Interface protection layer for positive electrode material of polymer solid-state battery, positive electrode material, all-solid-state battery and preparation method thereof

Abstract

This invention belongs to the field of solid-state battery cathode interface engineering technology, specifically relating to an interface protective layer for polymer solid-state battery cathode materials, a cathode material, an all-solid-state battery, and a method for preparing the same. The interface protective layer for polymer solid-state battery cathode materials is a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phases, forming a gradient structure from the inside out, with an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region. The aforementioned interface protective layer, cathode material, all-solid-state battery, and method for preparing the same can effectively suppress high-voltage interface side reactions and adaptively maintain good physical contact during long-term service.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state battery cathode interface engineering technology, specifically relating to an interface protective layer for polymer solid-state battery cathode materials, cathode materials, all-solid-state batteries and their preparation methods. Background Technology

[0002] After years of development, lithium-ion batteries have been widely used in portable electronics and electric transportation. With the increasing demand for higher energy density and safety in electric vehicles and other applications, all-solid-state batteries have attracted widespread attention due to their potential safety and energy density advantages. Among them, polymer solid electrolytes are considered one of the most promising solid electrolyte systems due to their high ionic conductivity and good processability. In all-solid-state battery systems, the cathode material is one of the key factors determining energy density. To achieve high specific energy, high capacity, and high voltage, nickel-rich layered ternary cathode materials (LiNi) are used. x Co y Mn 1-x-y O2 (and x≥0.8) is gradually becoming an important choice for high-energy-density batteries. However, the interfacial chemical compatibility between polymer electrolytes and oxide cathodes is one of the major bottlenecks limiting the performance of polymer all-solid-state batteries.

[0003] Polymer electrolytes, due to the oxidative decomposition of ether oxygen groups in their molecular chains at high voltages (>3.6V), exhibit relatively low initial oxidation-decomposition potentials. This potential mismatch with the operating voltage window of high-voltage oxide cathodes can induce severe interfacial side reactions. Furthermore, the low ionic conductivity of interfacial decomposition products hinders lithium-ion cross-interface transport, leading to continuous increase in interfacial impedance, intensified polarization, and accelerated capacity decay. Therefore, maintaining the advantages of high-voltage cathodes while suppressing the oxidative decomposition of polymer electrolytes at high potentials and reducing interfacial impedance growth has become a critical problem to be solved for the engineering application of polymer all-solid-state batteries.

[0004] To address the aforementioned interface failure issues, previous studies have proposed enhancing interface stability by constructing a protective layer on the cathode surface. For example, atomic layer deposition (ALD) allows for precise control over coating thickness and morphology, which is beneficial for improving the physical contact between the cathode and electrolyte. ALD has been used to construct approximately 2 nm thick fluorine-rich protective layers to suppress interfacial side reactions and impedance growth, while also consuming residual Li2CO3 and LiOH on the cathode surface to some extent.

[0005] Many existing protective layers focus more on chemical stability and initial contact improvement, but they lack a structured solution mechanism for "adaptive contact maintenance and densification" to address dynamic failures caused by particle deformation, interface microcracks, and contact degradation during cell service. Therefore, impedance rebound and performance degradation may still occur under long-term cycling and operating condition fluctuations.

[0006] Furthermore, insufficient attention has been paid to the degradation of physical contact during long-term battery cycling due to factors such as electrode particle volume changes and interfacial stress. Single, rigid ultrathin coatings are prone to cracking or peeling from the substrate under cyclic stress, leading to protective failure. Therefore, there is an urgent need for a cathode interface protective layer structure and method that can effectively suppress high-voltage interfacial side reactions, adaptively maintain good physical contact during long-term service, and is suitable for large-scale fabrication. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide an interface protection layer, cathode material, all-solid-state battery and preparation method thereof that can effectively suppress high-voltage interface side reactions and adaptively maintain good physical contact during long-term service.

[0008] To solve the above technical problems, the technical solution is as follows: an interface protection layer for the positive electrode material of polymer solid-state batteries, wherein the interface protection layer is a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase, forming a gradient structure from the inside to the outside of an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region.

[0009] In one embodiment, the thickness of the glass-ceramic composite layer is 5–200 nm, the average particle size of the lithium fluoride nanocrystals is 1–20 nm, and they are dispersed in a lithium borophosphate amorphous glass phase.

[0010] Based on the same inventive concept, a polymer solid-state battery cathode material is provided, comprising a single-crystal nickel-rich layered oxide, wherein the surface of the single-crystal nickel-rich layered oxide is provided with an interface protective layer as described above.

[0011] In one embodiment, the single-crystal nickel-rich layered oxide is LiNi. x Co y Mn 1-x-y O2, where x ≥ 0.80.

[0012] In one embodiment, the mass fraction of the interface protective layer is 0.05 wt% to 2.0 wt%, based on the total mass of the cathode material.

[0013] Based on the same inventive concept, an all-solid-state battery includes a positive electrode material, a polymer solid electrolyte layer, and a negative electrode. The positive electrode material is the positive electrode material as described above, and the solid electrolyte layer contains a polymer solid electrolyte selected from a PEO and LLZTO composite system.

[0014] Based on the same inventive concept, a method for preparing a polymer solid-state battery cathode material includes the following steps:

[0015] S1: Provides single-crystal nickel-rich layered oxide cathode powder; S2: Prepare coating precursor solutions or slurries containing fluorine-phosphorus sources and fluorine-boron sources; S3: Uniformly coat the surface of single-crystal nickel-rich layered oxide cathode powder with precursor solution or slurry; S4: Under an inert atmosphere, the coated cathode powder is subjected to thermal conversion treatment, causing the precursor to undergo condensation and glassization reactions, accompanied by in-situ fluorination reactions. A glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase is formed on the surface of the cathode powder, forming a gradient structure from the inside out, with an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region.

[0016] In one embodiment, in step S3, at least one of atomic layer deposition, atomization deposition, and fluidized bed spraying is used to uniformly prepare a coating precursor solution or slurry on the surface of a single-crystal nickel-rich layered oxide cathode powder.

[0017] In one embodiment, in step S2, the fluorinated phosphorus source is selected from at least one of LiPO2F2, NH4PO2F2, and metal fluorophosphates; the fluorinated boron source is selected from at least one of LiDFOB, LiBF4, and fluorinated borates; the molar ratio of the fluorinated phosphorus source to the fluorinated boron source is 0.2 to 5:1; the solvent of the precursor solution or slurry is at least one of acetonitrile, ethanol, isopropanol, and carbonate solvents; and the solid content of the precursor solution is 0.2 to 20 wt%.

[0018] In one embodiment, the heat conversion treatment temperature in S4 is 250–450 °C, the holding time is 0.5–5 h, and the heating rate is 0.5–10 °C / min; After step S4, step S5 is also included: densifying the polymer solid-state battery cathode material on which the interface protective layer is formed, wherein the densification process includes heat treatment at 120°C to 250°C for 0.2 to 3 hours, or hot pressing at 50 MPa to 200 MPa pressure.

[0019] Beneficial Effects: The aforementioned interface protection layer, cathode material, and all-solid-state battery used in polymer solid-state battery cathode materials exhibit a gradient structure from the inside out, forming an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region. The lithium borophosphate glass-ceramic phase near the cathode material is rich in viscoelastic and well-adhesive lithium borophosphate glass-ceramic phase, resulting in stronger interfacial adhesion and continuous coverage with the cathode surface. This allows for sustained interfacial bonding under compression molding, cyclic stress, and micro-deformation of particles, avoiding the shortcomings of relying solely on an ultrathin single inorganic layer, which is prone to coverage damage, contact degradation, or localized failure leading to impedance rebound during long-term service. Simultaneously, it reduces the risk of interfacial porosity and ion channel interruption, improving cell consistency and reliability. The outer layer (adjacent to the electrolyte) is rich in chemically stable and electronically insulating lithium fluoride nanocrystals, effectively blocking direct contact between the cathode active material and the polymer electrolyte under high voltage and inhibiting the oxidative decomposition reaction of the electrolyte. This gradient functional division of internal bonding and external isolation synergistically achieves long-term chemical and physical stability of the interface. Under fluctuating operating pressure and temperature, this material fills and stabilizes interfacial microcracks and micropores, helping to maintain a continuous ion transport pathway between the positive electrode and the polymer electrolyte and suppressing the increase in contact resistance. Compared to simply pursuing a thicker shielding layer or a higher inert component content, this invention, through the synergy of the glass phase and nanocrystals, improves interfacial stability while minimizing additional ion transport resistance, thus achieving a balance between high voltage stability, rate performance, and long cycle life, and improving the consistency of discharge output. Under high voltage conditions, it effectively suppresses the oxidative decomposition of the polymer solid electrolyte and interfacial side reactions, reducing the generation of low ionic conductivity decomposition products, thereby reducing interfacial impedance growth and polarization accumulation, and improving battery rate output, capacity retention, and cycle stability without changing the main polymer electrolyte formulation. This results in all-solid-state batteries using this interfacial protective layer exhibiting higher first-cycle capacity, better capacity retention, significantly reduced interfacial impedance growth, and better rate performance.

[0020] The above preparation method is based on solution deposition and medium-temperature thermal conversion. The process path is short, the equipment is highly versatile (such as fluidized bed), and the precursor cost is controllable. It is very suitable for industrial-scale production and solves the bottleneck of low throughput and high cost of high-precision deposition technology. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the polymer solid-state battery cathode material structure of the present invention.

[0023] Figure 2 This is a schematic diagram comparing the interface stability mechanism when there is no interface protective layer and when there is an interface protective layer of the present invention. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] Please see Figure 1-2 One embodiment of the interface protection layer for the positive electrode material of polymer solid-state batteries is a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase, forming a gradient structure from the inside out of an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region.

[0028] Preferably, the thickness of the glass-ceramic composite layer is 5–200 nm, the average particle size of the lithium fluoride nanocrystals is 1–20 nm, and they are dispersed in the lithium borophosphate amorphous glass phase to improve chemical stability and maintain lithium ion permeability.

[0029] Based on the same inventive concept, a polymer solid-state battery cathode material is also provided, comprising a single-crystal nickel-rich layered oxide, wherein the surface of the single-crystal nickel-rich layered oxide is provided with an interface protective layer as described above.

[0030] Preferably, the nickel-rich layered oxide is LiNi. x Co y Mn 1-x-y O2, where x≥0.80. The raw material for single-crystal nickel-rich layered oxides is powder material, and the D50 of the powder material is 1~15 μm, in order to balance energy density, compaction density and particle structure stability.

[0031] Preferably, the mass fraction of the interface protective layer is 0.05 wt% to 2.0 wt%, based on the total mass of the cathode material, to achieve a reasonable balance between interface stability and ion transport resistance.

[0032] Based on the same inventive concept, an all-solid-state battery is also provided, comprising a positive electrode material, a polymer solid electrolyte layer and a negative electrode, wherein the positive electrode material is the positive electrode material as described above, and the solid electrolyte layer comprises a polymer solid electrolyte selected from a PEO and LLZTO composite system.

[0033] A positive electrode composite electrode is prepared by combining the above-mentioned positive electrode material with a polymer solid electrolyte and a conductive agent. This composite electrode is then pressed and assembled with a polymer electrolyte membrane and a negative electrode to form an all-solid-state battery. Formation and cycle testing are subsequently performed to further stabilize the interface under operating pressure and electrochemical drive, achieving low-impedance transport. Preferably, the pressing pressure of the positive electrode material is 50–500 MPa to reduce interfacial contact impedance and improve molding strength. The negative electrode is one or more of lithium metal, graphite, hard carbon, or their composite negative electrodes. The mass ratio of active material, polymer solid electrolyte, and conductive agent in the positive electrode composite electrode is 50–90:10–45:0–10 to balance ion channels, electron network, and energy density. The negative electrode is at least one of lithium metal, graphite, hard carbon, or their composite negative electrodes.

[0034] During the fabrication of all-solid-state batteries, formation is carried out for 1 to 10 cycles at a rate of 0.05 to 0.5 C to promote interface stability and reduce early impedance rise.

[0035] Based on the same inventive concept, a method for preparing a polymer solid-state battery cathode material is also provided, comprising the following steps: S1: Provides single-crystal nickel-rich layered oxide cathode powder; Specifically, a single-crystal nickel-rich layered oxide cathode powder is provided, with controlled particle size distribution and dust removal and drying. Preferably, the powder undergoes low-temperature pretreatment to reduce surface-adsorbed water and weakly bound impurities, forming a stable and reproducible coating substrate. In one embodiment, the single-crystal nickel-rich layered oxide is LiNi. x Co y Mn 1-x-y O2, wherein x≥0.80, and the positive electrode powder D50 is 1~15μm, in order to balance energy density, compaction density and particle structure stability.

[0036] Preferably, the low-temperature pretreatment drying temperature is 80–150 °C, the time is 2–24 h, and the atmosphere is one or more of vacuum, argon or nitrogen, in order to reduce the risk of interfacial side reactions caused by adsorbed water.

[0037] S2: Prepare coating precursor solutions or slurries containing fluorine-phosphorus sources and fluorine-boron sources; Specifically, in one embodiment, the fluorinated phosphorus source is selected from at least one of LiPO2F2, NH4PO2F2 and metal fluoride phosphates; the fluorinated boron source is selected from at least one of LiDFOB, LiBF4 and fluorinated borates; so as to form a lithium boron phosphorus oxyfluoride network after conversion and precipitate lithium fluoride nanocrystals.

[0038] Preferably, the molar ratio of the fluorinated phosphorus source to the fluorinated boron source is 0.2 to 5:1.

[0039] The solvent used in the precursor solution or slurry is acetonitrile, ethanol, isopropanol, carbonate solvents or mixtures thereof; the solid content of the precursor solution is 0.2 to 20 wt% to balance deposition stability and protective layer uniformity.

[0040] Preferably, a complexing agent, a dispersing agent, and / or a temporary film-forming component are added during the preparation of the precursor solution or slurry to allow the precursor to spread uniformly on the particle surface during subsequent deposition steps and form a continuous precursor film layer after drying. The dispersing agent used is polyvinylpyrrolidone (PVP).

[0041] S3: Uniformly coat the surface of single-crystal nickel-rich layered oxide cathode powder with precursor solution or slurry; Preferably, at least one of atomic layer deposition, atomized deposition, and fluidized bed spraying is used to uniformly coat the surface of the single-crystal nickel-rich layered oxide cathode powder with a precursor solution or slurry. The inlet temperature for fluidized bed spraying is 60–180 °C, and the outlet temperature is 40–120 °C to avoid premature decomposition of the precursor and reduce agglomeration. When uniformly preparing the precursor solution or slurry coating on the cathode powder surface, the deposition amount is controlled; the precursor deposition amount ensures that the final interfacial protective layer mass fraction is 0.05–2.0 wt%, achieving a reasonable balance between interfacial stability and ion transport resistance. Preferably, mild drying conditions are applied after deposition to remove the solvent and prevent particle agglomeration.

[0042] S4: Under an inert atmosphere, the coated cathode powder undergoes thermal conversion treatment, causing the precursor to undergo condensation and glass transition reactions, accompanied by in-situ fluorination. This forms a glass-ceramic composite layer on the surface of the cathode powder, consisting of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phases, with a gradient structure in the thickness direction between the lithium borophosphate glass-ceramic phase enrichment region and the outer lithium fluoride enrichment region. During the heat treatment process, boron- and phosphorus-containing precursors (such as LiDFOB and LiPO2F2) preferentially undergo condensation reactions, gradually forming a Li-based composite layer on the surface of the cathode particles. + BO3 / BO4, PO4 and F -The resulting amorphous lithium-boron-phosphorus-oxygen-fluorine glass phase exhibits a certain degree of fluidity at the conversion temperature, filling micropores and interface defects on the precursor surface to some extent, thus enhancing the compactness and interfacial bonding strength of the protective layer. Simultaneously, fluoride ions (F...) generated from the decomposition of the fluorine-containing components... - Driven by concentration gradient and thermodynamics, fluoride ions diffuse directionally outward from the protective layer. In the outer region, fluoride ions combine with lithium ions, and lithium fluoride nanocrystals are precipitated through in-situ fluorination reactions, ultimately forming a continuous gradient structure with a highly adhesive glassy phase as the main component in the inner layer and a chemically inert lithium fluoride-rich outer layer.

[0043] Specifically, the thermal conversion treatment in S4 is performed at a temperature of 250–450 °C, a holding time of 0.5–5 h, and a heating rate of 0.5–10 °C / min. The inert atmosphere is argon or nitrogen, with an oxygen content of less than 500 ppm, to promote the glass transition reaction and in-situ fluorination while suppressing oxidation side reactions.

[0044] Preferably, after step S4, step S5 is further included: densifying the polymer solid-state battery cathode material on which the interface protective layer is formed, wherein the densification treatment includes heat treatment at 120°C to 250°C for 0.2 to 3 hours, or hot pressing at 50 MPa to 200 MPa pressure, to improve the bonding strength between the protective layer and the single-crystal nickel-rich layered oxide and reduce the interface porosity.

[0045] Example 1 A method for preparing an all-solid-state battery includes the following steps: LiNi single-crystal nickel-rich layered oxide cathode material 0.90 Co 0.05 Mn 0.05O2 with a D50 of 6 μm was dried in a vacuum oven at 120 °C for 12 h to obtain positive electrode powder, which was then cooled and placed in an argon atmosphere for later use. Using acetonitrile and ethanol (volume ratio 8:2) as solvent, fluorinated phosphorus source LiPO2F2 and fluorinated boron source LiDFOB (molar ratio 2:1) were added, controlling the solid content of the solution at 2.0 wt%. After stirring for 30 min and sonicating for 10 min, a homogeneous precursor solution was obtained. This precursor solution was deposited onto the surface of the positive electrode powder using a fluidized bed spraying method. The inlet temperature was 120 °C, the outlet temperature was 80 °C, and the spraying time was 45 min, resulting in a final protective layer mass fraction of approximately 0.30 wt%. After spraying, the powder was dried at 80 °C for 2 h in an argon atmosphere. Subsequently, the coated powder was placed in a tube furnace, and high-purity argon gas was introduced. The temperature was increased to 350 °C at a rate of 2 °C / min and held for 2 h, followed by natural cooling to obtain a polymer solid-state battery positive electrode material with an interface protective layer. The interface protective layer is approximately 30 nm thick, with a lithium borophosphate glass phase enrichment region near the single-crystal nickel-rich layered oxide side and a lithium fluoride nanocrystal enrichment region on the outer side. The lithium fluoride nanocrystals have a particle size of approximately 3–10 nm. To further stabilize the continuity of the coating, the polymer solid-state battery cathode material with the interface protective layer was incubated at 180 °C for 1 h under an argon atmosphere.

[0046] The polymer solid-state battery positive electrode material with an interface protective layer, polymer solid electrolyte PEO, and conductive agent are mixed and uniformly dispersed at a mass ratio of 70:25:5, and pressed at a pressure of 300 MPa to form a positive electrode composite layer. This composite layer is then pressed together with a PEO-LLZTO electrolyte membrane at a pressing pressure of 500 MPa. The negative electrode uses metallic lithium.

[0047] The circuit was cyclically converted to 0.1 C for 3 cycles, with a voltage window ranging from 2.75 V to 4.2 V. This was followed by 200 cycles at 0.5 C and rate testing. The test results were as follows: initial discharge capacity of 206 mAh / g, capacity retention of 88% after 200 cycles, initial interface impedance increasing from approximately 58 Ω to approximately 105 Ω after 200 cycles, and discharge capacity of approximately 152 mAh / g at 2 C.

[0048] Example 2 A method for preparing an all-solid-state battery includes the following steps: LiNi single-crystal nickel-rich layered oxide cathode material 0.88 Co 0.06 Mn 0.06O2, with a D50 of approximately 4 μm, was dried in a vacuum oven at 100 °C for 10 h to obtain positive electrode powder. After cooling, it was placed in a nitrogen atmosphere for later use. Using acetonitrile and ethanol at a volume ratio of 7:3 as solvent, fluorinated phosphorus source LiPO2F2 and fluorinated boron source LiDFOB were added at a molar ratio of 3:1, controlling the solid content of the solution to 5.0 wt%. 0.5 wt% polyvinylpyrrolidone was added as a dispersant. After stirring for 30 min and sonicating for 10 min, a uniform precursor slurry was obtained. The precursor slurry was spray-dried and deposited. The coated powder was collected and dried at 60 °C for 4 h in a nitrogen atmosphere to achieve a final protective layer mass fraction of approximately 0.15 wt%. Subsequently, the temperature was increased to 300 °C at 1 °C / min and held for 1 h in a nitrogen atmosphere to obtain a polymer solid-state battery positive electrode material with an interface protective layer. The interface protective layer was approximately 15 nm thick, with a higher lithium fluoride content on the outer surface than in the inner layer, and the inner layer exhibiting a continuous glass phase.

[0049] The polymer solid-state battery positive electrode material with an interface protective layer, polymer solid electrolyte PEO, and conductive agent are mixed and uniformly dispersed at a mass ratio of 70:25:5, and pressed at a pressure of 300 MPa to form a positive electrode composite layer. This composite layer is then pressed together with a PEO-LLZTO electrolyte membrane at a pressing pressure of 500 MPa. The negative electrode uses lithium metal.

[0050] The circuit was cyclically converted to 0.1 C for 3 cycles, with a voltage window ranging from 2.75V to 4.2V. This was followed by 200 cycles at 0.5 C and rate testing. The results were as follows: initial discharge capacity of 198 mAh / g, capacity retention of 76% after 200 cycles, initial interface impedance increasing from approximately 72 Ω to approximately 130 Ω after 200 cycles, and discharge capacity of approximately 142 mAh / g at 2 C.

[0051] Example 3 A method for preparing an all-solid-state battery includes the following steps: LiNi single-crystal nickel-rich layered oxide cathode material 0.92 Co 0.04 Mn 0.04O2, with a D50 of approximately 8 μm, was dried in a vacuum oven at 130 °C for 10 h to obtain positive electrode powder. After cooling, it was placed in an argon atmosphere for later use. Using acetonitrile as a solvent, fluorinated phosphorus source LiPO2F2 and fluorinated boron source LiDFOB were added at a molar ratio of 3:1, controlling the solid content of the solution at 1.6 wt%. After stirring for 30 min and sonicating for 10 min, a homogeneous precursor solution was obtained. This precursor solution was deposited onto the surface of the positive electrode powder using fluidized bed spraying at an inlet temperature of 150 °C and an outlet temperature of 95 °C. After drying, a second spraying deposition was performed using a LiBF4 solution. The resulting coated powder was heated to 400 °C at a rate of 3 °C / min and held for 1 h in an argon atmosphere, followed by natural cooling to obtain a polymer solid-state battery positive electrode material with an interface protective layer. The total thickness of the interface protective layer is approximately 80 nm. The protective layer has a lithium borophosphate glass phase enrichment region near the single-crystal nickel-rich layered oxide side and a lithium fluoride nanocrystal enrichment region on the outer side. The lithium fluoride nanocrystals have a particle size of approximately 2-8 nm. To improve long-term adhesion and resistance to contact degradation, the fabricated positive electrode composite electrode was hot-pressed at 200 ℃ and 100 MPa for 20 min to promote glass phase rearrangement and pore filling.

[0052] The polymer solid-state battery positive electrode material with an interface protective layer, polymer solid electrolyte PEO, and conductive agent are mixed and uniformly dispersed at a mass ratio of 70:25:5, and pressed at a pressure of 300 MPa to form a positive electrode composite layer. This composite layer is then pressed together with a PEO-LLZTO electrolyte membrane at a pressing pressure of 500 MPa. The negative electrode uses lithium metal.

[0053] The system was subjected to three cycles at 0.1 C with a voltage window ranging from 2.75 V to 4.2 V, followed by 200 cycles at 0.5 C and rate testing. The test results were as follows: the discharge specific capacity in the first cycle was 199 mAh / g, the capacity retention rate after 200 cycles was 79%, the initial interface impedance increased from approximately 78 Ω to approximately 116 Ω after 200 cycles, and the discharge specific capacity at 2 C was approximately 152 mAh / g.

[0054] Comparative Example 1 Compared with Example 1, Comparative Example 1 uses the same batch of single-crystal nickel-rich layered oxide cathode material LiNi. 0.90 Co 0.05 Mn 0.05 The positive electrode composite formulation, pressing pressure conditions, electrolyte system, negative electrode type, and formation and cycling test conditions are consistent with those in Example 1, but no surface coating or thermal conversion treatment is performed, i.e., no lithium borophosphate glass ceramic-lithium fluoride gradient protective layer is constructed.

[0055] Test results show: initial discharge capacity of 154 mAh / g; capacity retention of approximately 55% after 200 cycles at 0.5 C; initial interface impedance rapidly increased from approximately 94 Ω to approximately 420 Ω after 200 cycles; and discharge capacity of approximately 95 mAh / g at 2 C.

[0056] Comparative Example 2 Compared with Example 1, Comparative Example 2 uses the same batch of single-crystal nickel-rich layered oxide cathode material LiNi. 0.90 Co 0.05 Mn 0.05 The O2, positive electrode composite formulation, pressing pressure conditions, electrolyte system, negative electrode type, and formation and cycling test conditions were all consistent with those in Example 1, but only a single lithium fluoride layer was formed on the positive electrode surface, without introducing a lithium borophosphate glass phase or forming a gradient structure. Specifically, only LiBF4 precursor was used for fluidized bed spraying deposition, with the protective layer mass fraction controlled at 0.30 wt%. Subsequently, the temperature was increased to 350 ℃ at 2 ℃ / min and held for 2 h under an argon atmosphere, so that the precursor was mainly converted into a lithium fluoride layer, and the protective layer thickness was about 30 nm.

[0057] Test results show that the first discharge specific capacity is 185 mAh / g; the capacity retention rate after 200 cycles at 0.5 C is about 71%; the initial interface impedance increases from about 82 Ω to about 210 Ω after 200 cycles; and the discharge specific capacity at 2 C is about 125 mAh / g.

[0058] The electrical performance of the solid-state full cells in the examples and comparative examples is shown in Table 1: Table 1 Electrical properties of solid-state full cells

[0059] As shown in Table 1, the first-cycle discharge specific capacity of Example 1 was 206 mAh / g, and the capacity retention rate after 200 cycles at 0.5 C was 88%, both of which were superior to the comparative example. At the same time, the initial interface impedance of Example 1 was 58 Ω, and the interface impedance after 200 cycles was 105 Ω, which was significantly lower than the initial interface impedance of Comparative Example 1 (94 Ω) and the interface impedance after 200 cycles (420 Ω), and the initial interface impedance of Comparative Example 2 (82 Ω) and the interface impedance after 200 cycles (210 Ω). This indicates that after constructing a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase on the surface of the single-crystal nickel-rich layered oxide cathode, the present invention can effectively suppress the interfacial side reactions of polymer solid electrolytes under high voltage and slow down the impedance accumulation caused by decomposition products, thereby reducing polarization and maintaining a more stable interfacial ion transport pathway.

[0060] Furthermore, Example 1 exhibits a discharge specific capacity of 152 mAh / g at 2 C, which is significantly higher than that of Comparative Example 1 (95 mAh / g) and Comparative Example 2 (125 mAh / g). This indicates that while providing high-potential chemical isolation and electronic insulation, the gradient layer does not introduce excessive lithium-ion transport resistance. Instead, through the synergistic effect of the dense bonding of the inner glass phase and the stable barrier of the outer lithium fluoride enrichment region, it enhances the continuity of interfacial contact and the efficiency of ion migration across the interface, thereby improving the rate output.

[0061] Comparing Examples 2 and 3, it is evident that battery performance varies accordingly when the composition and structural gradient of the protective layer change. Example 2 exhibits a first-cycle discharge specific capacity of 198 mAh / g, a capacity retention of 76%, an initial interface impedance of 72 Ω, and 130 Ω after 200 cycles, with a 2C discharge specific capacity of 142 mAh / g. Example 3 shows a first-cycle discharge specific capacity of 199 mAh / g, a capacity retention of 79%, an initial interface impedance of 78 Ω, and 116 Ω after 200 cycles, with a 2C discharge specific capacity of 152 mAh / g. Both are significantly superior to the comparative examples, indicating that regardless of whether a single-stage deposition conversion or a stepwise deposition method is used to construct the gradient structure, the glass-ceramic protective layer described in this invention can reduce interface impedance growth and improve cycle stability to a certain extent. In particular, Example 3 demonstrates an interface impedance of 116 Ω and a 2C capacity of 152 mAh / g after 200 cycles, showing that stepwise deposition and subsequent stabilization treatment are beneficial for enhancing the continuous coverage of the gradient layer and the stability during service, thereby further suppressing interface contact degradation and improving high-rate performance.

[0062] Figure 2 This is a schematic diagram comparing the interface mechanism of an uncoated interface with that of the present invention, which is coated with a protective layer. Figure 2 In case a, the cathode particles are in direct contact with the polymer solid electrolyte without an interface protective layer. Under charging, discharging and high-potential conditions, they are more prone to interface decomposition reactions and the generation of an interface decomposition product layer with low ionic conductivity. This leads to obstructed ion migration across the interface, increased polarization, a rapid increase in interface impedance, and induction of capacity and rate performance degradation. Figure 2In Figure b, the interface protective layer of this invention is applied. This layer effectively isolates the positive electrode particles from the polymer solid electrolyte. The outer lithium fluoride nanocrystals suppress side reactions, while the inner lithium borophosphate amorphous glass phase enhances interfacial adhesion and promotes more continuous contact. This significantly slows down impedance growth and maintains a more stable ion transport pathway. This mechanism is consistent with the data in Table 1. The initial interface impedance of Example 1 was 58 Ω, and after 200 cycles, it was 105 Ω, significantly lower than the 94 Ω and 420 Ω of Comparative Example 1 and the 82 Ω and 210 Ω of Comparative Example 2. Furthermore, Example 1 achieved 88% capacity retention after 200 cycles at 0.5 C and a discharge specific capacity of 152 mAh / g at 2 C, demonstrating the comprehensive improvement in cycle life and rate capability resulting from interface stabilization.

[0063] In summary, this invention constructs a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase on the surface of the nickel-rich cathode. This suppresses the oxidative decomposition of the polymer electrolyte at high potentials and significantly slows down the increase in interfacial impedance, thereby resulting in higher usable capacity in the first cycle, better cycle retention, and stronger rate output capability. At the same time, the improved interfacial stability reduces the polarization accumulation and performance degradation trend in long-term cycling, thus enhancing the overall reliability and consistency of the battery.

[0064] The above are merely preferred embodiments of the present invention. It should be noted that the present invention is not limited to the above embodiments. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An interface protective layer for a polymer solid-state battery cathode material, characterized in that, The interface protective layer is a glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase, forming a gradient structure from the inside out, with an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region.

2. The interface protective layer according to claim 1, characterized in that, The thickness of the glass-ceramic composite layer is 5–200 nm, the average particle size of the lithium fluoride nanocrystals is 1–20 nm, and they are dispersed in the lithium borophosphate amorphous glass phase.

3. A polymer solid-state battery cathode material, comprising a single-crystal nickel-rich layered oxide, characterized in that, The surface of the single-crystal nickel-rich layered oxide is provided with an interface protection layer as described in any one of claims 1 to 2.

4. The cathode material according to claim 3, characterized in that, The single-crystal nickel-rich layered oxide is LiNi. x Co y Mn 1-x-y O2, where x ≥ 0.

80.

5. The positive electrode material according to claim 4, characterized in that, Based on the total mass of the cathode material, the mass fraction of the interface protective layer is 0.05 wt% to 2.0 wt%.

6. An all-solid-state battery, comprising a positive electrode material, a polymer solid electrolyte layer, and a negative electrode, characterized in that, The cathode material is the cathode material according to any one of claims 3 to 5, and the solid electrolyte layer comprises a polymer solid electrolyte, which is selected from the PEO and LLZTO composite system.

7. A method for preparing a polymer solid-state battery cathode material, characterized in that, Includes the following steps: S1: Provides single-crystal nickel-rich layered oxide cathode powder; S2: Prepare coating precursor solutions or slurries containing fluorine-phosphorus and fluorine-boron sources; S3: Uniformly coat the surface of single-crystal nickel-rich layered oxide cathode powder with precursor solution or slurry; S4: Under an inert atmosphere, the coated cathode powder is subjected to thermal conversion treatment, causing the precursor to undergo condensation and glassization reactions, accompanied by in-situ fluorination reactions. A glass-ceramic composite layer composed of lithium fluoride nanocrystals and lithium borophosphate amorphous glass phase is formed on the surface of the cathode powder, forming a gradient structure from the inside out, with an inner lithium borophosphate glass-ceramic phase enrichment region and an outer lithium fluoride enrichment region.

8. The method according to claim 7, characterized in that, In step S3, at least one of atomic layer deposition, atomization deposition, and fluidized bed spraying is used to uniformly prepare a coating precursor solution or slurry on the surface of the single-crystal nickel-rich layered oxide cathode powder.

9. The method according to claim 7, characterized in that, In step S2, the fluorinated phosphorus source is selected from at least one of LiPO2F2, NH4PO2F2 and metal fluorinated phosphates; the fluorinated boron source is selected from at least one of LiDFOB, LiBF4 and fluorinated borates; the molar ratio of the fluorinated phosphorus source to the fluorinated boron source is 0.2 to 5:1; the solvent of the precursor solution or slurry is at least one of acetonitrile, ethanol, isopropanol and carbonate solvents; and the solid content of the precursor solution is 0.2 to 20 wt%.

10. The method according to claim 7, characterized in that, The heat conversion treatment temperature described in S4 is 250–450℃, the holding time is 0.5–5 h, and the heating rate is 0.5–10 ℃ / min; After step S4, step S5 is also included: densifying the polymer solid-state battery cathode material on which the interface protective layer is formed, wherein the densification process includes heat treatment at 120°C to 250°C for 0.2 to 3 hours, or hot pressing at 50 MPa to 200 MPa pressure.

Images