TWI786805B - Solid state electrolyte structure - Google Patents

Abstract

The invention discloses a solid state electrolyte structure. For the solid state electrolytes containing titanium, a protecting layer is complete covered its surface thereof. The protecting layer made of solid metal oxide or organic polymer is utilized to effectively block the reduction reaction of titanium at lower voltage. Therefore, the pollution or affection for the electrode layer resulting from the titanium will be effectively prevented, and its chemical resistance is improved. Moreover, the application of the solid electrolytes containing titanium is greatly increased.By the protecting layer, the contact of the solid electrolytes is improved.The problems of the smaller or poor contact surface and the high resistance of the charge transfer are eliminated.

Description

Solid Electrolyte Structure

The invention relates to a solid electrolyte structure, in particular to a titanium-containing solid electrolyte structure with a protective layer.

Existing lithium-ion secondary batteries mainly use liquid electrolytes as the lithium-ion transmission medium. However, the volatile nature of liquid electrolytes will have adverse effects on the human body and the environment; at the same time, the flammability of liquid electrolytes is harmful to battery users It is also a great security risk.

Furthermore, one of the reasons for the unstable performance of lithium batteries at present is mainly because the electrode surface activity is relatively large (negative electrode) and the voltage is relatively high (positive electrode). Stability, and then produce the so-called exothermic reaction to form a passive protective film on the contact interface of the two. These reactions will consume the liquid electrolyte and lithium ions, and will also generate heat. Once a local short circuit occurs, the local temperature rises rapidly, and the passive protective film will become unstable at this time, and heat will be released at the same time; and this exothermic reaction can be accumulated, thus making the overall temperature of the battery continue to rise. Once the temperature of the battery increases to the initial temperature (or trigger temp) of the thermal runaway, thermal runaway will occur, which will cause damage to the battery, such as explosion or fire. cause considerable security concerns.

In recent years, solid-state electrolytes have become another research focus. They have ionic conductivity similar to liquid electrolytes, but they do not have the properties of liquid electrolytes that are easy to evaporate and burn. At the same time, the interface with the active material surface is relatively stable (both chemically and electrochemically). However, solid electrolytes are different from liquid electrolytes in that they have a small and poor contact surface with active materials and a low charge transfer reaction constant. Therefore, there is a problem that the charge transfer interface resistance with the positive and negative active materials in the electrode layer is relatively large. , is not conducive to the effective transmission of lithium ions, so it is still difficult to completely replace liquid electrolytes.

Furthermore, compared with liquid electrolytes, the cost of materials for solid electrolytes has also increased a lot. In order to reduce costs and control and improve the compatibility of materials themselves, various materials have been developed in recent years; among them, titanium aluminum phosphate Lithium (LATP) solid electrolyte, in addition to good ionic conductivity, has a considerable cost advantage. However, the low-voltage electrochemical resistance of lithium aluminum titanium phosphate (LATP) solid electrolyte is not good because it contains titanium components. When When it is precipitated, it will react with lithium (ion) to pollute the negative electrode layer, thereby affecting the normal performance of the electrochemical reaction, so it is difficult to expand its application range.

How to effectively and massively apply solid electrolytes while taking into account the cost and the improvement of the surface state of the solid electrolytes is an urgent problem to be solved in this field.

In view of this, the main purpose of the present invention is to provide a solid electrolyte structure that can solve the shortcomings of the above-mentioned conventional technology, not only the material cost is relatively low, but also can be applied to each electrode layer without limitation.

Another object of the invention is to provide a solid electrolyte structure, which can use the protective layer to prevent the precipitation of internal titanium components, and externally, it can solve the problem of high charge transfer resistance and low contact area caused by the contact surface of the solid electrolyte. various problems.

In order to achieve the above object, the present invention provides a solid electrolyte structure comprising There are solid electrolyte particles and a protective layer. The solid electrolyte particles are solid electrolytes containing titanium (Ti), and the protective layer is completely covered outside the solid electrolyte particles to prevent the reduction reaction of titanium components in the solid electrolyte particles and improve its low voltage. The high electrochemical resistance can effectively prevent the pollution of the titanium component to the electrode layer, and can expand the application range of the titanium-containing solid electrolyte.

Among them, the protective layer can be composed of solid oxide metal, polymer type or a combination thereof. For solid electrolyte particles, it can effectively prevent the reduction of titanium components and improve electrochemical resistance at low voltage; for solid electrolyte particles For the outside of the particle, the problem of high charge transfer resistance and low contact area generated by the contact interface of the solid electrolyte can also be solved by setting the protective layer, so it can achieve the best performance while taking into account cost and safety. ion conduction mode.

In the following detailed description by means of specific embodiments, it will be easier to understand the purpose, technical content, characteristics and effects of the present invention.

10: Solid electrolyte structure

11: Solid electrolyte particles

12: Protective layer

Figure 1 is a schematic diagram of a solid electrolyte structure provided by an embodiment of the present invention.

Fig. 2 is a titanium concentration distribution curve diagram of the solid electrolyte structure provided by the embodiment of the present invention.

As shown in Figure 1, it is a schematic diagram of the solid electrolyte structure provided by the embodiment of the present invention. The solid electrolyte structure 10 disclosed in the present invention is mainly composed of solid electrolyte particles 11 and a protective layer 12, wherein the solid electrolyte particles 11 contain a solid electrolyte of titanium (Ti), such as lithium aluminum titanium phosphate (LATP; Li _{1+ x} Al _x Ti _2-x (PO ₄ ) ₃ ) solid electrolyte, which has high ionic conductivity, good chemical and thermal stability, and low raw material and manufacturing costs. However, its chemical resistance is not good. When the titanium component in it is precipitated (especially under low pressure), it will not only change its surface properties, but also reduce the ionic conductivity of the surface. At the same time, because titanium will interact with lithium (ion ) reacts, which greatly increases the interfacial impedance, resulting in a significant decrease in the nature and efficiency of the electrochemical reaction.

Therefore, the present invention completely covers the solid electrolyte particles 11 by the protective layer 12 to prevent the precipitation of titanium components in the solid electrolyte particles 11. The thickness of the protective layer 12 is 10-500 nanometers and completely covers the solid electrolyte particles 11. On the surface, special attention should be paid here. The appearance of the solid electrolyte particles 11 shown in the figure is only for illustration, and its shape is not limited to a circle (sphere). Other spheres, flakes, and pages are all applicable. .

At the same time, because the solid electrolyte particles 11 still need to have a certain ionic conductivity and good chemical and thermal stability after coating the protective layer 12, the selected part of the material can be solid oxide metal, organic polymer Or a combination thereof, and its formation method can be sintering, infiltration, coating, etc., and the present invention is not limited to a specific process. In addition to the aforementioned LATP, the solid electrolyte particles 11 can also be various oxide-based solid electrolytes containing titanium components, such as Li _1+x+y (Al,Ga) _x (Ti,Ge) _2-x Si _y P _3-y O ₁₂ crystal, where 0≦x≦1 and 0≦y≦1, Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ , Li _3x La _2/3x TiO ₃ , Li _0.38 La _0.56 Ti _0.99 Al _0.01 O ₃ , Li _0.34 LaTiO _2.94 .

Please refer to Fig. 2, when the surface of the solid electrolyte particles 11 has a protective layer 12, it can be clearly seen that because of being hindered by the protective layer 12, the precipitation of titanium components (generally in the form of ions) will be completely restricted, and It will only appear inside the solid electrolyte particles 11. Therefore, for the solid electrolyte particles 11, the main function and purpose of the protective layer 12 is to prevent the titanium components from decomposing. out to the outside of the solid electrolyte structure 10.

Specifically, when the protective layer 12 is a solid metal oxide, the thickness is preferably about 10-50 nanometers, which can be, for example, niobium oxide (NbO _x ) and its derivatives, such as niobium trioxide (Nb ₂ O3 ), or lithium nitrate (LiNO _x ) and its derivatives. On the other hand, the protective layer 12 can also be lithium lanthanum zirconium oxide solid electrolyte (lithium lanthanum zirconium oxide; Li ₇ La ₃ Zr ₂ O ₁₂ ; LLZO), LLZO has relatively stable chemical resistance, and ionic conductivity, chemical and Thermal stability is also quite excellent, but its material and manufacturing costs are relatively high. Therefore, using LLZO to form the protective layer 12 on the surface of titanium-containing solid electrolyte particles 11 (such as LATP) can not only greatly reduce the cost , and at the same time, the chemical resistance of the solid electrolyte structure 10 can be improved by virtue of the relatively stable interface of LLZO, greatly increasing the range of applications.

When the protection layer 12 belongs to polymer, the thickness is preferably about 20-500 nm, and it can be a polymer ion-conducting material or a polymer-type solid electrolyte. For example, when the protective layer 12 is a polymer ion-conducting material, it can be selected from polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), potassium polymethacrylate (PMMA) and Polyvinylidene chloride (PVC), etc., are modified by adding a film-forming agent (such as a cross-linked film-forming material) and a plasticizer to further improve its film-forming property. After the film-forming agent is added, the aforementioned plasticizer can be retained or removed (only added during molding and removed after molding). The plasticizer mentioned above can be selected from propylene carbonate (PC), ethylene carbonate (EC), dimethylformamide (DMF), dimethylsulfoxide (DMSO).

In another embodiment, the protection layer 12 is a polymer ion conducting material added with a film-forming agent (such as a cross-linked film-forming material) and an ion liquid. This type of solid polymer electrolyte is used as the protective layer 12, in addition to preventing the titanium composition of the solid electrolyte particles 11 from analysing. Going out, because of its soft texture, covering the outer edge of the solid electrolyte particles 11 will greatly improve the state of the contact interface between the solid electrolyte particles 11, or between the solid electrolyte particles 11 and the active material, and effectively solve the problem. The problems derived from the high charge transfer resistance and low contact area, so the best ion conduction method can be achieved while taking into account cost and safety.

In the aforementioned embodiment of the protective layer 12 in the form of a polymer, ion donor materials, such as salts, can be added to increase the ion conduction capacity and become a solid electrolyte in the form of a polymer. Alternatively, it is in the form of a solid electrolyte composed of an ion-conducting material plus a film-forming agent and an ion-donating material.

In summary, the solid electrolyte structure provided by the present invention can effectively prevent the precipitation of titanium components inside the solid electrolyte particles and improve chemical resistance by utilizing the setting of the protective layer; and for the outside of the solid electrolyte particles, it can also Through the setting of the protective layer, the problems derived from the high charge transfer resistance and low contact area generated by the contact interface of the solid electrolyte are solved, so that the best ion conduction mode can be achieved while taking into account cost and safety.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Therefore, all equivalent changes or modifications based on the features and spirit described in the scope of the application of the present invention shall be included in the scope of the patent application of the present invention.

10: Solid electrolyte structure

11: Solid electrolyte particles

12: Protective layer

Claims (13)

A solid electrolyte structure, which includes: a solid electrolyte particle, which is a solid electrolyte containing titanium (Ti) components; and a protective layer, which completely covers the solid electrolyte particles to prevent the titanium component in the solid electrolyte particles from A reduction reaction occurs to improve the chemical resistance of the solid electrolyte particles; wherein the thickness of the protective layer is 50-500 nanometers. According to the solid electrolyte structure of claim 1, the solid electrolyte particles are lithium aluminum titanium phosphate (LATP) solid electrolytes. According to the solid electrolyte structure of claim 1, the protective layer is made of solid oxide metal, polymer or a combination thereof. According to the solid electrolyte structure of claim 3, the solid oxide metal is niobium trioxide (Nb ₂ O ₃ ) and its derivatives. According to the solid electrolyte structure of claim 3, the solid oxide metal is lithium nitrate (LiNO _x ) and its derivatives. According to the solid electrolyte structure of item 3 of the patent application, the solid oxide metal system is lithium lanthanum zirconium oxide (lithium lanthanum zirconium oxide; Li ₇ La ₃ Zr ₂ O ₁₂ ; LLZO). According to the solid electrolyte structure of item 3 of the scope of application, the polymer type is based on ion-conducting materials. According to the solid electrolyte structure described in item 7 of the scope of the patent application, wherein the ion The subconduction type material is selected from polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), potassium polymethacrylate (PMMA) or polyvinylidene chloride (PVC) system. According to the solid electrolyte structure of claim 7, the material of the protective layer contains a film-forming agent. According to the solid electrolyte structure of claim 9, the material of the protective layer contains a plasticizer. According to claim 9 of the solid electrolyte structure, the material of the protective layer contains ionic liquid (ion liquid). According to the solid electrolyte structure of claim 9, claim 10 or claim 11, the material of the protective layer includes an ion donor material. The solid electrolyte structure according to claim 12, wherein the ion-donating material is a salt.

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