Solid state battery – it is an opportunity and a challenge
Basic concepts and classification of solid state battery
Lithium batteries are mainly composed of cathode materials, anode materials, electrolytes, and separators. Lithium batteries are widely used in 3C electronic products, electric vehicles, motorcycle battery pack and large-scale energy storage. With the continuous innovation of power battery technology, traditional materials are difficult to meet the needs of battery cost reduction, efficiency improvement, and energy density improvement.
Table of Contents
There are two forms of electrolytes: liquid and solid. Lithium-ion batteries currently in use are mostly liquid organic solvent electrolytes, and highly chemically active, volatile, and flammable liquid electrolytes are the biggest safety hazard for lithium batteries.
As the number of charge and discharge of the battery increases, a series of physical and chemical changes will occur in the cell of the liquid electrolyte lithium battery, such as the reduction of active lithium and the continuous loss of the electrolyte, the dissolution of the transition metal of the cathode material leads to reversible capacity loss, the oxidative decomposition of the electrolyte, and the thermal runaway of the battery, etc., resulting in safety accidents.
Solid state battery uses non-flammable solid-state electrolyte instead of flammable and explosive organic electrolyte, which can greatly improve the safety and energy density of batteries, and are the long-term potential technical direction of existing material systems. At the same time, in terms of cathode and anode materials, solid state battery can completely follow the liquid lithium-ion battery material system, and there is more room for upgrading.
Solid state battery is divided into three types: semi-solid, quasi-solid, and all-solid. The mass percentage of the semi-solid liquid electrolyte is less than 10%, the mass percentage of the quasi-solid liquid electrolyte is less than 5%, and the all-solid state does not contain any liquid electrolyte. At present, the rapid industrialization process in China is basically semi solid state battery, and the industrialization of all solid state battery will take time.
Comparison of solid state battery and liquid lithium-ion battery
Compared with liquid batteries, solid state battery has better overall performance, mainly in terms of safety performance, energy density, cycle life, and operating temperature range.
| Solid state battery | Liquid lithium ion battery | |
|---|---|---|
| Cathode material | The existing cathode system can be continued with minimal changes, and at the same time, it can be compatible with other materials such as high-voltage materials. | Metal oxides, the mainstream are lithium iron phosphate, ternary and lithium cobalt oxide. |
| Anode material | It can continue the existing anode system and has the ability to be compatible with lithium metal anode. | Mainstream graphite, silicon-based anode can be used later. |
| Electrolyte | Instead of a solid electrolyte, there will be a part of the electrolyte in the transition phase. | Mainstream organic solvent + lithium hexafluorophosphate, adding new lithium salts, additives and other upgrades. |
| Separator | No need for a separator, the transition stage still requires a separator. | A separator is needed to avoid contact between cathode and anode, upgrade the composite separator, etc. |
| Advantages | High energy density, the electrochemical window can reach more than 5V, can match high-voltage materials, only transmit lithium ions, do not conduct electrons, and have good thermal stability. | The degree of industrialization and automation is high, the interface between the electrode and the electrolyte is in good contact, the expansion of the heavy electrode during the charge and discharge cycle is relatively controllable, and the conductivity per unit area is high. |
| Disadvantages | High interface resistance, poor stability with air, low ionic conductivity per unit area, poor specific power density at room temperature, high cost, and poor physical contact during cycling. | The organic electrolyte is volatile and flammable, the thermal stability of the battery system is poor, lithium ions and electrons may conduct simultaneously, and continuous interface side reactions. |
Traditional lithium ion battery structure using organic electrolyte will cause serious safety hazards due to overcharging, internal micro-short circuit and other abnormalities, such as electrolyte heating, decomposition, and flatulence. The solid electrolyte is non-flammable, high temperature resistant, non-corrosive, non-volatile, and has no leakage problem.
In liquid batteries, the growth of lithium dendrites is easy to pierce the separator, resulting in a short circuit, while the solid electrolyte has high mechanical strength, and the growth of lithium dendrites is slow and difficult to penetrate, thereby improving the safety performance of the battery.
Therefore, solid state battery can fundamentally reduce the occurrence of safety accidents. In addition, the solid electrolyte greatly reduces the distance between the cathode and anode, reducing the thickness of the battery, thereby increasing the energy density of the battery cell.
Main technical route of solid state battery
The cathode material of solid state battery is not much different from that of liquid lithium battery. Different technical routes are mainly distinguished by different electrolytes. According to the type of electrolyte, solid state battery mainly have three technical routes: polymers, oxides, and sulfides.
Polymers
The advantage is that it is easy to process, compatible with the existing production equipment and process of liquid electrolyte, and has good mechanical properties.
Its disadvantages are:
● The conductivity is too low, and it needs to be heated to a high temperature of 60 degrees to work normally;
● The stability is poor, it cannot be adapted to high-voltage cathode materials, and it will also cause fire and combustion at high temperatures;
● The electrochemical window is narrow, and the electrolyte is easily electrolyzed when the potential difference is too large (>4V).
Sulfides
The conductivity is the highest, and the electrochemical stability window is wide (above 5V), which has the most potential for development.
The main disadvantages are:
● Poor thermodynamic stability, and the thermal reaction initiation temperature range is 400−500°C;
● The preparation process is relatively complicated, and it is easy to react with water and oxygen in the air to produce highly toxic hydrogen sulfide gas.
Oxides
It has good electrical conductivity and stability, higher ionic conductivity than polymers, thermal stability up to 1000 degrees, and very good mechanical and electrochemical stability.
Its disadvantages are:
● Low conductivity relative to sulfide;
● There is a problem of rigid interface contact.
In terms of performance, the performance of oxide electrolytes is relatively balanced in all aspects, and other types of solid state electrolytes generally have performance shortcomings. The reduction stability, oxidation stability, thermal stability and other performance indicators of the oxide electrolyte are relatively excellent. Sulfide electrolytes have poor chemical stability and are prone to reactions. The lithium ion migration number and oxidation stability of polymer electrolytes need to be improved urgently.
Solid state battery industry chain and market space
The solid state battery industry chain is roughly the same as the liquid lithium battery industry chain, with major changes in the midstream electrolyte and anode materials. For all solid state battery, the separator will be completely replaced.
The industry generally believes that the large-scale mass production of all solid state battery will take 5-10 years, and the gradual route of solid-liquid hybrid batteries is more in line with the law of technological development and can be used as a transitional route. Solid-liquid hybrid batteries can achieve fast charging while maintaining high energy density.
On the other hand, solid state battery is expected to be commercialized starting from the high-end market, and gradually applied to electric vehicles, energy storage, wearable devices, military aviation and other fields. According to forecasts, the penetration rates of solid state battery in power batteries, consumer batteries, and other batteries will reach 10%, 20%, and 3% respectively in 2030, and the global market space is expected to reach 363.4 billion RMB.
Although China’s solid state battery industry is currently in its infancy, solid state battery is expected to achieve large-scale commercial application in China with technological progress. It is estimated that by 2030, China’s solid state battery shipments and market space will reach 251.1GWh and 20 billion RMB, respectively.
Conclusion
Although the application prospect of solid state battery technology is optimistic, the relevant basic theoretical research and production process exploration still have a long way to go. Solid state battery is an important development direction of lithium battery technology and industrial development.
Improving the comprehensive performance of electrodes and electrolyte materials, designing new current collector/electrode/electrolyte composite structures, and developing new manufacturing processes and equipment have basically become the industry’s consensus development path.
Peach
Hi, I am Peach, graduating from one of a well-known university in China. I have more than 5 year's experience in lithium battery industry.
All Posts Related post
Leave a comment