Application of lithium-rich lithium titanium phosphate in solid-state lithium metal battery and preparation method thereof

Abstract

This invention belongs to the field of all-solid-state lithium metal batteries, and discloses the application of a lithium-rich titanium phosphate lithium solid electrolyte in batteries and its preparation method. The chemical formula of the lithium-rich titanium phosphate lithium solid electrolyte is [chemical formula missing]. Studies have found that this solid electrolyte has a bulk room-temperature ionic conductivity exceeding [specific value missing] and exhibits good stability to lithium metal. Furthermore, a solid-state lithium metal battery assembled with a lithium iron phosphate cathode achieved a discharge specific capacity of [specific value missing] at 0.1C, and after 100 cycles at 0.2C, the capacity retention rate still reached over 92%. The lithium-rich titanium phosphate lithium solid electrolyte of this invention is not only low-cost, simple to prepare, and environmentally friendly, but also has high ionic conductivity and good stability to lithium metal, overcoming the shortcomings of NASICON-type solid electrolytes in terms of instability to lithium metal, and has great application prospects in the field of solid-state lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state lithium metal battery technology, and specifically relates to the application of lithium-rich titanium titanium phosphate in solid-state lithium metal batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density and long cycle life, have become the core power source for portable electronic devices, new energy vehicles, and smart grid energy storage systems. However, the liquid electrolytes used in traditional lithium-ion batteries (such as combinations of carbonate solvents and LiPF6 salts) have inherent safety hazards: the electrolyte is prone to volatility and leakage, and may cause thermal runaway under high temperature or overcharge conditions, leading to battery fire or even explosion. This problem seriously restricts the further application of lithium-ion batteries in high-end energy storage and electric vehicles.

[0003] Developing inherently safe solid-state electrolytes and assembling all-solid-state batteries is considered a core approach to fundamentally addressing the safety hazards of liquid electrolytes. Solid-state electrolytes not only possess leak-proof and non-flammable properties, but their high mechanical strength can also effectively suppress the growth of lithium dendrites on the surface of the lithium metal anode—lithium dendrite penetration is a key cause of short-circuit failure in traditional lithium batteries. Therefore, the combination of solid-state electrolytes and lithium metal anodes holds promise for constructing solid-state lithium metal batteries with energy densities exceeding 400 Wh / kg, far surpassing the performance ceiling of current commercial lithium-ion batteries (200-300 Wh / kg).

[0004] Solid electrolytes can be classified into three categories based on their chemical composition: inorganic solid electrolytes, organic solid electrolytes (such as polyethylene oxide (PEO)-based polymers), and organic-inorganic composite solid electrolytes. Among these, while organic solid electrolytes possess good flexibility and processability, their room temperature ionic conductivity is only [insert value here]. Furthermore, inorganic solid electrolytes have low mechanical strength, making it difficult to effectively prevent lithium dendrite growth. While composite solid electrolytes, by dispersing inorganic fillers in an organic matrix, can improve ionic conductivity and mechanical properties to some extent, they still suffer from poor interfacial compatibility and insufficient long-term cycle stability. In contrast, inorganic solid electrolytes possess higher ionic conductivity (some systems can reach [a certain level]). Excellent mechanical strength (Young's modulus typically >10 GPa) and wide electrochemical stability window ( ( ), has become a research hotspot in the field of solid electrolytes.

[0005] Among numerous inorganic solid electrolytes, NASICON (Sodium Super Ionic Conductor) type compounds, due to their three-dimensional open framework structure (space group R-3c), are suitable for Li... + Its rapid transmission provides a continuous channel, attracting significant attention from both academia and industry. A typical example is... (LTP) not only possesses the aforementioned structural advantages, but also features low raw material costs (high abundance of Ti and P elements in the Earth's crust), stability to water and air (no need for inert gas protection processing), and a wide electrochemical stability window. It has outstanding advantages such as... For example, Toyota Motor Corporation of Japan pointed out in a patent (WO2017165251A1) published in 2017 that LTP-based electrolytes can be used for battery assembly in air, which significantly reduces the production cost of all-solid-state batteries.

[0006] However, the room temperature ionic conductivity of pure-phase LTP is only... This is far from meeting the actual battery application requirements (≥ Its core bottleneck lies in the carriers ( The concentration is relatively low. To address this issue, researchers have developed a low-valence element doping modification strategy: partially replacing the low-valence cations with low-valence cations of similar radius. To maintain the material's electrical neutrality, additional [materials] will be introduced into the crystal lattice. This increases carrier concentration and ion mobility. Doping is the most representative modification method—the Goodenough team reported it for the first time. (LATP) series derivatives, when x=0.3, have a room temperature ionic conductivity that can reach This meets the threshold for practical application. Further research is needed. , Equal doping systems have also been developed, but LATP remains the mainstream research subject for NASICON-type electrolytes due to its superior overall performance.

[0007] Despite significant breakthroughs in ionic conductivity and other aspects of LTP and its derivatives (such as LATP), their application in lithium metal solid-state batteries still faces a key bottleneck—namely, the composition of LTP. Easily reduced by lithium metal This leads to a sharp increase in interfacial impedance, continuous electrolyte consumption, and eventual failure. To mitigate this problem, the industry typically adds an interfacial layer (an inorganic layer, such as ZnO, or an organic layer, such as PEO) to improve the interfacial instability between LTP or LATP and lithium metal. Currently, no NASICON-type solid electrolyte stable with lithium metal has been found. All reported LTP-based derivatives (including Al, Mg, and Zn doped systems) exhibit this instability. The problem of easy restoration.

[0008] Therefore, developing NASICON-type solid electrolytes that combine high ionic conductivity with stability to lithium metal is a key technological gap that will drive the practical application of all-solid-state lithium metal batteries, and has significant academic and industrial value. Summary of the Invention

[0009] Based on the above reasons, and addressing the problems or defects existing in the prior art, the present invention aims to provide an application of lithium-rich titanium phosphate lithium solid electrolyte in solid lithium metal batteries and its preparation method, solving or at least partially solving the problem of instability of existing NASICON materials with lithium metal: the lithium-rich titanium phosphate lithium material of the present invention has a high carrier concentration and exhibits ultra-high bulk room temperature ionic conductivity (> Furthermore, in the lithium-rich titanium lithium phosphate material of the present invention... It contains more than 85% of the total Ti content and has excellent stability to lithium metal.

[0010] To achieve the first objective of this invention, the technical solution adopted by this invention is as follows:

[0011] The application of the lithium-rich titanium phosphate lithium solid electrolyte of the present invention in solid-state lithium metal batteries, wherein the molecular formula of the lithium-rich titanium phosphate lithium is: .

[0012] Specifically, the It belongs to the orthorhombic crystal system, space group Pbcn.

[0013] Specifically, the Li 2.72 The XRD data of Ti2(PO4)3 crystal are as follows: angles are 20.7°, 23.1°, 24.5°, 27.5°, 29.2°, 33.6°, 36.4°, 47.8°, and 56.8°.

[0014] Specifically, the At the microscopic level, the particles have a particle morphology, and the particle size distribution is as follows: , , .

[0015] Specifically, the It appears as a black powder.

[0016] A second object of the present invention is to provide the above-described The preparation method includes the following steps:

[0017] After accurately weighing Li, Ti, and P sources by molar ratio, the samples were wet ball-milled. The milled powder was then dried and calcined. The calcined sample was then wet ball-milled again to obtain a finer powder. Powder; the finely ground powder is compressed and sintered to obtain the powder. Solid electrolyte sheet.

[0018] Preferably, the above-mentioned Li source can be , , One or more of them.

[0019] Preferably, the above-mentioned Ti source can be , , One or more of them.

[0020] Preferably, the above-mentioned P source can be , , One or more of them.

[0021] The molar ratio of Li source, Ti source and P source is (2.8~3.2):2:3, preferably 3:2:3.

[0022] Preferably, the solvent used in the above wet ball milling is anhydrous ethanol or isopropanol.

[0023] Preferably, the calcination and sintering temperatures are 700-900°C. o C, heating rate is 5 o The temperature is C / min, and the holding time is 8-12h.

[0024] Preferably, the calcination and sintering atmosphere consists of 5% (v / v) hydrogen and 95% (v / v) argon.

[0025] Preferably, the pressure in the above-mentioned tablet compression is 600-1000 MPa.

[0026] A third object of the present invention is to provide the aforementioned Li 2.72 Application of Ti2(PO4)3 in solid-state lithium metal batteries, wherein the solid-state lithium metal battery uses lithium metal as the negative electrode, and Li 2.72 Ti2(PO4)3 solid electrolyte sheet is a solid electrolyte, and lithium iron phosphate is the positive electrode composed of active materials.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention provides a novel lithium-rich titanium phosphate lithium solid electrolyte, its preparation method, and its application in lithium metal batteries. The invention provides… Solid electrolytes have the following advantages: 1) More than The invention exhibits excellent bulk room-temperature ionic conductivity, making it highly promising for applications. Furthermore, it demonstrates good stability against lithium metal; in static tests, the interfacial impedance remains unchanged for 7 days, and in dynamic tests, it maintains stable cycling for over 200 hours. Moreover, the preparation process is simple, low-cost, and highly reproducible, possessing potential practical value. This invention is of great significance for the development of lithium-metal-stable NASICON materials and can be extended to the development of other solid-state electrolyte materials for alkali metal batteries. Attached Figure Description

[0029] Figure 1 It is the calcined product obtained in Example 1 of this invention. X-ray diffraction pattern and scanning electron microscope image of the powder;

[0030] a—X-ray diffraction pattern, b—Scanning electron microscope image.

[0031] Figure 2 The sintered product obtained in Example 2 of this invention X-ray diffraction pattern and scanning electron microscope image of solid electrolyte sheet;

[0032] a—X-ray diffraction pattern, b—Scanning electron microscope image.

[0033] Figure 3 This is the result obtained in Embodiment 2 of the present invention. AC impedance spectrum and calculated activation energy diagram of solid electrolyte sheet;

[0034] a—AC impedance spectrum, b—activation energy spectrum.

[0035] Figure 4 This is the result obtained in Embodiment 2 of the present invention. Interfacial impedance diagram and cycling diagram of lithium symmetric battery assembled with solid electrolyte sheet as a function of time.

[0036] a—Interface impedance diagram, b—Circulation diagram.

[0037] Figure 5 This is the result obtained in Embodiment 3 of the present invention. Rate performance diagram, charge-discharge curve diagram, and cycle diagram of lithium metal battery assembled with solid electrolyte sheet;

[0038] a—Rate performance graph, b—Chart and discharge curve graph, c—Cycling graph.

[0039] Figure 6 These are the X-ray diffraction pattern and AC impedance pattern of the solid electrolyte obtained in Example 4 of this invention;

[0040] a—X-ray diffraction pattern, b—AC impedance pattern.

[0041] Figure 7 These are the X-ray diffraction pattern and AC impedance pattern of the solid electrolyte obtained in Example 5 of this invention;

[0042] a—X-ray diffraction pattern, b—AC impedance pattern. Detailed Implementation

[0043] The novel lithium-rich NASICON solid electrolyte synthesized in this invention It has an extremely high bulk room temperature ionic conductivity (> It exhibits excellent lithium stability (no significant increase in interface impedance in static lithium symmetric batteries, and stable cycling exceeding 200 hours in dynamic lithium symmetric batteries). This invention synthesizes [the product] using low-cost lithium, titanium, and phosphorus sources through a simple ball milling and calcination process. Solid electrolyte powder was further prepared by a pre-pressing and sintering process. Solid-state electrolyte sheets, when assembled into solid-state lithium metal batteries, exhibit excellent rate performance and cycle performance. The invention mentioned... Solid electrolytes not only have the advantages of low cost and environmental friendliness, but also exhibit excellent performance, making them highly promising for application in solid-state lithium metal batteries.

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] The method for calculating the ionic conductivity (σ) involved in the following embodiments of the present invention is as follows:

[0046] (Formula 1);

[0047] The parameters are defined as follows: L represents the thickness of the electrolyte sheet (cm), which needs to be measured at multiple points using a micrometer and the average value taken; S represents the effective area of ​​the electrolyte sheet (cm). R represents the resistance obtained from the fitting ( ).

[0048] The activation energy involved in the following embodiments of the present invention ( ) is calculated using the Arrhenius formula:

[0049] (Formula 2);

[0050] The parameters are defined as follows: A is the exponential factor, T is the absolute temperature (K), and k is the exponential factor. B It is the Boltzmann constant.

[0051] Example 1

[0052] This embodiment Solid electrolyte powder is prepared by ball milling and mixing raw materials followed by calcination. The specific preparation method is as follows:

[0053] (1) Mass ratio Accurate weighing , , Add 5mm diameter zirconia grinding balls to a 50mL stainless steel ball milling jar at a ball-to-material ratio of 5:1. Add isopropanol to the ball milling jar at a solution-to-raw material ratio of 1.5:1. Finally, add the accurately weighed raw material, seal the jar, and place it on a high-energy ball mill at a speed of 1200rpm for 120min. The working mode is 30min of grinding followed by 15min of rest.

[0054] (2) After ball milling, pour out the white slurry and place it in an 80℃ forced-air drying oven to dry;

[0055] (3) Spread the dried powder evenly in the tableting mold, apply pressure of 100 MPa, and hold for 1 min to obtain the precursor embryo;

[0056] (4) The precursor preform was placed in a tube furnace and calcined. The temperature was increased to 800°C at a rate of 5°C / min and held for 8 hours. Then it was naturally cooled to room temperature. The calcination atmosphere consisted of 5% (v / v) hydrogen and 95% (v / v) argon.

[0057] (5) The sample obtained above is prepared again by wet milling with a high-energy ball mill. Solid electrolyte powder, ball-to-powder ratio of 5:1, isopropanol:raw material = 1.5:1, ball milling speed of 1200 rpm, ball milling time of 120 min, working mode of 30 min ball milling, 15 min rest.

[0058] The black product prepared in Example 1 was subjected to phase analysis and morphological characterization. Figure 1 It is the result of Example 1 X-ray diffraction pattern and scanning electron microscope image of the powder. Figure 1 As can be seen from a, the positions of the diffraction peaks of the synthesized material are related to... The standard spectrum matches, meaning the synthesized material is However, for Example 1 and A comparison of the unit cell parameters of the standard cards revealed that the unit cell of Example 1 is smaller, as shown in Table 1. The smaller unit cell makes... The initial state energy is higher, resulting in a lower migration energy barrier, thus allowing ions to migrate faster. Figure 1 b is the result obtained in Example 1. Scanning electron microscope image of powder. (From...) Figure 1 As can be seen from b, the microstructure of its powder is a micro-nano-scale particle morphology.

[0059]

[0060] Example 2

[0061] This embodiment Solid electrolyte sheets are prepared by sintering, including the following steps:

[0062] (1) Weighing Example 1 Approximately 0.5g of solid electrolyte powder was spread evenly in a tableting mold, pressurized at 800MPa, held for 2 minutes, and then removed from the mold.

[0063] (2) The above The solid electrolyte preform was placed in a tube furnace for sintering, heated to 800°C at a rate of 5°C / min, held for 12 hours, and then cooled naturally to room temperature. The sintering atmosphere consisted of 5% (v / v) hydrogen and 95% (v / v) argon.

[0064] (3) The above The solid electrolyte sheet was polished with 320-grit, 1000-grit, 2000-grit, and 8000-grit sandpaper until its surface was smooth.

[0065] The black sample prepared in Example 2 Phase analysis and morphological structure characterization of solid electrolyte sheets were performed. Figure 2 It is obtained from Example 2 X-ray diffraction pattern and scanning electron microscope image of the solid electrolyte sheet. Figure 2 From a, we can see that the diffraction peak positions of the solid electrolyte sheet are related to... The standard spectrum matches, meaning the electrolyte tablet is... . Figure 2 b is the result obtained in Example 2. Scanning electron microscope image of the electrolyte sheet. (By...) Figure 2 b indicates that its surface is smooth and dense.

[0066] The results obtained in Example 2 Solid electrolyte sheet with conductive silver paste on the surface After drying, excess conductive silver paste on the sides of the blocked battery was polished off. The AC impedance of the blocked battery was tested at different temperatures using an Autolab electrochemical workstation. Test conditions: room temperature (25℃), test frequency 2MHz-0.1Hz, amplitude 50mV. Figure 3 It is obtained from Example 2 AC impedance spectroscopy and activation energy diagram of solid electrolyte sheet at room temperature. The bulk room-temperature ionic conductivity of the solid electrolyte is calculated according to formula (I), where: in formula (I), L = 0.115 cm and S = 1.52 cm. 2 ,Depend on Figure 3 From a, we can know that , , The bulk room temperature ionic conductivity of solid electrolytes is It surpasses most existing NASICON solid electrolytes; the overall ionic conductivity also reaches [a certain level]. It has great application potential. Calculated according to equation (II), The activation energy of solid electrolytes is ,like Figure 3 As shown in b.

[0067] The result obtained in Example 2 Solid electrolyte sheets and lithium metal form a solid-state lithium symmetric battery. Figure 4 a is The graph shows the change in interfacial impedance of a lithium-ion symmetric battery over time, measured by autolab. As can be seen from the graph, After being left to stand in air for up to 7 days, the interfacial impedance of the solid electrolyte sheet remained essentially unchanged, indicating its excellent stability to lithium metal. Figure 4 b is the cycling graph of a lithium-ion symmetric battery on the LAND CT2001 battery testing system, with test parameters at 40°C. , As can be seen from the figure, During a 200-hour cycling process, the lithium-symmetric battery with solid electrolyte did not experience a short circuit, except for a slight increase in polarization voltage, indicating that... Solid electrolytes can induce stable deposition / stripping of lithium ions on lithium metal surfaces.

[0068] Example 3

[0069] This embodiment demonstrates Solid-state lithium metal batteries are prepared using solid electrolyte sheets as the electrolyte.

[0070] First, dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 5% adhesive solution; then weigh out the required amount according to the specified ratio. , After being mixed evenly with the adhesive, a slurry is obtained, wherein: the slurry contains... , The mass ratio of PVDF to PVDF is 8:1:1; the slurry is then uniformly coated onto carbon-coated aluminum foil to prepare the positive electrode, and the process is controlled... The load capacity is The negative electrode shell, lithium metal sheet, and so on are sequentially placed. Solid electrolyte sheet, positive electrode sheet, spacer, spring sheet, and positive electrode shell are stacked and pressurized to assemble a 2032 coin cell. During assembly, 10 μL of commercial electrolyte is dropped between the solid electrolyte sheet and the positive electrode sheet. (To wet the interface.)

[0071] The lithium metal battery of Example 3 was tested for rate performance and cycle performance on a LAND CT2001 battery testing system. Rate performance test conditions: 25°C, 2.6-3.8V; Rate performance test method: sequentially charged and discharged at 0.1C, 0.2C, 0.5C, 1C, 2C, and finally back to 0.1C, cycling 5 times at each rate. Cycling performance test conditions: 25°C, 2.6-3.8V; Test method: 100 cycles at 0.2C. Figure 5 This shows the rate performance of lithium metal batteries at room temperature, along with charge-discharge curves and cycle charts at different rates. Figure 5 a, Solid-state batteries exhibit approximately [performance] at 0.1C. The specific capacity exhibited at 0.2C, 0.5C, 1C, and 2C are respectively , , , The capacity retention rate is 73% at 1C and 52% at 2C. Upon returning to 0.1C, it recovers to its initial specific capacity. The lower capacity retention rate at high rates may stem from a larger interfacial impedance between the electrolyte and the electrodes. Figure 5 As can be seen from b, this solid-state battery exhibits a stable charge and discharge platform. From Figure 5 As can be seen from c, the solid-state battery exhibits stable cycling performance, with a capacity retention of 92% after 100 cycles.

[0072] Example 4

[0073] This embodiment Solid electrolyte powder is prepared by ball milling and mixing raw materials followed by calcination. The preparation steps are basically the same as in Example 1. The only difference between Example 4 and Example 1 is that the Li source is... Ti source is P source is The solvent was anhydrous ethanol, and the molar ratio of Li:Ti:P was 2.8:2:3. The X-ray diffraction pattern and AC impedance spectroscopy of the final powder are shown below. Figure 6 As shown. By Figure 6 As can be seen from a, compared to Example 1, Example 4 exhibits additional diffraction peaks, indicating the presence of impurities in Example 4. Figure 6 b shows that the ionic conductivity of Example 4 is lower than that of Example 1, which is due to the presence of impurities.

[0074] Example 5

[0075] This embodiment Solid electrolyte powder is prepared by ball milling and mixing raw materials followed by calcination. The preparation steps are basically the same as in Example 1. The only difference between Example 5 and Example 1 is that the Li source is... Ti source is P source is , molar ratio = The final X-ray diffraction pattern and AC impedance spectrum of the powder are as follows: Figure 7 As shown. By Figure 7 As can be seen from a, the diffraction peaks of Example 5 are almost identical to those of Example 1, indicating that the phase composition of Example 5 is the same as that of Example 1. Figure 7 b indicates that the ionic conductivity of Example 5 is lower than that of Example 1. This may be because the additional lithium insertion causes the crystal structure to partially collapse, resulting in a lower ionic conductivity.

[0076] As can be seen from Examples 1, 4, and 5, molar ratio = All can be generated But only when molar ratio = When obtained The highest ionic conductivity is likely due to the generation of impurities when the Li content is low, which affects the ionic conductivity; while when the Li content is high, the additional lithium insertion causes the crystal structure to partially collapse, ultimately resulting in lower ionic conductivity.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An application of lithium-rich titanium titanium phosphate in solid-state lithium metal batteries, characterized in that: The lithium-rich titanium titanium phosphate is used as a solid electrolyte in solid-state lithium metal batteries, and its molecular formula is [missing information]. .

2. The application as described in claim 1, characterized in that: The aforementioned It is an orthorhombic crystal system, space group Pbcn.

3. The application as described in claim 2, characterized in that: The aforementioned The XRD data of the crystal are as follows: angles are 20.7°, 23.1°, 24.5°, 27.5°, 29.2°, 33.6°, 36.4°, 47.8°, and 56.8°.

4. The application as described in claim 1, characterized in that: The aforementioned Microscopically, it has a granular morphology, D 50 =400nm, D 90 =530nm, D 100 =610nm.

5. A method for preparing a lithium-rich lithium titanium phosphate solid electrolyte as described in any one of claims 1-4, characterized in that: The preparation method comprises the following steps: After weighing the Li, Ti, and P sources, wet ball milling was performed. The milled powder was dried and then calcined. The calcined sample was then wet ball milled again to refine the powder. Powder; obtained by pressing and sintering finely ground powder. Solid electrolyte.

6. The preparation method according to claim 5, characterized in that: The Li, Ti, and P sources were weighed at a molar ratio of Li:Ti:P = (2.8~3.2):2:

3.

7. The preparation method according to claim 5, characterized in that: The Li source is one or more of LiNO3, CH3COOLi, and Li2CO3; the Ti source is one or more of Ti2O3, TiO2, and Ti3O5; and the P source is one or more of (NH4)3PO4, (NH4)2HPO4, and NH4H2PO4.

8. The preparation method according to claim 5, characterized in that: The solvent used in wet ball milling is anhydrous ethanol or isopropanol.

9. The preparation method according to claim 5, characterized in that: The calcination and sintering temperature is 700-900℃, the heating rate is 5℃ / min, and the holding time is 8-12h; the calcination and sintering atmosphere consists of 5% (v / v) hydrogen and 95% (v / v) argon.

10. The preparation method according to claim 5, characterized in that: The pressure during tablet compression is 600-1000 MPa.

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