A mixed ionic ternary positive electrode material for a negative electrode-free battery, a preparation method thereof, and a negative electrode-free battery

Abstract

This invention provides a mixed-ion ternary cathode material for a cathodeless battery, its preparation method, and the cathodeless battery itself, belonging to the field of electrochemical energy storage technology. Addressing the problems of lithium dendrite growth, short cycle life, inability to introduce large-radius active alkali metal ions at a high proportion in high-nickel ternary cathode materials, and susceptibility to cation mixing and structural collapse in existing cathodeless batteries, this invention provides a material with the general formula Li... (1‑x) M x The cathode material of TMO2, wherein 0.40≤x≤0.60, M represents large-radius alkali metal ions, and TM represents ternary transition metal components, is prepared using a molten salt-interface energy barrier synergistic sintering process, combined with cationic anti-mixing additives and gradient temperature sintering. This invention can achieve a high proportion of active alkali metal introduction, eliminate cationic mixing, and form a low surface energy alloy in situ during charge and discharge, suppressing lithium dendrite formation at its source, significantly improving the cycle stability and safety of the anode-free battery. The mixed-ion ternary cathode material retains ≥85% of its capacity after 300 cycles at 1C within a voltage range of 2.6~4.3V.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a mixed-ion ternary cathode material for a negative electrode-free battery, its preparation method, and a negative electrode-free battery. Background Technology

[0002] Electrodeless batteries, also known as electrodeless lithium metal batteries, refer to battery systems where the negative electrode side is not pre-loaded with active lithium metal. Instead, a current collector serves as the negative electrode substrate, and energy storage is achieved through the deposition and dissolution of alkali metal ions from the positive electrode material on the current collector surface during charging and discharging. Compared to traditional graphite negative electrode batteries and pre-loaded lithium metal batteries, electrodeless batteries can maximize the system's mass energy density and volumetric energy density, making them one of the core development directions for next-generation high-energy-density energy storage devices, such as power batteries and large-scale energy storage batteries.

[0003] However, negative electrodeless batteries have a recognized commercialization bottleneck. During charge and discharge cycles, the uneven deposition of alkali metal ions on the surface of copper current collectors easily forms lithium dendrites. The continuous growth of dendrites can pierce the separator and cause internal short circuits in the battery, posing a serious safety hazard. At the same time, uneven deposition can lead to the generation of a large number of dead lithium, causing irreversible loss of active alkali metals, resulting in poor battery cycle reversibility and rapid decay of cycle life, which seriously restricts its industrialization process.

[0004] To improve the performance of layered oxide cathode materials, current technologies often introduce Na into high-nickel ternary cathode materials. + K + Large-radius alkali metal ions are introduced to increase the interlayer spacing of the material, suppress structural phase transitions during charge and discharge, and improve the cycle stability of the cathode material. However, the core purpose of introducing large-radius alkali metal ions in existing technologies is only to optimize the crystal structure of the cathode material itself, stabilize the layered framework, and improve the cycle or rate performance of the cathode. They are not designed to address the core requirement of dendrite suppression in cathode-less batteries, and therefore cannot control the ion deposition behavior on the anode side. Only when the total alkali metal substitution amount is sufficiently high can the concentration of alkali metal ions in the system support the formation of a continuous, uniform, and stable Li-alkali metal alloy deposition layer. If the substitution amount is insufficient, alkali metal ions can only be used as trace doping to regulate the crystal structure of the cathode material and cannot be used as an active ion source to control the deposition potential. Meanwhile, existing technologies all involve trace doping, with doping amounts typically not exceeding 10 mol%, making it impossible to introduce large quantities and high proportions of alkali metal ions. Such trace doping is merely lattice doping, and when large-radius alkali metal ions are introduced using traditional solid-state sintering or ordinary high-temperature sintering processes, the ion diffusion process is disordered, and cation mixing is very likely to occur. It is impossible to construct a mixed ion system that can participate in negative electrode deposition and obtain a layered structure with high crystallinity, no cation mixing, and no impurity phases.

[0005] In summary, existing technologies cannot achieve the large-scale active introduction of large-radius alkali metal ions, cannot solve the problem of cation mixing under high introduction amounts, and cannot suppress dendrites in electrodeless batteries. There is an urgent need in this field for a novel mixed-ion ternary cathode material and its preparation method to meet the safety and long-cycle requirements of electrodeless batteries. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, the present invention aims to provide a hybrid ion ternary cathode material for a negative electrode-free battery, its preparation method, and a negative electrode-free battery, thereby overcoming the shortcomings of the prior art.

[0007] The present invention employs the following technical solutions to achieve its objective: The first aspect of the present invention provides a mixed-ion ternary cathode material for a negative electrodeless battery, the mixed-ion ternary cathode material having the general chemical formula Li. (1-x) M x TMO2, wherein M is one or more of Na, K, Rb, and Cs, and 0.40≤x≤0.60; the TM contains a ternary transition metal component of Ni, Co, and Mn, wherein the molar percentage of Ni in the ternary transition metal component is ≥60%.

[0008] In the general chemical formula of the hybrid ionic ternary cathode material, the ions selected from M are all large-radius alkali metal ions, and their ionic radii are all greater than those of Li. + On the one hand, it can exist stably in the alkali metal layer, increasing the interlayer spacing of the material and reducing Li + This creates a diffusion barrier for insertion / extraction, improving rate performance, and on the other hand, it can interact with Li. + Together they form a mixed ion system, which deintercalates from the positive electrode during charging and discharging, and reacts with Li on the surface of the negative electrode current collector. + A Li-M metal alloy is co-deposited and formed in situ. This alloy has a lower surface energy, which significantly reduces the nucleation overpotential of metal deposition, achieving uniform deposition and fundamentally inhibiting the formation and growth of lithium dendrites. Simultaneously, different alkali metal ions have different deposition potentials, enabling stepwise deposition. The preferentially deposited alkali metals can serve as uniform nucleation sites, further guiding subsequent Li... + Uniform deposition.

[0009] Unlike existing technologies that rely on trace doping, this invention introduces a large number of large-radius alkali metal ions, with a total substitution amount of alkali metal M reaching 0.4~0.6. When x < 0.40, an effective mixed ion deposition system cannot be constructed, making it difficult to achieve alloying and dendrite suppression effects. When x > 0.60, the material can contain intercalated and deintercalated Li... +If the content is too low, the specific capacity of the battery will decrease significantly and fail to meet the energy storage requirements. Within the range of 0.40≤x≤0.60, the specific capacity of the material and the dendrite suppression effect of mixed ions can be balanced. At the same time, the preparation method of the present invention can maintain the pure phase layered structure.

[0010] The mixed-ion ternary cathode material has a layered pure-phase structure in space group R-3m, with an interlayer spacing of 4.70~4.90 Å for the (003) crystal plane obtained by X-ray diffraction. This structure is a classic crystal structure for ternary layered oxide cathodes, possessing two-dimensional alkali metal ion diffusion channels, enabling efficient insertion / extraction of alkali metal ions while avoiding side reactions caused by impurities, thus improving the electrochemical stability of the material. The material of this invention has no cation mixing; M is distributed only in the alkali metal layer, ensuring that all introduced alkali metal ions have insertion / extraction activity and can participate in ion insertion / extraction and negative electrode deposition during charge / discharge processes, while maintaining the integrity and stability of the layered structure and avoiding performance degradation caused by inactive ions.

[0011] Preferably, the TM further includes a high-valence dopant element, wherein the molar percentage of the high-valence dopant element in the TM is ≤5%, and the high-valence dopant element is selected from one or more of Al, Mg, Zr, Ti, W, Nb, and Mo.

[0012] A second aspect of the present invention provides a method for preparing the mixed-ion ternary cathode material for the negative electrodeless battery, comprising the following steps: (1) Raw material mixing: Weigh the ternary transition metal carbonate precursor, lithium source, alkali metal source corresponding to M, molten salt carrier, and cationic anti-mixing agent according to the target stoichiometric ratio, and mix them evenly to obtain mixed raw materials; (2) Gradient sintering: The mixed raw materials are placed in a sintering equipment with an oxygen atmosphere for the first stage of heating and sintering; the heating rate is reduced and the second stage of heating and sintering is carried out in the same sintering equipment. (3) Post-processing: After the sintered product is naturally cooled to room temperature, it is washed to remove residual molten salt and impurities, and then vacuum dried at 80~120℃ for 12~24h to obtain the mixed ion ternary cathode material.

[0013] Preferably, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxalate; the lithium source can be in hydrated form or in dehydrated form.

[0014] Preferably, the alkali metal source corresponding to M is selected from one or more of the following: the oxide (M2O), the carbonate (M2CO3), the sulfate (M2SO4), the hydroxide (MOH), and the nitrate (MNO3).

[0015] Preferably, the molten salt carrier is selected from one or more complex salts selected from alkali metal chlorides, alkali metal sulfates, and alkali metal carbonates. More preferably, the molten salt carrier is an alkali metal chloride. The alkali metal chloride is a complex salt formed from two or more of LiCl, NaCl, KCl, RbCl, and CsCl.

[0016] Preferably, the cationic anti-mixing agent is one or more of RbLuO2, RbYbO2, CsInSe2O6, and CsTe2O6, and the preparation method of RbLuO2, RbYbO2, CsInSe2O6, and CsTe2O6 includes the following steps: Rare earth oxides RE2O3 (RE=Yb or Lu) and Rb2O are mixed in a 1:1 molar ratio and quenched at 520~550℃ for 2~3 hours under an oxygen-free dry argon atmosphere to obtain RbREO2 (RE=Yb or Lu) composite oxide. The weighing and mixing of Rb2O are carried out in a glove box filled with inert gas. The preparation method of CsInSe2O6 includes the following steps: Cs2CO3 and In2O3 are mixed in a 1:1 molar ratio, pressed into tablets, and kept at 800℃ in air for 12-24 hours to obtain CsInO2; CsInO2 and SeO2 are mixed in a 1:2 molar ratio, pressed into tablets, placed in a vacuum-sealed tube and kept at 540℃-560℃ for 10-14 hours; after cooling, the mixture is regrinded, pressed into tablets, and placed in a vacuum-sealed tube again and kept at 540℃-560℃ for another 10-12 hours to obtain pure phase CsInSe2O6 powder; The preparation method of CsTe2O6 includes the following steps: CsNO3 (brand: Sigma-Aldrich) and TeO2 (brand: Sigma-Aldrich) are mixed in a molar ratio of 1:2 and heated at 550℃~650℃ for 10~12 hours in an air atmosphere to obtain pure phase CsTe2O6.

[0017] Preferably, the total molar ratio of the lithium source and the alkali metal source corresponding to M to the ternary transition metal carbonate precursor is 1.03:1 to 1.06:1, wherein the molar ratio of the alkali metal source corresponding to M is 0.4 to 0.6 of the total molar ratio of the lithium source and the alkali metal source corresponding to M; the mass ratio of the molten salt support to the ternary transition metal carbonate precursor is 1:1 to 10:1; and the amount of the cationic anti-mixing agent added is 0.1% to 10.0% of the total mass of the ternary transition metal carbonate precursor.

[0018] Preferably, the heating rate of the first stage of heating sintering is 1~3℃ / min, the temperature is raised to 500~600℃, and the holding temperature is 1~5h; the heating rate of the second stage of heating sintering is 0.1~0.5℃ / min, the temperature is raised to 720~800℃, and the holding temperature is 10~30h.

[0019] This invention employs a molten salt-interface barrier synergistic sintering method to prepare the aforementioned mixed-ion ternary cathode material. The preparation process includes four core stages: raw material mixing, gradient sintering, high-temperature stabilization, and post-treatment. During the gradient sintering stage, the ternary transition metal carbonate precursor decomposes, the molten salt forms a eutectic liquid phase, and the rubidium / cesium-based anti-mixing agent forms an R-3m interface layer on the crystal plane, selectively raising the energy barrier of the transition metal layer and initially establishing anti-mixing thermodynamic conditions. Subsequently, an ultra-low temperature gradient of 0.1~0.5℃ / min is used to avoid disrupting the thermodynamic equilibrium of the layered structure. Under the mass transfer of the molten salt liquid phase and the interface regulation of the agent, ions diffuse and rearrange in an orderly manner, with a large number of large-radius alkali metal ions occupying the alkali metal layer and not entering the transition metal layer, ensuring a pure-phase structure.

[0020] A third aspect of the present invention provides a negative electrode-free battery, comprising a positive electrode, a separator, and a negative electrode current collector, wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material is the mixed-ion ternary positive electrode material.

[0021] The preparation method of the positive electrode sheet includes: weighing the mixed ionic ternary positive electrode material, conductive agent, and binder in a weight ratio of (90~95):(3~4):(2~3), mixing them with NMP to prepare a positive electrode slurry, degassing it, coating it on high-purity aluminum foil with a scraper, drying it in sections, rolling it, and die-cutting it to form a positive electrode sheet.

[0022] The conductive agent is preferably one or more of conductive carbon black, carbon nanotubes, and graphene; the binder is preferably one or more of polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate, and hexafluoropropylene copolymer.

[0023] The diaphragm is one or more of the following: polypropylene (PP) diaphragm, polyethylene (PE) diaphragm, PP / PE composite diaphragm, ceramic-coated modified diaphragm, polyvinylidene fluoride (PVDF) coated diaphragm, and polyimide (PI) diaphragm.

[0024] The present invention adopts a negative electrode-free battery architecture, wherein the negative electrode sheet is directly composed of a negative electrode current collector, the negative electrode current collector is a copper foil, and the surface of the negative electrode current collector is not loaded with any negative electrode active material layer.

[0025] After the electrode stacking is completed, positive and negative electrode tabs are welded on respectively, and the battery is encapsulated with an aluminum-plastic composite film shell. After injecting ether-based electrolyte, the battery is left to stand at room temperature for 12-24 hours to obtain a negative electrode-free battery. The ether-based organic solvent in the ether electrolyte includes, but is not limited to, one or more of 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetrahydrofuran.

[0026] After the first charge, the mixed-ion ternary cathode material of the battery deposits a Li-M-containing binary or ternary alloy layer on the surface of the cathode current collector.

[0027] The negative electrode-free battery retains ≥85% of its capacity after 300 cycles at 1C within a voltage range of 2.6~4.3V.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces large-radius alkali metal ions M, which, during the charging and discharging process, allow M ions and lithium ions to be de-intercalated and intercalated together from the positive electrode and form a Li-M metal alloy in situ on the surface of the negative electrode current collector. This alloy layer has a low surface energy, which can significantly reduce the nucleation overpotential of metal deposition and induce uniform metal deposition, thereby fundamentally suppressing the formation of lithium dendrites and the generation of "dead lithium" in the negative electrode-free battery system.

[0029] 2. The cationic anti-mixing agent forms an interface layer on the crystal surface of the active material and selectively raises the energy barrier of the transition metal layer. Combined with an ultra-low-speed gradient heating process of 0.1~0.5℃ / min, it ensures that large-radius alkali metal ions accurately occupy the alkali metal layer sites under thermodynamic equilibrium, effectively avoiding the cationic mixing phenomenon and impurity phase formation under high-proportion substitution.

[0030] 3. Large-radius alkali metal ions play a supporting role in the alkali metal lattice layer, effectively expanding the interlayer spacing of the material, thereby reducing the diffusion barrier of lithium ions during charging and discharging, and significantly improving the rate performance of the material.

[0031] 4. This invention utilizes the eutectic liquid phase mass transfer environment provided by the molten salt carrier to enhance the diffusion dynamics of ions, and achieves a highly ordered R-3m pure phase layered structure even when the alkali metal ion substitution amount x reaches 0.4-0.6, ensuring that the material still has a high specific capacity when the substitution ratio is high.

[0032] 5. By adopting gradient sintering and segmented temperature control processes, the precursor decomposition, liquid phase nucleation and lattice rearrangement are completed step by step within the optimal temperature range. This solves the technical bottleneck of structural collapse when large-radius ions are introduced in large quantities in the traditional solid-state method, and improves the structural stability and cycle life of the mixed-ion ternary cathode material. Attached Figure Description

[0033] Figure 1 SEM image of the mixed ionic ternary material in Example 1; Figure 2 XRD pattern of the mixed-ion ternary material in Example 1; Figure 3 The first charge-discharge curve of the mixed-ion ternary material in Example 1 is shown. Figure 4 The cycling performance of the mixed-ion ternary material in an electrodeless battery as shown in Example 1; Figure 5 This is a SEM image of the negative electrode after mixed alkali metal deposition in the battery without a negative electrode in Example 1. Figure 6 The first charge-discharge curve of pure lithium ternary material is shown in Comparative Example 1. Figure 7 Comparative Example 1: Cycling performance of pure lithium ternary material in a negative electrode-free battery; Figure 8 The image shows the SEM image of the negative electrode of the battery without negative electrode 1 after lithium metal deposition. Figure 9 XRD pattern of the mixed-ion ternary material in Example 2; Figure 10 XRD pattern of the mixed ion ternary material in Example 3; Figure 11 XRD patterns of the material were prepared for Comparative Example 2; Figure 12 XRD patterns of the material were prepared for Comparative Example 3; Figure 13 XRD patterns of the material were prepared for Comparative Example 4; Figure 14 The image shows the XRD pattern of the negative electrode after the deposition of mixed alkali metals in the negative electrode-free battery of Example 1. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] In the following examples and comparative examples, the sources of raw materials or preparation methods are as follows: Ni 0.8 Co 0.1 Mn 0.1 The CO3 precursor was purchased from Zhejiang Huayou Cobalt.

[0037] Preparation method of RbLuO2 and RbYbO2: Rare earth oxides RE2O3 (RE=Yb or Lu) and Rb2O are mixed in a 1:1 molar ratio, and then quenched after being kept at 530℃ for 2 hours in an oxygen-free dry argon atmosphere to obtain RbREO2 (RE=Yb or Lu) composite oxides. The weighing and mixing of Rb2O are carried out in a glove box filled with inert gas.

[0038] Preparation method of CsTe2O6: CsNO3 and TeO2 are mixed at a molar ratio of 1:2 and heated in air at 600℃ for 12 hours to obtain pure phase CsTe2O6.

[0039] Preparation method of CsInSe2O6: Cs2CO3 and In2O3 are mixed in a 1:1 molar ratio, pressed into tablets, and kept in air at 800℃ for 15 hours to obtain CsInO2. CsInO2 and SeO2 are mixed in a 1:2 molar ratio, pressed into tablets, placed in a vacuum-sealed tube, and kept at 550℃ for 12 hours. After cooling, the mixture is regrinded, pressed into tablets, and placed in a vacuum-sealed tube again for 11 hours to obtain pure phase CsInSe2O6 powder.

[0040] Example 1

[0041] Step 1: Weigh 100g Ni 0.8 Co 0.1 Mn 0.1 For the CO3 precursor, weigh lithium hydroxide monohydrate and sodium carbonate monohydrate at a total alkali metal to TM molar ratio of 1.05:1, wherein the molar ratio of Li to Na is 0.6:0.4. Weigh LiCl-NaCl composite molten salt at a mass ratio of molten salt to precursor of 2:1 (LiCl-NaCl molar ratio 1:1). Weigh 2wt% of RbLuO2 from the precursor mass. Place all raw materials in a high-speed mixer and mix at 3000 rpm for 30 min to obtain a uniformly mixed raw material. Step 2: Place the mixed raw materials in a crucible and put it into an oxygen atmosphere tube furnace. Heat the furnace to 550°C at a heating rate of 2°C / min under an oxygen atmosphere and hold for 2 hours. Continue heating the furnace to 720°C at a heating rate of 0.5°C / min under an oxygen atmosphere and hold for 15 hours. Step 3: After sintering, allow the furnace to cool naturally to room temperature. Remove the product and wash it three times with deionized water to remove residual molten salt and soluble impurities. Then, place the washed product in a vacuum drying oven and dry it at 100°C under vacuum for 18 hours to obtain the mixed-ion ternary cathode material with the chemical formula Li. 0.6 Na 0.4 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0042] The morphology of the mixed-ion ternary material prepared in this embodiment is as follows: Figure 1 The image shows a small-particle single-crystal powder. X-ray diffraction was performed using a Cu Kα target with a scanning range of 10°–80° and a scanning rate of 0.5° / min. The XRD diffraction pattern is shown below. Figure 2 Only the diffraction signal of the layered structure of the R-3m space group appeared in the (003) crystal plane. The interlayer spacing of the obtained (003) crystal plane was 4.70~4.90 Å. There were no diffraction signals of any other impurity phases, indicating that the mixed ion ternary material prepared in this embodiment is a layered pure phase structure.

[0043] Example 2

[0044] Step 1: Weigh 100g Ni 0.8 Co 0.1 Mn 0.1 For the CO3 precursor, weigh lithium hydroxide monohydrate, sodium carbonate, and potassium carbonate at a total alkali metal to TM molar ratio of 1.05:1, where the Li:Na:K molar ratio is 0.4:0.45:0.15. Weigh LiCl-NaCl-KCl composite molten salt at a molten salt to precursor mass ratio of 3:1 (LiCl-NaCl-KCl molar ratio 1:1:1). Weigh 3 wt% of CsTe2O6 as the precursor. Place all raw materials in a high-speed mixer and mix at 3000 rpm for 30 min to obtain a uniformly mixed raw material. Step 2: Place the mixed raw materials in a crucible and put it into an oxygen atmosphere tube furnace. Heat the furnace to 550°C at a heating rate of 2°C / min under an oxygen atmosphere and hold for 2 hours. Continue heating the furnace to 750°C at a heating rate of 0.3°C / min under an oxygen atmosphere and hold for 20 hours. Step 3: After sintering, allow the furnace to cool naturally to room temperature. Remove the product and wash it three times with deionized water to remove residual molten salt and soluble impurities. Then, place the washed product in a vacuum drying oven and dry it at 100°C under vacuum for 18 hours to obtain the mixed-ion ternary cathode material with the chemical formula Li. 0.4 Na 0.45 K 0.15 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0045] Example 3

[0046] Step 1: Weigh 100g Ni 0.8 Co 0.1 Mn 0.1For the CO3 precursor, weigh lithium hydroxide monohydrate, potassium carbonate, and rubidium carbonate at a total alkali metal to TM molar ratio of 1.03:1, where the Li:K:Rb molar ratio is 0.6:0.35:0.05. Weigh LiCl-KCl-RbCl composite molten salt at a molten salt to precursor mass ratio of 2:1 (LiCl-KCl-RbCl molar ratio 2:1:0.2). Weigh 1.5 wt% of RbLuO2 from the precursor mass. Place all raw materials in a high-speed mixer and mix at 3000 rpm for 30 min to obtain a uniformly mixed raw material. Step 2: Place the mixed raw materials in a crucible and put it into an oxygen atmosphere tube furnace. Heat the furnace to 550°C at a heating rate of 2°C / min under an oxygen atmosphere and hold for 2 hours. Continue heating the furnace to 760°C at a heating rate of 0.5°C / min under an oxygen atmosphere and hold for 20 hours. Step 3: After sintering, allow the furnace to cool naturally to room temperature. Remove the product and wash it three times with deionized water to remove residual molten salt and soluble impurities. Then, place the washed product in a vacuum drying oven and dry it at 100°C under vacuum for 18 hours to obtain the mixed-ion ternary cathode material with the chemical formula Li. 0.6 K 0.35 Rb 0.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0047] Example 4

[0048] Step 1: Weigh 100g Ni 0.8 Co 0.1 Mn 0.1 For the CO3 precursor, lithium hydroxide monohydrate, potassium carbonate, and cesium carbonate were weighed at a total alkali metal to TM molar ratio of 1.06:1, with the molar ratio of Li, K, and Cs being 0.5:0.45:0.05. A LiCl-KCl-CsCl composite molten salt (LiCl-KCl-CsCl molar ratio 2:1:0.1) was weighed at a molten salt to precursor mass ratio of 2.5:1. 2 wt% of the precursor CsInSe2O6 was also weighed. All raw materials were placed in a high-speed mixer and mixed at 3000 rpm for 30 min to obtain a uniformly mixed raw material. Step 2: Place the mixed raw materials in a crucible and put it into an oxygen atmosphere tube furnace. Heat the furnace to 550°C at a heating rate of 3°C / min under an oxygen atmosphere and hold for 2 hours. Continue heating the furnace to 720°C at a heating rate of 0.5°C / min under an oxygen atmosphere and hold for 20 hours. Step 3: After sintering, allow the furnace to cool naturally to room temperature. Remove the product and wash it three times with deionized water to remove residual molten salt and soluble impurities. Then, place the washed product in a vacuum drying oven and dry it at 100°C under vacuum for 24 hours to obtain the mixed-ion ternary cathode material with the chemical formula Li. 0.5 K 0.45 Cs 0.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0049] Comparative Example 1 Step 1: Weigh 100g Ni 0.8 Co 0.1 Mn 0.1 For the CO3 precursor, weigh lithium hydroxide monohydrate at a Li to TM molar ratio of 1.05:1, without adding any alkali metal source, molten salt carrier, or cationic anti-mixing agent. Place the raw materials in a high-speed mixer and mix at 3000 rpm for 30 min to obtain a uniformly mixed raw material. Step 2: Place the mixed raw materials in a crucible and put it into an oxygen atmosphere tube furnace. Heat the furnace to 550°C at a heating rate of 2°C / min under an oxygen atmosphere and hold for 2 hours. Continue heating the furnace to 720°C at a heating rate of 2°C / min under an oxygen atmosphere and hold for 15 hours. Step 3: After sintering, the product is allowed to cool naturally to room temperature in the furnace. The washed product is then placed in a vacuum drying oven and dried at 100°C under vacuum for 18 hours to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2 ternary cathode material.

[0050] Comparative Example 2 The difference between this comparative example and Example 1 is that no RbLuO2 cationic anti-mixing agent is added; the other steps are the same as in Example 1.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that LiCl-NaCl composite molten salt is not added; the other steps are the same as in Example 1.

[0052] Comparative Example 4 The difference between this comparative example and Example 1 is that step 2 is as follows: the mixed raw materials are placed in a crucible and then placed in an oxygen atmosphere tube furnace, and heated to 720°C at a heating rate of 2°C / min under an oxygen atmosphere, and held at that temperature for 17 hours; the other steps are the same as in Example 1.

[0053] Comparative Example 5 The difference between this comparative example and Example 1 is that the molar ratio of Li to Na is 0.8:0.2, while the other steps are the same as in Example 1.

[0054] Comparative Example 6 The difference between this comparative example and Example 1 is that the molar ratio of Li to Na is 0.2:0.8, while the other steps are the same as in Example 1.

[0055] The performance of the above-mentioned examples and comparative examples of negative electrode-free soft-pack batteries was tested: The mixed-ion ternary positive electrode material prepared in the examples and comparative examples was used as the active material. It was weighed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 95:3:2 and then mixed with NMP to prepare a positive electrode slurry. After degassing, it was coated on high-purity aluminum foil with a doctor blade, dried in sections, rolled and die-cut to form a positive electrode sheet. A stacked soft-pack structure was adopted, consisting of a positive electrode sheet, a separator, high-purity copper foil (without additional negative electrode active material) and an aluminum-plastic composite film shell. After welding the positive and negative electrode tabs, it was sealed, injected with ether electrolyte, and allowed to stand and form to complete the assembly. The Blue Electric test system was used to test the constant current charge and discharge mode in a constant temperature environment of 25±2℃ and a voltage window of 2.6~4.3V. The electrochemical parameters such as capacity retention rate, first discharge capacity and first coulombic efficiency after 300 cycles at 1C were recorded in Table 1.

[0056] Table 1. Cyclic capacity, capacity retention, and coulombic efficiency test data for the examples and comparative examples.

[0057] Example 1 exhibited an initial discharge specific capacity of 183.1 mAh / g, an initial coulombic efficiency of 92.17%, and an average voltage plateau of 3.57 V, demonstrating good electrochemical activity. Example 2 (Na+K disubstituted, x=0.60) and Example 4 (Cs monosubstituted, x=0.50) showed initial discharge specific capacities of 161.8 mAh / g and 169.3 mAh / g, respectively, slightly lower than Example 1. This is due to the reduced proportion of active Li⁺ in the material caused by the high alkali metal substitution; however, their initial coulombic efficiencies both exceeded 92%, indicating good structural integrity and minimal irreversible capacity loss during the initial charge-discharge process. The charge-discharge curves of the electrodeless battery prepared from the mixed-ion ternary material of Example 1 are shown below. Figure 3 Compared to the ordinary ternary lithium material in Comparative Example 1 ( Figure 6 The voltage plateau and specific capacity decreased, but the cycle reversibility of the electrodeless battery prepared by the mixed-ion ternary material in Example 1 was significantly improved, with a reversible capacity retention rate of up to 87.2% after 300 cycles. Figure 4 ), far exceeding the negative electrode-free battery assembled with ordinary ternary lithium materials in Comparative Example 1 ( Figure 7This is because, during the in-situ formation of the self-generated negative electrode during charging, the co-deposition of large-radius alkali metal ions with lithium and the deposition of lithium alone exhibit significant behavioral differences.

[0058] After charging cycles, the battery was disassembled, and XRD tests were performed on the deposited layer on the surface of the high-purity copper foil in Example 1. Figure 14 Clear diffraction signals of lithium and sodium can be observed, which are the self-generated negative electrode 1 formed after the first charge, indicating the co-deposition of lithium and large-radius alkali metals. The presence of large-radius alkali metal ions directly changes the nucleation and growth direction of lithium, increases the critical current density of the negative electrode, and ultimately achieves dendrite-free, dense, and uniform co-deposition of lithium and large-radius alkali metals. Figure 5 Lithium deposition alone exhibits a dendritic morphology with a high specific surface area. Figure 8 Dendritic morphology increases the contact area between the negative electrode and the electrolyte, exacerbating side reactions between the electrolyte and the negative electrode and consuming active lithium; it also makes it easier for lithium to detach from the negative electrode current collector, forming "dead lithium," leading to a large and rapid loss of active lithium source and a rapid decay of the battery's reversible capacity.

[0059] After 300 cycles at 1C, the capacity retention rates of Examples 1-4 were 87.2%, 89.6%, 85.5%, and 86.4%, respectively, all remaining above 85%. Among them, Example 2 showed the best cycling stability because the Na+K dual alkali metal system can form a more stable Li-Na-K ternary alloy deposition layer, further reducing surface energy and improving dendrite suppression.

[0060] XRD diffraction pattern of the mixed-ion ternary material prepared by Example 2 ( Figure 9 Only the diffraction signal of the R-3m space group layered structure appeared in the sample, with no diffraction signals of any other impurity phases, indicating that the mixed-ion ternary material prepared in Example 2 is a pure phase with a layered structure. Its (003) crystal plane diffraction peak is slightly forward compared to Example 1, indicating that its interplanar spacing is expanded due to the incorporation of more large-radius alkali metal ions.

[0061] XRD diffraction pattern of the mixed-ion ternary material prepared in Example 3 ( Figure 10 The diffraction signal of the layered structure of the R-3m space group was observed in the sample, with no diffraction signal of any other impurity phases, indicating that the mixed ionic ternary material prepared by Example 3 is a pure phase with a layered structure.

[0062] Compared to Example 1, the cathode material prepared by Comparative Example 2 has a different XRD diffraction pattern due to the lack of anti-mixing agent during the preparation process. Figure 11In addition to the diffraction signal of the layered structure in the R-3m space group, diffraction signals of the rock salt structure impurity phase in the Fm-3m space group also appeared, indicating that the anti-mixing agent can effectively suppress the cation mixing between large-radius gold metal ions and transition metal ions; the cathode material prepared by Comparative Example 3, due to the lack of molten salt in the preparation process, has an XRD diffraction pattern ( Figure 12 In addition to the diffraction signal of the layered structure of the R-3m space group, diffraction signals of lithium-sodium impurity phases that did not fully participate in the reaction also appeared, indicating that molten salt can effectively promote mass transfer between reactants.

[0063] Compared to Example 1, the cathode material prepared by Comparative Example 4, due to the lack of precise temperature control during preparation, exhibits a different XRD diffraction pattern. Figure 13 In addition to the diffraction signals of the layered structure in the R-3m space group, a small number of diffraction signals of the rock salt structure impurities in the Fm-3m space group also appeared, indicating that the ultra-low-speed heating can effectively avoid the destruction of the thermodynamic equilibrium of the layered structure under the synergistic effect of the additives, and achieve precise locking of the layered structure.

[0064] The capacity retention rates of Comparative Examples 2-4 after 300 cycles ranged from 69.8% to 75.4%, but were still significantly lower than those of the Examples. This is directly related to structural defects such as cation mixing and impurity phase formation. Structural instability leads to continuous dissolution of active materials and structural collapse during cycling. In Comparative Example 5, the substitution amount of alkali metal Na was 0.2%, which is not distinguishable from the trace doping of alkali metals in the prior art. Limited by the Na ion concentration and insertion / extraction potential, the actual number of sodium ions that can be extracted to participate in the co-deposition of the negative electrode is very limited, which cannot effectively suppress dendrites, resulting in low battery reversibility. In Comparative Example 6, the total substitution amount of alkali metal was 0.8%, which also showed a weakening of the co-deposition effect. Moreover, the positive electrode operating voltage and capacity were close to those of the sodium battery system, resulting in an energy density much lower than that of Examples 1-4.

[0065] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0066] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0067] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A hybrid ternary cathode material for use in a negative electrodeless battery, characterized in that, The chemical formula of the material is Li. (1-x) M x TMO2, wherein M is one or more of Na, K, Rb, and Cs, wherein 0.40≤x≤0.60; TM contains a ternary transition metal component of Ni, Co, and Mn, wherein the molar percentage of Ni in the ternary transition metal component is ≥60%; the crystal of the mixed ion ternary cathode material is a layered pure phase structure of space group R-3m, and the interlayer spacing of the (003) crystal plane obtained by X-ray diffraction is 4.70~4.90 Å.

2. A method for preparing a mixed-ion ternary cathode material for a negative electrodeless battery as described in claim 1, characterized in that, The steps include: (1) Raw material mixing: Weigh the ternary transition metal carbonate precursor, lithium source, M source, molten salt carrier and cationic anti-mixing agent according to the target stoichiometric ratio, and mix them evenly to obtain mixed raw materials; (2) Gradient sintering: The mixed raw materials are placed in a sintering equipment with an oxygen atmosphere for the first stage of heating and sintering; the heating rate is reduced and the second stage of heating and sintering is carried out in the same sintering equipment. (3) Post-processing: After the sintered product is naturally cooled to room temperature, it is washed to remove residual molten salt and impurities, and then vacuum dried at 80~120℃ for 12~24h to obtain the mixed ion ternary cathode material; The molten salt carrier is one or more composite salts selected from alkali metal chlorides, alkali metal sulfates, and alkali metal carbonates. The cationic anti-mixing agent is selected from one or more of RbLuO2, RbYbO2, CsInSe2O6, and CsTe2O6; The heating rate of the first stage of sintering is 1~3℃ / min, the temperature is raised to 500~600℃, and the holding time is 1~5h; the heating rate of the second stage of sintering is 0.1~0.5℃ / min, the temperature is raised to 720~800℃, and the holding time is 10~30h.

3. The preparation method according to claim 2, characterized in that, The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxalate; the M source is selected from one or more of the oxide, carbonate, sulfate, hydroxide, and nitrate corresponding to M.

4. The preparation method according to claim 2, characterized in that, The mass ratio of the molten salt support to the ternary transition metal carbonate precursor is 1:1 to 10:1, and the total molar amount of the lithium source and the M source is 1.03:1 to 1.06:

1.

5. The preparation method according to claim 2, characterized in that, The amount of the cationic anti-mixing agent added is 0.1 to 10.0 wt% of the total mass of the ternary transition metal carbonate precursor.

6. A negative electrode-free battery, comprising a positive electrode, a separator, and a negative electrode current collector, characterized in that, The positive electrode includes a positive electrode active material, which comprises the mixed-ion ternary positive electrode material for a negative electrode-free battery as described in claim 1.

7. The negative electrode-free battery according to claim 6, characterized in that, After the first charge, the mixed-ion ternary cathode material of the battery deposits a Li-M-containing binary or ternary alloy layer on the surface of the cathode current collector.

8. The negative electrode-free battery according to claim 6, characterized in that, The negative electrode-free battery retains ≥85% of its capacity after 300 cycles at 1C within a voltage range of 2.6~4.3V.

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