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

Abstract

The present application relates to the field of all-solid-state lithium ion batteries, and particularly relates to a wide working voltage composite electrolyte for all-solid-state lithium ion batteries, a preparation method and application thereof. The present application provides a simple and efficient method for comprehensively improving the voltage window and the ability to inhibit dendrite growth of lithium borohydride-based solid electrolyte. The composite electrolyte can achieve a stable voltage window of 0-10V at room temperature, has a critical current density as high as 21.65mA cm ‑2 , and can complete 1000h continuous constant voltage electroplating stripping test in the high voltage interval of 10.0V, and the electrochemical stability is extremely excellent. The present application has important significance for improving the working voltage and energy density of lithium ion batteries and promoting the large-scale commercialization of solid-state electrolyte.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state lithium-ion batteries, and more particularly to a wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries, its preparation method, and its application. Background Technology

[0002] 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 major technical problems: low energy density and poor safety. Currently, replacing liquid electrolytes with all-solid-state electrolytes can solve these problems. Furthermore, all-solid-state electrolytes can simultaneously match high-voltage cathodes and lithium metal to achieve higher energy densities. However, most inorganic all-solid-state electrolytes have narrow voltage windows, leading to severe oxidation and decomposition of their all-solid-state lithium batteries at high voltages, resulting in serious performance degradation.

[0003] Lithium borohydride (LBO) as a solid-state electrolyte has the advantage of thermodynamic stability against metallic lithium, eliminating the need to consider anode-side interfacial reactions when used in all-solid-state lithium-ion batteries. However, LBO solid electrolytes still have significant problems. First, due to the high local electron density of borohydride ions, they are prone to delocalization under external field excitation, leading to anion oxidation and a narrow thermodynamic oxidation window of only 2.8V. Second, the high bulk electronic conductivity of LBO electrolytes results in severe dendrite growth problems.

[0004] Currently, the main methods for improving the voltage window of lithium borohydride-based solid electrolytes (LBOHs) include: 1. Introducing more electronegative anions to enhance the overall oxidation stability of borohydride ions, such as introducing lithium fluoride or lithium chloride. 2. Destroying / replacing the structure of the borohydride anion, such as partially replacing lithium borohydride with high-borides or sulfides. Work on reducing electronic conductivity mainly focuses on introducing inert second phases with low electronic conductivity into lithium borohydride, such as alumina or silicon oxide, and compounds that react to form ionic / covalent bonds, such as ammoniaborane. However, systematic research and modification methods for LBOHs-based solid electrolytes that operate at high voltages and suppress dendrite formation have not yet been proposed, resulting in a significant gap between LBOHs-based solid electrolytes and their commercial viability.

[0005] Therefore, adopting simple and efficient methods to comprehensively improve the voltage window and dendrite growth suppression capability of lithium borohydride-based solid electrolytes is essential for achieving a comprehensive improvement in the performance of solid electrolytes and their large-scale commercial application. Summary of the Invention

[0006] To overcome the current shortcomings of the lack of systematic research and modification methods for lithium borohydride-based solid electrolytes (LBOHs) in high-voltage operation and dendrite suppression, which has resulted in a significant gap between LBOHs and their commercial viability, this invention provides a simple and efficient method to comprehensively improve the voltage window and dendrite growth suppression capability of LBOHs-based LBOHs. The resulting composite electrolyte can be matched with existing high-voltage lithium-ion batteries and can be adapted to cathode materials with higher operating voltages in the future, significantly widening the operating voltage window of lithium-ion batteries. This is of great significance for the large-scale commercial application of solid-state electrolytes and improving the energy density of lithium-ion batteries.

[0007] A wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries, comprising a lithium borohydride-based solid electrolyte and a polymer coating layer covering its surface.

[0008] The voltage window of the wide-operating-voltage composite electrolyte is greater than or equal to 6V, and can reach up to 10V.

[0009] The lithium borohydride-based solid electrolyte has a mass percentage of 70-99 wt.%.

[0010] The polymer coating layer has a mass percentage of 1-30 wt.%;

[0011] The composition of the lithium borohydride-based solid electrolyte includes lithium borohydride, aluminum oxide, and lithium iodide; based on the total molar ratio of the three raw materials as 100%, lithium borohydride accounts for 40-50%, aluminum oxide accounts for 20-25%, and lithium iodide accounts for 20-25%.

[0012] The polymer coating layer is polymethyl methacrylate, with a thickness selected from 1–100 nm; the degree of polymerization of polymethyl methacrylate is selected from 250–20000.

[0013] Further explanation: The preparation method of the wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries includes:

[0014] The raw materials, including lithium borohydride-based solid electrolyte, lithium borohydride, alumina, and lithium iodide, are mixed with polymethyl methacrylate by high-energy ball milling and uniformly mixed into powder.

[0015] The high-energy ball milling time is 96 hours, and the ball milling speed is 530 rpm;

[0016] The ball milling media are made of agate, and the ball-to-material ratio for high-energy ball milling is 100-800:1;

[0017] The ball milling atmosphere is an inert atmosphere of argon;

[0018] Subsequently, the powder obtained from the high-energy ball milling was reacted in situ using a melting reaction method, and the sample was collected to complete the preparation.

[0019] To further explain, the in-situ melting reaction preparation process is completed in a general-purpose all-solid-state electrolyte test mold. The in-situ melting reaction process is carried out at a certain temperature and a certain constant pressure, and the entire process is completed in a glove box with an inert atmosphere of argon.

[0020] The in-situ melting reaction temperature is 130-180℃; further, the reaction temperature is 150℃.

[0021] The in-situ melting reaction time is 1-5 hours; further, the reaction time is 1 hour.

[0022] The constant pressure of the in-situ melting reaction is 200–500 MPa; further, the constant pressure is 300 MPa.

[0023] The present invention has the following advantages: 1. The composite electrolyte of the present invention can achieve a stable voltage window of 0-10V at room temperature, with a maximum voltage of 21.65mA cm⁻¹. -2 It has a critical current density and can complete 1000h of continuous constant voltage electroplating peeling test in a high voltage range of 10.0V, with extremely excellent electrochemical stability.

[0024] 2. When the composite electrolyte of the present invention is matched with the lithium cobalt oxide cathode and lithium metal anode to form an all-solid-state battery, it can achieve a capacity retention rate of up to 100% for 200 cycles within a voltage window of 3.0–4.2V; and can achieve reversible and stable charge-discharge cycle performance within a voltage window of 3.0–5.0V.

[0025] 3. The composite electrolyte of this invention is prepared using a conventional high-energy ball milling process, supplemented by a two-step in-situ melting reaction. The preparation process induces a reaction between polymethyl methacrylate and lithium borohydride-based solid electrolyte to form a covalent coordination compound (OCH3). x BH 4-x Thermodynamically enhanced 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 capability. This preparation process does not add an electrolyte preparation step or additional preparation costs; it is simple to operate, offers strong controllability in material preparation, and is perfectly suited for industrial production needs. Attached Figure Description

[0026] Figure 1 Transmission electron microscopy image of the wide operating voltage composite electrolyte material prepared in Example 1;

[0027] Figure 2 The energy spectrum of the wide operating voltage composite electrolyte material prepared in Example 1 is shown below.

[0028] Figure 3 X-ray photoelectron spectrum of oxygen for the wide operating voltage composite electrolyte material prepared in Example 1; (b) X-ray photoelectron spectrum of boron; (c) 13 NMR spectrum of carbon in solid state; (d) 11 NMR spectrum of boron in solid state;

[0029] Figure 4 The electronic and ionic conductivity of the wide working voltage composite electrolyte material prepared in Example 1 from -30 to 150 °C as a function of temperature.

[0030] Figure 5 The cyclic voltammetry curves of the wide operating voltage composite electrolyte material prepared in Example 1 are shown below.

[0031] Figure 6 The lithium cobalt oxide half-cell assembled from the wide-operating-voltage composite electrolyte material prepared in Example 1 operates at 60 mA g. -1 At current densities of (a) and (b) current density, the initial charge-discharge curves are shown in the voltage window of 3.0–4.2 V; the cycle performance curves are also shown. (At 12 mAg) -1 (c) Cyclic performance curves under a current density of 3.0-5.0V in a voltage window;

[0032] Figure 7 (a) Critical current density at room temperature and (b) continuous lithium plating peeling curve at an applied voltage of 10.0 V for the wide working voltage composite electrolyte material prepared in Example 1.

[0033] Figure 8 The wide operating voltage composite electrolyte material prepared in Example 2 (a) 13 (b) Carbon solid NMR spectrum; 11 NMR spectrum of boron solid;

[0034] Figure 9 Cyclic voltammetry curves of the wide operating voltage composite electrolyte material prepared in Example 2;

[0035] Figure 10 The lithium cobalt oxide half-cell assembled using the wide-operating-voltage composite electrolyte material prepared in Example 2 operates at 60 mAg. -1 At current densities of (a) and (b) current density, the initial charge-discharge curves are shown in the voltage window of 3.0–4.2 V; the cycle performance curves are also shown. (At 12 mA g) -1 (c) Cyclic performance curves under a current density of 3.0-5.0V in a voltage window;

[0036] Figure 11 (a) Critical current density at room temperature and (b) continuous lithium plating peeling curve at an applied voltage of 10.0V for the wide working voltage composite electrolyte material prepared in Example 2.

[0037] Figure 12 The cyclic voltammetry curves of the wide operating voltage composite electrolyte material prepared in Example 3 are shown.

[0038] Figure 13 The lithium cobalt oxide half-cell assembled using the wide-operating-voltage composite electrolyte material prepared in Example 3 operates at 60 mAg. -1 At current densities of (a) and (b) current density, the initial charge-discharge curves are shown in the voltage window of 3.0–4.2 V; the cycle performance curves are also shown. (At 12 mA g) -1 (c) Cyclic performance curves under a current density of 3.0-5.0V in a voltage window;

[0039] Figure 14 (a) Critical current density at room temperature and (b) continuous lithium plating peeling curve at an applied voltage of 10.0V for the wide working voltage composite electrolyte material prepared in Example 3.

[0040] Figure 15 Cyclic voltammetry curves of the wide operating voltage composite solid electrolyte material prepared in Example 4;

[0041] Figure 16 The lithium cobalt oxide half-cell assembled from the wide-operating-voltage composite electrolyte material prepared in Example 4 operates at 60 mAg. -1 (a) Initial charge-discharge curves within a voltage window of 3.0–4.2 V at the given current density; (b) Cyclic performance curves;

[0042] Figure 17 Cyclic voltammetry curves of the solid electrolyte material prepared in Comparative Example 1;

[0043] Figure 18 The lithium cobalt oxide half-cell assembled using the solid electrolyte material prepared for Comparative Example 1 was tested at 60 mA g. -1 (a) Initial charge-discharge curves within a voltage window of 3.0–4.2 V at the given current density; (b) Cyclic performance curves;

[0044] Figure 19 The critical current density of the solid electrolyte material prepared in Comparative Example 1 at room temperature;

[0045] Figure 20 Cyclic voltammetry curves of the solid electrolyte material prepared in Comparative Example 2;

[0046] Figure 21The lithium cobalt oxide half-cell assembled using the solid electrolyte material prepared for Comparative Example 2 was tested at 60 mA g. -1 At the given current density, (a) charge-discharge curves within a voltage window of 3.0–4.2 V; (b) cycle performance curves;

[0047] Figure 22 The critical current density of the solid electrolyte material prepared for Comparative Example 2 at room temperature. Detailed Implementation

[0048] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] Example 1

[0050] A lithium borohydride-based solid electrolyte, with a molar ratio of 25% alumina, 25% lithium iodide, and 50% lithium borohydride, was ball-milled with polymethyl methacrylate (PMMA) of degree of polymerization 10000. The mass ratio of lithium borohydride-based solid electrolyte to PMMA was 95:5. The ball-milled product was sieved to obtain a powder sample. Subsequently, the powder sample underwent an in-situ melting reaction to obtain the final composite electrolyte. The in-situ melting reaction process was carried out at a reaction temperature of 150℃, a reaction time of 1 h, and a constant pressure of 300 MPa.

[0051] The electrochemical performance of the solid electrolyte prepared in this embodiment was characterized using a dedicated solid-state battery test mold, assembled in an argon-filled glove box with water and oxygen contents both less than 0.1 ppm. Lithium plating stripping cycle testing employed a lithium symmetric battery, with both electrode materials being lithium alloys. Voltage window testing utilized a half-cell cyclic voltammetry test, using lithium foil on one side and a lithium cobalt oxide cathode on the counter electrode side. Constant current charge-discharge testing was used to assess the electrochemical performance of the half-cell.

[0052] The morphology of the composite electrolyte material prepared in this embodiment was characterized, and its high-resolution transmission electron microscopy image is shown below. Figure 1 As shown in the figure, a uniform amorphous coating layer with a thickness of approximately 3 nm can be observed on the surface of the composite electrolyte particles in this embodiment. Further energy dispersive spectroscopy (EDS) analysis was performed on this layer (e.g.,...). Figure 2 This indicates that carbon, iodine, and aluminum are uniformly distributed on the surface of the secondary particles in the electrolyte. The carbon originates from polymethyl methacrylate (PMMA), suggesting that PMMA coats the surface of the lithium borohydride-based solid electrolyte.

[0053] Figure 3 In the figure, (a) shows the X-ray photoelectron spectrum of the O1s phase of the composite electrolyte, and (b) shows its B1s phase. The XPS results indicate that the sample after in-situ melting reaction contains a novel phase composition, (OCH3).x BH 4-x (c) is a composite electrolyte. 13 The NMR spectrum of carbon solid showed 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 complex electrolyte. 11 The solid-state NMR spectrum of B shows two locations corresponding to (OCH3)4B and (OCH3). x BH 4-x The characteristic peaks of the [organism / electrolyte] are observed. In summary, the test results indicate that the composite electrolyte sample obtained after high-energy ball milling and in-situ melting reaction produces covalent (OCH3) [electrolyte]. x BH 4-x .

[0054] Figure 4 The electronic and ionic conductivities of the composite electrolyte in this embodiment are shown in the temperature range of -30 to 150 °C. The results indicate that at room temperature, the electronic conductivity of the composite electrolyte is only 4 × 10⁻⁶. -10 S cm -2 The ionic conductivity is 5.1 × 10⁻⁶. -4 S cm -2 More importantly, the electronic conductivity of this composite electrolyte remains 6-7 orders of magnitude lower than its ionic conductivity across the entire temperature range.

[0055] Figure 5 The cyclic voltammetry curves for the composite electrolyte in this embodiment show the voltage window. The results indicate that the electrolyte provides a stable voltage window of 0–10.0 V at room temperature, and the maximum oxidative decomposition current is only 0.85 μA. These results demonstrate that the composite electrolyte synthesized in this embodiment exhibits excellent ultra-high voltage electrochemical stability.

[0056] Figure 6 (a) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The charge-discharge curves at a current density within a voltage window of 3.0-4.2V show that the initial discharge specific capacity is 111.20 mAh g. -1 . Figure 6 (b) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The cycling performance curves at the current density are shown in the figure. It can be seen from the figure that the electrolyte can maintain stable capacity during long cycles, and the capacity retention rate is as high as 100% after 200 cycles. Figure 6 (c) The lithium cobalt oxide half-cell assembled in this embodiment is tested at 12 mA g. -1Cycling performance curves were obtained at a current density within a voltage window of 3.0–5.0 V. The results show that its initial discharge specific capacity reaches a high 149.60 mAh g⁻¹. -1 It can maintain stable reversible charge-discharge cycles for up to 20 cycles.

[0057] Figure 7 (a) shows the test curve of the critical current density of the lithium symmetric battery assembled in this embodiment at room temperature. As can be seen from the figure, its critical current density at room temperature is as high as 21.65 mA cm⁻¹. -2 . Figure 7 (b) shows the continuous lithium plating stripping curve of the lithium symmetric battery assembled in this embodiment at room temperature under an applied voltage of 10.0V. The results show that the composite electrolyte in this embodiment still maintains stable overpotential cycling after 1000h of plating stripping, and there is no tendency for short circuit.

[0058] The above conclusions demonstrate that the composite electrolyte in this embodiment exhibits excellent dendrite suppression performance over an extremely wide voltage window, making it a composite electrolyte with a wide operating voltage range.

[0059] Example 2

[0060] The preparation process of the composite electrolyte is basically the same as that in Example 1, except that the reaction temperature in the in-situ melting reaction process is adjusted to 130°C. The assembly and testing process of the all-solid-state lithium-ion battery is the same as that in Example 1.

[0061] Figure 8 (a) is the composite electrolyte in this embodiment. 13 The carbon solid NMR spectrum results showed similarities to those in Example 1. 13 There is a shielding effect on carbon, corresponding to (OCH3). x BH 4-x Compounds. Figure 8 (b) is 11 The solid-state NMR spectrum of boron shows two locations corresponding to (OCH3)4B and (OCH3). x BH 4-x The characteristic peaks. The only difference between this embodiment and Example 1 is the amount of chemical shift, indicating the different degrees of BO coordination.

[0062] Figure 9 The cyclic voltammetry curves for the composite electrolyte in this embodiment show that the 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, this demonstrates that the composite electrolyte synthesized in this embodiment has a stable high voltage window similar to that of Example 1.

[0063] Figure 10(a) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The charge-discharge curves at a current density within a voltage window of 3.0-4.2V show an initial discharge specific capacity of 98.00 mAh g. -1 . Figure 10 (b) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The cycling performance curves at the specified current density are shown in the figure. As can be seen from the figure, the electrolyte can maintain stable capacity during long cycles, and the capacity retention rate is as high as 81.60% after 100 cycles. Figure 10 (c) The lithium cobalt oxide half-cell assembled in this embodiment is tested at 12 mA g. -1 Cycling performance curves were obtained at the specified current density within a voltage window of 3.0–5.0 V. The results show that the first discharge specific capacity of the aforementioned half-cell is as high as 137.60 mAh g⁻¹. -1 It can still maintain a stable reversible cycle within 20 cycles.

[0064] 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⁻¹. -2 . Figure 11 (b) is the continuous electroplating stripping curve of the lithium symmetric battery assembled in this embodiment under an applied voltage of 10V. As can be seen from the figure, the composite electrolyte in this embodiment is similar to that in Example 1. After 500h of electroplating stripping, it still maintains cycling with a stable overpotential and has no tendency to short circuit.

[0065] In summary, this embodiment shows that the composite electrolyte synthesized in this embodiment is a wide operating voltage composite electrolyte similar to that in Example 1.

[0066] Example 3

[0067] The preparation process of the composite electrolyte is basically the same as that in 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 in Example 1.

[0068] Figure 12 The voltage window cyclic voltammetry curve of the composite electrolyte in this embodiment shows that the electrolyte can provide a stable voltage window of 0-10.0V at room temperature, and the maximum oxidation decomposition current is only 1.85μA, indicating that the composite electrolyte synthesized in this embodiment has a stable voltage window similar to that in Example 1.

[0069] Figure 13 (a) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1The charge-discharge curves at a current density within a voltage window of 3.0-4.2V show an initial discharge specific capacity of 109.50 mAh g. -1 . Figure 13 (b) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The cycling performance curves at the specified current density are shown in the figure. As can be seen from the figure, the electrolyte can maintain stable capacity during long cycles, and the capacity retention rate is as high as 94.20% after 100 cycles. Figure 13 (c) The lithium cobalt oxide half-cell assembled in this embodiment is tested at 12 mA g. -1 Cycling performance curves were obtained at a current density within a voltage window of 3.0–5.0 V. The results show that the first discharge specific capacity of the aforementioned half-cell is as high as 129.60 mAh g⁻¹. -1 It can still maintain a stable and reversible cycle within 20 cycles.

[0070] Figure 14 (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 18.50 mA cm⁻¹. -2 . Figure 14 (b) is the continuous lithium electroplating stripping curve of the lithium symmetric battery assembled in this embodiment under an applied voltage of 10V. The results show that the composite electrolyte in this embodiment is similar to that in Example 1. After 500h of electroplating stripping, it still maintains cycling with a stable overpotential and has no tendency to short circuit.

[0071] In summary, this embodiment shows that the composite electrolyte synthesized in this embodiment is a wide operating voltage composite electrolyte similar to that in Example 1.

[0072] Example 4

[0073] The preparation process of the composite electrolyte is basically the same as that in Example 1, except that the reaction pressure in the in-situ melting reaction process is adjusted to 250 MPa. The assembly and testing process of the all-solid-state lithium-ion battery is the same as that in Example 1.

[0074] Figure 15 Based on the voltage window of the composite electrolyte in this embodiment, it can be concluded that the 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 embodiment has a stable voltage window similar to that of Example 1.

[0075] Figure 16 (a) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The charge-discharge curves at the specified current density within a voltage window of 3.0–4.2 V show an initial discharge specific capacity of 99.00 mAh g. -1 . Figure 16 (b) The lithium cobalt oxide half-cell assembled in this embodiment at 60 mA g -1 The cycling performance curves at current densities show that the electrolyte can maintain capacity stability during long cycles, with a capacity retention of up to 74.4% after 100 cycles.

[0076] In summary, this embodiment shows that the composite electrolyte synthesized in this embodiment is a wide operating voltage composite electrolyte similar to that in Example 1.

[0077] Comparative Example 1

[0078] The preparation process of the solid electrolyte is basically the same as that in Example 1, except that the in-situ melting reaction process was not used; instead, the ball-milled powder was pressed into a solid electrolyte at 300 MPa. The assembly and testing process of the all-solid-state lithium-ion battery is the same as that in Example 1.

[0079] Figure 17 The voltage window of the solid electrolyte in this comparative example is shown in the figure. It can be concluded that this electrolyte undergoes severe oxidation at room temperature (2.8V), with a maximum oxidation decomposition current as high as 316.20 μA. This indicates that the solid electrolyte synthesized in this comparative example has a narrow voltage window and is extremely unstable at higher voltages.

[0080] Figure 18 (a) The lithium cobalt oxide half-cell assembled for this comparative example was tested at 60 mA g. -1 The charge-discharge curves at a current density within a voltage window of 3.0-4.2V show an initial discharge specific capacity of 48.00 mAh g. -1 . Figure 18 (b) The lithium cobalt oxide half-cell assembled for this comparative example was tested at 60 mA g. -1 Cycling performance curves at different current densities revealed that the electrolyte failed after only 40 cycles. This indicates that the electrochemical performance of the solid electrolyte synthesized in this comparative example is significantly inferior to that of Example 1.

[0081] Figure 19 The critical current density test curve of the lithium symmetric battery assembled in this comparative example at room temperature shows that its critical current density is 3.85 mA cm⁻¹. -2 .

[0082] In summary, the solid electrolyte obtained in this comparative example has a narrow voltage window and a low critical current density, which cannot match the working voltage of the lithium cobalt oxide cathode, and it is not a composite electrolyte with a wide working voltage.

[0083] Comparative Example 2

[0084] The preparation process of the solid electrolyte is basically 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. The assembly and testing process of the all-solid-state lithium-ion battery is the same as in Example 1.

[0085] Figure 20 The voltage window of the solid electrolyte in this comparative example shows that it undergoes severe oxidation at room temperature (2.7V), 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.

[0086] Figure 21 (a) The lithium cobalt oxide half-cell assembled for this comparative example was tested at 60 mA g. -1 The charge-discharge curves at a current density within a voltage window of 3.0-4.2V show an initial discharge specific capacity of 72.00 mAh g. -1 . Figure 21 (b) The lithium cobalt oxide half-cell assembled for this comparative example was tested at 60 mA g. -1 The cycling performance curves at the specified current densities revealed a significant capacity decay that began after 20 cycles. This indicates that the electrochemical performance of the solid electrolyte synthesized in this comparative example is significantly inferior to that of Example 1.

[0087] Figure 22 The critical current density test curve for the lithium-ion symmetric battery assembled in this comparative example at room temperature shows that its critical current density is 3.15 mA cm⁻¹. -2 .

[0088] In summary, the solid electrolyte obtained in this comparative example has a narrow voltage window and a low critical current density, which cannot match the working voltage of the lithium cobalt oxide cathode, and it is not a composite electrolyte with a wide working voltage.

[0089] Comparative Example 3

[0090] The preparation process of the solid electrolyte is basically the same as in Example 1, except that during high-energy ball milling, polymethyl methacrylate was not added to coat the lithium borohydride-based solid electrolyte, and the ball-milled powder was not treated with an in-situ melting reaction process; instead, the ball-milled powder was simply pressed into a solid electrolyte at 300 MPa. The assembly and testing process of the all-solid-state lithium-ion battery is the same as in Example 1.

[0091] Tests showed that the solid electrolyte in the comparative example underwent severe oxidation and chemical reaction with lithium cobalt oxide, which degraded its intrinsic electrochemical stability and prevented it from completing the test normally. Therefore, it cannot be used as a solid electrolyte for all-solid-state lithium-ion batteries.

[0092] The above embodiments and comparative examples have described in detail the preferred embodiments of the present invention; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries, comprising a lithium borohydride-based solid electrolyte and a polymer coating layer on the surface of the lithium borohydride-based solid electrolyte, characterized in that: The voltage window of the wide-operating-voltage composite electrolyte is greater than or equal to 6V, and can reach up to 10V. The lithium borohydride-based solid electrolyte comprises lithium borohydride, aluminum oxide, and lithium iodide. The polymer coating layer is derived from polymethyl methacrylate; The lithium borohydride-based solid electrolyte comprises 70-99 wt.% by mass. The polymer coating layer accounts for 1-30 wt.% of the total mass.

2. The wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries according to claim 1, characterized in that: In the lithium borohydride-based solid electrolyte, with the total molar ratio of lithium borohydride, alumina, and lithium iodide being 100%, lithium borohydride accounts for 50-60%, alumina accounts for 20-25%, and lithium iodide accounts for 20-25%.

3. The wide operating voltage composite electrolyte for all-solid-state lithium-ion batteries according to claim 1, characterized in that: The thickness of the polymethyl methacrylate coating is selected from 1-100 nm, and the degree of polymerization of polymethyl methacrylate is 250-20000.

4. A method for preparing a wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries according to any one of claims 1-3, characterized in that, include: The raw materials, including lithium borohydride-based solid electrolyte, are mixed with polymethyl methacrylate by high-energy ball milling to form a uniform powder. Subsequently, the powder is reacted in situ under certain temperature and constant pressure conditions by in-situ melting reaction, and the sample is collected to complete the preparation.

5. The method for preparing a wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries according to claim 4, characterized in that, The high-energy ball mill has a milling time of 96 hours and a milling speed of 530 rpm. The high-energy ball milling media are made of agate, and the ball-to-material ratio of the high-energy ball mill is 100-800:1; The high-energy ball milling atmosphere is an inert atmosphere of argon.

6. The method for preparing a wide-operating-voltage composite electrolyte for all-solid-state lithium-ion batteries according to claim 4, characterized in that, The in-situ melting reaction temperature is 130-180℃; The in-situ melting reaction time is 1-5 hours; The in-situ melting constant pressure is 200-500 MPa.

7. The application of a wide-operating-voltage composite electrolyte in all-solid-state lithium-ion batteries, characterized in that, It includes a lithium-ion battery positive electrode, a negative electrode, and a composite electrolyte, wherein the composite electrolyte is prepared by the method according to any one of claims 4-6.

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