KR20220117398A - Solid electrolyte composition for low temperature sintering and solid electrolyte produced using the composition - Google Patents

Abstract

The present invention relates to a composition for an oxide-based solid electrolyte capable of low-temperature sintering, and an oxide-based solid electrolyte manufactured using the composition. The present invention can improve battery capacity. The present invention includes Li_2O, Al_2O_3, GeO_2, P_2O_5, Bi_2O_3, SrCO_3 and MgO.

Description

A composition for a low-temperature sinterable oxide-based solid electrolyte and an oxide-based solid electrolyte prepared 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 by using the composition.

Today, portable devices such as smart phones and tablet PCs are deeply penetrating into our daily lives and are increasingly becoming an indispensable part of 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 along with the spread of mobile devices such as mobile phones and notebook PCs with the superiority of high energy density and output voltage as weapons. Its use is expanding as a power source for

In particular, as environmental regulations are strengthened to respond to climate change caused by global warming, interest in eco-friendly electric vehicles is very high.

As the required characteristics of lithium secondary batteries for electric vehicles, high power density capable of rapid charging, high energy density per weight and volume, price, and safety can be considered. Securing safety in the event 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 a risk of explosion under overheating and overcharging, and has a property of being easily ignited in the presence of an ignition source. It has a disadvantage of lowering the performance and stability of the battery.

Recently, as an event in which a fire occurred while driving an electric vehicle and burned out 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 replace liquid electrolytes with solids so that no ignition or explosion occurs due to the decomposition reaction of the electrolyte, so safety can be greatly improved.

Such an all-solid-state battery can increase safety compared to a conventional lithium secondary battery, and an oxide-based solid electrolyte having excellent ionic conductivity can be applied instead of a combustible organic solvent. 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), and the like have been developed.

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

Among the oxide-based solid electrolytes, a sintering test was conducted using a garnet-type LLZO solid electrolyte with low reactivity with the cathode material, but most of the LLZO solid electrolyte crystallizes at a high temperature of 1,100° C. .

On the other hand, the conventional oxide-based solid electrolyte has high interfacial resistance with the positive and negative electrode materials, making it difficult to use alone as an electrolyte for an all-solid-state battery. electrolytes were developed.

Polymer electrolytes have excellent flexibility, but due to polarization, the movement directions of ions are different from each other, so there is a problem in that a voltage decrease or resistance in a battery is increased due to a relative ion velocity difference. In addition, it has low ionic conductivity at room temperature and low thermal stability, making it difficult to use when exposed to high-temperature heat and decomposed at high voltage.

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

It is also an object of the present invention to provide a solid electrolyte that can be crystallized at a relatively low temperature through a combination of constituents.

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

In order to achieve the above object, the present invention provides 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.

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

b) making the composition into an amorphous state by quenching after melting and

c) It provides a method for producing a solid electrolyte, characterized in that it comprises the step of pulverizing after crystallization at 800-850 ℃.

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

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

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

When the composition of the present invention containing MgO is used, low-temperature crystallization is possible when preparing a solid electrolyte, and sintering with the positive electrode is also possible at low temperature.

The solid electrolyte prepared from the composition of the present invention is stable even at a high voltage, and has the effect of improving the battery capacity.

The present invention can lower the interface resistance through sintering between the cathode material and the solid electrolyte, and can solve the thin film, 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 (eg, an organic polymer), thereby solving a problem in which safety is deteriorated 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 ionic conductivity, is stable even at high voltage, and enables to improve battery capacity there is

1 to 3 are thermal characteristic data of the solid electrolyte prepared in Examples 1 to 3 of the present invention.
4 is a graph of ion conductivity of the solid electrolyte prepared in Example 2 of the present invention.
5 is an 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 the present specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventor may appropriately define the concepts of the terms in order to best describe his invention. Based on the principle, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In the case of polymer electrolytes, the present inventors have found that, although flexibility is excellent, lithium ions and anions (PF ₆ ^- , ClO ₄ ^- , BF ₄ ^- , etc.) are simultaneously involved in ion conduction (Bi -ionic conduction) characteristic, the anion does not contribute at all to the electrode reaction of a lithium secondary battery, but rather induces polarization or decomposes, thereby increasing the resistance in 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 lowered, so it is difficult to use when exposed to high temperature heat, and has a property of being decomposed at high voltage. Efforts were made to develop a solid electrolyte.

As a result, the present inventors added Bi ₂ O ₃ and SrCO ₃ to one of the oxide solid electrolytes, LAGP (lithium-aluminum-germanium-phosphate, Li ₂ O-Al ₂ O ₃ -GeO ₂ -P ₂ O ₅ ). 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 is prepared in a glassy state through melting at a high temperature and then crystallized at 850° C. or higher. It has ion-conducting properties. After mixing the solid electrolyte with ion-conducting properties and the cathode material, sintering is possible when sintering at 850°C. Through this, a CoAl ₂ O ₄ phase was generated and the anode crystal structure was changed.

This is a result of not only an increase in the interfacial resistance between the positive electrode material and the solid electrolyte but also the deterioration of the positive electrode material. proceeded. However, below 850°C, especially below 750°C, ion conduction properties could not be expressed because sintering did not occur between the positive electrode material and the LAGP-BiSr solid electrolyte, so that an interface could not be created.

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

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

According to one embodiment, the composition of the present invention may contain 0.1-10% by weight of MgO, preferably 0.5-7% by weight, based on the total weight of the composition. When the composition of the present invention contains MgO in the above content, low-temperature crystallization is possible without degrading the ionic conductivity of the solid electrolyte, and an all-solid-state battery can be manufactured without a side reaction with the cathode material.

According to one embodiment, the composition of the present invention may contain 0.1-10 wt% of Bi ₂ O ₃ , preferably 1.0 to 6.0 wt%, more preferably 1.5 to 5.0 wt%, based on the total weight of the composition together with the MgO. and SrCO ₃ 0.1-10% by weight, preferably 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 content, the raw material of the solid electrolyte has high-temperature fluidity, so that it can be molded at a relatively low temperature and at the same time exhibit 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 a decrease in safety when exposed to high temperature heat when using an existing organic binder, and the existing organic binder In the case of using , it is possible to prevent no ion conduction properties or deterioration of the ion conduction properties, to have high ionic conductivity, to be stable even at high voltages, and to improve the battery capacity.

According to one embodiment, the composition of the present invention may contain 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 includes Bi ₂ O ₃ , SrCO ₃ and MgO in the above content, it can be molded at a relatively low temperature compared to LAGP electrolyte, does not decompose at high voltage, has high ion conductivity, has excellent thermal stability, and has excellent thermal stability at low temperature It has the advantage that crystallization is possible.

According to one embodiment, the present invention 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 MgO provides a composition for a high agent electrolyte. When the composition of the present invention contains Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO in the same amount as above, the solid electrolyte obtained therefrom is a positive electrode material and a solid Through sintering between electrolytes, the interfacial resistance can be lowered, thin film formation and large area are possible, and the low strength problem can be solved.

The present invention provides a solid electrolyte prepared by crystallizing an oxide-based solid electrolyte composition comprising 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 is capable of low-temperature crystallization when manufacturing a solid electrolyte, and After mixing, the solid electrolyte-containing battery may be manufactured by sintering at a relatively low temperature.

The crystallizable 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.

Specifically, the solid electrolyte of the present invention is

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) making the composition into an amorphous state by quenching after melting and

c) crystallization at 800-850° C. and then pulverizing.

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

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

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 the 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 less in order to prevent a side reaction 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 the thin film, large area, and low strength. For example, it can be used in a multilayer ceramic capacitor (MLCC, Multi Layer Ceramic Condenser, Multi Layer Ceramic Capacitor).

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

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

In the first step, 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 is prepared and melted, quenched, crystallized, and pulverized , and a step of preparing a solid electrolyte through a classification step.

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

The positive electrode may be manufactured by forming a positive electrode active material layer including a positive electrode active material on a current collector mainly made of a good conductor such as aluminum. The positive electrode active material layer may be manufactured by a gas 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 available in the art may be used. 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 available in the art is possible.

The cathode active material may be used without limitation as long as it is commonly used in lithium ion batteries. The positive electrode active material may include, but is not limited to, LiCoO ₂ , LiNiO ₂ , LiNi _x Co _y Mn _z O ₂ , LiMn ₂ O ₄ , and LiFePO ₄ . The positive electrode active material layer may additionally include a solid ion conductor or a hybrid solid ion conductor in addition to the positive electrode active material. Since the positive electrode active material layer additionally includes the above-described solid ion conductor, the interfacial resistance with the solid electrolyte layer in contact with the positive electrode may be reduced, ionic conductivity may be improved in the positive electrode active material layer, and thermal stability of the positive electrode may be improved can be In addition, the cathode active material layer may additionally include a conductive material, a binder, and the like. The conductive material, the binder, and the like can be used as long as they 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 above-described solid ion conductor in the negative electrode active material layer. The anode 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 material.

The third step consists of sintering the solid electrolyte obtained in the first step by positioning it between the positive electrode and the negative electrode obtained in the second step, and through this, an all-solid-state 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 a side reaction 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 in order to clarify the gist of the present invention.

Examples 1 to 3 and Comparative Examples 1 to 8. Solid electrolyte preparation

The composition for a solid electrolyte (Examples 1 to 3) according to the present invention 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, and a solid electrolyte was prepared therefrom. did.

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

Comparative Example 1 is a LAGP-type solid electrolyte without an additive, Comparative Example 2 includes Bi ₂ O ₃ as an additive to the LAGP-type solid electrolyte in an amount of 1.5 parts by weight, and Comparative Example 3 is an additive to the LAGP-type solid electrolyte Bi ₂ O ₃ is contained in an amount of 3.0 parts by weight, Comparative Example 4 contains SrCO ₃ as an additive to the LAGP type solid electrolyte in an amount of 1.5 parts by weight, and Comparative Example 5 contains SrCO ₃ 3.0 as an additive to the LAGP type solid electrolyte and Bi ₂ O ₃ as an additive to the LAGP-type solid electrolyte in an amount of 3.0 parts by weight and SrCO ₃ in an amount of 1.5 parts by weight. Although Comparative Example 7 is also a LAGP-type solid electrolyte, as a control example, it was prepared as described in Solid State Ionics 318 (2018) 27-34 , and Comparative Example 8 was yttria (Y ₂ O ₃ ) in LAGP of Comparative Example 1. ) 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 shown in Table 1 above. The 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 glass transition temperature is lowered by the addition of Bi _{2 O 3 and/or SrCO 3 to LAGP and with the increase in the amount of Bi 2 O 3 and / or} SrCO ₃ added. 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. Ion Conductivity Measurement of Solid Electrolyte

The ionic conductivity of the solid electrolytes prepared in Comparative Examples 1 to 8 was measured and 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 conductivity of the solid electrolytes prepared in Examples 1 to 3.

- Measuring 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 ionic conductivity (lithium ion conductivity) also increases with the addition of Bi ₂ O ₃ and/or SrCO ₃ to LAGP and increases with the increase of the amount of Bi ₂ O ₃ and/or SrCO ₃ In addition, the MgO of the present invention In the case of Examples 1 to 3 in which was added, it can be seen that the ionic conductivity was 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 photograph, compared to the solid electrolyte of Comparative Example 6 in which MgO was not added, the solid electrolyte of Example 1 in which 1 wt% of MgO was added and of Example 2 in which 3 wt% of MgO was added had improved high-temperature fluidity and increased particle binding. It can be seen that the tendency becomes clear when the MgO content is increased. Therefore, it can be seen that the sintering properties are improved when MgO is added.

Claims (10)

Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ and MgO-containing composition for an oxide-based solid electrolyte The composition for an oxide-based solid electrolyte according to claim 1, characterized in that it can be crystallized at a temperature of 800-850° C. when the solid electrolyte is prepared. The composition for an oxide-based solid electrolyte according to claim 1, comprising 0.1-10 wt% of MgO based on the total weight of the composition The composition for an oxide-based solid electrolyte according to claim 3, comprising 0.1-10 wt% of Bi ₂ O ₃ and 0.1-10 wt% of SrCO ₃ based on the total weight of the composition The composition for an oxide-based solid electrolyte according to claim 1, comprising 1-20 wt% of Bi ₂ O ₃ , SrCO ₃ and MgO based on the total weight of the composition. The method according to claim 1, 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 Based on the total weight of the composition O ₃ 0.1-10 wt%, SrCO ₃ Oxide-based solid electrolyte composition comprising 0.1-10 wt% and MgO 0.1-10 wt% 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) making the composition into an amorphous state by quenching after melting and
c) crystallization at 800-850° C. and then pulverizing. The method according to claim 7, wherein the melting temperature is 1200-1500 °C and the quenching temperature is 300 °C or less. Li ₂ O, Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Bi ₂ O ₃ , SrCO ₃ Oxide-based solid electrolyte prepared by crystallizing a composition containing MgO All-solid-state lithium secondary battery comprising the oxide-based solid electrolyte of claim 9

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