Boroxide-based solid electrolyte and method for producing the same

Abstract

This invention relates to Li, which is produced from LiOH or Li2CO3, H3BO3 or B2O3, and LiCl raw materials. 4+x B7O 12+x / 2 This invention provides a lithium chloroborasite-based solid electrolyte having a composition of Cl(x=0~1), thereby providing an all-solid-state electrolyte for all-solid-state secondary batteries with improved safety and ionic conductivity.

Description

[Technical Field]

[0001] This invention relates to an all-solid-state electrolyte for an all-solid-state secondary battery with improved safety and ionic conductivity. [Background technology]

[0002] A secondary battery is a battery composed of one or more electrochemical cells that can be charged and discharged. Currently, lithium-ion batteries are leading the way, being used in essential small electronic devices (such as smartphones). Lithium-ion batteries have advantages over conventional lead-acid batteries in terms of environmental toxicity and the memory effect (a phenomenon in which the discharge voltage decreases and the discharge capacity becomes smaller than the nominal capacity when the battery is repeatedly charged during use), and they also have superior energy density per unit mass / volume.

[0003] While rechargeable batteries generally have a higher initial cost than disposable batteries, their advantage lies in their ability to be recharged multiple times before replacement, resulting in significantly lower overall costs and environmental impact. Some rechargeable battery types can be used with the same size and voltage as disposable batteries and are interchangeable.

[0004] However, the electrolyte (liquid or gel) inside lithium-ion batteries poses a risk of ignition and explosion due to thermal propagation. In fact, numerous explosion incidents have led to increasing concerns about their stability.

[0005] Therefore, replacing liquid electrolytes with solid electrolytes to compensate for these shortcomings offers the following advantages:

[0006] The risk of fire and explosion due to temperature changes and external shocks is significantly reduced, and since safety devices and separation membranes to protect against temperature changes and external shocks are unnecessary, it is possible to reduce costs and achieve higher capacity while maintaining the same size.

[0007] Because there is no risk of fire, the space freed up by the removal of the cooling system, which occupies more than 30% of the battery pack space, can be filled with additional battery cells, thereby increasing the energy density.

[0008] In liquid electrolytes, the separation membrane that physically isolates the positive and negative electrodes to prevent electrical short circuits is unnecessary, thus enabling volume reduction and cost savings.

[0009] Lithium metal, which has excellent performance such as having a capacity 10 times greater than graphite but could not be used due to the risk of fire and explosion between electrodes, can now be used as a negative electrode active material, thus enabling high capacity in the same size.

[0010] On the other hand, sulfide-based solid electrolytes using Li2S-P2S5-LiCl ternary raw materials with an argyrodite crystal structure have been developed as such all-solid electrolytes. However, these conventional sulfide-based solid electrolytes pose a risk because they can generate harmful compounds such as hydrogen sulfide (H2S). In other words, in reality, there are many discussions and challenges regarding solid electrolyte materials, high resistance at the active material-electrolyte boundary (interfacial resistance), and manufacturing processes. Therefore, the need has emerged for the development of a safe and mass-producible solid electrolyte that can essentially eliminate the dangers of conventional sulfide-based solid electrolytes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The present invention aims to manufacture a borate-based solid electrolyte material with high purity and ionic conductivity and a particle shape, and to apply it to the lithium-ion conductor of an all-solid-state battery.

[0012] Furthermore, by supplying borate-based solid electrolyte materials to industry, we aim not only to gain an economic advantage but also to ensure superior safety in raw material handling. [Means for solving the problem]

[0013] The inventors, after several years of research to produce a solid electrolyte that meets the needs of industry, have synthesized a lithium chloroborasite-based solid electrolyte. The solid electrolyte of the present invention is Li 4+x B7O 12+x / 2 This is lithium chloroborasite with a composition of Cl(x=0~1).

[0014] The aforementioned lithium chloroborasite is characterized by being manufactured from LiOH or Li2CO3, H3BO3 or B2O3, and LiCl raw materials, and has a Li ion conductivity of 1.0 × 10⁻⁶ at room temperature (25°C). -6 Characterized by being S / cm or higher.

[0015] Furthermore, the lithium chloroborasite is characterized by being nanoparticles with a diameter of 10 nm to 300 μm. Preferably, the particle size is 0.8 to 80 μm in diameter, more preferably 1 to 20 μm. As the particle size decreases, the density can be increased, which is advantageous for ionic conductivity, but there are manufacturing difficulties, and if the particles are too large, the density and homogeneity of the solid electrolyte membrane decrease.

[0016] Li of the present invention 4+x B7O 12+x / 2 A lithium chloroborasite solid electrolyte having a composition of Cl(x=0~1) is characterized by being manufactured by a step of mixing LiOH or Li2CO3 with H3BO3 or B2O3 and LiCl raw materials; a step of melting the raw material mixture at 600°C or higher and rapidly cooling it; and a step of recovering the molten material after cooling and pulverizing it.

[0017] The lithium chloroborasite-based solid electrolyte of the present invention solves the environmental stability problem of conventional argyrodite-based sulfide solid electrolytes, where P2S5 and Li2S, used as raw materials, react with water to generate hydrogen sulfide (H2S). Therefore, by manufacturing secondary batteries containing this electrolyte, it is possible to replace conventional secondary batteries using liquid electrolytes in the market. [Effects of the Invention]

[0018] Synthesize the lithium chloroboracite-based solid electrolyte of the present invention to provide a solid electrolyte having a particle shape, high purity, and high ionic conductivity.

[0019] In addition, the lithium chloroboracite-based solid electrolyte of the present invention can solve the problem of environmental stability in which P2S5 and Li2S used as raw materials of conventional argyrodite-based sulfide solid electrolytes react with moisture to generate hydrogen sulfide (H2S).

[0020] Furthermore, by manufacturing a secondary battery including the lithium chloroboracite-based solid electrolyte of the present invention, it is possible to replace secondary batteries using conventional liquid electrolytes and sulfide-based solid electrolytes in the market.

Brief Description of Drawings

[0021] [Figure 1] XRD data of lithium chloroboracite. [Figure 2] SEM image showing the particle size of lithium chloroboracite of 2 to 40 μm. [Figure 3] Image after gold plating of lithium chloroboracite. [Figure 4] SEM-BSE (Back Scattered Electron), a photograph for confirming the coating thickness of lithium chloroboracite after gold plating in FIG. 3. [Figure 5] Data obtained by measuring the Li ion conductivity at room temperature after gold plating. [Figure 6] Graph showing the change in ionic conductivity of the solid electrolyte of the present invention with temperature.

Best Mode for Carrying Out the Invention

[0022] Preferred embodiments of the present invention will be described in detail. The following description of the embodiments is provided by way of example and is not limited thereto. 1. Composition of solid electrolytes

[0023] The solid electrolyte of the embodiment of the present invention has the lithium chloroborasite composition shown below (see XRD data in Figure 1).

[0024] Li 4+x B7O 12+x / 2 Cl(x=0~1)

[0025] Lithium chloroborasite of the above composition is produced from LiOH or Li2CO3, H3BO3 or B2O3, and LiCl raw materials, resulting in higher ionic conductivity and lower activation energy. 2. Confirmation of ionic conductivity under sample conditions

[0026] The solid electrolyte of one embodiment of the present invention, when measured at room temperature of 25°C after sintering, has a Li ion conductivity of 1.0 × 10⁻⁶. -6 The values ​​were S / cm or higher.

[0027] -Electrical conductivity model / measurement conditions- EIS SP-300, Scan fi=7.0MHz, ff=1.0 Hz, Nd=10 points per decade sinus amplitude Va=20.0 mV, pw=0.10, Na=2, E Range=-10V~10V 3. Manufacturing of all-solid-state rechargeable batteries

[0028] All-solid-state secondary batteries are manufactured by first preparing a positive electrode layer, a negative electrode layer, and a solid electrolyte layer using the methods described below, and then stacking them.

[0029] The solid electrolyte may be a solid electrolyte having a composition according to an embodiment of the present invention. In one embodiment, the borate-based solid electrolyte is produced by treating the starting materials of the borate-based solid electrolyte by a method such as a dissolution quenching method or a mechanical milling method. Further, after such treatment, firing can be performed. When additional firing is performed, crystallization of the solid electrolyte proceeds, and the characteristics of electrical conductivity appear.

[0030] The solid electrolyte of one embodiment of the present invention is produced by the following manufacturing method. First, LiOH or Li2CO3, H3BO3 or B2O3, and LiCl raw materials are mixed at a mixing ratio corresponding to lithium chloroboracite having a composition of Li 4+x B7O 12+x / 2 Cl(x = 0 to 1).

[0031] The positive electrode layer, the negative electrode layer, and the solid electrolyte layer are laminated so that the solid electrolyte layer is sandwiched between the positive electrode layer and the negative electrode layer, and then rolled to fabricate all-solid-state secondary battery of one embodiment of the present invention. Comparative Examples and Examples

[0032]

Table 1

[0033] Comparative Example 1: Bulk lithium chloroboracite Comparative Example 2: Realization of ionic conductivity by pulverization Comparative Example 2 vs. Examples 1 and 2: Comparison by particle size Comparative Example 2 vs. Example 3: Comparison by firing time Example 3 vs. Example 4: Comparison by size at changed firing time Comparative Example 2 vs. Example 5: Comparison by firing temperature Comparative Example 2 vs. Example 6: Comparison by size at changed firing temperature Examples 1 to 6: Production of solid electrolyte

[0034] Lithium chloroborate was produced by mixing LiOH or Li2CO3 with H3BO3 or B2O3 and a LiCl raw material to create a lithium chloroborate with the following composition (see XRD data in Figure 1).

[0035] Li 4+x B7O 12+x / 2 Cl(x=0~1)

[0036] Comparative Examples 1-2: In the same manner as in Examples 1-6, LiOH or Li2CO3, H3BO3 or B2O3, and LiCl raw materials were mixed to produce solid electrolytes of lithium chloroborasite having the following compositions, and their ionic conductivity and stability were evaluated.

[0037] Li 4+x B7O 12+x / 2 Cl(x=0~1) <Evaluation of ionic conductivity of solid electrolytes>

[0038] The ionic conductivity of the solid electrolyte obtained in this invention was measured by the following method (see Table 1).

[0039] Pressing solid electrolyte (pressure 100 MPa / cm²) 2 Pellets were prepared by ) . Next, as in Figure 2, Au coating was performed to prepare pellets for ionic conductivity measurement, and the Li ionic conductivity at room temperature (25°C) was measured using an AC impedance measuring device at room temperature. The ionic conductivity was 1.8 × 10⁻⁶. -6 The values ​​were S / cm or higher.

[0040] In addition, ionic conductivity was measured while varying the temperature to 40°C, 50°C, 60°C, 70°C, and 80°C.

[0041] As shown in Figure 4, SEM-BSE (Back Scattered Electron) confirmed that the coating thickness of the lithium chloroborasite after gold plating in Figure 3 was 90-100 nm. <Stability of solid electrolytes>

[0042] The stability of conventional lithium electrolytes is due to the contact and reaction between cations and anions, requiring the use of separation membranes, etc. However, in the case of the solid electrolyte of the present invention, the cations and anions are separated by the solid electrolyte, so they do not come into contact and are therefore stable.

[0043] It is widely known that when sulfides are used as materials for all-solid electrolytes, hydrogen sulfide is generated according to the following formula, and therefore, they must be manufactured in a moisture-free environment.

[0044] MS (sulfide) + H2O → MO (metal oxide) + H2S 2MS (sulfide) + O2 → 2MO (metal oxide) + 2S

[0045] On the other hand, the oxide-based lithium chloroborasite of the present invention has the advantage of having very low reactivity with moisture in the air, and even if a reaction occurs, it does not contain sulfur, thus not generating hydrogen sulfide, which is a harmful substance.

[0046] The solid electrolyte of the present invention, manufactured as described above, has the following advantages.

[0047] 1) Solid electrolytes offer superior safety because they are free from the risk of evaporation due to temperature changes or leakage due to external impacts, do not undergo volume swelling, and do not exhibit explosive or ignition properties even under extreme external conditions such as heat and pressure.

[0048] 2) It is possible to manufacture stackable bipolar electrodes in which negative and positive electrodes are coupled to both sides of the current collector. By applying bipolar electrodes, high voltages of 10V or more can be achieved with a single cell. For example, to achieve 14.4V with a lithium-ion battery, it is necessary to arrange four 3.6V batteries, but with an all-solid-state battery, it is possible with a single cell. Due to the effect of single-cell design, the volume is reduced by decreasing the separator membrane, current collector, cell casing material (pouch), etc., and the BMS (Battery Management System) is minimized, so a high energy density per unit volume can be achieved.

[0049] 3) Unlike liquid electrolytes, a desolvation reaction is not required to separate lithium ions from the solvent. Since the charge-discharge reaction is immediately reflected as a diffusion reaction of lithium ions within the solid, high power output is possible.

[0050] 4) Compared to conventional organic electrolytes, it can ensure stable performance over a wide temperature range. In particular, high ionic conductivity is expected at low temperatures. The biggest concern for electric vehicle users is that battery performance deteriorates in winter, reducing driving range. If a Tesla Model X is left overnight with a 50% charge on a cold day, the charge level will drop to 30% the next morning. The advent of solid-state batteries will eliminate concerns about low-temperature environments.

[0051] 5) The battery structure is simple and does not require a separation membrane. In the manufacturing process, a slurry-like solid electrolyte is coated onto the positive electrode active material. Various forms of multilayer cells can be realized through a continuous process without a liquid electrolyte injection step.

Claims

1. Li ４＋ｘ B ７ O １２＋ｘ／２ A lithium chloroborasite solid electrolyte having a composition of Cl (x = 0 to 1).

2. The lithium chloroborasilite is LiOH or Li ２ CO ３ and H ３ BO ３ or B ２ O ３ and is produced from LiCl raw materials, and the solid electrolyte according to claim 1 is characterized in that

3. The Li ion conductivity is 1.0 × 10⁻⁶ at room temperature (25°C). －６ The solid electrolyte according to claim 1, characterized in that it is S / cm or higher.

4. The solid electrolyte according to claim 1, characterized in that the lithium chloroborasite is a nanoparticle with a diameter of 10 nm to 300 μm.

5. A secondary battery comprising a solid electrolyte according to any one of claims 1 to 4.

6. LiOH or Li ２ CO ３ and H ３ BO ３ or B ２ O ３ The process of mixing the LiCl raw material; A step of melting the raw material mixture at 600°C or higher and rapidly cooling it; and The process involves cooling the molten material, recovering it, and then firing and crushing it; Li ４＋ｘ B ７ O １２＋ｘ／２ A method for producing a lithium chloroborasite solid electrolyte having a composition of Cl (x = 0 to 1).

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