly, the electronic conductivity of the composite electrolyte remains 6-7 orders of magnitude smaller than the ionic conductivity over the entire temperature range.

[0066] Figure 5 shows the voltage window cyclic voltammetry curve of the composite electrolyte of this example. The results show that the electrolyte provides a stable voltage window of 0-10.0 V at room temperature, with a maximum oxidative decomposition current of only 0.85 μA. This result demonstrates that the composite electrolyte synthesized in this example has excellent ultra-high voltage electrochemical stability.

[0067] Figure 6 (a) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 The charge and discharge curves in the voltage window of 3.0-4.2V at a current density of 1.5V show that the first discharge capacity is 111.20 mA g -1 Figure 6 (b) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 The cycling performance curve at a current density of 12 mA g is shown in the figure. It can be seen from the figure that the composite electrolyte can maintain stable capacity in long cycles, and the capacity retention rate is as high as 100% after 200 cycles. Figure 6 (c) shows the performance of the lithium cobalt oxide half-cell assembled in this example at 12 mA g -1 The cycling performance curve in the voltage window of 3.0-5.0 V at a current density of 1.5 V was obtained. The results show that its first discharge capacity is as high as 149.60 mA g -1 , and can maintain stable reversible charge and discharge cycles within 20 cycles.

[0068] Figure 7 (a) shows the critical current density test curve of the lithium symmetrical battery assembled in this embodiment at room temperature. It can be seen from the figure that the critical current density at room temperature is as high as 21.65 mA cm -2 Figure 7(b) shows the continuous lithium plating-stripping curve of the lithium symmetric battery assembled in this example at room temperature under an applied voltage of 10.0 V. The results show that after 1000 hours of plating-stripping, the composite electrolyte in this example can still maintain cycling at a stable overpotential without any short-circuiting tendency.

[0069] The above conclusions prove that the composite electrolyte in this embodiment has excellent dendrite suppression performance in an extremely wide voltage window and is a composite electrolyte with a wide operating voltage.

[0070] Example 2

[0071] The preparation process of the composite electrolyte is substantially the same as that of Example 1, except that the reaction temperature in the in-situ melting reaction process is adjusted to 130° C. The assembly and testing processes of the all-solid-state lithium-ion battery are the same as those of Example 1.

[0072] Figure 8(a) shows the composite electrolyte in this embodiment. 13 The results of the carbon solid NMR spectrum show that, similar to those in Example 1, 13 There is a shielding effect on carbon, corresponding to (OCH3) xBH 4-x Compound. Figure 8(b) 11 In the solid-state NMR spectrum of boron, two regions corresponding to (OCH3)4B and (OCH3) can be observed. x BH 4-x The only difference between this example and Example 1 is the amount of chemical shift, which indicates the different degree of BO coordination.

[0073] Figure 9 shows the voltage window cyclic voltammetry curve of the composite electrolyte of this example. It can be concluded that this material provides a stable voltage window of 0-6.0V at room temperature, and the maximum oxidative decomposition current is only 6.85μA. In summary, the composite electrolyte synthesized in this example has a stable high voltage window similar to that of Example 1.

[0074] Figure 10 (a) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 At a current density of 1.5 volts, the charge and discharge curves in the voltage window of 3.0-4.2 V show that the first discharge capacity is 98.00 mA·h·g. -1 Figure 10 (b) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 The cycling performance curve at a current density of 12 mA g is shown in the figure. It can be seen from the figure that the composite electrolyte can maintain stable capacity in long cycles, and the capacity retention rate is as high as 81.60% after 100 cycles. Figure 10 (c) shows the performance of the lithium cobalt oxide half-cell assembled in this example at 12 mA g -1 The cycling performance curves at the voltage window of 3.0-5.0 V show that the first discharge capacity of the half-cell is as high as 137.60 mA·h·g -1 , and can still maintain stable reversible circulation within 20 cycles.

[0075] Figure 11 (a) shows the critical current density test curve of the lithium symmetric battery assembled in this embodiment at room temperature, indicating that its critical current density is 16.60 mA·cm -2 Figure 11(b) shows the continuous electroplating-stripping curve of the lithium symmetrical battery assembled in this embodiment under an applied voltage of 10V. It can be seen from the figure that the composite electrolyte in this embodiment is similar to that in Example 1. After 500h of electroplating-stripping, it still maintains the cycle at a stable overpotential and has no short-circuiting tendency.

[0076] In summary, it is shown that the composite electrolyte synthesized in this example is a composite electrolyte with a wide operating voltage similar to that of Example 1.

[0077] Example 3

[0078] The preparation process of the composite electrolyte is basically the same as that of Example 1, except that the reaction time in the in-situ melting reaction process is adjusted to 2 hours. The assembly and testing process of the all-solid-state lithium-ion battery is the same as that of Example 1.

[0079] Figure 12 is a voltage window cyclic voltammetry curve of the composite electrolyte in this example. It can be concluded that the electrolyte can provide a stable voltage window of 0-10.0 V at room temperature, and the maximum oxidation decomposition current is only 1.85 μA, indicating that the composite electrolyte synthesized in this example has a stable voltage window similar to that of Example 1.

[0080] Figure 13 (a) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 At a current density of 1.5 volts, the charge-discharge curve in the voltage window of 3.0-4.2 V shows that the first discharge capacity is 109.50 mA·h·g. -1 Figure 13 (b) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 The cycling performance curve at a current density of 12 mA g is shown in the figure. It can be seen from the figure that the electrolyte can maintain stable capacity in long cycles, and the capacity retention rate is as high as 94.20% after 100 cycles. Figure 13 (c) shows the performance of the lithium cobalt oxide half-cell assembled in this embodiment at 12 mA g -1 The cycling performance curves at the voltage window of 3.0-5.0 V show that the first discharge capacity of the half-cell is as high as 129.60 mA·h·g -1 , and can still maintain stable and reversible circulation within 20 cycles.

[0081] Figure 14 (a) shows the critical current density test curve of the lithium symmetrical battery assembled in this embodiment at room temperature, indicating that its critical current density is 18.50 mA cm -2 Figure 14(b) shows the continuous lithium plating-stripping curve of the lithium symmetrical battery assembled in this example under an applied voltage of 10 V. The results show that the composite electrolyte in this example is similar to that in Example 1. After 500 hours of plating-stripping, it still maintains cycling at a stable overpotential and has no short-circuiting tendency.

[0082] In summary, it is shown that the composite electrolyte synthesized in this example is a composite electrolyte with a wide operating voltage similar to that of Example 1.

[0083] Example 4

[0084] The preparation process of the composite electrolyte is substantially the same as that of Example 1, except that the reaction pressure in the in-situ melting reaction process is adjusted to 250 MPa. The assembly and testing processes of the all-solid-state lithium-ion battery are the same as those of Example 1.

[0085] Figure 15 shows the voltage window cyclic voltammetry curve of the composite electrolyte of this example. It can be concluded that this electrolyte provides a stable voltage window of 0-10.0 V at room temperature, and the maximum oxidative decomposition current is only 1.15 μA. This indicates that the composite electrolyte synthesized in this example has a stable voltage window similar to that of Example 1.

[0086] Figure 16 (a) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 At a current density of 1.5 volts, the charge and discharge curves in the voltage window of 3.0-4.2 V show that the first discharge capacity is 99.00 mA·h·g. -1 Figure 16 (b) shows the lithium cobalt oxide half-cell assembled in this embodiment at 60 mA·g -1 The cycling performance curve at a current density of 1.5 GHz shows that the electrolyte can maintain stable capacity in long cycles, and the capacity retention rate is as high as 74.4% after 100 cycles.

[0087] In summary, it is shown that the composite electrolyte synthesized in this example is a composite electrolyte with a wide operating voltage similar to that of Example 1.

[0088] Comparative Example 1

[0089] The solid electrolyte preparation process was essentially the same as in Example 1, except that the in-situ melting reaction process was not used, and the ball-milled powder was simply pressed into the solid electrolyte at 300 MPa. The assembly and testing processes for the all-solid-state lithium-ion battery were the same as in Example 1.

[0090] Figure 17 shows the voltage window cyclic voltammetry curve of the solid electrolyte in this comparative example. It can be concluded that the electrolyte undergoes severe oxidation at 2.8V at room temperature, with a maximum oxidation decomposition current as high as 316.20μA. This indicates that the solid electrolyte synthesized in this comparative example has a narrow voltage window and is extremely unstable at higher voltages.

[0091] Figure 18 (a) shows the lithium cobalt oxide half-cell assembled in this comparative example at 60 mA g -1 At a current density of 1.5 volts, the charge and discharge curves in the voltage window of 3.0-4.2 V show that the first discharge capacity is 48.00 mA·h·g. -1 Figure 18 (b) shows the lithium cobalt oxide half-cell assembled in this comparative example at 60 mA g -1 The cycling performance curve at a current density of 100 nm and 100 nm showed that the electrolyte failed after 40 cycles, indicating that the electrochemical performance of the solid electrolyte synthesized in this comparative example was significantly inferior to that of Example 1.

[0092] FIG19 is a critical current density test curve of the lithium symmetrical battery assembled in this comparative example at room temperature, indicating that its critical current density is 3.85 mA·cm -2 .

[0093] In summary, the solid electrolyte obtained in this comparative example has a narrow voltage window and a low critical current density, and cannot match the operating voltage of the lithium cobalt oxide positive electrode. It is not a composite electrolyte with a wide operating voltage.

[0094] Comparative Example 2

[0095] The preparation process of the solid electrolyte was essentially the same as that of Example 1, except that polymethyl methacrylate was not added to coat the lithium borohydride-based solid electrolyte during high-energy ball milling. The assembly and testing processes of the all-solid-state lithium-ion battery were the same as those of Example 1.

[0096] Figure 20 shows the voltage window cyclic voltammetry curve of the solid electrolyte in this comparative example. It can be concluded that the electrolyte undergoes severe oxidation at 2.7V at room temperature, with a maximum oxidation decomposition current as high as 74.50μA. This indicates that the solid electrolyte synthesized in this comparative example has a narrow voltage window and is extremely unstable at higher voltages.

[0097] Figure 21 (a) shows the lithium cobalt oxide half-cell assembled in this comparative example at 60 mA g -1 At a current density of 1.5 volts, the charge-discharge curve in the voltage window of 3.0-4.2 V shows that the first discharge capacity is 72.00 mA·h·g. -1 Figure 21 (b) shows the lithium cobalt oxide half-cell assembled in this comparative example at 60 mA g -1 The cycling performance curve at a current density of 100 nm and 100 nm showed that significant capacity decay began to occur after 20 cycles, indicating that the electrochemical performance of the solid electrolyte synthesized in this comparative example was significantly inferior to that of Example 1.

[0098] FIG22 is a critical current density test curve of the lithium symmetrical battery assembled in this comparative example at room temperature, indicating that its critical current density is 3.15 mA·cm -2 .

[0099] In summary, the solid electrolyte obtained in this comparative example has a narrow voltage window and a low critical current density, and cannot match the operating voltage of the lithium cobalt oxide positive electrode. It is not a composite electrolyte with a wide operating voltage.

[0100] Comparative Example 3

[0101] The solid electrolyte preparation process was essentially the same as in Example 1, except that polymethyl methacrylate was not added to coat the lithium borohydride-based solid electrolyte during high-energy ball milling, and the ball-milled powder was not treated using an in-situ melt reaction process. Instead, the ball-milled powder was simply pressed into a solid electrolyte at 300 MPa. The assembly and testing processes for the all-solid-state lithium-ion battery were the same as in Example 1.

[0102] After testing, the solid electrolyte in this comparative example underwent severe oxidation reaction and severe chemical reaction with lithium cobalt oxide, which deteriorated its intrinsic electrochemical stability and could not complete the test normally, and could not be used as a solid electrolyte for all-solid-state lithium-ion batteries.

[0103] The above embodiments and comparative examples describe the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the contents disclosed in the present application and fall within the scope of protection of the present application.

Claims

1. A wide working voltage composite electrolyte for an all-solid-state lithium-ion battery, comprising a lithium borohydride-based solid electrolyte and a high molecular polymer coating layer coated on the surface of the lithium borohydride-based solid electrolyte, characterized in that: The voltage window of the wide working voltage composite electrolyte is greater than or equal to 6V and is up to 10V; The lithium borohydride-based solid electrolyte comprises lithium borohydride, aluminum oxide and lithium iodide; The high molecular polymer coating layer is polymethyl methacrylate; The lithium borohydride-based solid electrolyte accounts for 70 to 99 wt.% of the mass of the wide working voltage composite electrolyte; The mass proportion of the high molecular polymer coating layer to the wide working voltage composite electrolyte is 1 to 30 wt.%.

2. The wide working voltage composite electrolyte according to claim 1, characterized in that: In the lithium borohydride-based solid electrolyte, taking the total molar amount of lithium borohydride, aluminum oxide and lithium iodide as 100%, the lithium borohydride accounts for 50-60% of the total molar amount, the aluminum oxide accounts for 20-25% of the total molar amount, and the lithium iodide accounts for 20-25% of the total molar amount.

3. The wide working voltage composite electrolyte according to claim 1, characterized in that: The thickness of the high molecular polymer coating layer is 1 to 100 nm.

4. The wide operating voltage composite electrolyte according to claim 1 or 3, characterized in that: The polymerization degree of the polymethyl methacrylate is 250 to 20,000.

5. The wide operating voltage composite electrolyte according to claim 1, characterized in that: The high molecular polymer coating layer is an amorphous coating layer.

6. The wide operating voltage composite electrolyte according to claim 1, characterized in that: The wide working voltage composite electrolyte includes covalent (OCH3) x BH 4-x .

7. The method for preparing the wide working voltage composite electrolyte according to any one of claims 1 to 6, characterized in that: include: Lithium borohydride, aluminum oxide, lithium iodide and polymethyl methacrylate are subjected to high-energy ball milling, and the obtained mixture powder is reacted at a certain temperature and a certain constant pressure in an in-situ melting reaction manner, and samples are collected to obtain the wide working voltage composite electrolyte.

8. The preparation method according to claim 7, characterized in that: The high-energy ball milling time is 96 hours, and the ball milling speed is 530 rpm; The ball milling medium of the high energy ball mill is agate, and the ball-to-material ratio of the high energy ball mill is 100-800:1; The ball milling atmosphere of the high energy ball mill is an argon atmosphere.

9. The preparation method according to claim 7 or 8, characterized in that: The high energy ball milling further includes screening.

10. The preparation method according to claim 7, characterized in that: The temperature of the in-situ melting reaction is 130-180°C; The time of the in-situ melting reaction is 1 to 5 hours; The pressure of the in-situ melting reaction is 200-500 MPa.

11. Application of the wide working voltage composite electrolyte according to any one of claims 1 to 6 or the wide working voltage composite electrolyte prepared by the preparation method according to any one of claims 7 to 10 in an all-solid-state lithium-ion battery, characterized in that: The all-solid-state lithium-ion battery comprises a lithium-ion battery positive electrode, a negative electrode and the wide operating voltage composite electrolyte.

12. An all-solid-state lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode and a composite electrolyte with a wide working voltage; The wide operating voltage composite electrolyte is the wide operating voltage composite electrolyte described in any one of claims 1 to 6 or the wide operating voltage composite electrolyte prepared by the preparation method described in any one of claims 7 to 10.

13. The all-solid-state lithium-ion battery according to claim 12, characterized in that: The material of the positive electrode includes lithium cobalt oxide; The negative electrode material includes lithium metal 。

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