Solid electrolyte for solid-state battery

Abstract

This invention relates to a solid electrolyte for all-solid-state batteries. According to one embodiment of the invention, the solid electrolyte for all-solid-state batteries is formed from an oxide having the chemical formula Li4B7-xAlxO12Cl, where x satisfies 2.25 ≤ x ≤ 2.76.

Description

Solid electrolytes for all-solid-state batteries The present invention relates to a solid electrolyte for all-solid-state batteries. Recently, the use of secondary batteries has been increasing significantly in various fields, from IT equipment such as mobile phones to electric vehicles and energy storage devices. Lithium-ion batteries, which use liquid electrolytes, are the most widely used secondary batteries. However, when an external impact is applied to the battery, there is a risk of leakage of the liquid electrolyte, necessitating additional components and devices to ensure safety. Recently, to improve the safety of secondary batteries, the development of all-solid-state batteries using solid electrolytes has been actively pursued. Solid electrolytes for all-solid-state batteries include polymer electrolytes, oxide electrolytes, and sulfide electrolytes. Sulfide-based solid electrolytes have the highest ionic conductivity, but they also have the problem of reacting with moisture and producing hydrogen sulfide gas. Polymer-based electrolytes have the advantages of relatively simple manufacturing processes and can be used with existing lithium-ion battery processes, but they have the disadvantage of significantly low ionic conductivity. Oxide-based electrolytes offer the advantage of superior safety over sulfide-based electrolytes, but they also have relatively low ionic conductivity. Furthermore, oxide-based electrolytes generally require high sintering temperatures of 1,000°C or higher, potentially significantly increasing manufacturing costs. [Problems to be solved by the invention] The present invention is intended to solve the above-mentioned problems of the conventional technology, and its purpose is to provide a solid electrolyte for all-solid-state batteries that can be sintered at low temperature and has excellent ionic conductivity. [Technical means to solve the problem] According to one embodiment of the present invention, the solid electrolyte for all-solid-state batteries comprises Li 4B 7-x Al x O 12 The oxide of the chemical formula of Cl is formed. In the above chemical formula, x satisfies 2.25≤x≤2.76. According to the solid electrolyte for an all-solid-state battery of one embodiment of the present invention, in the aforementioned chemical formula, x may satisfy 2.25≤x≤2.49. According to the solid electrolyte for an all-solid-state battery of one embodiment of the present invention, in the aforementioned chemical formula, x may satisfy x=2.25. According to an embodiment of the present invention, the solid electrolyte for all-solid-state batteries has an ionic conductivity of 1.44×10 -5 to 1.73×10 -4S / cm. According to an embodiment of the present invention, the solid electrolyte for an all-solid-state battery may have a crystal structure with a lattice constant of a=b=c=13.393 (Å). According to an embodiment of the present invention, the solid electrolyte for all-solid-state batteries can be composed of Li 2CO 3. H 3BO 3. Al 2O 3 and LiCl precursor powder production. In addition, the solid electrolyte for an all-solid-state battery according to the present invention may further include other additional structures within the scope that does not impair the technical concept of the present invention. [Effects of the Invention] According to one embodiment of the present invention, a solid electrolyte for an all-solid-state battery can be sintered at low temperature and has excellent ionic conductivity. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings to the extent that a person having ordinary knowledge in the technical field to which the present invention belongs can easily implement them. In order to clearly illustrate the present invention, the description of parts not related to the present invention has been omitted. It should be understood that the specific shapes, structures, and characteristics described in the specification can be changed from one embodiment to another without departing from the spirit and scope of the present invention, and the position or configuration of individual components can also be changed without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, but it should be understood that the scope of the present invention includes the scope claimed in the claims of the patent application and all scopes equivalent thereto. FIG1 is a diagram schematically showing a cross section of an all-solid-state battery. 1 , the all-solid-state battery (10) includes an anode (11), a cathode (12), and a solid electrolyte layer (13). The solid electrolyte layer (13) is disposed between the anode (11) and the cathode (12) and can be in contact with the anode (11) and the cathode (12), respectively. The anode (11) and the cathode (12) can each include an anode active material layer and a cathode active material layer, and the anode active material layer and the cathode active material layer can each be in contact with the solid electrolyte layer (13). The anode (11) and the cathode (12) can be bonded to the solid electrolyte layer (13) by sintering. That is, the anode (11), the cathode (12) and the solid electrolyte layer (13) can be sintered to form a whole. In FIG1 , an all-solid-state battery (10) is shown as including one anode (11), one cathode (12), and one solid electrolyte layer (13). However, the present invention is not limited thereto. An all-solid-state battery can also be constructed in a form in which the anode, cathode, and solid electrolyte layer are each formed of a plurality of layers. Alternatively, a so-called stacked all-solid-state battery can be constructed in which a plurality of anodes, cathodes, and solid electrolyte layers are alternately stacked. According to one embodiment of the present invention, the solid electrolyte layer (13) includes an oxide-based electrolyte as a solid electrolyte. As oxide-based solid electrolytes, there are known sodium superion conductor (Nasicon) type such as LAGP and garnet type such as LLZO. It is known that through continuous research and development, the ion conductivity of such oxide-based solid electrolytes has been improved to 10 -4 S / cm level. However, further improvements in ionic conductivity using the aforementioned sodium superion conductor and garnet oxide-based solid electrolytes are limited. Furthermore, even if these oxide-based solid electrolytes can achieve a certain degree of excellent ionic conductivity, the increased manufacturing costs associated with high-temperature sintering are unavoidable, as mentioned above. In one embodiment of the present invention, a novel oxide-based solid electrolyte that overcomes the limitations of conventional oxide-based solid electrolytes is used to reduce the sintering temperature and ensure excellent ionic conductivity. According to one embodiment of the present invention, the solid electrolyte for all-solid-state batteries may have a boron oxide crystal structure such as boracite. In one embodiment, the solid electrolyte for all-solid-state batteries may be formed of an oxide containing Li, B, Al, and Cl. For example, the solid electrolyte for all-solid-state batteries may contain Li 2O, B 2O 3. Al 2O 3 and LiCl. In the composition of the solid electrolyte, Li 2O can function as a network modifier, providing Li ions to improve ionic conductivity. In the composition of the solid electrolyte, B 2O 3 can function as a network former and as a low-temperature component to lower the sintering temperature. In the composition of solid electrolyte, Al 2O 3 can function as a network modifier, increasing the lattice constant of the boron oxide crystal structure. Therefore, in the aforementioned crystal structure, a wider migration path for Li ions can be ensured, thereby improving ionic conductivity. In forming the composition of the solid electrolyte, LiCl plays the following roles: it increases the amount of Li ions in the solid electrolyte to improve ionic conductivity, and Cl ions enter the network structure to form a network structure in which two anions coexist, thereby expanding the volume of the network structure. Thus, by forming the solid electrolyte according to one embodiment of the present invention from an oxide containing Li, B, Al, Cl, and V, the sintering temperature is reduced, Li ions are provided, and the flow path of Li ions is ensured, thereby achieving excellent ionic conductivity. According to one embodiment of the present invention, the composition formula of the solid electrolyte can be expressed as follows. (1) Li 4B 7-x Al x O 12 Cl According to one embodiment of the present invention, x in the aforementioned chemical formula may satisfy the following. (2) 2.25≤x≤2.76 According to one embodiment of the present invention, x in the aforementioned chemical formula may preferably satisfy the following. (3) 2.25≤x≤2.49 According to one embodiment of the present invention, x in the aforementioned chemical formula may be more preferably 2.25. When the solid electrolyte has the aforementioned chemical formula and x satisfies the aforementioned range, low-temperature sintering can be performed, and excellent ion conductivity can be ensured. According to one embodiment of the present invention, the solid electrolyte can be made of Li 2CO 3. H 3BO 3. Al 2O 3 and LiCl precursor powders. According to one embodiment of the present invention, the precursor powders are mixed and crushed, then placed in an Al crucible and melted at approximately 800°C to 1,200°C for approximately 30 minutes. The melt is then cooled on quenching rolls, crushed into fine particles, and sieved to obtain particles with a size of less than 10 μm. The solid electrolyte is then sintered for approximately 3 hours to produce it. As described above, the solid electrolyte according to one embodiment of the present invention can be sintered at low temperatures. Specifically, the sintering temperature of the solid electrolyte according to one embodiment of the present invention is about 500°C to about 600°C. When the solid electrolyte according to one embodiment of the present invention is sintered at the aforementioned temperature, it exhibits a thermal conductivity of about 1.44×10 -5 to 1.73×10 -4 S / cm ionic conductivity. On the other hand, the solid electrolyte according to one embodiment of the present invention has excellent ionic conductivity and is non-hygroscopic. Therefore, even if moisture enters the all-solid-state battery, the battery performance will not be degraded, and stable and excellent performance can be maintained. Experimental example In order to evaluate the characteristics of the solid electrolyte according to one embodiment of the present invention, ab initio molecular dynamics (AIMD) was used to perform simulations of the ionic conductivity of the solid electrolyte. FIG2 is a diagram showing the crystal structure of a solid electrolyte according to an embodiment of the present invention, showing a simulated crystal structure. Referring to FIG2 , it can be confirmed that BO 3 and AlO 4 mixed to form a crystal structure. To evaluate the ionic conductivity characteristics, the Li ion migration distance over time was measured in the crystal structure of Figure 2, and the ion diffusion coefficient (D) under high temperature conditions was calculated. FIG3 is a diagram showing a simulation of the movement distance of Li ions according to one embodiment of the present invention. FIG3(a) is a diagram simulating the movement of Li ions from a crystal structure, and FIG3(b) is a graph showing the mean square value (MSD) of the movement distance of the simulated Li ions at each time. The ion diffusion coefficient (D) can be calculated from the following formula 1 based on the mean square value of the travel distance of Li ions per time. [Formula 1] Where t represents time, r(t) and r(0) represent the position and initial position of the Li ion particle at time t, respectively. FIG. 4 is a graph showing ion diffusion coefficients under a plurality of temperature conditions and ion diffusion coefficients at room temperature estimated based on the same according to an embodiment of the present invention. First, the ion diffusion coefficient (D) was calculated under three different high-temperature conditions. The results are shown in the plots in Figure 4(a). As shown in the figure, it can be confirmed that the natural logarithm (lnD) of the ion diffusion coefficient (D) under the three high-temperature conditions is inversely proportional to the temperature (that is, proportional to the reciprocal of the temperature). The ion diffusion coefficient under such high temperature conditions was calculated using the Arrhenius equation. This can be expressed by the following equations 2 and 3. [Equation 2] [Mathematical formula 3] in, represents the ion diffusion coefficient at room temperature, represents the activation energy, represents the Boltzmann constant, and T represents the absolute temperature. As described above, the ion diffusion coefficient at room temperature ( ). The ionic conductivity (σ) of the solid electrolyte can be calculated using the following Mathematical Formula 4 (Nernst-Einstein equation) based on the calculated ion diffusion coefficient. [Mathematical Formula 4] Where N represents the number of Li ion particles in a unit cell, q represents the charge of the Li ion, and V represents the volume of the unit cell. represents the Boltzmann constant, and T represents the absolute temperature. First, generate Li 4B 4Al 3O 12 Cl (LCBA), Li 4B 7O 12 After the two crystalline phases of Cl(LCB), the unit cell of LCBA crystal is AlO Part of 4 is replaced by BO 4 and generated the conditions for the examples. Then, full-scale molecular dynamics simulation was performed on each example to calculate the ion diffusion coefficient and ion conductivity at room temperature. FIG5 is a graph showing the ion diffusion coefficient (D) and ion conductivity (σ) of the solid electrolyte according to the embodiment of the present invention and the comparative example. Specifically, FIG5 shows ... 4 replaced by BO Graph of ion diffusion coefficient (D) and ion conductivity (σ) at the level of 4. 5 (a), it can be confirmed that the 4% residual AlO The highest ion diffusion coefficient was observed in the solid electrolyte when the ratio of 4 was 75%. Similarly, referring to FIG5(b), it can be confirmed that the ion diffusion coefficient was not significantly increased when the ion diffusion coefficient was not significantly increased. 4% residual AlO In the solid electrolyte where the ratio of 4 is 75%, the ion conductivity shows a peak. Table 1 shows the ionic conductivity values ​​of the solid electrolytes according to the embodiments of the present invention and the comparative examples. 4 Residual ratio shows that the AlO in the unit cell is 4 replaced by BO 4, and calculated the ionic conductivity in each case. Specifically, it is divided into AlO The ionic conductivity was calculated for the cases where the residual ratio was 100% (i.e., no replacement), 92%, 83%, 75%, 67%, and 0% (i.e., all replacement). [Table 1] Refer to Table 1, AlO The solid electrolytes with a residual ratio of 4 of 75% to 92% (ie, Examples 2 to 4) have a 1.44×10 -5 S / cm or more excellent ionic conductivity. In Example 2, where the residual ratio of 4 was 75%, 1.73×10 -4 S / cm very excellent ionic conductivity. In contrast, in AlO 4 All replaced with BO Comparative Example 1 and AlO 4 not replaced by BO In Comparative Example 2 of 4, 1.15×10 -5Low ionic conductivity below S / cm. Thus, it can be confirmed that as AlO is added to the solid electrolyte of the LCBA crystal phase, 4 replaced by BO 4. It can be sintered at low temperature and can ensure excellent ionic conductivity, especially when AlO When the residual ratio of 4 is set to 75% to 92%, especially when it is 75%, the ion conductivity is very excellent. 4 is 75% to 92% in the case of a residual ratio of 4B 7-x Al x O 12 In Cl, 2.25≤x≤2.76 is satisfied. In AlO When the residual ratio of 4 is 75%, x is 2.25. 4B 7-x Al x O 12 The crystal structure of the solid electrolyte of the embodiment (i.e., Example 2) in which x is 2.25 was shown in FIG. 1 , and the lattice constant at this time was determined to be a=b=c=13.393 (Å). The present invention has been described above using specific matters such as specific constituent elements and limited embodiments, but the aforementioned embodiments are only provided to facilitate a more comprehensive understanding of the present invention, and the present invention is not limited thereto. Anyone having ordinary skill in the technical field to which the present invention belongs can make various modifications and variations based on such descriptions. Therefore, the concept of the present invention should not be limited to the embodiments described above, and not only the scope of the patent application described later, but also the owners of the equivalent or equivalent modifications to the scope of the patent application belong to the scope of the concept of the present invention. 10: All-solid-state battery 11: Anode 12: Cathode 13: Solid electrolyte layer FIG1 is a diagram schematically showing a cross section of an all-solid-state battery. FIG. 2 is a diagram showing the crystal structure of a solid electrolyte according to an embodiment of the present invention. FIG. 3 is a diagram showing a simulation of measuring the migration distance of Li ions according to an embodiment of the present invention. FIG. 4 is a graph showing ion diffusion coefficients under a plurality of high temperature conditions and ion diffusion coefficients at room temperature estimated based on the same according to an embodiment of the present invention. FIG. 5 is a graph showing the ion diffusion coefficient and ion conductivity of solid electrolytes according to examples and comparative examples of the present invention. 10: All-solid-state batteries 11: Anode 12: cathode 13: Solid electrolyte layer

Claims

1. A solid electrolyte for an all-solid-state battery, which is formed from an oxide having the chemical formula Li4B7-xAlxO12Cl and satisfies 2.25≤x≤2.

76.

2. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein, It satisfies 2.25≤x≤2.

49.

3. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein, The expression x = 2.25 is satisfied.

4. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein, The ionic conductivity ranges from 1.44 × 10⁻⁵ to 1.73 × 10⁻⁴ S / cm.

5. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein, The lattice constant of the crystal structure is a=b=c=13.393 (Å).

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