Solid electrolyte for all-solid-state batteries

Abstract

The present invention relates to a solid electrolyte for all-solid-state batteries. According to an embodiment of the present invention, the solid electrolyte for all-solid-state batteries comprises an oxide having the chemical formula Li4B7-xAlxO12Cl, wherein x satisfies 2.25 ≤ x ≤ 2.76.

Description

Solid electrolyte for all-solid-state batteries

[0001] The present invention relates to a solid electrolyte for an all-solid-state battery.

[0002] Recently, the use of secondary batteries has increased significantly in various fields, from IT devices such as mobile phones to electric vehicles and energy storage devices.

[0003] Among secondary batteries, lithium-ion batteries, which use liquid electrolytes, are the most widely used. However, liquid electrolytes pose a risk of leakage if the battery is subjected to external shocks, necessitating the use of additional components and devices to ensure safety.

[0004] Recently, active development of all-solid-state batteries using solid electrolytes has been underway to improve the safety of secondary batteries. Solid electrolytes for all-solid-state batteries include polymer electrolytes, oxide electrolytes, and sulfide electrolytes. Sulfide solid electrolytes have the highest ionic conductivity, but they have the problem of reacting with moisture to produce hydrogen sulfide gas. Polymer electrolytes offer the advantages of a relatively simple process and compatibility with existing lithium-ion battery processes, but their significantly low ionic conductivity is a drawback.

[0005] Oxide-based electrolytes offer superior safety compared to sulfide-based electrolytes, but their ionic conductivity is relatively low. Furthermore, oxide-based electrolytes typically require high sintering temperatures, typically exceeding 1,000°C, which can significantly increase manufacturing costs.

[0006] The present invention is intended to solve the problems of the prior art described above, and its purpose is to provide a solid electrolyte for an all-solid-state battery that can be sintered at low temperatures and has excellent ionic conductivity.

[0007] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention is Li4B 7-x Al x O 12It consists of an oxide having the chemical formula Cl. In the chemical formula, x satisfies 2.25≤x≤2.76.

[0008] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention may satisfy 2.25≤x≤2.49 in the chemical formula.

[0009] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention may satisfy x=2.25 in the chemical formula above.

[0010] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention has an ionic conductivity of 1.44×10 -5 1.73×10 -4 It could be S / cm.

[0011] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention may have a lattice constant of a crystal structure of a=b=c=13.393 (Å).

[0012] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention can be manufactured from precursor powders of Li2CO3, H3BO3, Al2O3, and LiCl.

[0013] In addition, the solid electrolyte for an all-solid-state battery according to the present invention may further include other additional components within a range that does not impair the technical idea of ​​the present invention.

[0014] According to one embodiment of the present invention, a solid electrolyte for an all-solid-state battery can have excellent ionic conductivity while being capable of low-temperature sintering.

[0015] Figure 1 is a drawing schematically showing a cross-section of an all-solid-state battery.

[0016] FIG. 2 is a drawing showing the crystal structure of a solid electrolyte according to one embodiment of the present invention.

[0017] FIG. 3 is a diagram showing a simulation of measuring the movement distance of Li ions according to one embodiment of the present invention.

[0018] Figure 4 is a graph showing ion diffusion coefficients at multiple high-temperature conditions and ion diffusion coefficients at room temperature estimated therefrom according to one embodiment of the present invention.

[0019] Figure 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.

[0020] [Explanation of symbols]

[0021] 10: All-solid-state batteries

[0022] 11: Bipolar

[0023] 12: Cathode

[0024] 13: Solid electrolyte layer

[0025] Hereinafter, with reference to the attached drawings, a preferred embodiment of the present invention will be described in detail to a degree that a person having ordinary skill in the art to which the present invention pertains can easily practice the present invention.

[0026] To clearly explain the present invention, descriptions of parts irrelevant to the present invention have been omitted. It should be understood that specific shapes, structures, and characteristics described in the specification may be modified and implemented from one embodiment to another without departing from the spirit and scope of the present invention, and that the location or arrangement of individual components may also be changed without departing from the spirit and scope of the present invention.

[0027] Accordingly, the detailed description set forth below is not intended to be limiting, and the scope of the present invention should be accepted as encompassing the scope claimed in the claims and all scopes equivalent thereto.

[0028] Figure 1 is a drawing schematically showing a cross-section of an all-solid-state battery.

[0029] Referring to Fig. 1, the all-solid-state battery (10) includes a positive electrode (11), a negative electrode (12), and a solid electrolyte layer (13). The solid electrolyte layer (13) is disposed between the positive electrode (11) and the negative electrode (12), and can be in contact with the positive electrode (11) and the negative electrode (12), respectively. The positive electrode (11) and the negative electrode (12) can each have a positive electrode active material layer and a negative electrode active material layer, and the positive electrode active material layer and the negative electrode active material layer can each be in contact with the solid electrolyte layer (13).

[0030] The positive electrode (11) and the negative electrode (12) can each be joined to the solid electrolyte layer (13) by sintering. That is, the positive electrode (11), the negative electrode (12), and the solid electrolyte layer (13) can be sintered as one body.

[0031] In Fig. 1, an all-solid-state battery (10) is illustrated as including one layer each of a positive electrode (11), a negative electrode (12), and a solid electrolyte layer (13), but the present invention is not limited thereto, and an all-solid-state battery may be configured in a form in which the positive electrode, the negative electrode, and the solid electrolyte layer are each composed of multiple layers. Alternatively, the all-solid-state battery may be configured in a form in which a positive electrode, a negative electrode, and a solid electrolyte layer are alternately laminated in multiple layers, a so-called laminated all-solid-state battery.

[0032] The solid electrolyte layer (13) according to one embodiment of the present invention includes an oxide-based electrolyte as a solid electrolyte.

[0033] As oxide-based solid electrolytes, Nasicon type such as LAGP and Garnet type such as LLZO are known, and through continuous research and development, the ionic conductivity of these oxide-based solid electrolytes has been increased to 10 -4 It is known to have improved to the S / cm level.

[0034] However, there are limits to further improving ionic conductivity with the above-mentioned NASICON-type and garnet-type oxide-based solid electrolytes. Furthermore, these oxide-based solid electrolytes are sintered at high temperatures exceeding 1,000°C. Therefore, even if a certain degree of excellent ionic conductivity can be achieved, as described above, the increased manufacturing costs associated with high-temperature sintering are unavoidable.

[0035] In one embodiment of the present invention, a novel oxide-based solid electrolyte is used that overcomes the limitations of conventional oxide-based solid electrolytes, thereby securing excellent ionic conductivity while lowering the sintering temperature.

[0036] A solid electrolyte for an all-solid-state battery according to one embodiment of the present invention may have a boron oxide crystal structure, such as boracite. In one embodiment, the solid electrolyte for an all-solid-state battery may be formed of an oxide including Li, B, Al, and Cl. For example, the solid electrolyte for an all-solid-state battery may include Li2O, B2O3, Al2O3, and LiCl.

[0037] In the composition of the solid electrolyte, Li2O can function as a network modifier and plays a role in improving ionic conductivity by providing Li ions.

[0038] In the composition of the solid electrolyte, B2O3 can function as a network forming agent and, as a low-temperature component, plays a role in lowering the sintering temperature.

[0039] In the composition of the solid electrolyte, Al2O3 can function as a network modifier and increase the lattice constant of the boron oxide crystal structure. Accordingly, a wider migration path for Li ions can be secured in the crystal structure, thereby improving ionic conductivity.

[0040] In the composition of the solid electrolyte, LiCl increases the amount of Li ions in the solid electrolyte, thereby improving ionic conductivity, and Cl ions enter the network structure, forming a network structure in which two types of anions coexist, thereby expanding the volume of the network structure.

[0041] In this way, the solid electrolyte according to one embodiment of the present invention is made of an oxide including Li, B, Al, and Cl, thereby providing Li ions and securing a flow path for Li ions while lowering the sintering temperature, thereby obtaining excellent ion conductivity.

[0042] According to one embodiment of the present invention, the chemical formula of the solid electrolyte can be expressed as follows.

[0043] (1) Li4B 7-x Al x O 12 Cl

[0044] According to one embodiment of the present invention, x in the chemical formula may satisfy the following.

[0045] (2) 2.25≤x≤2.76

[0046] According to one embodiment of the present invention, x in the chemical formula may preferably satisfy the following.

[0047] (3) 2.25≤x≤2.49

[0048] According to one embodiment of the present invention, x in the chemical formula may be more preferably 2.25.

[0049] When the solid electrolyte has the above chemical formula and x satisfies the above range, low-temperature sintering is possible while ensuring excellent ionic conductivity.

[0050] A solid electrolyte according to one embodiment of the present invention can be manufactured from precursor powders of Li2CO3, H3BO3, Al2O3, and LiCl. According to one embodiment of the present invention, the precursor powders are mixed and pulverized, then placed in an Al crucible and melted at a temperature of about 800°C to 1,200°C for about 30 minutes. Thereafter, the melt is cooled on a quenching roller, pulverized into fine particles, and then sieved to obtain fine particles having a size of 10 μm or less. Thereafter, the solid electrolyte can be manufactured by sintering for about 3 hours.

[0051] As described above, the solid electrolyte according to one embodiment of the present invention is capable of low-temperature sintering. Specifically, the sintering temperature of the solid electrolyte according to one embodiment of the present invention is about 500°C to about 600°C.

[0052] The solid electrolyte according to one embodiment of the present invention, when sintered at the above temperature, has a molecular weight of about 1.44×10 at room temperature. -5 1.73×10 -4 It exhibits an ionic conductivity of S / cm.

[0053] Meanwhile, the solid electrolyte according to one embodiment of the present invention possesses excellent ionic conductivity and non-hygroscopicity. Accordingly, even if moisture enters the all-solid-state battery, the battery's performance is not degraded and it maintains stable and excellent performance.

[0054]

[0055] Experimental example

[0056] In order to evaluate the characteristics of a solid electrolyte according to one embodiment of the present invention, a simulation of the ionic conductivity of the solid electrolyte was performed by applying ab initio molecular dynamics (AIMD).

[0057] Fig. 2 is a diagram illustrating the crystal structure of a solid electrolyte according to one embodiment of the present invention, and represents a crystal structure represented by simulation. Referring to Fig. 2, it can be confirmed that BO3 and AlO4 are mixed to form a crystal structure.

[0058] To evaluate the ionic conductivity characteristics, the movement distance of Li ions over time in the crystal structure of Fig. 2 is measured to calculate the ionic diffusion coefficient (D) under high temperature conditions.

[0059] FIG. 3 is a diagram showing a simulation of measuring the movement distance of Li ions according to one embodiment of the present invention. FIG. 3 (a) is a diagram simulating a state in which Li ions move from a crystal structure state, and FIG. 3 (b) is a graph showing the mean square distance (MSD) of the movement distance of Li ions over time according to the simulation.

[0060] The ion diffusion coefficient (D) can be calculated using the following mathematical formula 1 based on the square root of the time-dependent movement distance of Li ions.

[0061]

[0062] Here, t represents time, and r(t) and r(0) represent the position and initial position of the Li ion particle at time t, respectively.

[0063] Figure 4 is a graph showing the ion diffusion coefficient at multiple temperature conditions and the ion diffusion coefficient at room temperature estimated therefrom according to one embodiment of the present invention.

[0064] First, the ion diffusion coefficient (D) under three different high-temperature conditions was calculated, and the results are indicated by dots in Fig. 4 (a). As shown, it can be confirmed that the natural logarithm value (ln D) of the ion diffusion coefficient (D) under the three high-temperature conditions is inversely proportional to the temperature (i.e., proportional to the reciprocal of the temperature).

[0065] With reference to the ion diffusion coefficient at these high-temperature conditions, the ion diffusion coefficient at room temperature was calculated using the Arrhenius equation. This can be expressed by the following mathematical equations 2 and 3.

[0066]

[0067]

[0068] Here, D0 represents the ion diffusion coefficient at room temperature, and E a is the activation energy, k B is the Boltzmann constant, and T represents the absolute temperature.

[0069] As above, the ion diffusion coefficient at room temperature (D0) can be estimated from the ion diffusion coefficient (D) at three high temperature conditions.

[0070] The ionic conductivity (σ) of the solid electrolyte can be calculated using the following mathematical equation 4 (Nernst-Einstein equation) based on the calculated ionic diffusion coefficient.

[0071]

[0072] Here, N represents the number of Li ion particles in a unit cell, q represents the charge of Li ions, V represents the volume of the unit cell, and k represents the B is the Boltzmann constant, and T represents the absolute temperature.

[0073] First, Li4B4Al3O 12 Cl(LCBA), Li4B7O 12 After generating two Cl(LCB) crystal phases, some of the AlO4 in the unit cell of the LCBA crystal was replaced with BO4 to generate exemplary conditions. Subsequently, simulations were performed for each exemplary embodiment by applying first-principles molecular dynamics, and the ionic diffusion coefficient and ionic conductivity at room temperature were calculated.

[0074] Fig. 5 is a graph showing the ion diffusion coefficient (D) and ion conductivity (σ) of solid electrolytes according to examples and comparative examples of the present invention. Specifically, Fig. 5 is a graph showing the ion diffusion coefficient (D) and ion conductivity (σ) according to the degree of substitution of AlO4 with BO4 in a unit cell in an LCBA crystal phase.

[0075] Referring to (a) of Fig. 5, it can be confirmed that the ionic diffusion coefficient is highest in the solid electrolyte when the proportion of residual AlO4 not substituted with BO4 is 75%. Similarly, referring to (b) of Fig. 5, it can be confirmed that the ionic conductivity shows a peak in the solid electrolyte when the proportion of residual AlO4 not substituted with BO4 is 75%.

[0076] Table 1 shows the ionic conductivity values ​​of the solid electrolytes according to each embodiment and comparative example of the present invention. In Table 1, the degree of substitution of AlO4 with BO4 in a unit cell in the LCBA crystal phase is expressed as the AlO4 residue ratio, and the ionic conductivity was calculated in each case. Specifically, the ionic conductivity was calculated by dividing the cases into cases where the AlO4 residue ratio was 100% (i.e., not substituted), 92%, 83%, 75%, 67%, and 0% (i.e., fully substituted).

[0077] Classification Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Comparative Example 2 AlO4 Residual Ratio O% (LCB) 67% 75% 83% 92% 100% (LCB-A) Ionic Conductivity (S / cm) 9.185×10 -8 1.021×10 -5 1.730×10 -4 3.120×10 -5 1.436×10 -5 1.149×10 -5

[0078] Referring to Table 1, the solid electrolytes having a residual ratio of AlO4 of 75% to 92% (i.e., Examples 2 to 4) have a mass of 1.44×10 -5It has an excellent ionic conductivity of more than S / cm. Among them, in Example 2 where the residual ratio of AlO4 is 75%, it is 1.73×10 -4 It exhibits excellent ionic conductivity of S / cm.

[0079] In comparison, in Comparative Example 1 where AlO4 was completely replaced with BO4 and Comparative Example 2 where AlO4 was not replaced with BO4, 1.15×10 -5 It exhibits low ionic conductivity of less than S / cm.

[0080] In this way, by replacing AlO4 with BO4 in the solid electrolyte of the LCBA crystal, low-temperature sintering is possible while securing excellent ionic conductivity, and in particular, when the residual ratio of AlO4 is 75% to 92%, it can be confirmed that the ionic conductivity is very excellent when it is 75%. Here, when the residual ratio of AlO4 is 75% to 92%, the chemical formula is Li4B. 7-x Al x O 12 In Cl, 2.25≤x≤2.76 is satisfied, and when the residual ratio of AlO4 is 75%, x is 2.25. Figure 2 shows the chemical formula (Li4B 7-x Al x O 12 The crystal structure of the solid electrolyte according to the embodiment (i.e., embodiment 2) in which x is 2.25 in Cl) is illustrated, and the lattice constant at this time is measured as a=b=c=13.393 (Å).

[0081] Although the present invention has been described above with specific details such as specific components and limited examples, the above examples are provided only to help a more general understanding of the present invention, and the present invention is not limited thereto, and those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations based on this description.

[0082] Therefore, the idea of ​​the present invention should not be limited to the embodiments described above, and all things that are modified equally or equivalently to the claims described below as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. As a solid electrolyte for an all-solid-state battery, Li4B 7-x Al x O 12 It consists of an oxide having the chemical formula Cl, satisfying 2.25≤x≤2.76, Solid electrolyte for all-solid-state batteries.

2. In paragraph 1, satisfying 2.25≤x≤2.49, Solid electrolyte for all-solid-state batteries.

3. In paragraph 1, satisfying x=2.25, Solid electrolyte for all-solid-state batteries.

4. In paragraph 1, Ionic conductivity is 1.44×10 -5 Inside 1.73×10 -4 S / cm, Solid electrolyte for all-solid-state batteries.

5. In paragraph 1, The lattice constant of the crystal structure is a=b=c=13.393(Å). Solid electrolyte for all-solid-state batteries.

6. In paragraph 1, Manufactured from precursor powders of Li2CO3, H3BO3, Al2O3 and LiCl, Solid electrolyte for all-solid-state batteries.

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