A method for modifying an all-solid-state lithium battery electronic barrier and lithiumophilic interface

Abstract

The present application relates to a kind of solid electrolyte, preparation method and all-solid-state lithium battery, belong to all-solid-state lithium battery technical field.The present application provides a brand-new anhydrous polyphosphoric acid induced double strategy, establishes a layer (~30nm) intermediate layer on LLZTO, the intermediate layer has the dual role of lithiumophilic and electron blocking.Compared with the method that has been reported to remove Li2CO3 by treating garnet SSEs with aqueous acid solution, anhydrous PPA can remove surface impurities without damaging garnet SSEs.At the same time, the generated lithium polyphosphate intermediate layer contains lithiumophilic OH-groups remaining from PPA, which can promote the uniform diffusion of molten Li on the surface of LLZTO pellets and provide a protective barrier to inhibit Li dendrite penetration.

Description

Technical Field

[0001] This invention relates to a solid electrolyte, its preparation method, and an all-solid-state lithium battery, belonging to the field of all-solid-state lithium battery technology. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, existing lithium-ion batteries are unable to meet the ever-increasing demands for energy density, cycle life, and safety. Replacing flammable and toxic liquid electrolytes with inorganic solid-state electrolytes (SSEs) is an ideal solution. To date, a comprehensive exploration has been conducted on SSEs, including garnet, NASICON, sulfides, and perovskites. Among these, garnet SSEs, such as Li... 6.4 La3Zr 1.4 Ta 0.6 O 12 and Li 6.5 L a3 Zr 1.5 Nb 0.5 O 12 Due to its good chemical stability with lithium metal, wide electrochemical window, and high lithium-ion conductivity (up to 1 mS / cm), it is suitable for use in lithium metal applications. -1 It is expected to become one of the candidate materials for the next generation of high-safety solid-state lithium battery electrolytes.

[0003] Although garnet SSEs have significant advantages, two major problems still need to be solved before the practical application of garnet-based solid-state lithium metal batteries (GSSBs): (1) The lithium-phobic Li2CO3 passivation layer makes the contact between garnet SSEs and metallic Li poor, resulting in an interface resistance as high as hundreds of Ωcm. 2 When garnet SSEs are exposed to air, H + / Li + The transformation occurs to form LiOH, which then captures CO2 from the atmosphere, generating Li2CO3 on the surface of garnet SSEs. (2) During the exfoliation-deposition process, the formation and propagation of lithium dendrites induced by electron attack in garnet leads to rapid short circuits in SSEs. Recent studies have shown that Li|garnet interface Li + The reason for the uneven flux distribution is Li + It tends to accumulate in defects and voids, and grows Li dendrites when it encounters electrons.

[0004] To address these two major challenges, the academic community has made numerous efforts. To overcome the first difficulty, many methods have been developed to reduce the interfacial impedance between garnet SSE and lithium metal, such as inorganic surface coatings (ZnO, Al2O3, BN, Cu3N, SnN). xThe treatment methods include pretreatment with inorganic surface coatings (LiF, Ge, Sb, Mg, C, Au, and Ag), molten lithium (Li@50% graphite, Li@50%-Na, Li@33% Zn, Li@30%-Sn, Li@1%-Si3N4), pretreatment in acidic aqueous solutions (HCl, H3BO3, H3PO4, citric acid), and heat treatment at temperatures >700°C. While inorganic surface coatings or molten lithium can promote solid-solid contact between garnet SSEs and lithium metal, a harmful lithium-ion insulating Li2CO3 passivation layer remains. For heat treatment or acidic aqueous solution treatment of garnet SSEs to remove Li2CO3, the heat treatment process often results in the loss of Li from the garnet, while acidic aqueous solution treatment is detrimental to water-sensitive garnet SSEs. Furthermore, the above strategies have limitations regarding electron attack / leakage. How to address the second challenge—the rapid short circuits in GSSBs caused by lithium dendrites—remains an unresolved issue. In this regard, garnet SSEs with rationally designed organic surface coatings, such as PEO, PVDF, PAA, and PDMS, are frequently used. Compared to inorganic coatings, these organic coatings can form an electronically barrier interface between the garnet SSE and lithium metal; however, at room temperature, the ionic conductivity of organic coatings is poor. Furthermore, achieving nanoscale thicknesses of organic coatings is difficult. Therefore, to ensure the successful development of GSSBs, further efforts are needed to explore promising Li|garnet interface solutions. Summary of the Invention

[0005] This invention provides a novel anhydrous polyphosphoric acid (PPA)-induced dual strategy in garnet Li 6.4 La3Zr 1.4 Ta 0.6 O 12 A ~30 nm intermediate layer was formed on LLZTO, which has both lithiophilic and electron-barrier properties. Compared with the previously reported method of removing Li₂CO₃ by treating garnet SSEs with aqueous acid, anhydrous PPA can remove surface impurities without damaging the garnet SSEs. Meanwhile, the generated lithium polyphosphate intermediate layer (Li-PPA) contains residual lithiophilic OH- groups from PPA, which can promote the uniform diffusion of molten Li on the LLZTO surface and provide a protective barrier to inhibit Li dendrite penetration. The results show that the Li|garnet interface impedance modified by Li-PPA is low, approximately 4 Ωcm. 2 Li-PPA modified LLZTO Li‖Li symmetric cells at 0.2 and 0.5 mA cm⁻¹ -2Under suitable conditions, it can cycle stably, and even after 2500 hours of continuous stripping-deposition, no Li dendrite penetration into LLZTO or a significant increase in interfacial impedance was observed. The Li-PPA modified LLZTO electrolyte sheet exhibits excellent compatibility with the LiFePO4 cathode, cycling for over 500 cycles. It also shows promising applications in solar energy systems, demonstrating the practical feasibility of GSSBs.

[0006] The technical solution is:

[0007] A solid electrolyte for use in an all-solid-state lithium battery includes a solid electrolyte sheet and a polymeric material having the following structure loaded on at least one side of the electrolyte sheet:

[0008]

[0009] The solid electrolyte sheet is made of tantalum-doped lithium lanthanum zirconium oxide (LLZTO).

[0010] The above-mentioned method for preparing solid electrolytes includes the following steps:

[0011] This causes Li2CO3 to form on the surface of the solid electrolyte sheet;

[0012] The solid electrolyte sheet is placed in a solvent containing polyphosphoric acid for reaction.

[0013] The polyphosphoric acid has undergone dehydration treatment.

[0014] The aforementioned dehydration treatment refers to... Molecular sieve water removal treatment.

[0015] The polyphosphoric acid has a concentration of 5-20 wt% in the solvent, which is an alcohol solvent.

[0016] The reaction time is 0.1-10 min.

[0017] The formation of Li2CO3 on the surface of the solid electrolyte sheet is achieved by reacting LLZTO with air.

[0018] The Li2CO3 has a thickness of 0.1-5 μm.

[0019] An all-solid-state lithium battery, wherein the assembly structure of the negative electrode and electrolyte layer includes bonded Li and electrolyte sheets, and a polymeric material as shown below is contained between the interface of the Li and electrolyte sheets:

[0020]

[0021] The above-mentioned method for manufacturing all-solid-state lithium batteries includes the following steps:

[0022] The solid electrolyte described above is brought into contact with molten Li to cause a surface reaction.

[0023] A method for eliminating the Li2CO3 layer on the surface of LLZTO electrolyte in an all-solid-state lithium battery and improving battery performance includes the following steps: treating the surface of the LLZTO electrolyte with anhydrous polyphosphoric acid and then reacting it with molten Li.

[0024] The battery performance characteristics include: ionic conductivity, electron blocking effect, impedance, and cycle stability.

[0025] Beneficial effects

[0026] A lithium-loving electron-barrier interlayer for GSSBs was prepared by a one-step chemical process. This interlayer was formed in situ on a garnet-type LLZTO electrolytic cell via a simple and rapid reaction between anhydrous polyphosphoric acid (PPA) and surface impurities.

[0027] Considering that acidic "aqueous solution" treatment is detrimental to water-sensitive garnet electrolytes, an "anhydrous" PPA is proposed for the first time here. It has at least three advantages in GSSBs: (1) Anhydrous PPA can quickly (within 2 minutes) remove surface contaminants without damaging LLZTO. Even when the PPA treatment time is extended to 30 minutes, no LiOH peaks or etched holes are observed; (2) The Li-PPA layer containing OH- groups remaining from the PPA can promote the uniform spread of molten Li on the LLZTO surface. After PPA treatment, the point-to-point contact mode is also changed to face-to-face contact (the contact angle is greatly reduced from 120° to 30°); (3) The Li-PPA interlayer provides an electron shielding effect to suppress the growth of Li dendrites in GSSBs.

[0028] The electronic conductivity of PPA-LLZTO is 1.2 × 10⁻⁶. -9 S cm -1 The electronic conductivity of the original LLZTO is 4.07 × 10⁻⁶. -8 S cm -1 The interfacial impedance of Li|LLZTO is an order of magnitude lower. Therefore, the interfacial impedance of Li|LLZTO decreases significantly from 370 Ω·cm at 25 °C to 4 Ω·cm. 2 The Li|PPA-LLZTO|Li battery exhibited a 1.8 mA cm⁻¹ -2 The CCD has a relatively high efficiency. In long-term constant current charge-discharge tests, the symmetrical cell of PPA-LLZTO showed excellent performance at 0.2 mA cm⁻¹. -2 Stable cycling for over 2500 hours at current density, at 0.5 mA cm⁻¹ -2 Stable cycling performance exceeding 500 hours at current density. Furthermore, the all-solid-state Li|PPA-LLZTO|PEO-LFP battery exhibits a capacity of 149.3 mAh g⁻¹ at 1C.-1 Its high initial capacity means that even after 500 cycles, its capacity retention rate remains as high as 92.3%. Attached Figure Description

[0029] Figure 1 Anhydrous PPA induces the transformation of Li₂CO₃ into a Li-PPA layer. (a) Schematic diagram of the preparation process and formation mechanism of the Li-PPA-Li interface. (b) Image of air-aged LLZTO (Air-LLZTO) after immersion in anhydrous PPA solution. (c) SEM images of Air-LLZTO and PPA-treated LLZTO (PPA-LLZTO) at different times. (d) HRTEM image of LLZTO treated with PPA for 2 min. (Inset) The fringe spacing is 0.21 nm, corresponding to the (611) lattice plane of LLZTO. (e) STEM image of LLZTO treated with PPA for 2 min and corresponding elemental mappings of P, O, La, Zr and Ta. (f) XRD patterns of Air-LLZTO and PPA-LLZTO treated for 1–30 min.

[0030] Figure 2 (a) XRD and (b) Raman spectra of Air-LLZTO and Pristine-LLZTO.

[0031] Figure 3 SEM top views of different concentrations of PPA (a) 1%, (b) 5%, (c) 10% and (d) 20% for Li2CO3 removal.

[0032] Figure 4 Top-view SEM image of Air-LLZTO and corresponding EDS mapping.

[0033] Figure 5 (a) Optical photographs and SEM images of Air-LLZTO after 30 min of PPA treatment. (b) Li|PPA-LLZTO-30 min|Li cell at 0.2 mA cm -2 Room temperature cycling diagram.

[0034] Figure 6 Initial LLZTO samples before and after PPA treatment were characterized by (a) XPS, (b) XRD and (c) Raman.

[0035] Figure 7 Characterization and analysis of Li-PPA-coated LLZTO. (a) Raman spectra of Pristine-LLZTO, Air-LLZTO and PPA-LLZTO. (b, c) XPS analysis of C1s and P2p spectra on the surface of Air-LLZTO before and after PPA treatment.

[0036] Figure 8 (a) FTIR spectra measured from LLZTO, Li-PPA, Air-LLZTO, and PPA-LLZTO. (b) Comparison of the infrared spectra of the prepared Li-PPA with those of standard Li3PO4. FTIR spectra of the standard Li3PO4 sample at 940 and 1650 cm⁻¹. -1 No OH stretching vibration peak was detected at that location.

[0037] Figure 9 Comparison of lithiophilicity and electron blocking properties. (a,b) Schematic diagram of the interface between Li|LLZTO and Li|PPA-LLZTO. (c) Optical images of molten Li droplets on LLZTO and PPA-LLZTO. SEM cross-sectional images at the interfaces of (d,e) Li|LLZTO and (f,g) Li|PPA-LLZTO. (h) Potentially constant polarization curves of LLZTO and PPA-LLZTO at 1V using a silver blocking electrode at room temperature. (i) Electron conductivity of LLZTO and PPA-LLZTO using a silver blocking electrode as a function of applied voltage.

[0038] Figure 10 (a) Comparison of EIS between Ag|PPA-LLZTO|Ag lithium-ion blocking cells and Li|PPA-LLZTO|Li symmetric cells. (b) Comparison of EIS between Ag|PPA-LLZTO|Ag and Ag|Air-LLZTO|Ag lithium-ion blocking electrodes.

[0039] Figure 11 Electrochemical performance characterization of LLZTO and PPA-LLZTO lithium-ion symmetric batteries. (a, b) Comparison of EIS spectra and critical current density (CCD) of Li|LLZTO|Li and Li|PPA-LLZTO|Li batteries. (c) At 0.2 mA cm⁻¹ -2 After 2500 hours of cycling, EIS images and magnified SEM images of the Li|PPA-LLZTO interface are shown. (d,e) Li|PPA-LLZTO|Li cell at 0.2 mA / cm². -2 Constant current cycling tests were conducted on (f,g)Li|PPA-LLZTO|Li cells as the current density increased from 0.1 to 0.5 mA / cm². -2 Rate performance at 0.5 mA cm -2 Time-voltage curves for a long-term cycle of 500h.

[0040] Figure 12 At 0.1mA cm -2 Deposition / lithiation cycle test diagram of Li|LLZTO|Li symmetric cell at room temperature.

[0041] Figure 13 (ac) Optical and top-view SEM images of initial LLZTO and PPA-LLZTO after Li plating / deplating in Li symmetric cells. (d) LLZTO in Li|PPA-LLZTO|Li cell cells at 0.2 mA cm⁻¹ -2 Optical images after 500 hours of cycling.

[0042] Figure 14 Electrochemical performance of PPA-LLZTO all-solid-state lithium metal batteries. (a) Discharge specific capacity and corresponding coulombic efficiency at 1C at 60℃ as a function of cycle number. (b) All-solid-state Li|PPA-LLZTO|PEO-LiFePO4 4( (c) Construction diagram of LFP battery. (d, e) Relationship between battery voltage and specific capacity at different cycle numbers. (f) Rate performance and charge / discharge voltage curves for corresponding cycle periods. (g) Prototype diagram of photocorrelated solid-state Li|PPA-LLZTO|PEO-LFP battery. (h) Photographs of solid-state Li|PPA-LLZTO|PEO-LFP battery powered by depleted energy and solar charging.

[0043] Figure 15 (a) Cycling performance of conventional all-solid-state Li|LLZTO|PEO-LiFePO4 batteries at 1℃ and 60℃; (b) Corresponding voltage curves.

[0044] Figure 16 Cross-sectional scanning electron microscope image and corresponding EDS spectrum of LiFePO4 composite cathode.

[0045] Figure 17 Impedance EIS plots of (a) Li|PPA-LLZTO|PEO-LiFePO4 battery and (b) Li|LLZTO|PEO-LiFePO4 battery at 60°C.

[0046] Figure 18 Battery performance diagram. Detailed Implementation

[0047] Garnet-based solid-state lithium metal batteries (GSSBs) offer advantages such as high energy density and high safety. However, achieving a stable and compatible Li|garnet electrolyte interface in GSSBs remains a significant challenge due to electron leakage and the presence of lithium-phobic Li₂CO₃ impurities. To address these issues, we report a simple and readily applicable surface chemistry approach: transforming the harmful Li₂CO₃ contamination layer into an ultrathin lithium polyphosphate (Li-PPA) layer through an anhydrous polyphosphoric acid (PPA)-induced in-situ substitution reaction without disrupting the water-sensitive garnet electrolyte. In particular, the Li-PPA interlayer not only promotes the uniform diffusion of molten Li but also forms a robust electron shielding layer, suppressing Li dendrite formation. Results show that the assembled lithium-symmetric battery exhibits a very low interfacial impedance (4 Ωcm) at 25 °C. 2 ) and a relatively high critical current density (1.8 mA / cm²) -2 This allows the symmetrical cell to operate at 0.2 mA / cm². -2 It can cycle for over 2500 hours at a current density. Furthermore, the GSSB with a LiFePO4 cathode can provide 149.3 mAh g / L at 1C rate. -1 The specific capacity remains at 92.3% of its initial capacity even after 500 cycles, and it can also be used for solar energy storage. In summary, this interface engineering strategy is highly feasible for GSSB. Preparation of LLZTO solid electrolyte sheets.

[0048] Ta-doped garnet Li was synthesized using a solid-state method. 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) Electrolyte Sheets. First, weigh out the following ingredients according to the stoichiometric ratio of LLZTO: LiOH·H₂O (Aladdin, 99.99%, with an excess of 15wt% LiOH·H₂O in the raw materials to compensate for the volatilization of Li-containing components at high temperatures), La₂O₃ (Aladdin, 99.99%), ZrO₂ (Aladdin, 99.9%), and Ta₂O₅ (Aladdin, 99.99%). Using isopropanol as a solvent, mix the ingredients at 400 rpm for 2 hours to obtain a homogeneous slurry. After drying, calcine the slurry at 900℃ for 16 hours in a muffle furnace. The pre-calcined powder is then ball-milled again for 2 hours to obtain finer LLZTO powder. A certain mass of the powder is then weighed into a 15mm diameter stainless steel mold and pressed into raw blank discs. Finally, the raw blank discs are covered with an appropriate amount of precursor powder in an MgO crucible and sintered at 1150℃ for 16 hours. The surface area of ​​the obtained LLZTO electrolyte sheet is approximately 1 cm². 2 It is mechanically ground and polished to a thickness of approximately 700μm.

[0049] PPA process for LLZTO

[0050] Dissolve 0.1g PPA in 12mL of isopropanol (IPA, after...) The LLZTO garnet electrolyte was dehydrated using molecular sieves and heated and stirred at 60°C for 12 hours to form a homogeneous solution. The prepared LLZTO garnet electrolyte was aged in air for 2 days, forming a Li₂CO₃ layer approximately 1–2 μm thick on the electrolyte surface. Then, in an argon-filled glove box, the aged LLZTO sheets (referred to as Air-LLZTO) were immersed in a 10% PPA IPA solution for 2 minutes. During this process, polyphosphoric acid (PPA) reacted in situ with the Li₂CO₃ contaminant layer (mainly Li₂CO₃ and LiOH) to form a Li-PPA layer. Finally, the PPA-treated electrolyte sheet (referred to as PPA-LLZTO) was washed with IPA, excess solvent was absorbed with lint-free paper, and it was dried at 120°C for 1 hour on a heated plate in a glove box, thus preparing PPA-LLZTO.

[0051] Battery assembly

[0052] (1) Lithium-ion symmetric battery assembly

[0053] Li|LLZTO|Li Symmetrical Cell: Li foil is melted at 250°C and evenly coated onto both sides of the LLZTO electrolyte. The CR2025 coin cell is assembled under 500 psi pressure on a coin cell sealing machine.

[0054] Li|PPA-LLZTO|Li symmetric cell: Molten lithium was directly and uniformly coated on both sides of the prepared PPA-LLZTO electrolyte, and after cooling, it was sealed in a CR2025 button cell under a pressure of 500 psi.

[0055] (2) Assembly of all-solid-state lithium metal batteries

[0056] Preparation of LiFePO4 cathode: Active materials LiFePO4, Super P, PEO (Mw = 60w), and LiTFSI were mixed in acetonitrile at a mass ratio of 6:1:2:1 and stirred overnight. The resulting uniformly mixed slurry was coated onto carbon-coated aluminum foil and then dried in a vacuum oven at 80°C for 24 hours. The active material loading in the resulting cathode was approximately 1.5 mg / cm³. -2 .

[0057] Preparation of the PEO buffer layer: PEO, LiTFSI, and 0.05 g LLZTO nanoparticles were mixed in 15 mL acetonitrile at a stoichiometric ratio of EO:Li = 8:1 and stirred at 60 °C for 12 h to obtain a PEO precursor solution. The precursor solution was coated onto the prepared LiFePO4 cathode sheet using a doctor blade to prepare the PEO buffer layer, and then dried in a vacuum oven at 60 °C for 24 h to remove the solvent. Finally, the prepared PEO-LiFePO4 composite cathode was cut into Φ8 discs.

[0058] Full cell assembly: Using LiFePO4 as the positive electrode material, a PEO film as the interfacial buffer layer between the positive electrode LiFePO4 and the electrolyte LLZTO, and Li|PPA-LLZTO or Li|LLZTO as the negative electrode and electrolyte, a fully solid-state battery is assembled and labeled as Li|PPA-LLZTO|PEO-LiFePO4 or Li|LLZTO|PEO-LiFePO4. 4. .

[0059] Electrochemical testing methods

[0060] To measure the lithium-ion conductivity of LLZTO, Ag films were deposited on both sides of LLZTO to prepare an Ag|LLZTO|Ag lithium-ion blocking battery. The ionic conductivity of the LLZTO electrolyte sheet was measured using a Solartron 1260 impedance analyzer. The measurement frequency range was 1Hz to 1MHz, and the AC voltage used was 20mV. The ionic conductivity was calculated using the following formula: Σ=L / (R*A), where Σ is the ionic conductivity (S / cm). -1 R represents the total impedance shown in the EIS plot, L represents the thickness of LLZTO, and A represents the effective area between LLZTO and the blocking Ag electrode. Deposition / stripping curves were acquired using a battery testing system (Blue Electric CT3002A). The electronic conductivity of LLZTO and PPA-LLZTO was tested by a potentiostatic polarization experiment. During the experiment, a DC voltage of 1V was applied for 3600s, and the recording rate was 1s. -1 Ag was sputtered onto both sides of LLZTO to form ion-blocking electrodes with a contact area of ​​0.55 cm². 2 Electron conductivity can be expressed by the formula... Calculate, where σ e denoted as electronic conductivity, d as LLZTO thickness, I as steady-state current, A as contact area between LLZTO and the blocking electrode, and U as applied DC voltage.

[0061] Given LLZTO's sensitivity to both air and water, anhydrous polyphosphoric acid (PPA) was used to remove the Li2CO3 passivation layer from the LLZTO surface, instead of the acidic aqueous solution reported previously. A simple and easy-to-implement PPA pretreatment method is as follows: Figure 1As shown. After LLZTO is exposed to air for 2 days, harmful Li2CO3 (produced by two side reactions: Li 6.4 La3Zr 1.4 Ta 0.6 O 12 +xH2O→Li 6.4-x H x La3Zr 1.4 Ta 0.6 O 12 +x LiOH, LiOH+1 / 2CO2→1 / 2Li2CO3+1 / 2H2O) can be XRD ( Figure 2 a), Raman ( Figure 2 b) was clearly detected, and LLZTO (Air-LLZTO for short) aged for 2 days was selected as a comparative experiment.

[0062] Li obtained from Air-LLZTO + The electrical conductivity is 3.5 × 10⁻⁶. -4 S cm -1 Pure PPA (Alfa Aesar) was dissolved in isopropanol (via... Molecular sieve drying) yielded anhydrous PPA solutions of varying concentrations (1–20 wt%). Figure 3 As shown, the Li₂CO₃ layer on Air-LLZTO cannot be completely removed in 1 wt% PPA, but it can be completely removed in the PPA concentration range of 5–20 wt%. Therefore, in this study, a PPA concentration of 10 wt% was selected as the treatment solution. It can be seen that a uniform Li-PPA layer with residual OH groups was constructed on the LLZTO surface through the in-situ transformation reaction between PPA and Li₂CO₃. Subsequently, the reaction between molten Li and the OH groups of Li-PPA is the main driving force for the uniform spread of molten Li on LLZTO. Simultaneously, a lithium-intercalated Li-PPA-Li layer is generated at the Li|LLZTO interface. Figure 1 Figure b shows a sealed vial after Air-LLZTO was contacted with a 10 wt% anhydrous PPA solution. The resulting bubbles indicate a spontaneous reaction: Li₂CO₃ + PPA → Li-PPA + CO₂↑ + H₂O. Figure 1 c and Figure 1 As shown in d, with the rapid progress of the PPA treatment, the Li2CO3 passivation layer gradually disappeared after 2 minutes, and a thin nano-coating (Li-PPA) with a thickness of approximately 30 nm was visible on the surface of LLZTO (PPA-LLZTO) after 2 minutes of PPA treatment. Comparison with the elemental mapping of Air-LLZTO (… Figure 4), in scanning transmission electron microscopy (STEM, Figure 1 In the element mapping of the selected region in e), the coexistence of Li-PPA and LLZTO can be observed. Figure 1 f represents the XRD patterns of Air-LLZTO and PPA-LLZTO. For Air-LLZTO, the diffraction peaks around 21.3° and 23.4° are attributed to the (110) and (200) crystal planes of Li₂CO₃ (PDF 01-087-0729), consistent with previous reports. At different PPA treatment times, the diffraction peak intensities of Li₂CO₃ decreased significantly after 1 min and disappeared completely after 2 min, consistent with the observed bubble duration. Notably, even extending the PPA treatment time to 30 min did not result in a LiOH peak. Figure 1 f) or obvious pores ( Figure 5 The Li|PPA-LLZTO-30min|Li cell was generated at 0.2 mA cm⁻¹. -2 It can cycle at room temperature for over 300 hours at current density. Furthermore, such as... Figure 6 As shown, XPS, XRD, and Raman all indicate that no additional peaks or peak shifts appeared in the initial LLZTO before and after soaking in PPA solution for 30 minutes. This suggests that the PPA pretreatment method can effectively remove harmful Li2CO3 without damaging the LLZTO matrix.

[0063] To reveal the surface composition, we explored control groups with three different surface states of LLZTO. For example... Figure 7 As shown in Figure a, Raman spectroscopy was used to measure initial LLZTO (polished with sandpaper), Air-LLZTO, and PPA-LLZTO. For initial LLZTO, the values ​​were 123, 246, 375, 645, and 734 cm⁻¹. -1 The five characteristic peaks correspond to its cubic garnet phase, while 123 and 246 cm⁻¹ -1 The characteristic peaks are related to the Li-O bond. For air-aged LLZTO, the peak at 158 ​​cm⁻¹ is... -1 The weak peak and 1090cm -1 The strong peak is attributed to CO3 2- The stretching and contracting vibrations indicate the presence of Li₂CO₃ and the poor stability of LLZTO to ambient air. After PPA treatment, compared to Air-LLZTO, typical CO₃²⁻… 2- The peaks have disappeared, while at 750, 953, and 1041 cm⁻¹... -1 The new peak at that location is due to V sThe stretching vibrations of (POP), V1(PO4), and V3(PO4) are characteristic peaks of the polyphosphate phase, indicating that harmful Li2CO3 has been successfully converted into Li-PPA. X-ray photoelectron spectroscopy (XPS) of C1s and P2p further confirms this result. Figure 7 The C1s spectrum of b Air-LLZTO showed two peaks centered at 285.0 and 289.9 eV, respectively, originating from C-C bonds and OC=O species (such as Li₂CO₃). Unlike Air-LLZTO, PPA-LLZTO showed only a small C1s peak at 289.9 eV, consistent with previous XRD and SEM measurements, indicating that 2 min of PPA treatment was sufficient to remove Li₂CO₃. Figure 7 The p 2p spectrum of PPA-LLZTO shows two peaks at 133.3 and 134.5 eV, which belong to the 2p phase of phosphate. 3 / 2 and 2p 1 / 2 The composition was analyzed, and no XPS signal was observed in the P 2p spectrum of Air-LLZTO, confirming the formation of a phosphate-based coating on LLZTO during PPA treatment. Since lithiophilic functional groups (such as -OH) promote the uniform diffusion of molten lithium, LLZTO surface coatings containing lithiophilic functional groups are highly desirable. The functional groups of Li-PPA were further detected by Fourier transform infrared spectroscopy (FTIR). Figure 8 A control group of LLZTO with different surface states was explored. Compared with the FTIR pattern of the initial LLZTO, the Air-LLZTO showed better performance at 863 and 1482–1438 cm⁻¹. -1 A strong characteristic peak was found at [location], attributed to the asymmetric stretching vibration of the C=O bond and CO32-. 2- The out-of-plane bending vibrations confirmed the presence of Li₂CO₃. For the PPA-LLZTO surface, these Li₂CO₃ peaks disappeared, while those at 940 and 1650 cm⁻¹ remained. -1 New absorption peaks were detected at [value missing], which are attributed to the stretching vibrations of the hydroxyl groups in the p-OH groups. Notably, [values ​​missing] were observed at 940 and 1650 cm⁻¹ in the control sample Li₃PO₄. -1 No OH stretching vibrations were observed at 940 and 1650 cm⁻¹, while the FTIR spectra of the prepared Li-PPA powder showed no significant vibrations at these locations. -1 The presence of a strong characteristic peak at this location, consistent with that of LLZTO powder treated with PPA, confirms the presence of OH groups in Li-PPA. Based on these results, we can conclude that the Li-PPA coating obtained on PPA-LLZTO is lithium polyphosphate rich in OH groups.

[0064] like Figure 9As shown in Figure a, LLZTO containing Li₂CO₃ is not well compatible with the Li metal anode, resulting in discontinuous point-to-point contact at the Li|LLZTO interface, consistent with the expected lithium-phobic garnet surface and previous studies. As expected, replacing LLZTO with PPA-LLZTO transforms the point-to-point interfacial contact into a face-to-face contact. Figure 9 (b) This close contact between surfaces allows for better transmission of Li through the interface. + In addition, contact angle tests were conducted to examine the wetting behavior of LLZTO and PPA-LLZTO on lithium. Figure 9 As shown in Figure c, molten Li forms spherical shapes on the lithium-phobic LLZTO particles (contact angle approximately 120°). In contrast, the contact angle of PPA-LLZTO decreases significantly from around 120° to 30°, indicating that the surface state of LLZTO successfully changed from lithium-phobic to lithium-philic with the help of PPA treatment. Scanning electron microscopy cross-sectional images further verified the wettability of Li on LLZTO and PPA-LLZTO. As shown in the figure, micron-sized voids or gaps can be seen at the Li|LLZTO interface. Figure 9 d and Figure 9 (e), while no voids or gaps were observed on the Li|PPA-LLZTO interface. Figure 9 f and g of 9).

[0065] To evaluate the ionic conductivity of the Li-PPA-Li layer at the Li|PPA-LLZTO interface, Figure 10 The EIS plots of Li|PPA-LLZTO|Li, Ag|PPA-LLZTO|Ag, and Ag|Air-LLZTO|Ag batteries were compared. When a noble metal (such as Ag) is used as the lithium-ion blocking electrode, the appearance of a long tail at low frequencies indicates that the LLZTO particles have ionic properties. When lithium metal is used as the blocking electrode, the long tail disappears at low frequencies, indicating that the Li-PPA-Li layer has good lithium-ion conductivity. To investigate the electron blocking effect of the Li-PPA-Li layer, the electronic conductivity of pristine LLZTO and PPA-LLZTO was measured using our previous testing methods. Figure 9 The h-values ​​describe the it curves obtained by polarizing two samples at room temperature using a lithium-ion-blocked Ag electrode with 1V-DC polarization. Electron conductivity (σ) e σ can be calculated using the formula. e = (d×I) / (A×U). Where d is the LLZTO thickness, I is the steady-state current, A is the contact area between LLZTO and the silver blocking electrode, and U is the applied voltage. Due to the electron blocking effect of the Li-PPA-Li layer on PPA-LLZTO, the calculated electronic conductivity of PPA-LLZTO is (1.2×10⁻⁶). -9S cm -1 ) compared to the initial LLZTO (4.07×10) -8 S cm -1 It is an order of magnitude lower. Furthermore, such as... Figure 9 As shown in Figure i, the electron blocking effect of PPA-LLZTO can be maintained under different voltages (0.5–4V) that represent the actual operating conditions of the battery.

[0066] Inspired by PPA-LLZTO, which possesses the aforementioned lithiophilic and electron-blocking properties, the interfacial resistance and electrochemical stability of Li|PPA-LLZTO were tested. Figure 11 As shown in a, from Li| initial LLZTO (approximately 370 Ωcm) 2 ) to Li|PPA-LLZTO (approximately 4Ωcm) 2 The anode-electrolyte interface impedance was significantly reduced, indicating that the improved solid-solid contact benefited from the lithium-affinity properties of PPA-LLZTO. The lithium dendrite penetration behavior of initial LLZTO and PPA-LLZTO in Li symmetric cells was investigated, and their critical current densities (CCD, defined as the highest applied current density that a solid electrolyte can withstand for lithium penetration short circuits) were compared. Figure 11 Figure b shows the CCD test results measured at room temperature. The Li|PPALLZTO|Li cell exhibits a 1.8 mA cm⁻¹. -2 The Li|initial LLZTO|Li cell exhibited a relatively high CCD value, while under the same testing conditions, the Li|initial LLZTO|Li cell showed a lower CCD value (0.3 mAcm). -2 (Consistent with previous reports). The significant increase in the CCD value of the Li|PPA-LLZTO|Li cell is likely due to the enhanced electron blocking properties of the PPA-induced intermediate layer, which ultimately suppresses electron transport to LLZTO.

[0067] The long-term stability of the Li|garnet interface was evaluated using a room-temperature constant current exfoliation-deposition test. (EIS figure) Figure 11 c) and cross-sectional scanning electron microscopy ( Figure 11 The inset (c) shows that even after 2500 hours of cycling in Li-symmetric cells, the Li|PPA-LLZTO interface remained in close contact, with only a slight increase in interfacial resistance (<1 Ωcm). 2 ). Figure 11 d and Figure 12 The cycle performance of the initial LLZTO and PPA-LLZTO symmetric cells was compared. Figure 12 As shown, at 0.1 mAcm -2At low current densities, the initial Li|LLZTO|Li cell exhibited a high charge-discharge ΔV (~50mV) and a rapid short circuit after 110 hours of cycling. In contrast, the Li|PPA-LLZTO|Li cell showed a high ΔV at 0.2mA cm⁻¹. -2 It exhibits a low voltage of ΔV to 25mV at current densities. Figure 11 The d and 11e) of the Li|pristine LLZTO|Li battery were able to withstand long-term cycle testing exceeding 2500 hours without internal short circuits. Anatomical analysis of the original Li|Li battery showed that at 0.1 mA cm⁻¹ 2 After 120 hours of cycling, Li dendrites grew through the initial LLZTO particles ( Figure 13 (ac). Figure 13 In diagrams b and c, the yellow dashed lines (circled areas) represent the movement trajectories of Li spots. Li dendrites propagate through these trajectories, causing short circuits in the battery. For example... Figure 13 As shown in d, in stark contrast, at 0.2 mAcm -2 After 500 hours of cycling, no Li dendrite propagation signal was observed in the PPA-LLZTO particles. To further demonstrate the feasibility of the Li|PPA-LLZTO interface at high current densities, the rate performance of the Li|PPA-LLZTO|Li battery was evaluated. Figure 12 As shown in f, in the Li|PPA-LLZTO|Li symmetric cell, the current density gradually increases from 0.1, 0.3 to 0.5 mA / cm². -2 Then maintain at 0.5 mAcm -2 Cyclic testing was conducted. Clearly, the charge-discharge curve ΔV of Li stripping-deposition showed that even as the voltage gradually increased from 10 mV to 65 mV, it remained stable at 0.5 mA / cm². -2 It achieves good cycle stability during long-term cycling, up to 500 hours, and exhibits stable voltage hysteresis. Figure 12 (g), verifying the robust interface between Li metal and PPA-LLZTO.

[0068] Besides the stability of the Li|garnet interface in symmetric cells, the long-term interface stability of all-solid-state lithium metal batteries is crucial for their practical applications. For example... Figure 14 a and Figure 15 As shown, to highlight the superiority of PPA-LLZTO over virgin LLZTO in all-solid-state lithium metal full cells, PEO-LiFePO4 (LFP) composite material was used as the positive electrode and Li metal as the negative electrode to prepare button-type Li|PPA-LLZTO|PEO-LFP cells and Li|LLZTO|PEO-LFP cells. Figure 14 b and Figure 16The PEO-LFP composite cathode consists of a 16 μm thick LFP active layer (LFP powder, Super P, and PEO8-LiTFSI) and a 10 μm thick PEO functional layer (used to enhance the contact between the positive electrode and the garnet electrolyte). Figure 14 As shown in a, the all-solid-state Li|PPA-LLZTO|PEO-LFP battery operates at 0.26 mA cm⁻¹. -2 (1C) exhibits good long-term stability and provides 149.3 mAh g. -1 Its high specific capacity, maintaining 92.3% capacity after 500 cycles, and an average coulombic efficiency of >99%. In comparison, such as Figure 15 As shown, the all-solid-state Li|LLZTO|PEO-LFP battery delivered 95.5 mAh g in the first cycle. -1 The Li|PPA-LLZTO|PEO-LFP battery exhibits low specific capacity and a rapid capacity decline after 25 cycles. Furthermore, it displays a small overpotential (<0.1V). Figure 14 c) The electrochemical charge-discharge curve and low total impedance (132 Ωcm) 2 , Figure 17 a) , while Li|LLZTO|PEO-LFP batteries have large charge / discharge overpotentials (<0.8V, Figure 15 (b) and high total impedance (818 Ωcm) 2 , Figure 17 (b). It should be noted that the purpose of the above long-term cycling test is to demonstrate that no short circuit caused by lithium dendrite growth will occur during the cycling process of the all-solid-state lithium metal battery using the initial garnet electrolyte, indicating the feasibility of the all-solid-state battery based on the highly stable Li|PPA-LLZTO interface. Figure 14 The value of d shows the rate performance of the full cell under different current densities from 0.1 to 2C during charge and discharge. Figure 14 As shown in Figure e, the Li|PPA-LLZTO|PEO-LFP battery can provide 153, 152, 150, 148, and 144 mAh g at current densities of 0.1, 0.2, 0.5, 1, and 2C, respectively. -1 High specific capacity and a well-defined charge / discharge plateau. Solar energy can provide abundant renewable energy. Due to the instability of solar energy, its energy storage will become crucial. Considering the flammable and toxic liquid electrolytes used in traditional lithium-ion batteries, continued development of safer, enhanced solid-state lithium metal batteries for solar energy storage is essential. Figure 14As shown in f, a prototype solar-correlated solid-state Li|PPA-LLZTO|PEO-LFP cell was fabricated under illumination to better evaluate its application in a solar charging system for solar energy storage. The depleted solid-state Li|PPA-LLZTO|PEO-LFP cell could barely power an LED light strip. Figure 14 (g). A solid-state Li|PPA-LLZTO|PEO-LFP battery charged by solar energy (connected to a solar cell, receiving 224W of solar radiation energy input for 5 minutes) easily illuminates an LED light strip. Figure 14 The study (h) verified the significant feasibility of the designed solid-state lithium metal battery for solar energy storage.

Claims

1. A solid electrolyte used in all-solid-state lithium batteries, characterized in that, Includes a solid electrolyte sheet, and a polymeric material having the following structure loaded on at least one side of the electrolyte sheet: ； The solid electrolyte sheet is made of tantalum-doped lithium lanthanum zirconium oxide. The method for preparing the solid electrolyte includes the following steps: This causes Li2CO3 to form on the surface of the solid electrolyte sheet; The solid electrolyte sheet is placed in a solvent containing polyphosphoric acid for reaction; The polyphosphoric acid described herein has undergone dehydration treatment; The dehydration treatment mentioned refers to water removal treatment using 4 Å molecular sieves; The polyphosphoric acid has a concentration of 5-20 wt% in the solvent, which is an alcohol solvent; The reaction time is 2-10 min; The formation of Li2CO3 on the surface of the solid electrolyte sheet is achieved by reacting tantalum-doped lithium lanthanum zirconium oxide with air; the Li2CO3 has a thickness of 0.1-5 μm.

2. A fully solid-state lithium battery, characterized in that, It includes an assembly structure containing a negative electrode and an electrolyte layer, including bonded Li and electrolyte sheets, and a polymeric material as shown below is contained between the interface of the Li and electrolyte sheets: ； The manufacturing method of the all-solid-state lithium battery includes the following steps: The solid electrolyte of claim 1 is obtained by contacting molten Li with it to cause a surface reaction.

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