Positive electrode material and preparation method and application thereof
By modifying LiFeCl4 with anion doping, the ionic conductivity of halide cathode materials was improved, solving the problem of limited active material ratio in all-solid-state batteries and realizing the application of cathode materials with high energy density and low cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UNIV OF CHINESE ACAD OF SCI
- Filing Date
- 2025-12-30
- Publication Date
- 2026-05-01
AI Technical Summary
The low intrinsic ionic conductivity of existing halide cathode materials necessitates the addition of a large amount of solid electrolyte in all-solid-state batteries, limiting the mass ratio of active materials, affecting energy density, and increasing costs.
By anion doping LiFeCl4 with substances such as O²⁻, S²⁻, Br⁻, or I⁻, the crystal structure of LiFeCl4 can be modified, thereby improving its intrinsic ionic conductivity and reducing its dependence on solid electrolytes.
It significantly increased the mass ratio of active material in the cathode to over 90%, improving the energy density of all-solid-state batteries and reducing costs, while also simplifying the interface and improving cycle stability.
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Figure CN121964575A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery technology, and relates to a cathode material, its preparation method, and its application. Background Technology
[0002] In traditional batteries, cathode materials are mostly limited to oxides and phosphates due to the easy solubility of halides in organic electrolytes. In all-solid-state batteries, halides, with their good ionic conductivity and oxidation stability, not only serve as solid electrolytes but also show potential as cathode active materials. The development of all-solid-state batteries has greatly broadened the range of cathode material choices. Currently reported halide cathode materials include Li3TiCl6, FeCl3, and Li2FeCl4. Among these materials, Li2FeCl4 has been studied as an iron-based halide cathode, providing capacity through the Fe²⁺ / Fe³⁺ variable valence reaction, and at a lower cost. However, like most cathode active materials, Li2FeCl4 has a low intrinsic ionic conductivity, which means that a considerable proportion (usually 20-30%) of solid electrolyte must be added to construct ion transport channels when preparing composite cathodes. This severely limits the mass percentage of active material in the cathode, typically only reaching 70%, thus restricting the energy density of all-solid-state batteries.
[0003] Reference 1 (ACS Energy Lett. 2024, 9, 5464−5470) uses Li₂FeCl₄ as the positive electrode active material and combines it with a solid electrolyte (such as Li₂FeCl₄). 2.75 In 0.75 Zr 0.25 The technical solution involves mixing FeCl3 and a conductive agent to form a composite positive electrode. This solution utilizes the electrochemical activity of Fe, but due to its insufficient intrinsic ionic conductivity, an additional solid electrolyte must be introduced, which affects the proportion of active material and thus the energy density. Reference 2 (Nature Sustainability, 2024, 7(11):1492-1500) uses FeCl3 as the positive electrode active material. This solution utilizes the electrochemical activity of Fe, but due to its insufficient intrinsic ionic conductivity, an additional solid electrolyte must be introduced, which affects the proportion of active material and thus the energy density.
[0004] The aforementioned technologies have the following drawbacks: Limited proportion of positive electrode active material, thus affecting energy density: Due to the low intrinsic ionic conductivity, a large amount (20-30%) of solid electrolyte must be mixed into the positive electrode to ensure ion transport. This directly reduces the mass proportion of active material, limiting the battery's volume and gravimetric energy density. Cost-performance trade-off: To obtain high ionic conductivity, the introduced electrolyte is often a material containing rare metals (such as In, Y), increasing cost and weakening the cost advantage of iron-based materials. Interface complexity: Numerous interfaces exist between the active material and electrolyte particles, potentially introducing additional interfacial impedance and affecting long-term cycling stability.
[0005] Therefore, there is a need to provide a cathode material, its preparation method, and its application. Summary of the Invention
[0006] To overcome the shortcomings of existing technologies, a cathode material, its preparation method, and its application are provided.
[0007] This invention is achieved through the following scheme:
[0008] A cathode material is anion-doped LiFeCl4.
[0009] The anion is O²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x O x 0 <x≤0.5。
[0010] The anion is S²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x S x 0 <x≤0.5。
[0011] The anion is Br⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x Br x 0 <x≤1。
[0012] The anion is I⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x I x 0 <x≤1。
[0013] A method for preparing a positive electrode material, the method comprising the following steps:
[0014] Step 1: Weigh the raw materials LiCl, FeCl3, and anionic dopant;
[0015] Step 2: Ball mill the weighed raw materials to obtain a uniform powder, which is the finished positive electrode material. High-energy mechanical ball milling is usually used, and the milling is carried out at 200-500 rpm for 2-12 hours.
[0016] Both steps one and two are carried out in an inert gas environment, such as argon or nitrogen.
[0017] The anionic dopant is one of Li2O, Li2S, LiBr, and LiI, and the amount of the anionic dopant matches the general formula of the corresponding cathode material.
[0018] An application of a cathode material used to prepare a cathode for an all-solid-state battery.
[0019] The cathode material accounts for more than 90% of the mass of the cathode.
[0020] The beneficial effects of this invention are as follows:
[0021] 1. The cathode material provided by this invention effectively improves the intrinsic ionic conductivity of LiFeCl4 by anion doping. In traditional all-solid-state batteries, halide cathode materials such as Li2FeCl4 have low ionic conductivity, requiring the introduction of a large amount of solid electrolyte to construct ion transport channels. However, in this invention, doping with anions such as O²⁻, S²⁻, Br⁻, or I⁻ can intervene in the crystal structure, introducing appropriate lattice distortion or expanding ion migration channels, thereby promoting lithium-ion diffusion. This structural modification directly enhances the material's own ion conductivity, reduces dependence on additional solid electrolytes, and lays the foundation for constructing a more efficient cathode.
[0022] 2. Due to the improved intrinsic ionic conductivity, the proportion of solid electrolyte required to be added during the preparation of the composite cathode can be significantly reduced. This allows the mass percentage of active material in the cathode to be increased to over 90%, thereby directly improving the mass energy density and volumetric energy density of the all-solid-state battery. The problem of limited active material proportion in traditional solutions is alleviated, the cathode composition is simplified, the energy density bottleneck is broken, and it better meets the development needs of high-energy-density batteries.
[0023] 3. This invention also reduces the overall cost of all-solid-state batteries. Traditional technologies often use solid electrolytes containing rare metals such as indium or yttrium to ensure ion transport, increasing raw material costs. However, by improving the performance of LiFeCl4 through anion doping, the amount of these expensive electrolytes used is reduced, fully leveraging the lower cost advantage of iron-based materials. This makes the battery more economical and sustainable while maintaining good electrochemical performance.
[0024] 4. The reduction in solid electrolyte particles in the positive electrode simplifies the interface between the active material and the electrolyte. This reduction in the number of interfaces helps decrease interfacial impedance and reduces potential interfacial side reactions and degradation during long-term cycling. Therefore, this invention not only improves the ion conduction efficiency of the positive electrode but also contributes to improving the cycle stability and reliability of all-solid-state batteries, providing a more stable performance guarantee for practical applications. Attached Figure Description
[0025] Figure 1 LiFeCl 3.6 O 0.2 Ionic conductivity;
[0026] Figure 2 LiFeCl 3.2 O 0.4 Ionic conductivity;
[0027] Figure 3 LiFeCl 3.2 O 0.4 |Li3InCl6|LPSC|Li-In all-solid-state battery. Detailed Implementation
[0028] The present invention will be further described below with reference to specific embodiments:
[0029] A cathode material is anion-doped LiFeCl4.
[0030] The anion is O²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x O x 0 <x≤0.5。
[0031] The anion is S²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x S x 0 <x≤0.5。
[0032] The anion is Br⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x Br x 0 <x≤1。
[0033] The anion is I⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x I x 0 <x≤1。
[0034] A method for preparing a positive electrode material, the method comprising the following steps:
[0035] Step 1: Weigh the raw materials LiCl, FeCl3, and anionic dopant;
[0036] Step Two: Using high-energy mechanical ball milling, the weighed raw material is ball-milled at 200 rpm for 2 hours, followed by ball milling at 500 rpm for 10 hours to obtain a uniform powder, which is the finished positive electrode material. In practical applications, in addition to the mechanical ball milling method mentioned above, solid-state sintering or liquid-phase ion exchange methods can also be used to synthesize the target product. Both Step One and Step Two are carried out in an inert gas environment.
[0037] The anionic dopant is one of Li2O, Li2S, LiBr, and LiI, and the amount of the anionic dopant matches the general formula of the corresponding cathode material.
[0038] An application of a cathode material used to prepare a cathode for an all-solid-state battery.
[0039] The cathode material constitutes more than 90% of the cathode by mass. Based on the "self-supporting" cathode concept of this invention, while ensuring the self-sufficiency of the ion pathway, a very small amount (e.g., <5%) of high-performance solid electrolyte can still be introduced to further optimize the interface or improve the initial efficiency.
[0040] This invention provides a novel halide cathode material with high ionic conductivity suitable for all-solid-state batteries, addressing the critical issue that existing halide cathode materials require additional electrolytes due to their low intrinsic ionic conductivity. By modifying LiFeCl4, this invention significantly improves its ionic conductivity. When used as a cathode material in all-solid-state batteries, this material eliminates the need for an additional solid electrolyte, achieving a "self-supporting" effect in ionic conductivity. This significantly increases the mass ratio of active material in the cathode, leading to a breakthrough in the energy density of all-solid-state batteries.
[0041] The present application will be further described below with reference to specific embodiments:
[0042] Suitable anion doping can alter the crystal structure of LiFeCl4, expanding lithium-ion migration channels or creating new migration pathways, thereby significantly reducing the lithium-ion migration barrier and improving its bulk ionic conductivity. Taking Li2O as an anion dopant, the core of this invention lies in anion doping LiFeCl4 to obtain the general formula LiFeCl4. 4-2x O x The positive electrode active material is made to have a sufficiently high intrinsic ionic conductivity, thereby enabling the "self-transport" of ions in the positive electrode.
[0043] Step 1: According to the stoichiometric ratio of LiFeCl 4-2x O x(x = 0.1, 0.2, 0.3, 0.4, 0.5) Accurately weigh the raw materials LiCl, FeCl3, and Li2O. All operations are performed in an argon-filled glove box.
[0044] Step 2: Using high-energy mechanical ball milling, the mixed raw materials were ball milled at 200 rpm for 2 hours to obtain a uniform powder, followed by ball milling at 500 rpm for 10 hours to obtain a uniform LiFeCl₂. 4-2x O x powder.
[0045] Performance data and results:
[0046] Ionic conductivity: The ionic conductivity of different doped samples was measured using AC impedance spectroscopy. The ionic conductivity of LiFeCl4 is approximately 10⁻⁻⁻⁶. 6 S / cm, while LiFeCl 3.6 O 0.2 The ionic conductivity (x=0.2) can reach 8.9×10⁻ 5 S / cm ( Figure 1 ), LiFeCl 3.2 O 0.4 The ionic conductivity at (x=0.4) can reach 1.5 × 10⁻ 4 S / cm ( Figure 2 This represents an increase of approximately two orders of magnitude.
[0047] Cathode preparation and all-solid-state battery performance: 95wt% LiFeCl 3.4 O 0.2 The powder was mixed with 5 wt% conductive carbon black (such as Super P) and no additional solid electrolyte was added to directly prepare the positive electrode sheet. An all-solid-state battery was then assembled using this positive electrode, a lithium-indium alloy negative electrode, and a Li3InCl6 electrolyte layer.
[0048] Performance Comparison: Compared to Li₂FeCl₄ cathodes containing 40% electrolyte and FeCl₃ cathodes containing 40% electrolyte, the "electrolyte-free" cathode of this invention increases the active material content from 55% to 95%. Calculations show that the energy densities of the Li₂FeCl₄ and FeCl₃ battery cathodes are 252 Wh / kg and 350 Wh / kg, respectively. The modified LiFeCl₄... 3.6 O 0.2 The positive electrode energy density of the battery is 476Wh / kg, which significantly improves the positive electrode energy density of the battery.
[0049] This invention optimizes the intrinsic ionic conductivity of the active material, thereby significantly increasing the proportion of active material in the cathode (up to 95%), thus directly and significantly improving the mass and volumetric energy density of all-solid-state batteries. It also simplifies the cathode structure and reduces costs: the cathode composition is simplified from a ternary system of "active material, ionic conductive agent (i.e., solid electrolyte), and electronic conductive agent" to a binary system of "active material and electronic conductive agent," eliminating the need for expensive solid electrolytes, reducing material costs, and simplifying the electrode fabrication process.
[0050] Reduced interface issues: Since the cathode does not require mixing different types of solid electrolyte particles, the solid-solid interface is reduced, which is expected to lower interfacial impedance and improve the cycle stability of the battery. Opening up new applications for materials: The originally poor-performing electrolyte material LiFeCl4 has been successfully developed into a high-performance cathode material through ingenious modification, providing new ideas for the material design of halide solid-state batteries.
[0051] This invention improves the intrinsic ionic conductivity of LiFeCl4 through anion doping, which significantly reduces the amount of solid electrolyte added in the positive electrode. This achieves a higher proportion of active material and energy density while ensuring ion transport, and reduces cost and interface complexity.
[0052] Although the technical solutions of the present invention have been described and enumerated in detail, it should be understood that modifications to the above embodiments or the adoption of equivalent alternatives are obvious to those skilled in the art. Such modifications or improvements made without departing from the spirit of the present invention are all within the scope of protection claimed by the present invention.
Claims
1. A cathode material, characterized in that: The cathode material is anion-doped LiFeCl4.
2. The cathode material according to claim 1, characterized in that: The anion is O²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x O x 0 <x≤0.5。 3. The cathode material according to claim 1, characterized in that: The anion is S²⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-2x S x 0 <x≤0.5。 4. The cathode material according to claim 1, characterized in that: The anion is Br⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x Br x 0 <x≤1。 5. The cathode material according to claim 1, characterized in that: The anion is I⁻, and the general formula of the positive electrode material is LiFeCl₂. 4-x I x 0 <x≤1。 6. A method for preparing the cathode material according to any one of claims 1-5, characterized in that, The method includes the following steps: Step 1: Weigh the raw materials LiCl, FeCl3, and anionic dopant; Step 2: Ball mill the weighed raw materials to obtain a uniform powder, which is the finished positive electrode material.
7. The method for preparing a positive electrode material according to claim 6, characterized in that: Both steps one and two are performed in an inert gas environment.
8. The method for preparing a positive electrode material according to claim 6, characterized in that: The anionic dopant is one of Li2O, Li2S, LiBr, and LiI, and the amount of the anionic dopant matches the general formula of the corresponding cathode material.
9. An application of the cathode material as described in any one of claims 1-5, characterized in that: The cathode material is used to prepare cathodes for all-solid-state batteries.
10. The application of the cathode material according to claim 9, characterized in that: The cathode material accounts for more than 90% of the mass of the cathode.