KR20230102050A - Solid electrolyte composition for low temperature sintering and solid electrolyte produced using the composition - Google Patents

Abstract

It relates to a composition for an oxide-based solid electrolyte capable of low-temperature sintering, and an oxide-based solid electrolyte prepared using the composition.

Description

Composition for low-temperature sintering oxide-based solid electrolyte and oxide-based solid electrolyte produced using the composition {Solid electrolyte composition for low temperature sintering and solid electrolyte produced using the composition}

It relates to a composition for an oxide-based solid electrolyte capable of low-temperature sintering, and an oxide-based solid electrolyte prepared using the composition.

Today, portable devices such as smart phones and tablet PCs are deeply infiltrating into our daily lives and are increasingly becoming indispensable to our lives. It is no exaggeration to say that this is all thanks to advances in battery technology.

Since mass production began in 1991, lithium secondary batteries have developed rapidly with the spread of mobile devices such as cell phones and notebook PCs with the excellence of high energy density and output voltage as weapons. Recently, electric vehicles (xEV) and power storage systems (ESS) Its use as a power source is expanding.

In particular, as environmental regulations are strengthened to respond to climate change due to global warming, interest in eco-friendly electric vehicles is very high, and major automakers around the world recognize electric vehicles as a next-generation growth engine and are accelerating technology development.

As the required characteristics of lithium secondary batteries for electric vehicles, high power density capable of rapid charging, high energy density per weight/volume, price, and safety can be considered. Securing safety in case of an accident is the most important requirement.

However, in the case of lithium secondary batteries, the organic electrolyte used for the movement of lithium ions has the risk of explosion in overheated and overcharged conditions, and is easily ignited when there is an ignition source, and when a side reaction occurs in the battery, gas is released. This has the disadvantage of deteriorating the performance and stability of the battery.

Recently, as a fire broke out while driving an electric vehicle and was announced through the media, the demand for the development of an all-solid-state battery with ultimate safety is increasing.

All-solid-state batteries can significantly improve safety by replacing liquid electrolytes with solid ones so that no ignition or explosion occurs due to the decomposition reaction of the electrolyte.

These all-solid-state batteries can increase safety compared to existing lithium secondary batteries, and oxide-based solid electrolytes with excellent ionic conductivity can be applied instead of flammable organic solvents. As the oxide-based solid electrolyte, LSTP (Lithium Silicon Titanium Phosphate), LATP (Lithium Aluminum Titanium Phosphate), LLZO (Lithium Lanthanum Zirconium Oxide), LLT (Lithium Lanthanum Titanium Oxide), etc. have been developed.

US Patent Publication 2015-0263380 Registered Patent No. 10-1324729 Registered Patent No. 10-2177718

Among oxide-based solid electrolytes, sintering tests were conducted using garnet-type LLZO solid electrolyte, which has low reactivity with cathode materials. .

On the other hand, the conventional oxide-based solid electrolyte has high interfacial resistance with the cathode and anode materials, so it is difficult to use it alone as an electrolyte for an all-solid-state battery. electrolyte was developed.

In the case of polymer electrolytes, flexibility is excellent, but the moving directions of ions are different due to polarization, so there is a problem in that voltage decreases or increases resistance in a battery due to a relative speed difference of ions. In addition, it has low ionic conductivity and low thermal stability at room temperature, so it is difficult to use when exposed to high temperature heat and has characteristics of decomposition at high voltage.

Therefore, an object of the present invention is to provide an oxide-based solid electrolyte that is not decomposed at high voltage, has high ionic conductivity, and has excellent thermal stability, while supplementing the interface resistance between anode and cathode materials, which is the biggest drawback of oxide-based solid electrolytes, and which can be prepared in air. It is to provide a solid electrolyte.

Another object of the present invention is to provide a solid electrolyte capable of crystallization at a relatively low temperature through a combination of components.

Another object of the present invention is to provide a solid electrolyte that is sintered at a low temperature due to its high high-temperature fluidity.

In order to achieve the above object, the present invention includes Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO, and 0.1-8% by weight of MgO based on the total weight of the composition. It provides a composition for an oxide-based solid electrolyte comprising

The present invention relates to a) preparing a composition for an oxide-based solid electrolyte comprising Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO

b) melting the composition at 1200-1500 ° C and then quenching it below 300 ° C to make it amorphous; and

c) providing a solid electrolyte manufacturing method comprising the step of pulverizing after crystallization at 800-850 ° C.

The present invention crystallizes a composition comprising Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO and containing 0.1-8% by weight of MgO based on the total weight of the composition. It provides an oxide-based solid electrolyte prepared by

The present invention provides a lithium secondary battery including the oxide-based solid electrolyte.

If the composition for preparing a solid electrolyte of the present invention is used, it is possible to prepare a solid electrolyte that has high temperature fluidity and can be crystallized at a relatively low temperature and at the same time exhibits high ionic conductivity.

The use of the composition of the present invention including MgO has advantages in that low-temperature crystallization is possible during preparation of the solid electrolyte and sintering with the anode is also possible at low temperature.

The solid electrolyte prepared from the composition of the present invention is stable even at high voltage, and has an effect of enabling battery capacity to be improved.

The present invention can lower the interfacial resistance through sintering between the cathode material and the solid electrolyte, and can solve thinning, large area, and low strength, so that it can be applied to various applications.

The present invention makes it possible to manufacture a solid electrolyte without using an organic binder (for example, an organic polymer), thereby solving the problem of deterioration in safety when exposed to high temperature heat when using an existing organic binder. In addition, when an existing organic binder is used, the effect of providing a solid electrolyte that prevents no ion conductivity or deterioration of ion conductivity, has high ion conductivity, is stable even at high voltage, and enables to improve battery capacity. there is

1 to 3 are thermal characteristic data of solid electrolytes prepared in Examples 1 to 3 of the present invention.
4 is an ionic conductivity graph of the solid electrolyte prepared in Example 2 of the present invention.
5 is a SEM photograph of the solid electrolyte prepared in Comparative Example 6 and Examples 1 and 2 of the present invention.

Hereinafter, the present invention will be described in detail. The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors can properly define the concept of terms in order to best explain their invention. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention.

In the case of the present inventors, the polymer electrolyte has excellent flexibility, but since it is prepared by adding lithium salt from the outside, lithium ions and anions (PF ₆ ^- , ClO ₄ ^- , BF ₄ ^-, etc.) are simultaneously involved in ion conduction, cation conduction (Bi -ionic conduction) characteristics, it was recognized that anion does not contribute at all in the actual electrode reaction of a lithium secondary battery, but rather causes polarization or decomposition to increase internal resistance of the battery. In addition, the present inventors have recognized that when a polymer electrolyte is included, ion conductivity is low at room temperature, thermal stability is reduced, it is difficult to use when exposed to high temperature heat, and it has a characteristic of decomposition at high voltage. Efforts were made to develop solid electrolytes.

As a result, the present inventors added Bi ₂ O ₃ and SrCO ₃ to LAGP (lithium-aluminum-germanium-phosphate, Li ₂ O-Al ₂ O ₃ -GeO ₂ -P ₂ O ₅ ), which is one of the oxide solid electrolytes. developed solid electrolytes. The LAGP-BiSr (Li ₂ O-Al ₂ O ₃ -GeO ₂ -P ₂ O ₅ -Bi ₂ O ₃ -SrCO ₃ ) solid electrolyte was prepared in a glass state through melting at a high temperature and then crystallized at 850 ° C or higher. It has ion conductive properties. After mixing the solid electrolyte with ion conductive properties and the cathode material, sintering is possible when sintering at 850℃, but the reaction between the Co component in the cathode material and the LAGP-BiSr solid electrolyte material by heat treatment at 850℃ As a result, the CoAl ₂ O ₄ phase was created and the anode crystal structure was changed.

This is the result of not only the increase in interface resistance between the cathode material and the solid electrolyte but also the deterioration of the anode material. proceeded. However, below 850 ° C, especially below 750 ° C, sintering between the cathode material and the LAGP-BiSr solid electrolyte was not performed, so that the interface was not formed, so that the ion conduction characteristics were not expressed.

Accordingly, the inventors of the present invention have tried to find a material that lowers the thermal properties to increase high-temperature flowability. As a result, when MgO is added, it is found that sintering is possible without side reactions with the cathode material even at 750 ° C. or less, and the present invention has been completed.

That is, the present invention is a composition for preparing a solid electrolyte that does not decompose at high voltage, has high ionic conductivity, has excellent thermal stability, and can compensate for the interfacial resistance between the cathode and anode materials, which is a disadvantage of oxide-based solid electrolytes. Li ₂ A composition for an oxide-based solid electrolyte containing O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO is provided.

According to one embodiment, the composition of the present invention may include 0.1 to 10% by weight, preferably 0.5 to 7% by weight of MgO based on the total weight of the composition. When the composition of the present invention includes MgO in the above amount, there are advantages in that low-temperature crystallization is possible without reducing the ionic conductivity of the solid electrolyte and that an all-solid-state battery can be manufactured without side reactions with the cathode material.

According to one embodiment, the composition of the present invention may contain 0.1 to 10% by weight, preferably 1.0 to 6.0% by weight, more preferably 1.5 to 5.0% by weight of Bi ₂ O ₃ based on the total weight of the composition together with the MgO. It may be, SrCO ₃ 0.1-10% by weight, preferably within the range of 1.0 to 6.0% by weight, more preferably 1.5 to 5.0% by weight. When the composition for an oxide-based solid electrolyte of the present invention contains Bi ₂ O ₃ and SrCO ₃ in the above amounts, the raw material of the solid electrolyte has high-temperature fluidity and can be molded at a relatively low temperature while exhibiting high ionic conductivity. . In particular, it is possible to manufacture a solid electrolyte without using an organic binder (for example, an organic polymer), thereby solving the problem of deterioration in safety when exposed to high temperature heat when using an existing organic binder, and existing organic binders. In the case of using, it is possible to prevent no ion conduction property or deterioration of ion conduction property, maintain high ion conductivity, be stable even at high voltage, and improve battery capacity.

According to one embodiment, the composition of the present invention may include 1-20% by weight, preferably 2-15% by weight of Bi ₂ O ₃ , SrCO ₃ and MgO based on the total weight of the composition. When the composition of the present invention contains Bi ₂ O ₃ , SrCO ₃ and MgO in the above amounts, it can be molded at a relatively low temperature compared to the LAGP electrolyte, does not decompose at high voltage, has high ionic conductivity, and has excellent thermal stability while low temperature It has the advantage that crystallization is possible.

According to one embodiment, the present invention is based on the total weight of the composition Li ₂ O 1-20% by weight, Al ₂ O ₃ 1-10% by weight, GeO ₂ 20-60% by weight, P ₂ O ₅ 20-60% by weight %, Bi ₂ O ₃ 0.1-10% by weight, SrCO ₃ 0.1-10% by weight, and MgO 0.1-10% by weight. When the composition of the present invention includes Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO in the above amounts, the solid electrolyte obtained therefrom is a positive electrode material and a solid Interfacial resistance can be lowered through sintering between electrolytes, thin film and large area can be achieved, and the problem of low strength can be solved.

The present invention provides a solid electrolyte prepared by crystallizing a composition for an oxide-based solid electrolyte including Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO.

The composition for an oxide-based solid electrolyte containing Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO of the present invention can be crystallized at a low temperature during the manufacture of a solid electrolyte, and the cathode and After mixing, a battery including a solid electrolyte may be prepared by sintering at a relatively low temperature.

The crystallization temperature of the solid electrolyte is 800-850 ° C., and the solid electrolyte of the present invention has the advantage of showing high ionic conductivity even when crystallized at a relatively low temperature as described above, and also having a low sintering temperature with the cathode material thereafter.

Specifically, the solid electrolyte of the present invention

a) preparing a composition for an oxide-based solid electrolyte containing Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO

b) melting and then quenching the composition to make it amorphous; and

c) pulverization after crystallization at 800-850 ° C.

The melting temperature may be 1200-1500 °C and the quenching temperature may be 300 °C or less. When the melting and quenching temperatures are as described above, a homogeneous solid electrolyte having excellent ionic conductivity can be prepared.

A battery may be manufactured by mixing the prepared solid electrolyte with a positive electrode and sintering it.

In addition, since the composition for a solid electrolyte of the present invention can be sintered at a low temperature, a battery can be manufactured by mixing with a positive electrode in an amorphous state and then sintering at a low temperature.

When mixing with the positive electrode, the sintering temperature is preferably 750° C. or lower to prevent side reactions of the positive electrode.

The solid electrolyte of the present invention can lower the interfacial resistance between the cathode material and the solid electrolyte, and can be applied to various applications because it can solve thinning, large area, and low strength. For example, it can be used for multilayer ceramic capacitors (MLCC, Multi Layer Ceramic Condenser, Multi Layer Ceramic Capacitor).

The present invention provides an all-solid-state lithium secondary battery including a positive electrode: a negative electrode, and the oxide-based solid electrolyte between the positive electrode and the negative electrode.

The all-solid lithium secondary battery of the present invention can be manufactured as follows.

In the first step, a composition for an oxide-based solid electrolyte containing Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO is prepared and melted, quenched, crystallized, and pulverized. , and a step of preparing a solid electrolyte through a classification step.

The second step consists of preparing an anode and a cathode simultaneously with or after the first step.

The cathode may be manufactured by forming a cathode active material layer including the cathode active material on a current collector mainly made of a good conductor such as aluminum. The cathode active material layer may be prepared by a vapor phase method or a solid phase method. The vapor phase method may be pulse laser deposition (PLD), sputtering deposition, chemical vapor deposition (CVD), etc., but is not limited thereto, and any method that can be used in the art is possible. The solid phase method may be a sintering method, a sol-gel method, a doctor blade method, a screen printing method, a slurry casting method, a powder pressing method, etc., but is not necessarily limited thereto, and any method usable in the art is possible.

The cathode active material may be used without limitation as long as it is commonly used in a lithium ion battery. Preferably, the cathode active material includes LiCoO ₂ , LiNiO ₂ , LiNi _x Co _y Mn _z O ₂ , LiMn ₂ O ₄ , and LiFePO ₄ , but is not limited thereto. The cathode active material layer may additionally include a solid ion conductor or a hybrid solid ion conductor in addition to the cathode active material. By additionally including the solid ion conductor in the positive electrode active material layer, interface resistance between the positive electrode and the solid electrolyte layer in contact with the positive electrode can be reduced, ionic conductivity within the positive electrode active material layer can be improved, and thermal stability of the positive electrode can be improved. It can be. In addition, the positive electrode active material layer may additionally include a conductive material, a binder, and the like. The conductive material, binder, and the like may be any material that can be used in the art.

The negative electrode may be manufactured in the same manner as the positive electrode except that the negative electrode active material is used instead of the positive electrode active material. The negative electrode may additionally include the solid ion conductor described above in the negative electrode active material layer. Any negative electrode active material may be used without limitation as long as it is commonly used in lithium ion batteries. For example, it may include at least one selected from the group consisting of lithium metal, lithium oxide, lithium alloy, lithium alloy oxide, transition metal oxide, non-transition metal oxide, and carbon-based materials.

The third step consists of sintering the solid electrolyte obtained in the first step by placing it between the positive electrode and the negative electrode obtained in the second step, through which an all-solid lithium secondary battery can be finally obtained. The sintering temperature is preferably 750°C or less. When the sintering temperature is as described above, an all-solid-state battery can be manufactured without side reactions of the cathode material.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention. However, in describing the present invention, descriptions of already known functions or configurations will be omitted to clarify the gist of the present invention.

Examples 1 to 3 and Comparative Examples 1 to 8. Solid Electrolyte Preparation

A composition for a solid electrolyte according to the present invention (Examples 1 to 3) was prepared in parts by weight as shown in Table 1 below, and a composition for a solid electrolyte as a control (Comparative Examples 1 to 8) was prepared to prepare a solid electrolyte therefrom. did

After mixing each component of the solid electrolyte composition, it was melted at 1400 ° C, quenched at 300 ° C to prepare an amorphous solid electrolyte, and then heat-treated at 830-850 ° C and pulverized to prepare a crystalline solid electrolyte.

Comparative Example 1 is a LAGP-type solid electrolyte containing no additives, Comparative Example 2 includes 1.5 parts by weight of Bi ₂ O ₃ as an additive to the LAGP-type solid electrolyte, and Comparative Example 3 is an additive to the LAGP-type solid electrolyte. Bi ₂ O ₃ was included in an amount of 3.0 parts by weight, Comparative Example 4 included SrCO ₃ in an amount of 1.5 parts by weight as an additive to the LAGP type solid electrolyte, and Comparative Example 5 included 3.0 parts by weight of SrCO ₃ as an additive to the LAGP type solid electrolyte. Comparative Example 6 includes 3.0 parts by weight of Bi ₂ O ₃ and 1.5 parts by weight of SrCO ₃ as additives to the LAGP type solid electrolyte. Comparative Example 7 is also a LAGP-type solid electrolyte, but as a control, it was prepared as described in Solid State Ionics 318 (2018) 27-34 , and Comparative Example 8 was prepared as described in the LAGP of Comparative Example 1 with yttria (Y ₂ O ₃ ) in an amount of 5.0 parts by weight.

In Examples 1 to 3, a solid electrolyte composition containing MgO together with Bi ₂ O ₃ and SrCO ₃ as an additive to a LAGP type solid electrolyte was prepared, and a solid electrolyte was prepared therefrom.

comparative example Example ingredient
(parts by weight) One 2 3 4 5 6 7 8 One 2 3 Li ₂ O 4.8 4.8 4.7 4.8 4.7 4.7 5.4 Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ 4.7 4.7 4.7 Al ₂ O ₃ 2.3 2.3 2.3 2.3 2.3 2.3 6.1 2.3 2.3 2.3 GeO ₂ 45.4 44.4 44 44.4 44 43.5 37.6 43.5 43.5 43.5 P ₂ O ₅ 47.5 47 46 47 46 45 51 45 45 45 Bi ₂ O ₃ 1.5 3 3 3 3 3 SrCO ₃ 1.5 3 1.5 1.5 1.5 1.5 Y ₂ O ₃ 5 MgO One 3 5 Li ion
conductivity
(S/cm) 4.1×10 ^-4 5.6×10 ^-4 6.1×10 ^-4 5.3×10 ^-4 5.2×10 ^-4 7.3×10 ^-4 3.1×10 ^-4
( Solid State Ionics 318 (2018) 27-34) 5.0×10 ^-4
(US20150263380A1) 7.6×10 ^-4 8.2×10 ^-4 7.5×10 ^-4 heat
special
castle T _g (℃) 536.8 510.8 506.8 512.4 512.4 503.4 549.3 - 503.4 501.2 494.5 T _dsp (℃) 573.1 556.9 555.2 556.8 555.6 542.3 592.5 - 549.3 547.2 540.6 CTE
(x10 ^-7 /℃) 84.9 88.6 89.6 89.3 90.4 84.9 81.2 - 90.7 91.2 90.8

Experimental Example 1. Measurement of glass transition temperature of solid electrolyte

The glass transition temperatures of the solid electrolytes prepared in Comparative Examples 1 to 8 were measured and are shown in Table 1 above. Thermal characteristic data of the solid electrolytes prepared in Examples 1 to 3 are shown in FIGS. 1 to 3, respectively, and the glass transition temperature values are shown in Table 1 above.

As shown in Table 1, it can be seen that the addition of Bi ₂ O ₃ and/or SrCO ₃ to LAGP lowers the glass transition temperature as the amount of Bi ₂ O ₃ and/or SrCO ₃ increases. In addition, in the case of Examples 1 to 3 in which MgO of the present invention was added, it can be seen that the glass transition temperature was lowered.

Experimental Example 2. Measurement of ion conductivity of solid electrolyte

The ionic conductivities of the solid electrolytes prepared in Comparative Examples 1 to 8 were measured and are shown in Table 1 above. The ionic conductivity was measured while varying the thickness of the solid electrolyte prepared in Example 2, and the results are shown in FIG. 4. Table 1 shows the ionic conductivities of the solid electrolytes prepared in Examples 1 to 3.

- Measurement equipment: Zennium/ Zahner, Germany (impedance analyzer)

- Measurement conditions (Frequency range: 1Hz~4MHz, AC amplitude voltage: 50mV, Temperature: Room temperature)

It can be seen that the ion conductivity (lithium ion conductivity) is also increased by the addition of Bi ₂ O ₃ and/or SrCO ₃ to LAGP and as the amount of Bi ₂ O ₃ and/or SrCO ₃ is increased. In addition, MgO of the present invention In the case of Examples 1 to 3 with the addition of, it can be seen that the ionic conductivity is higher.

Experimental Example 3. SEM image of solid electrolyte

SEM images of the solid electrolytes prepared in Comparative Example 6, Example 1 and Example 2 were measured and shown in FIGS. 5(a), 5(b) and 5(c), respectively.

According to the SEM picture, compared to the solid electrolyte of Comparative Example 6 without MgO, the solid electrolytes of Example 1 in which 1 wt% of MgO was added and Example 2 in which 3 wt% of MgO was added were improved in high-temperature fluidity, resulting in increased particle bonding. It can be confirmed that, when the MgO content is increased, the tendency becomes clear. Therefore, it can be seen that the sintering properties are improved when MgO is added.

Claims (8)

A composition for an oxide-based solid electrolyte comprising Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ , and MgO, and 0.1 to 8 wt % of MgO based on the total weight of the composition. The composition for an oxide-based solid electrolyte according to claim 1, which is characterized in that it can be crystallized at a temperature of 800-850 ° C when preparing a solid electrolyte. The composition for an oxide-based solid electrolyte according to claim 1, comprising 0.1 to 10% by weight of MgO based on the total weight of the composition. The composition for an oxide-based solid electrolyte according to claim 1, comprising 1-20% by weight of Bi ₂ O ₃ , SrCO ₃ and MgO based on the total weight of the composition. The method according to claim 1, based on the total weight of the composition Li ₂ O 1-20% by weight, Al ₂ O ₃ 1-10% by weight, GeO ₂ 20-60% by weight, P ₂ O ₅ 20-60% by weight, Bi ₂ A composition for an oxide-based solid electrolyte comprising 0.1-10 wt% of O ₃ , 0.1-10 wt% of SrCO ₃ and 0.1-8 wt% of MgO a) preparing a composition for an oxide-based solid electrolyte containing Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO
b) melting the composition at 1200-1500 ° C and then quenching it below 300 ° C to make it amorphous; and
c) a solid electrolyte manufacturing method comprising the step of pulverizing after crystallization at 800-850 ° C. Prepared by crystallizing a composition containing Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO, and containing 0.1-8% by weight of MgO based on the total weight of the composition. Oxide-based solid electrolyte All-solid lithium secondary battery comprising the oxide-based solid electrolyte of claim 7

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