What powder materials are needed to produce an all-solid-state battery?

All-solid-state lithium battery with solid electrolyte instead of organic liquid electrolyte is expected to solve the two key problems of low energy density and short service life of traditional lithium ion battery, and it is in line with the development direction of large-capacity new chemical energy storage technology in the future.  All solid state lithium battery, each part mostly adopts inorganic powder material, through the integration technology to form the whole battery.

Solid electrolyte powder

Solid electrolyte plays the role of lithium ion transport in all-solid lithium ion battery.  Solid electrolyte can be divided into organic polymer electrolyte and inorganic solid electrolyte, the former includes solid polymer electrolyte and gel polymer electrolyte, the latter includes oxide based solid electrolyte and sulfide based solid electrolyte.

Oxide electrolyte powder  

Taking the garnet solid electrolyte Li7La3Zr2O12 powder as an example, the traditional preparation methods of LLZO are mainly solid phase method and sol-gel method.  The conductivity of LLZO at room temperature obtained by solid phase method is higher than that by sol-gel method.  LLZO powder with better properties can also be obtained by field - assisted sintering or oxygen - atmosphere sintering.  In addition, LLZO has good stability to air, does not react with lithium metal, sintered body has excellent mechanical strength, and is expected to become an ideal solid-state electrolyte material for all-solid-state lithium battery.  

Take NASICON solid electrolyte LATP as an example: Its preparation methods mainly include solid phase method, mechanical ball milling method, hydrothermal method, sol-gel method and coprecipitation method, etc.  Among them, solid-phase method is one of the simplest and convenient methods to prepare LATP due to its simple preparation steps and short time.  Some researchers used hydrothermal assisted solid-phase method to prepare LATP powder with rhomboid morphology by preheating at 600℃.  The LATP electrolyte powder is diamond shaped with high crystallinity and uniform particle size distribution.

Sulphide electrolyte powder  

With good grain boundary contact and high ionic conductivity under mechanical pressure, all-solid lithium ion batteries using sulfide electrolytes can be obtained by simple mechanical pressure method at room temperature.  The composite anode layer of the battery is composed of cathode material, sulfide solid electrolyte and conductive carbon particles.  The positive electrode layer, solid electrolyte layer and metal negative electrode layer are successively put into the mold, and the all-solid battery is prepared by applying mechanical pressure on both ends of the positive and negative electrodes.  

High energy ball milling with mechanical alloying is a conventional method for the preparation of sulphide solid electrolytes, whose products are powders of several to tens of microns.  Due to the "room temperature sintering" effect of sulfide solid electrolyte, the close contact between particles can be realized by cold pressing at about 300 MPa. Therefore, powder cold pressing technology has been widely used in the preparation of all-solid-state batteries based on sulfide solid electrolyte.

Li-P-S-based sulfide systems, such as Li-Ge-P-S ceramics and Li2S-P2S5 glass ceramics, have higher li-ion conductivity than 10-3S/cm at room temperature, and their powder blocks after cold pressing have very low grain boundary resistance, that is, very high grain boundary li-ion conductivity.  

Electrode powder material

As lithium ion provider in battery system, cathode materials mainly include LiCoO2, spinel LiMn2O4, olivine LiFePO4, Lini1/3MN1/3Co1/3O2 and other ternary materials.  And Li2MnO3·LiMO2 (M=Ni, Co, Mn and other transition metals) with rich Li2MnO3·LiMO2 layered structure.  

The anode is the place where lithium occurs in the battery charging process, mainly including graphite, lithium metal and its alloys, silicon and tin based materials, metal oxides and so on.  The above battery anode and anode materials, including lithium iron phosphate, ternary materials, graphite anode, silicon carbon anode and other mainstream electrode materials are powder form.  

Ternary cathode powder material  

Nickel-cobalt-manganese ternary cathode materials for lithium ion batteries are favored by the market due to their high energy density and good cycling performance, but they have disadvantages of high surface residual alkali and poor safety performance.  Inorganic solid electrolyte has the characteristics of high ionic conductivity and high structural stability.  The inorganic solid electrolyte material is coated on the surface of the ternary cathode material particles, so that the ternary cathode material does not directly contact the electrolyte, which solves the safety and circulation problems of the ternary cathode material from the root.  

Researchers at oak ridge national laboratory in the United States have used magnetron sputtering technology to sputter Li3PO4 targets into ternary cathode material powders at a power of 80W in N2 atmosphere at 20mTorr.  In a rich three yuan positive electrode material of lithium Li1.2 Mn0.525 Ni0.175 Co0.1 O2 particles in the surface evenly coated with a layer of very thin layers of Lipton.  LiPON - coated lithium - rich ternary composite cathode material shows excellent stability.  

New form of lithium powder anode

Different roughness of lithium electrode surface leads to uneven surface charge distribution, which leads to uneven lithium deposition. Lithium dendrites are formed in the charging and discharging process. Therefore, changing the morphology of lithium anode and increasing the specific surface area can effectively inhibit the generation of lithium dendrites.  Due to its large specific surface area, the interface stability of the new lithium powder electrode can be improved by using lithium metal powder as the negative electrode.  Microemulsion method is a common method for preparing lithium powder electrode. The diameter of lithium powder obtained by microemulsion method is 10 ~ 40µm, and the specific surface area is 4.5 ~ 6 times that of lithium plate.  

Conductive powder

The development of all-solid-state lithium battery has made rapid progress since the new century, especially the all-solid-state lithium battery based on sulphide electrolyte.  The typical structure of all solid state lithium battery cathode in anode materials for lithium metal or alloy, the middle tier for sulfide electrolyte, other side for the composite anode, electrolyte composite anode is usually a conductive agent, a mixture of active material and electrolyte, in order to realize the active material particles in the solid electrode smooth conduction of the lithium ions and electrons.  

Some researchers studied the effect of composite conductive additives on the performance of all-solid-state lithium sulfur battery with elemental sulfur as active substance, and found that acetylene Black (AB) as conductive carbon material was significantly better than Super P and Ketjen Black.  When the mass ratio of sulfur to acetylene black to solid electrolyte is 40:20:40, the solid-state lithium-sulfur battery has good electrochemical performance at room temperature and 60℃.  

In addition to acetylene black (AB), carbon nanotube (CNTs) powder was also used as a conductive agent.  Both AB and CNTs have their advantages and disadvantages as positive electronic conductors. After combining the two conductive agents, researchers found that the initial discharge specific capacity and cycle stability of the all-solid-state battery were improved, which was much higher than the capacity of the previous two conductive agents when used alone.  This is because AB can be filled in the particle gap to increase the compaction density, while CNTs conduct electricity in a certain range for a long time. The combination of the two gives full play to their respective advantages to improve the cycling performance of the all-solid-state battery.

Packing powder

Among solid polymer electrolytes, PEO has become the focus of solid electrolyte research due to its advantages of good safety, low cost, easy preparation, high energy density, good electrochemical stability, and good compatibility with lithium salts. However, its low ionic conductivity cannot meet the requirements of practical application.

By adding inorganic ceramic filler to construct PEO - based composite solid electrolyte, the ionic conductivity can be improved effectively.  The added inorganic ceramic fillers include inert inorganic ceramic fillers and ionic conductor inorganic ceramic fillers.  Inert inorganic ceramic filler mainly refers to SiO2, Al2O3, TiO2, MgO, ZnO, ZrO2 oxide powder without lithium ion.  

The addition of inorganic ceramic filler can not only reduce the crystallinity of PEO and increase the proportion of its amorphous region, but also indirectly or directly affect the mobility of lithium ions through the interaction with PEO and lithium salts, thus improving the ionic conductivity of PEO solid polymer electrolyte.