Lithium phosphate solid electrolyte target material for preparing thin-film lithium battery and preparation method of lithium phosphate solid electrolyte target material

Abstract

The invention relates to the technical field of solid-state electrolyte, in particular to a lithium phosphate solid-state electrolyte target material for preparing a thin-film lithium battery and a preparation method, and the preparation method comprises the following steps: S1, synthesizing tetragonal-phase barium titanate nanoparticles as an inner core through a hydrothermal method; s2, coating the surface of the inner core with a lithium-aluminum-titanium phosphate precursor by adopting a sol-gel method, and performing heat treatment to form core-shell powder with a middle shell layer; s3, the surface of the core-shell powder is wrapped with a lithium germanium molybdenum zinc oxide precursor through a hydrothermal method, and triple core-shell structure powder is formed after a hydrothermal reaction; and S4, putting the triple core-shell structure powder into a discharge plasma sintering furnace, and sintering to obtain the target material. The lithium phosphate solid electrolyte target material with a special structure is formed through the preparation process, and shows excellent performance in lithium symmetric batteries, electrochemical stability windows and full battery long cycle performance tests, the safety of the batteries is improved, and the cycle life of the batteries is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid electrolyte, and particularly relates to a lithium phosphate solid electrolyte target material for preparing a thin film lithium battery and a preparation method. BACKGROUND

[0002] In the all-solid-state battery system, the solid electrolyte plays a key role in conducting lithium ions and separating the positive and negative electrodes. Among them, the thin film all-solid-state lithium battery has unique advantages such as ultra-thin, flexible, and compatibility with microelectronic technology, and shows great application potential in frontier fields such as micro-sensors, implantable medical devices, smart cards and advanced consumer electronics. One of the key processes for preparing such thin film batteries is physical vapor deposition technology, especially magnetron sputtering technology. Lithium phosphate-based materials usually have a stable crystal structure, providing a suitable channel for the migration of lithium ions, thus ensuring their intrinsic ionic conductivity as electrolytes. Lithium phosphate-based materials have excellent electrochemical stability and are not easily oxidized when matched with high-voltage positive electrode materials, which helps to widen the operating voltage window of the battery and thus improve the energy density. At the same time, its chemical properties are stable and it is not easy to react with electrode materials, which helps to ensure the long-term cycle stability of the battery.

[0003] The patent with the patent publication number CN114057480A discloses a lithium phosphate solid electrolyte target material for preparing a thin film lithium battery and a preparation method, which includes a premixing step, a ball milling step, a sieving step, a pressing step, a sintering step and a cooling step, and can be specially suitable for the scheme of preparing an all-solid-state thin film lithium battery by using a magnetron sputtering coating method. The patent with the patent publication number CN119069782A discloses a lithium phosphate solid electrolyte for preparing a lithium battery and a preparation method thereof, which includes a substrate layer and a sputtering layer, and improves the stability of the product under multiple cycles.

[0004] In the prior art, lithium phosphate solid electrolyte targets are usually prepared by traditional methods such as normal pressure sintering. On the one hand, the high temperature and long holding time required by the process easily causes lithium element to volatilize, resulting in a deviation of the stoichiometric ratio of the target material, low density and coarse grains, which causes the mechanical strength of the finally obtained target material to be insufficient. In the process of magnetron sputtering, such target materials are easy to produce micro-particle pollution, causing defects such as pinholes in the deposited electrolyte film, and increasing the risk of short circuit of the battery. On the other hand, there is thermodynamic instability between the traditional lithium phosphate electrolyte and the metal lithium negative electrode, and the interface is easy to have a side reaction, forming a solid-state interface film with low ionic conductivity, which hinders the transmission of lithium ions, leading to a decrease in coulombic efficiency and deterioration of rate performance, and also causing rapid capacity decay and safety risks in the cycle process due to interface contact deterioration and lithium dendrite growth, which restricts the reliability and service life of the thin film all-solid-state battery. SUMMARY

[0005] In order to solve the problems mentioned in the background art, the present application provides a lithium phosphate solid-state electrolyte target material for preparing a thin film lithium battery and a preparation method.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: The preparation method of the lithium phosphate solid-state electrolyte target material for preparing a thin film lithium battery comprises the following steps: S1, synthesizing barium titanate nanoparticles with tetragonal phase as the inner core by a hydrothermal method; S2, coating a lithium aluminum titanium phosphate precursor on the surface of the inner core by a sol-gel method, and forming a core-shell powder with an intermediate shell layer after heat treatment; S3, coating a lithium germanium molybdenum zinc oxide precursor on the surface of the core-shell powder by a hydrothermal method, and forming a triple core-shell structure powder after hydrothermal reaction; S4, placing the triple core-shell structure powder in a spark plasma sintering furnace to obtain the target material after sintering.

[0007] Further, the process of synthesizing barium titanate nanoparticles with tetragonal phase in step S1 is as follows: taking barium hydroxide and titanium dioxide as raw materials, dispersing them in 8-12 M KOH aqueous solution according to a Ba / Ti molar ratio of 1.05-1.10, and performing hydrothermal reaction at 200-220℃ for 18-24h, and then washing the reaction product with dilute acetic acid and deionized water and drying.

[0008] Further, the molar ratio of lithium, aluminum, titanium and phosphorus elements in the lithium aluminum titanium phosphate precursor in step S2 is Li:Al:Ti:P = 1.3:0.3:1.7:3.

[0009] Further, the heat treatment conditions in step S2 are as follows: heating to 600-700℃ at a heating rate of 3-10℃ / min in an inert atmosphere, and holding for 30-120min.

[0010] Further, the process of coating by a sol-gel method in step S2 is as follows: dispersing barium titanate nanoparticles in anhydrous ethanol, and under the combined action of stirring and ultrasonic, adding a precursor sol formed by dissolving lithium source, aluminum source, titanium source and phosphorus source in anhydrous ethanol dropwise.

[0011] Further, the molar ratio of lithium, germanium, molybdenum and zinc elements in the lithium germanium molybdenum zinc oxide precursor in step S3 is Li:Ge:Mo:Zn = 3:0.4:0.4:0.2.

[0012] Further, ascorbic acid is added as a reducing agent in the precursor solution in step S3.

[0013] Further, the hydrothermal reaction in step S3 is carried out under the conditions of a reaction temperature of 170-190 DEG C, a reaction time of 10-14 h, and a reaction solvent of a mixture of ethylene glycol and deionized water.

[0014] Further, the spark plasma sintering in step S4 is carried out under the conditions of a sintering temperature of 500-550 DEG C, an axial pressure of 100-120 MPa, and a holding time of 1-5 min.

[0015] Further, during the sintering temperature rising process, the pressure is applied when the temperature reaches 350-450 DEG C, and gradually rises to the target pressure, and the sintering temperature rising rate is 100-200 DEG C / min.

[0016] Further, the lithium source is selected from lithium nitrate, the aluminum source is selected from aluminum isopropoxide, the titanium source is selected from tetrabutyl titanate, and the phosphorus source is selected from triethyl phosphate.

[0017] Advantages of the present application: 1. The present application adopts a step-by-step wet chemical synthesis and a spark plasma sintering technology. A triple core-shell structure is constructed by sequentially constructing a ferroelectric barium titanate as an inner core, a fast ionic conductor lithium titanium aluminum phosphate as an intermediate layer, and a lithium germanium molybdenum zinc oxide as an outer shell. The spark plasma sintering process is carried out under low temperature, high pressure, and short time conditions, which suppresses the volatilization of lithium elements and the mutual diffusion of elements between the functional layers at high temperature, thereby ensuring the accuracy of the stoichiometric ratio of the target material, the purity of the phase, and the integrity of the nanoscale core-shell structure.

[0018] 2. The present application utilizes the spontaneous polarization effect of the inner core ferroelectric material to realize field enhancement of ion transmission. The strong local electrostatic field generated by the barium titanate core penetrates into the lithium titanium aluminum phosphate intermediate layer, effectively reducing the activation energy barrier of lithium ion migration in the interstitial gap, thereby significantly improving the migration rate of lithium ions.

[0019] 3. The outermost layer of lithium germanium molybdenum zinc oxide in the present application generates an in-situ nanocomposite interface layer containing metal nanocrystals and lithium ion conductors. The interface layer has good ion and electron mixed conduction properties, can homogenize the lithium ion flow at the interface, eliminate local current density concentration, thereby effectively suppressing the nucleation and growth of lithium dendrites, improving the safety and cycle life of the battery. In addition, the introduction of zinc component can further optimize the lithium deposition behavior by forming a lithium-zinc alloy phase, and endow the interface with excellent kinetic stability. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present application.

[0021] Embodiment 1 A preparation method of a lithium phosphate solid-state electrolyte target material for preparing a thin film lithium battery, comprising the following steps: S1, taking barium hydroxide (Ba(OH)2·8H2O) and titanium dioxide (TiO2) as raw materials, controlling the molar ratio of Ba to Ti to be 1:1.05, dispersing the above-mentioned raw materials in 8 M potassium hydroxide (KOH) aqueous solution, stirring for 30 min, transferring the mixed solution to a polytetrafluoroethylene-lined stainless steel hydrothermal reaction kettle, placing the reaction kettle in an oven, reacting at 200℃ for 24 h, after the reaction is completed, cooling to room temperature, washing the obtained product with 0.1 M dilute acetic acid and deionized water for 3 times, and drying in a vacuum drying oven at 80℃ for 12 h to obtain barium titanate nanoparticles in tetragonal phase; S2, dispersing the barium titanate nanoparticles prepared in S1 in anhydrous ethanol at a mass ratio of 1:50, ultrasonic dispersing at a rotation speed of 300 rpm and a power of 100 W, slowly dropping a precursor sol prepared from lithium nitrate, aluminum isopropoxide, tetrabutyl titanate and triethyl phosphate (molar ratio Li:Al:Ti:P=1.3:0.3:1.7:3) at a rate of 1 mL / min, continuing to stir for 2 h after the dropping is completed, and then drying at 50℃ for 12 h to obtain a precursor powder, heating the precursor powder to 600℃ at a rate of 3℃ / min under a nitrogen atmosphere, and heat treating for 120 min to obtain a core-shell powder; S3, dispersing the core-shell powder prepared in S2 in a mixed solvent of ethylene glycol and deionized water (volume ratio 2:1), adding lithium nitrate (LiNO3), germanium dioxide (GeO2), ammonium molybdate ((NH4)6Mo7O 24 ·4H2O) and zinc nitrate (Zn(NO3)2), controlling the molar ratio to be Li:Ge:Mo:Zn=3:0.4:0.4:0.2, and adding ascorbic acid at 1.0 times the total molar amount of germanium, molybdenum and zinc, and carrying out a hydrothermal reaction on the mixed solution, the reaction conditions being 170℃ and 14 h, after the reaction is completed, washing the product and vacuum drying at 70℃ to obtain a triple core-shell structure powder.

[0022] S4, the triple core-shell structure powder obtained in step S3 is subjected to spark plasma sintering, and the sintering process is as follows: the temperature is raised at a rate of 100 ℃ / min, when the temperature reaches 350 ℃, the pressure is started to be applied, and gradually increased to 100 MPa, and then kept at 500 ℃ and 100 MPa for 5 min, and then the target material is obtained after furnace cooling.

[0023] Example 2 A preparation method of a lithium phosphate solid-state electrolyte target material for preparing a thin film lithium battery, comprising the following steps: S1, barium hydroxide and titanium dioxide are weighed as raw materials, the molar ratio of Ba to Ti is controlled to be 1:1.08, the above raw materials are dispersed in a 10 M potassium hydroxide aqueous solution, stirred for 30 min, and then the mixed solution is transferred to a polytetrafluoroethylene-lined stainless steel hydrothermal reactor, the reactor is placed in an oven, and reacted at 210 ℃ for 21 h, after the reaction is completed, it is cooled to room temperature, the obtained product is washed with 0.1 M dilute acetic acid and deionized water for 3 times, and then dried in a vacuum drying box at 80 ℃ for 12 h to obtain barium titanate nanoparticles in tetragonal phase; S2, the barium titanate nanoparticles prepared in S1 are dispersed in anhydrous ethanol at a mass ratio of 1:50, ultrasonic dispersion is carried out at a rotation speed of 300 rpm and a power of 100 W, a precursor sol prepared from lithium nitrate, aluminum isopropoxide, tetrabutyl titanate and triethyl phosphate (molar ratio Li:Al:Ti:P=1.3:0.3:1.7:3) is slowly added dropwise at a rate of 1 mL / min, and then stirring is continued for 2 h after the dropwise addition is completed, and then dried at 50 ℃ for 12 h to obtain a precursor powder, and then the precursor powder is heated to 650 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and kept for 60 min for heat treatment to obtain a core-shell powder; S3, the core-shell powder prepared in S2 is dispersed in a mixed solvent of ethylene glycol and deionized water (volume ratio 2:1), lithium nitrate, germanium dioxide, ammonium molybdate and zinc nitrate are added, the molar ratio is controlled to be Li:Ge:Mo:Zn=3:0.4:0.4:0.2, and ascorbic acid is added at 1.0 times the total molar amount of germanium, molybdenum and zinc, and then the mixed solution is subjected to hydrothermal reaction, the reaction condition is 180 ℃, and the reaction is carried out for 12 h, after the reaction is completed, the product is washed and dried at 70 ℃ under vacuum to obtain a triple core-shell structure powder.

[0024] S4, the triple core-shell structure powder obtained in step S3 is subjected to spark plasma sintering, and the sintering process is as follows: the temperature is raised at a rate of 100 ℃ / min, when the temperature reaches 350 ℃, the pressure is started to be applied, and gradually increased to 100 MPa, and then kept at 500 ℃ and 100 MPa for 5 min, and then the target material is obtained after furnace cooling.

[0025] Example 3 A preparation method of a lithium phosphate solid electrolyte target material for preparing a thin film lithium battery, comprising the following steps: S1, taking barium hydroxide and titanium dioxide as raw materials, controlling the molar ratio of Ba to Ti to be 1:1.10, dispersing the above raw materials in a 12 M potassium hydroxide aqueous solution, stirring for 30 min, transferring the mixed solution to a polytetrafluoroethylene-lined stainless steel hydrothermal reaction kettle, placing the reaction kettle in an oven, reacting at 220℃ for 18h, after the reaction is completed, cooling to room temperature, washing the obtained product with 0.2 M dilute acetic acid and deionized water for 3 times, and drying in a vacuum drying box at 80℃ for 12h to obtain barium titanate nanoparticles in tetragonal phase.

[0026] S2, dispersing the barium titanate nanoparticles prepared in S1 in anhydrous ethanol at a mass ratio of 1:50, ultrasonic dispersing at a rotation speed of 300 rpm and a power of 100 W, slowly adding a precursor sol prepared from lithium nitrate, aluminum isopropoxide, tetrabutyl titanate and triethyl phosphate (molar ratio Li:Al:Ti:P=1.3:0.3:1.7:3) at a rate of 1 mL / min, continuing to stir for 2h after the addition is completed, and then drying at 50℃ for 12h to obtain a precursor powder, heating the precursor powder to 700℃ at a rate of 10℃ / min under a nitrogen atmosphere, and heat treating for 30min to obtain a core-shell powder; S3, dispersing the core-shell powder prepared in S2 in a mixed solvent of ethylene glycol and deionized water (volume ratio 2:1), adding lithium nitrate, germanium dioxide, ammonium molybdate and zinc nitrate, controlling the molar ratio to be Li:Ge:Mo:Zn=3:0.4:0.4:0.2, and adding ascorbic acid at 1.0 times the total molar amount of germanium, molybdenum and zinc, and carrying out a hydrothermal reaction on the mixed solution, the reaction conditions being 190℃ for 10h, and the product being washed and dried at 70℃ under vacuum to obtain a triple core-shell structure powder; S4, discharging the triple core-shell structure powder obtained in S3 to carry out spark plasma sintering, the sintering process being: heating at a rate of 200℃ / min, starting to apply pressure when the temperature reaches 450℃, and gradually increasing to 120 MPa, and heat treating at 550℃ and 120 MPa for 1min, and obtaining the target material after cooling in the furnace.

[0027] Comparative Example 1 A comparative preparation method of a lithium phosphate solid electrolyte target material for preparing a thin film lithium battery, comprising the following steps: S1, prepare barium titanate (BTO) nanoparticles, lithium aluminum titanium phosphate (LATP) powder and lithium germanium molybdenum zinc oxide (LGMZO) precursor powder respectively, the preparation method of BTO is the same as step S1 of embodiment 1, the LATP powder is synthesized by a solid phase method, lithium carbonate, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate are weighed according to the molar ratio of Li:Al:Ti:P=1.3:0.3:1.7:3, ball-milled and mixed, and then calcined at 800°C for 10h, and the LGMZO precursor is synthesized by a coprecipitation method: the corresponding nitrate is weighed according to the molar ratio of Li:Ge:Mo:Zn=3:0.4:0.4:0.2, dissolved in deionized water, and the pH is adjusted to 9 with ammonia water, and the precipitate is filtered, washed and dried to obtain; S2, weigh the three powders of BTO, LATP and LGMZO prepared in step S1 according to the same proportion as the theoretical stoichiometry of the final target material of embodiment 1, and place them in a planetary ball mill, with anhydrous ethanol as the medium, and ball mill for 12h; S3, the mixed powder after drying is loaded into a mold with a diameter of 2 inches, and cold-pressed into a green body under a pressure of 100MPa; S4, the green body is placed in a muffle furnace, heated to 900°C at a heating rate of 5°C / min in an air atmosphere, and sintered at atmospheric pressure for 10h, and then cooled in the furnace to obtain a comparative target material.

[0028] Comparative Example 2 A comparative preparation method for preparing a lithium phosphate solid-state electrolyte target material for a thin film lithium battery, comprising the following steps: S1, the preparation processes of steps S1, S2 and S3 of this comparative example are exactly the same as those of embodiment 2, and a composite powder with a triple core-shell structure is obtained; S2, the triple core-shell structure powder obtained in step S1 is loaded into a mold with a diameter of 2 inches, and cold-pressed into a green body under a pressure of 100MPa; S3, the green body is placed in a muffle furnace, heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and sintered at atmospheric pressure for 10h, and then cooled in the furnace to obtain a comparative target material.

[0029] Comparative Example 3 A comparative preparation method for preparing a lithium phosphate solid-state electrolyte target material for a thin film lithium battery, comprising the following steps: S1, the preparation processes of steps S1 and S2 of this comparative example are exactly the same as those of embodiment 3, and a core-shell powder is obtained; S2, the core-shell powder prepared in step S1 is subjected to spark plasma sintering, and the sintering process is as follows: the temperature is raised at a rate of 200 ℃ / min, when the temperature reaches 450 ℃, the pressure is started to be applied, and gradually increased to 120 MPa, and then kept at 550 ℃ and 120 MPa for 1 min, and then cooled in the furnace to obtain the comparative target material.

[0030] The target materials prepared in Examples 1-3 and Comparative Examples 1-3 are used to deposit solid electrolyte thin films on substrates covered with lithium metal current collectors, with a radio frequency power of 100 W, a target-substrate distance of 65 mm, and a deposition time of 2000 min. The thickness of all the thin films is ensured to be uniform, with a thickness of 1±0.02 μm. The battery assembly is performed in an argon glove box. The deposited electrolyte thin films are cut into circular pieces with a diameter of 16 mm using a microtome. On one side of the electrolyte thin film, a piece of lithium metal with a diameter of 15.8 mm and a thickness of 200 μm is placed using a precision point film machine, and another piece of the same lithium metal is placed on the other side of the thin film. The lithium metal is placed in a CR2032 type battery shell, and a pressure of 5-10 MPa is provided by a spring or a gasket, and then the battery is sealed using a battery sealing machine.

[0031] The assembled symmetric battery is placed in a thermostat at 25 ℃ for 2 h, and then connected to an electrochemical workstation or a battery test system, and the test program is set as follows: mode: constant current cycling; current density: 0.2 mA / cm 2 ; single cycle time: current reversal is performed once every 60 min. The cycling is continued until the battery voltage fluctuation exceeds ±2 V or the test time reaches 1000 h. The results are shown in Table 1: Table 1. Constant current cycling test results of lithium symmetric batteries (0.2 mA / cm 2 )

[0032] Note: >1000 h means that when the test is stopped at 1000 h, the battery has not short-circuited and the performance is stable.

[0033] Similarly, the asymmetric battery is assembled in a glove box, and the structure is: Li| electrolyte thin film| stainless steel. The lithium metal sheet is used as the counter electrode and the reference electrode, and the stainless steel sheet is used as the working electrode. After the battery is placed, it is connected to an electrochemical workstation. Linear sweep voltammetry is used, and the test parameters are set as follows: initial potential: open circuit potential; terminal potential: 6.0 V (vs. Li + / Li); scan rate: 1 mV / s. The voltage value corresponding to the current value starting to significantly increase, which exceeds 1 μA / cm 2 , is determined as the oxidation decomposition potential of the electrolyte. The results are shown in Table 2: Table 2. Test results of electrochemical stability window (linear sweep voltammetry)

[0034] LiCoO2(LCO) as the positive active material, mixed with conductive agent (acetylene black), binder (PVDF) at a mass ratio of 8:1:1, adjusted into slurry with N-methyl pyrrolidone as solvent, coated on aluminum foil, dried, rolled and cut into small round pieces. In the glove box, assemble the full battery, structure: LCO positive electrode | electrolyte film sputtered by each target material | metal lithium negative electrode, packaged into button cell.

[0035] After the battery is placed at 25°C, it is placed on the battery test system, and first activated at a small current of 0.1C (1C=140mA / g) for 3 cycles. The constant current charge-discharge cycle test is carried out at a rate of 1C, and the voltage range is set to 3.0-4.25V (vs. Li + / Li). Cycle until the capacity retention rate is less than 80% or the cycle number reaches 500. Record the charge-discharge specific capacity and coulombic efficiency of each cycle. The results are shown in Table 3: Table 3. Full battery long cycle performance test results (1C rate, 3.0-4.25V)

[0036] As can be seen from Table 1, the initial overpotential of Examples 1-3 is low (42-47mV), and the short-circuit time is greater than 1000h, and the overpotential at the end of the cycle is also low (55-62mV). It shows that the solid-state electrolyte film formed by the target material prepared in the example has excellent lithium ion conduction performance and good interface stability. Through the fine preparation process of multi-step hydrothermal reaction and discharge plasma sintering, the powder with triple core-shell structure is formed, which is beneficial to the rapid transmission of lithium ions, and at the same time reduces the growth of lithium dendrites, thereby improving the cycle stability of the battery and reducing the overpotential.

[0037] The initial overpotential of Comparative Example 1 is as high as 126mV, and the cycle to short-circuit time is only 29h. Since Comparative Example 1 uses solid phase method to synthesize LATP powder, co-precipitation method to synthesize LGMZO precursor, then simple ball milling and normal pressure sintering, the structure of the prepared target material is not uniform, the combination between components is not tight, there are many defects, which leads to the obstruction of lithium ion conduction, the growth of lithium dendrites, and the rapid deterioration of the battery performance.

[0038] The initial overpotential of Comparative Example 2 is 95mV, and the cycle to short-circuit time is 127h. Although the same steps as Example 2 are used to obtain a powder with a triple core-shell structure, cold pressing and normal pressure sintering are used in the subsequent process, compared with discharge plasma sintering of the example, it is difficult to achieve ideal densification during the sintering process, resulting in defects such as pores in the electrolyte film, uneven lithium ion transmission, increased risk of lithium dendrite growth, and affected the cycle performance of the battery.

[0039] The initial overpotential of Comparative Example 3 was 51 mV, and the time to short circuit was 283 h. Compared with Example 3, Comparative Example 3 lacked the subsequent hydrothermal reaction step in forming the triple core-shell structure, only obtained a core-shell powder, and the structure was relatively simple, which was less effective than the triple core-shell structure of Example 3 in lithium ion conduction and inhibition of lithium dendrite growth, and thus the battery performance was also poorer.

[0040] As can be seen from Table 2, the oxidative decomposition potentials of Examples 1-3 were relatively high (5.01-5.12 V vs. Li + / Li), and the electrochemical stability windows were relatively wide (~5.0-5.1 V). The target materials prepared in the examples had special chemical compositions and structures, and stable chemical bonds were formed between the elements, so that the electrolyte thin film was not prone to oxidative decomposition reaction at a high potential, thereby having good electrochemical stability.

[0041] The oxidative decomposition potential of Comparative Example 1 was only 4.35 V vs. Li + / Li, and the electrochemical stability window was relatively narrow (~4.3 V). The preparation method of Comparative Example 1 resulted in a non-uniform target material structure, and there were many impurities and defects, which were prone to oxidative decomposition reaction at a high potential, thereby reducing the electrochemical stability of the electrolyte.

[0042] The oxidative decomposition potential of Comparative Example 2 was 4.68 V vs. Li + / Li, and the electrochemical stability window was ~4.7 V. Although a triple core-shell structure powder was obtained in the early stage, the difference in the subsequent sintering process resulted in a lower density and structural integrity of the electrolyte thin film than that of the examples, so that the stability at a high potential was reduced.

[0043] The oxidative decomposition potential of Comparative Example 3 was 5.05 V vs. Li + / Li, and the electrochemical stability window was ~5.0 V. Compared with Example 3, the subsequent hydrothermal reaction step was lacking, and the difference in the structure made it slightly inferior to Example 3 in terms of electrochemical stability.

[0044] As can be seen from Table 3, the initial specific discharge capacity of Examples 1-3 was relatively high (150.5-154.8 mAh / g), the cycle life was greater than 500 times (the capacity retention rate was ≥80%), the capacity retention rate after 500 cycles was relatively high (82.3-86.8%), and the average coulombic efficiency was close to 99.9%. The solid-state electrolyte thin film formed by the target material prepared in the examples had excellent lithium ion conduction performance, good interface stability, and a relatively wide electrochemical stability window, which could ensure that the battery maintained a high charge and discharge specific capacity and coulombic efficiency during long-term cycling.

[0045] The initial discharge specific capacity of the comparative example 1 was only 118.6 mAh / g, the cycle life was only 135 times (capacity retention rate ≥80%), the capacity retention rate was reduced to 58.2% at 150 times, and the average coulombic efficiency was 98.60%. The target material preparation method of the comparative example 1 resulted in poor electrolyte film performance, blocked lithium ion conduction, poor interface stability, narrow electrochemical stability window, and rapid capacity decay of the battery during the cycle process.

[0046] The initial discharge specific capacity of the comparative example 2 was 139.7 mAh / g, the cycle life was 285 times (capacity retention rate ≥80%), the capacity retention rate was 71.5% at 300 times, and the average coulombic efficiency was 99.45%. Although the triple core-shell structure powder was obtained in the early stage, the subsequent sintering process was insufficient, which resulted in poorer electrolyte film performance than the examples, and affected the cycle performance of the battery.

[0047] The initial discharge specific capacity of the comparative example 3 was 148.9 mAh / g, the cycle life was 205 times (capacity retention rate ≥80%), the capacity retention rate was 73.8% at 220 times, and the average coulombic efficiency was 99.88%. Compared with example 3, the lack of subsequent hydrothermal reaction step resulted in poor performance in the full battery long cycle performance due to the structural difference.

[0048] In summary, the lithium phosphate solid-state electrolyte target material with a special structure was formed by the preparation process of examples 1-3, which showed excellent performance in lithium symmetric battery, electrochemical stability window and full battery long cycle performance test. Due to the insufficient preparation process of the comparative examples, the target material performance was poor, which affected the performance indicators of the battery, and improved the safety and cycle life of the battery.

[0049] In the description of the specification, the description of the terms "preparation example", "example”, “each example” and the like means that the specific features, structures, materials or characteristics described in conjunction with the example or preparation example are included in at least one example or preparation example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same example or preparation example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more examples or preparation examples in a suitable manner.

[0050] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent substitutions or changes to the technical solution and inventive concept of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for producing a lithium phosphate solid-state electrolyte target material for a thin-film lithium battery, characterized by, The method comprises the following steps: S1, synthesizing tetragonal barium titanate nanoparticles as an inner core by a hydrothermal method; S2, coating a lithium aluminum titanium phosphate precursor on the surface of the inner core by a sol-gel method, and forming a core-shell powder with an intermediate shell after heat treatment; S3, coating a lithium germanium molybdenum zinc oxide precursor on the surface of the core-shell powder by a hydrothermal method, and forming a triple core-shell structure powder after hydrothermal reaction; S4, placing the triple core-shell structure powder in a spark plasma sintering furnace to obtain a target material after sintering.

2. The production method according to claim 1, characterized by, In step S1, the process of synthesizing tetragonal barium titanate nanoparticles by a hydrothermal method is as follows: taking barium hydroxide and titanium dioxide as raw materials, dispersing them in a 8-12 M KOH aqueous solution according to a Ba / Ti molar ratio of 1.05-1.10, and performing hydrothermal reaction at 200-220℃ for 18-24h, and then washing the reaction product with dilute acetic acid and deionized water and drying.

3. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of lithium, aluminum, titanium and phosphorus in the lithium aluminum titanium phosphate precursor is Li:Al:Ti:P=1.3:0.3:1.7:3; The heat treatment conditions are as follows: heating to 600-700℃ at a heating rate of 3-10℃ / min in an inert atmosphere, and maintaining the temperature for 30-120min.

4. The method of claim 1, wherein, In step S2, the process of coating by a sol-gel method is as follows: dispersing the barium titanate nanoparticles in anhydrous ethanol, and adding a precursor sol formed by dissolving lithium source, aluminum source, titanium source and phosphorus source in anhydrous ethanol dropwise under the joint action of stirring and ultrasonic.

5. The preparation method according to claim 1, characterized in that, In step S3, the molar ratio of lithium, germanium, molybdenum and zinc in the lithium germanium molybdenum zinc oxide precursor is Li:Ge:Mo:Zn = 3:0.4:0.4:0.2; Ascorbic acid is added as a reducing agent in the precursor solution.

6. The method of claim 1, wherein, In step S3, the hydrothermal reaction conditions are as follows: a reaction temperature of 170-190℃, a reaction time of 10-14h, and a mixed solvent of ethylene glycol and deionized water as the reaction solvent.

7. The preparation method according to claim 1, characterized in that, In step S4, the spark plasma sintering conditions are as follows: a sintering temperature of 500-550℃, an axial pressure of 100-120 MPa, and a holding time of 1-5min.

8. The production method according to claim 1 or 7, characterized by, During the sintering heating process, the pressure is applied when the temperature reaches 350-450℃, and the heating rate of sintering is 100-200℃ / min.

9. The preparation method according to claim 4, characterized in that, The lithium source is selected from lithium nitrate, the aluminum source is selected from aluminum isopropoxide, the titanium source is selected from tetrabutyl titanate, and the phosphorus source is selected from triethyl phosphate.

10. A phosphoric acid lithium solid-state electrolyte target material for preparing a thin film lithium battery, which is prepared by the preparation method of any one of claims 1-9.

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