● Background significance of solid-state battery development

With the rapid development of the new energy industry, including the rapid increase in demand for power batteries and energy storage batteries, lithium-ion batteries have ushered in a revolutionary technology iteration. The energy density of the power battery has increased from 120wh/kg to 350wh/kg today, and the pure electric endurance of the electric vehicle has also increased from 200km to 700km. However, lithium-ion batteries, which are the core components of electric vehicles, still have huge room for improvement.

Energy density still hampers the development of the energy storage industry, poor safety is also the biggest factor restricting the development of lithium-ion batteries, the sharp decline in low-temperature performance leads to the slow process of promoting the northern market, these urgent problems promote the subversive renewal of lithium-ion materials themselves, making solid-state batteries have epoch-making significance.

 

 

Solid-State Battery Concepts and Benefits
 

 

A solid-state battery means that all the materials that make up a lithium-ion battery are solid materials, including the electrolyte is also replaced by a liquid for a solid-state lithium-ion conductive material, eliminating the diaphragm, greatly simplifying the process route, and improving the safety of the battery. Solid-state batteries have the advantages of high energy density, high voltage window and high safety;
 

① In terms of energy density, the solid-state battery has no electrolyte and diaphragm, and is replaced by a thin electrolyte layer, which greatly reduces the quality. The energy density can reach 700Wh/kg, or even higher, far exceeding the current liquid lithium-ion battery with an energy density of 300Wh/kg.

② Voltage window, relative to the electrolyte, solid electrolyte does not participate in chemical reactions, can choose a larger voltage difference between the positive and negative materials, with a wide electrochemical window, charge and discharge pressure difference is greater, can improve the battery energy density.

In terms of safety, the solid electrolyte has the characteristics of non-flammability, wide applicable temperature window, non-corrosive, weak volatility, high safety and reliability, and will not explode in the face of mechanical abuse and thermal abuse.

 

 

Classification of Solid Electrolytes

 

Although solid-state batteries have many advantages, solid-state batteries are still in the research and development stage, and various technical routes with electrolyte materials as the core have not yet been unified. Many key technology routes are still in the exploratory stage, and the technology path is diversified. Solid electrolyte materials, as the key core materials of solid-state batteries, are mainly divided into four categories: polymers, oxides, sulfides and halides.

The polymer electrolyte [1] is simple to prepare, flexible and processable, but the polymer is easy to crystallize at ambient temperature, resulting in limited room temperature ionic conductivity, and the thermodynamic instability of the interface also limits the compatibility with high-voltage cathode materials. Poor mechanical properties are difficult to completely inhibit the growth of lithium dendrites;

The oxide electrolyte [2] has high mechanical strength, good thermal stability and air stability, and wide electrochemical window, but the room temperature ionic conductivity is low, and the solid-solid interface contact between the positive and negative electrodes is poor, and the electrolyte is usually thicker, which greatly reduces The volume energy density of the battery;

Sulfide electrolyte [3] has high room temperature conductivity, good ductility, moderate hardness, good interface physical contact and good mechanical properties, but the electrochemical window is narrow, the interface stability with positive and negative electrodes is poor, and it is very sensitive to moisture, and can react with trace water in the air to release toxic hydrogen sulfide gas;

Halide electrolyte [4] is similar to sulfide. Due to its outstanding advantages such as high ionic conductivity, good compatibility of high-voltage positive electrode and excellent mechanical deformability, it can overcome the defects of poor interfacial contact of oxide electrolyte and narrow electrochemical window of sulfide electrolyte at the same time, and has become a research hotspot in the field of all-solid-state batteries. However, the extremely poor reduction stability of halide electrolyte and its sensitivity to wet air limit its application.

 

 

Difficulties and Transitional Measures of All-solid-state Battery

 

The interface contact problem of all-solid-state battery is one of the most important problems at present. The lack of fluidity of solid electrolyte, the main contact mode of the interface is point-to-point contact, the solid-solid contact area is small, resulting in the larger impedance than liquid battery and the uneven distribution of current density, restricting the industrial application of solid-state battery.
 

On the other hand, it is difficult to develop a suitable solid-state electrolyte and electrode material system, and the current process technology of solid-state batteries is not yet mature, especially there are some challenges in large-scale production.

In addition, the materials used in solid-state batteries are mostly new materials, and the cost is relatively high. Due to the immature manufacturing process and the large investment in production equipment and processes, the production cost of solid-state batteries remains high under the current circumstances.

Semi-solid batteries, as a transitional solution for liquid batteries and all-solid-state batteries, are favored by many battery manufacturers and OEMs. Semi-solid-state batteries generally use in-situ curing technology to introduce polymer gel network, through the positive material, negative material surface or diaphragm on both sides of the coating/coating solid electrolyte, while retaining part of the traditional liquid electrolyte as a wetting agent, to achieve solid-liquid mixing state.

Compared with liquid batteries, semi-solid-state batteries introduce solid electrolytes, which can improve energy density and safety on the basis of existing systems; compared with all-solid-state batteries, semi-solid-state batteries retain part of the electrolyte, improving conductivity and Interface contact problems. The production route and equipment of semi-solid-state batteries are basically the same as those of existing liquid batteries, so some suppliers have already achieved mass production in 2024.

 

 

Research and application status of solid state battery at home and abroad

 

In 2012, Solid Power of the United States established partnerships with automakers such as BMW, Ford, and Hyundai to study new battery technologies. At present, Solid Power has developed a sample energy density of about 320 Wh/kg, and is focusing on building a pilot line for solid-state batteries. It is expected to assist BMW in the integration test of solid-state battery prototype vehicles in 2025. Quantum Scape, in partnership with Volkswagen Group, has announced that it will advance the testing of multi-layer solid-state batteries, which is an important manifestation of Quantum Scape's progress towards commercially viable solid-state batteries for electric vehicles.

For solid-state batteries, Japanese companies have certain first-mover advantages in basic research and patent layout. Toyota, Honda, Panasonic, Hitachi and other companies have obvious advantages. Among these companies, Toyota took the lead in developing solid-state batteries, and its goal is the second-generation sulfide all-solid-state battery, which has the largest number of patents for solid-state batteries.

South Korea has also been actively working on solid-state batteries. Judging from the number of patents published on solid-state batteries in South Korea, LG Chemical, Samsung, Hyundai and other companies have made remarkable achievements in solid-state battery research. South Korea, Samsung has launched a key research on the second-generation sulfide solid-state battery technology. The company plans to build an all-solid-state battery test production line and conduct large-scale production in 2027.

Domestic Ningde Times, BYD, FAW, SAIC, Weilan New Energy and Geely received special funds from the state 6 billion in May 24 for the research and development of solid-state batteries. The support of this national policy represents that the speed of solid-state battery research and development will be further improved, and the time to land will be shorter. The first-generation semi-solid battery jointly developed by Qingtao Energy and SAIC has been mass-produced on a new car of the Zhiji brand in 2024. In June 2023, Weilan New Energy officially delivered the semi-solid-state battery to Weilai. In December, Weilai ET7 carried the 150kWh ultra-long battery pack delivered by Weilan New Energy, with a measured endurance of over 1000 kilometers, causing great repercussions both inside and outside the industry. Ningde era announced that it will mass produce solid-state batteries on a small scale in 2027. If the maturity of all-solid-state batteries is expressed by 1-9 figures, the current maturity of Ningde era is at the level of 4.

 

 

Gao Rui power layout of the future

 

In response to future technological innovation, Gaorui Power has a deep layout in the field of solid-state battery integrated technology, and is committed to solving solid-state material problems and breaking through the performance bottleneck of lithium battery.

The company's research and development center mainly to semi-solid electrolyte precursor, solid electrolyte (sulfide, halide and composite polymer), negative active materials, positive and negative binders, positive and negative side artificial SEI layer and other directions as the entry point, focusing on solving the difficulties and pain points in solid-state batteries. At present, Gaorui Power has invested 500w to build a solid-state battery material research and development laboratory, forming a complete solid-state battery material development, preparation and innovation platform, and will continue to invest more than 1000w in the future, which will be used to jointly build a mass production ton-level solid-state battery material industry chain with upstream and downstream suppliers.

At the same time, Gao Rui signed a deep-level project cooperation with Central South University in 2023. At present, he has successfully applied for several provincial solid-state battery projects. The cooperation aims to promote the technology development of industry-university-research integration, realize point-to-point technology sharing, and enlarge the laboratory-level results to the ground.

Gaorui Power has always focused on the development of cutting-edge technology, and aims to contribute to the development of China's lithium-ion batteries.

 

 

References:

[1] Z. Lee, J. Fu, X. Week, S. Gui, L. Wei, Yang, Li, X. Guo, Ionic conduction in polymer-based solid electrolytes. Adv. Sci. 2023,10,2201718.
[2] Zhang Q,Liu K,Wen Y,et al. Research progress of solid lithium ion electrolytes based on polymer and rare earth oxide LLTO/LLZO composites. Engineering reports. 2022; 4(1):e12448.
[3] Zeng,D.,Yao,J.,Zhang,L. et al. The use of chlorine-rich sulfide inorganic solid electrolytes promotes good interfacial properties of lithium-based batteries. Nat Commun 13,1909 (2022).
[4] He,B.,Zhang,F.,Xin,Y., et al. Halogen chemistry of solid electrolytes in all-solid-state batteries. Nat Rev Chem 7,826-842 (2023).