Halide solid electrolyte with electrochemical activity and preparation method and application thereof

Abstract

The invention discloses a halide solid electrolyte with electrochemical activity and a preparation method and application thereof, the solid electrolyte is a zirconium-doped ferric lithium chloride solid electrolyte, the chemical general formula of the solid electrolyte is LiFe1-4x / 3MxCl4, M is a metal element with the valence state higher than + 3, 0 lt; xlt; 1. According to the halide solid-state electrolyte with the electrochemical activity, the ionic conductivity order of magnitude is improved, the room-temperature ionic conductivity is improved to 10 <-3 > S / cm from 10 <-6 > S / cm by three orders of magnitude, so that the material is changed from'unavailability 'to'high performance', and the application requirement of an all-solid-state battery is met.

Description

An electrochemically active halide solid electrolyte, its preparation method and application Technical Field

[0001] This invention belongs to the field of battery technology and relates to an electrochemically active halide solid electrolyte, its preparation method, and its application. Background Technology

[0002] Solid-state lithium batteries, as an emerging energy storage technology, completely eliminate the safety hazards of liquid batteries, such as leakage, combustion, and explosion, by using solid electrolytes instead of traditional liquid electrolytes. They also promise higher energy density and longer lifespan. Solid electrolytes primarily function to conduct lithium ions and isolate the positive and negative electrodes to prevent short circuits. Their ionic conductivity, chemical stability, and mechanical strength directly affect the overall battery performance. An ideal solid-state electrolyte should possess characteristics such as high ionic conductivity, low electronic conductivity, a wide electrochemical window, good interfacial compatibility, and low cost.

[0003] To reduce the cost of solid-state electrolytes, researchers have turned their attention to material systems based on elements abundant in the Earth's crust. Among them, iron (Fe) has become an ideal candidate due to its abundant reserves and low price. As early as 1980, LiFeCl4 was reported as a potential lithium-ion conductor.

[0004] By doping Li3FeCl6 with Zr, the ionic conductivity is only increased to 0.37 mS / cm, limiting its practical applications. Literature reports indicate that it is only used in composite cathode materials to compensate for the inherent ionic conductivity of the cathode material itself; it has not been used in the electrolyte portion of batteries. In experiments, the electrolyte used was still the rare metal solid electrolyte Li3YCl6.

[0005] Doping Li₂ZrCl₆ with Fe, although Li₂ZrCl₆ is reduced from 4 x 10⁻⁶ -4 The S / cm ratio has been increased to nearly 1 mS / cm, but the content of the rare metal Zr remains relatively high. Whether based on Li3FeCl6 or Li2ZrCl6, the electrolytes mentioned above all have a high Li content, making it difficult to reduce electrolyte costs.

[0006] The aforementioned existing technologies share the following limitations:

[0007] Insufficient improvement in conductivity: The ionic conductivity of Li3FeCl6 doping did not reach the practical threshold of 10⁻³ S / cm, although Li2ZrCl6 doping can increase the conductivity from 10⁻³ S / cm. 4The S / cm ratio was increased to 10⁻³ S / cm, but the improvement was relatively small. Cost control was incomplete: the doping scheme still relied on rare metals (such as Zr), failing to fully utilize the low-cost advantage of iron-based materials, and the lithium content was high. Functionality was limited: the electrolytes were all non-electrochemically active, becoming "inert" after the introduction of the cathode composite, reducing the battery's energy density.

[0008] Therefore, there is a need to provide an electrochemically active halide solid electrolyte, its preparation method, and its applications. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this paper provides an electrochemically active halide solid electrolyte, its preparation method, and its applications.

[0010] This invention is achieved through the following scheme:

[0011] An electrochemically active halide solid electrolyte, wherein the solid electrolyte is a doped lithium iron chloride solid electrolyte with the general chemical formula LiFe 1-4x / 3 M x Cl4, where M is a metallic element with a valence state higher than +3, 0 <x<1。

[0012] M is related to Fe 3+ Metal cations with different valence states but similar ionic radii, wherein M is one of Zr, Ti, Sn, and Hf.

[0013] The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0 <x<0.54。

[0014] The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0.18 < x ≤ 0.36.

[0015] A method for preparing an electrochemically active halide solid electrolyte includes the following steps:

[0016] Step 1: According to the stoichiometric ratio of LiFe 1-4x / 3 Zr x Weigh the raw materials LiCl, FeCl3, and ZrCl4 (x=0, 0.18, 0.27, 0.36, 0.54);

[0017] Step 2: The mixed raw materials from Step 1 are subjected to high-energy ball milling to obtain a uniform powder, which is the finished product of electrochemically active halide solid electrolyte. Typically, ball milling is performed at 200-400 rpm for 4-10 hours.

[0018] Both Step 1 and Step 2 are carried out in an inert gas environment, such as argon or nitrogen.

[0019] Application of a solid-state electrolyte with electrochemically active halide, application of the zirconium-doped lithium iron chloride solid-state electrolyte in a all-solid-state battery.

[0020] The all-solid-state battery includes LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) and conductive carbon black mixture as the positive electrode, Li-In as the negative electrode, where LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) is the solid-state electrolyte, and Li3YCl3Br3 is the negative electrode protective layer.

[0021] The positive electrode of the all-solid-state battery further includes one of LiCoO2 and Li2FeCl4.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. By introducing a metal element with a valence higher than trivalent into the lithium iron chloride matrix for doping, the present invention successfully prepares a solid-state electrolyte with electrochemically active halide. On the basis of maintaining the main framework of the material, by introducing cation vacancy defects, the transmission path of lithium ions is effectively optimized. The substitution of high-valence zirconium ions for trivalent iron ions results in a local excess of positive charge in the lattice. To maintain the overall electrical neutrality of the material, cation vacancies will spontaneously form in the crystal. The generation of these vacancies reduces the energy barrier that needs to be overcome when lithium ions migrate in the lattice, thereby greatly improving the conduction efficiency of lithium ions and achieving an order-of-magnitude leap in the room-temperature ionic conductivity of the material.

[0024] 2. The core components of the solid-state electrolyte of the present invention are iron and chlorine with rich reserves, and only a small amount of zirconium element is introduced as a dopant, while the relative content of lithium element is relatively low. This component design strategy enables the material to get rid of the dependence on a variety of expensive rare metals at the source. Compared with the existing technologies that still rely on high-content rare metals or high-lithium-content solid-state electrolytes of halides, the material system of this application focuses more on using elements with higher abundances in the earth's crust, which provides a feasible solution for fundamentally controlling the raw material cost of solid-state electrolytes.

[0025] 3. Unlike conventional solid-state electrolytes that only function as ion conductors, the material in this application utilizes the inherent electrochemical activity of iron. When this electrolyte is applied to the positive electrode side of an all-solid-state battery and combined with active materials, the iron ions in the electrolyte can directly participate in the electrochemical process through reversible redox reactions. This means that the electrolyte not only plays the traditional role of an ion conductor in the battery but also contributes additional reversible capacity as an active material. This characteristic avoids the problem of traditional inactive electrolytes merely adding "inert mass" to the positive electrode, thereby helping to improve the overall mass energy density of the battery.

[0026] 4. The zirconium-doped lithium iron chloride solid electrolyte of this application achieves high ionic conductivity, low raw material cost, and intrinsic electrochemical activity simultaneously through unique doping chemistry and composition design. High ionic conductivity ensures low internal resistance and good rate performance, while low cost and activity contribution provide a new material option for developing high-energy-density, low-cost all-solid-state batteries. The combination of these characteristics enables this material to better meet the key requirements for core electrolyte materials in practical all-solid-state battery applications. Attached Figure Description

[0027] Figure 1 shows the LiFe of the present invention. 1-4x / 3 Zr x Electrochemical impedance spectroscopy data of Cl4 solid electrolyte at x=0;

[0028] Figure 2 shows the LiFe of the present invention. 1-4x / 3 Zr x Electrochemical impedance spectroscopy data of Cl4 solid electrolyte at x=0.36;

[0029] Figure 3 shows the LiCoO2|LiFe of the present invention. 1-4x / 3 Zr x Charging and discharging data of Cl4(x=0.36)|Li3YCl3Br3|Li-In all-solid-state battery;

[0030] Figure 4 shows the Li2FeCl4|LiFe of the present invention. 1-4x / 3 Zr x Charging and discharging data of Cl4(x=0.36)|Li3YCl3Br3|Li-In all-solid-state battery. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments:

[0032] An electrochemically active halide solid electrolyte, wherein the solid electrolyte is a doped lithium iron chloride solid electrolyte with the general chemical formula LiFe 1-4x / 3 M xCl4, where M is a metallic element with a valence state higher than +3, 0 <x<1。

[0033] M is related to Fe 3+ Metal cations with different valence states but similar ionic radii, wherein M is one of Zr, Ti, Sn, Hf, etc.

[0034] The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0 <x<0.54。

[0035] The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0.18 < x ≤ 0.36.

[0036] This invention provides an electrochemically active halide solid electrolyte with an order-of-magnitude improvement in ionic conductivity, increasing the room-temperature ionic conductivity from 10... -6 S / cm increased to 10 -3 The S / cm ratio represents a three-order-of-magnitude improvement, transforming the material from "unusable" to "high-performance," thus meeting the application requirements of all-solid-state batteries. This invention utilizes zirconium (Zr) as a metallic element with a valence state higher than +3 (such as Zr). 4+ ), in the chemical formula LiFe 1-4x / 3 Zr x Cl4 partially substitutes for Fe 3+ Due to the difference in valence state, cation vacancy defects are introduced, optimizing the lithium-ion migration pathway in the crystal structure. Zr 4+ Fe replacement 3+ This leads to an excess of positive charge. In order to maintain electroneutrality, cation vacancies are generated in the crystal, thereby lowering the energy barrier for lithium ion migration and improving ion conduction efficiency.

[0037] Figures 1 and 2 show LiFe 1-4x / 3 Zr x Electrochemical impedance spectroscopy (EIS) data for the Cl4 solid electrolyte at x=0 and x=0.36. From the data, the lithium-ion conductivity of LiFeCl4 is 1.6 × 10⁻⁶. -6 S / cm, while Zr-doped solid electrolyte LiFe 0.52 Zr 0.36 The ionic conductivity of Cl4 is 1.09 × 10⁻⁶. -3 S / cm, ion conductance increased by nearly 3 orders of magnitude.

[0038] A method for preparing an electrochemically active halide solid electrolyte includes the following steps:

[0039] Step 1: According to the stoichiometric ratio of LiFe 1-4x / 3 Zr x Cl4 (x = 0, 0.18, 0.27, 0.36, 0.54), accurately weigh the raw materials LiCl, FeCl3 and ZrCl4.

[0040] Step 2: Perform high-energy ball milling on the mixed raw materials in Step 1 to obtain uniform powder, which is the finished product of the electrochemically active halide solid electrolyte. Usually, ball milling is carried out at a speed of 200 - 400 rpm for 4 - 10 hours. In the preparation method of the present invention, in addition to the mechanical ball milling method, the solid-state reaction method can also be used to prepare the electrolyte, that is, the raw materials are mixed and sintered at a certain temperature.

[0041] Both Step 1 and Step 2 are carried out in an inert gas environment, such as argon or nitrogen.

[0042] An application of an electrochemically active halide solid electrolyte, the application of the zirconium-doped lithium iron chloride solid electrolyte in an all-solid-state battery. <s

[0043] The all-solid-state battery includes LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) and a conductive carbon black mixture as the positive electrode, Li-In as the negative electrode, where LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) is the solid electrolyte, and Li3YCl3Br3 is the negative electrode protective layer. The positive electrode of the all-solid-state battery also includes one of LiCoO2, Li2FeCl4, etc. The application of an electrochemically active halide solid electrolyte in the present invention utilizes the electrochemistry of the Fe element in the electrolyte. When used as a positive electrode electrolyte, it can provide additional capacity, which helps to improve the energy density of the all-solid-state battery. When the iron (Fe) element is used as a positive electrode electrolyte, it can provide additional capacity through the Fe 2+ / Fe<s 3+ redox pair, thereby improving the energy density of the all-solid-state battery and avoiding the problem of the traditional non-active electrolyte becoming an "inert mass" after being introduced into the positive electrode. During the charge and discharge process, the Fe ions in the electrolyte can undergo a reversible redox reaction and directly participate in charge storage, which not only compensates for the deficiency of the ion conductivity of the positive electrode material itself but also increases the overall capacity.

[0044] Briefly list two applications of the electrolyte of the present invention in an all-solid-state battery below.

[0045] I. LiCoO2| LiFe 1-4x / 3 Zr x Cl4 (x = 0.36)|Li3YCl3Br3|Li-In all-solid-state battery

[0046] In this invention, LiCoO2 and LiFe are used. 1-4x / 3 Zr x A mixture of Cl4 (x=0.36) and conductive carbon black is used as the positive electrode, and LiFe... 1-4x / 3 Zr x Cl4 (x=0.36) is the solid electrolyte, Li-In is the negative electrode, and Li3YCl3Br3 serves as the negative electrode protective layer, forming an all-solid-state battery. The charge / discharge data are shown in Figure 3, with a discharge capacity of 152.8 mAh / g. Due to the LiFe... 1-4x / 3 Zr x The Cl4 (x=0.36) electrolyte itself contains Fe with variable valence. When it is used as part of the positive electrode, during charge and discharge (3.7 V vs. Li), + / Li), Fe 2+ / Fe 3+ Highly reversible, contributing additional capacity. This makes the battery's actual discharge capacity higher than that of batteries using inactive solid electrolytes (in the prior art, batteries that also use LiCoO2 as the cathode material but use inactive Li3InCl6 as the solid electrolyte have a discharge capacity of only 127 mAh / g).

[0047] II. Li₂FeCl₄|LiFe 1-4x / 3 Zr x Cl4(x=0.36)|Li3YCl3Br3|Li-In all-solid-state battery

[0048] Li2FeCl4, LiFe 1-4x / 3 Zr x Cl4 (x=0.36) and conductive carbon black are mixed as the positive electrode, and LiFe is used. 1-4x / 3Zr x The battery is an all-solid-state battery consisting of a Cl4 (x=0.36) solid electrolyte, Li3YCl3Br3 as a protective layer, and Li-In as the negative electrode. The charge and discharge data of the battery are shown in Figure 4. The discharge capacity is 146.8 mAh / g, which is higher than the theoretical capacity of the positive electrode active material (Li2FeCl4) (124 mAh / g, ACS Energy Lett. 2024, 9, 5464−5470).

[0049] In the development of all-solid-state batteries, the room-temperature ionic conductivity of the solid electrolyte is one of the core indicators determining its practicality. While iron-based halide solid electrolytes based on crustal elements, such as lithium iron chloride, offer cost advantages, their intrinsic ionic conductivity is typically low, making it difficult to meet the battery's requirements for rapid ion transport. In existing technologies, a common improvement approach is cation doping of these materials. However, conventional doping strategies, such as elemental substitution in lithium-rich lithium iron chloride or lithium zirconium chloride matrices, often only improve conductivity to a limited range, failing to overcome the key hurdle for achieving high-performance applications. A major limitation behind this is that the selection and introduction of doping elements have not sufficiently optimized the lithium-ion migration channels in the crystal structure.

[0050] This application employs a technique for doping lithium iron chloride with zirconium, a metallic element with a valence state higher than trivalent. This technique utilizes the valence difference between the dopant ion and the substituted ion to create defects in the crystal lattice that facilitate ion conduction. When tetravalent zirconium ions replace trivalent iron ions in the original lattice, an excess of positive charge is introduced locally. To maintain the overall electroneutrality of the crystal, cation vacancies are correspondingly generated in the lattice. These vacancies, spontaneously formed by the charge compensation effect, become additional sites and fast channels for lithium ion migration, significantly reducing the activation energy for lithium ion diffusion in the solid-state lattice. Therefore, compared to undoped lithium iron chloride, the zirconium-doped material exhibits an order-of-magnitude improvement in lithium-ion conductivity, thus solving the problem of insufficient ionic conductivity in the basic material.

[0051] After initially addressing the issue of ionic conductivity, cost control of solid-state electrolytes became the next key focus. Some existing high-performance halide solid-state electrolytes either rely on rare metals such as zirconium as their main component or require maintaining a high lithium content to ensure conductivity. These factors contribute to increased overall material costs, diminishing their potential for large-scale application. Although previous doping strategies improved performance, if the dopant elements themselves are expensive or introduced in inappropriate proportions, the low-cost advantage of iron-based materials cannot be fully realized. Therefore, the solid-state electrolyte of this application uses abundant and inexpensive iron and chlorine as the main framework elements. The introduction of zirconium as a dopant serves to create the structural defects required for conductivity, rather than acting as the main structure; therefore, its required doping amount is relatively low. Simultaneously, through a rational chemical formula design, the lithium content in the material is controlled at a relatively low level. This design approach, which uses abundant elements as the main component, introduces only a small amount of dopant, and reduces the active lithium content, effectively controls the overall cost of raw materials while achieving high ionic conductivity, making the electrolyte more suitable for the economic requirements of commercial applications.

[0052] Besides conductivity and cost, traditional solid-state electrolytes are typically considered electrochemically inert components in batteries, meaning they only conduct ions and do not participate in redox reactions. When combined with positive electrode active materials, this electrolyte increases the inactive mass of the electrode, thus lowering the overall energy density of the battery. This is a problem that urgently needs to be solved in the pursuit of high-energy-density batteries. The iron element in lithium iron chloride, the base material selected in this application, possesses reversible electrochemical activity. Through the aforementioned zirconium doping treatment, we have perfectly preserved this characteristic of iron ions while improving its ion conductivity. When this electrolyte is used in the positive electrode composite of an all-solid-state battery, it not only performs the function of rapidly conducting lithium ions, but the iron ions in its lattice can also undergo reversible redox reactions during charge and discharge, contributing additional reversible capacity to the battery. This means that the electrolyte transforms from a traditional "inert medium" into an "active contributor," thereby avoiding the introduction of "inert mass" into the positive electrode and providing a new approach to improving the energy density of all-solid-state batteries.

[0053] 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 halide solid electrolyte with electrochemical activity, characterized in that: The solid electrolyte is a doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 M x Cl4, where M is a metallic element with a valence state higher than +3, 0 <x<1。 2. The electrochemically active halide solid electrolyte according to claim 1, characterized in that: M is related to Fe 3+ Metal cations with different valence states but similar ionic radii, wherein M is one of Zr, Ti, Sn, and Hf.

3. The electrochemically active halide solid electrolyte according to claim 1, characterized in that: The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0 <x<0.54。 4. The electrochemically active halide solid electrolyte according to claim 3, characterized in that: The solid electrolyte is a zirconium-doped lithium iron chloride solid electrolyte with the chemical formula LiFe. 1-4x / 3 Zr x Cl4, where 0.18 < x ≤ 0.

36.

5. A method for preparing a halide solid electrolyte with electrochemical activity as described in any one of claims 1-4, characterized in that, The method includes the following steps: Step 1: According to the stoichiometric ratio of LiFe 1-4x / 3 Zr x Weigh raw materials LiCl, FeCl3, and ZrCl4 (x=0, 0.18, 0.27, 0.36, 0.54); Step 2: Perform high-energy ball milling on the mixed raw materials from Step 1 to obtain a uniform powder, which is the finished product of electrochemically active halide solid electrolyte.

6. The method for preparing an electrochemically active halide solid electrolyte according to claim 5, characterized in that: Both steps one and two are performed in an inert gas environment.

7. The application of a solid halide electrolyte with electrochemical activity as described in any one of claims 1-4, characterized in that: The zirconium-doped lithium iron chloride solid electrolyte is used in all-solid-state batteries.

8. The application of the electrochemically active halide solid electrolyte according to claim 7, characterized in that: The all-solid-state battery includes LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) and a mixture of conductive carbon black as the positive electrode, Li-In as the negative electrode, where LiFe 1-4x / 3 Zr x Cl4 (0 < x < 0.54) is the solid electrolyte, and Li3YCl3Br3 is the negative electrode protective layer.

9. The application of the electrochemically active halide solid electrolyte according to claim 8, characterized in that: The positive electrode of the all-solid-state battery also includes one of LiCoO2 and Li2FeCl4.

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