Solid state lithium battery vs liquid lithium battery - what is solid state battery prospect

Solid state lithium battery is considered to be the next-generation power battery technology that breaks the energy density and safety of traditional lithium-ion batteries. Once the industrialization barrier of solid state lithium battery is broken through, it is expected to subvert the traditional lithium-ion battery industry, which may greatly impact the traditional electrolyte and separator industry chain, and further affect the cathode and anode materials and their upstream and downstream industry chains.

1. Comparing solid state lithium battery vs liquid lithium battery

Traditional liquid lithium batteries have certain defects, and solid-state batteries are expected to become candidates for a new generation of high-performance lithium batteries.

2. Solid state lithium battery is considered to be next generation power battery technology

With the rapid rise of electric vehicles, the demand for power lithium-ion batteries will continue to grow. It is estimated that the global lithium-ion battery production capacity will reach 700 million terawatt hours (TWh) by 2030.

At present, the cathode materials of power lithium-ion batteries are mainly lithium iron phosphate and nickel-cobalt-manganese ternary materials, and the anode materials are mainly artificial graphite. At present, the energy density of mainstream lifepo4 battery is below 200 Wh/kg (Wh/kg), and the energy density of ternary lithium batteries is between 200 and 300 Wh/kg, which is close to the upper limit of the current battery electrochemical system.

Electrolyte, as the blood of traditional lithium-ion batteries, has an important impact on battery capacity, operating temperature range, cycle performance and safety.

At present, lithium-ion batteries mostly use liquid organic matter and lithium salts as electrolytes. Most liquid solvents have low boiling points and flash points, and will flash at relatively low temperatures. Once the liquid leaks or the heat is out of control, it is very easy to catch fire or explode, causing safety anxiety. At the same time, the liquid electrolyte system restricts the use of high-voltage cathode materials, which further limits the improvement of battery energy density, which brings mileage anxiety.

Solid state lithium battery is considered to be the next-generation power battery technology that breaks the energy density and safety of traditional lithium-ion batteries. The biggest difference from traditional lithium-ion batteries is that solid state lithium battery use solid electrolytes instead of traditional electrolyte systems and diaphragms.

It is expected to significantly improve the safety, energy density and service life of batteries, and has become one of the key layout directions of related enterprises in the global industrial chain. Many countries have listed it as a key development industry and clarified their development plans and goals.

2. Types of solid state batteries

The cathode and anode materials of solid state lithium battery is roughly the same as those of current lithium-ion batteries, and the difference is mainly in the electrolyte. According to the different electrolyte content in the battery, solid state lithium battery can be divided into semi-solid, quasi-solid and all-solid. According to the different solid electrolytes used, it can be divided into polymer solid-state batteries, sulfide solid-state batteries, and oxide solid-state batteries.

● Polymer electrolyte is mainly composed of polymer matrix and lithium salt. It has the advantages of high ionic conductivity at high temperature, easy processing, and controllable interface impedance of electrolyte/electrode. It is the earliest technical route for industrialization. Its main disadvantage is the low ionic conductivity at low temperatures.

● Oxide electrolytes have relatively high room temperature conductivity, good electrochemical stability, and good cycle performance, but poor interface contact between the electrolyte and the cathode and anode materials leads to high interfacial impedance.

● Sulfide electrolytes have the highest room temperature conductivity, but the interface stability between the electrolyte and the electrode material is poor, and the electrolyte is easily oxidized.

3. Layout of global companies in the field of solid state lithium battery

As a core component, solid-state electrolyte largely determines the key performance indicators of solid state lithium battery. It can be said that whether solid state lithium battery can be industrialized is closely related to whether solid-state electrolytes can achieve industrial breakthroughs.

At present, there are still many technical difficulties in all-solid-state batteries that need to be overcome. For example, the low ionic conductivity of the electrolyte at room temperature, the high interface impedance between the electrolyte and the electrode lead to a significant increase in the internal resistance of the battery, poor cycle performance, and poor rate performance have not yet been resolved.

It is a more realistic solution at this stage to improve the electrolyte/electrode interface impedance by adding part of the electrolyte, and at the same time improve the room temperature ionic conductivity to improve the energy density and safety of the battery, that is, to develop semi-solid batteries.

At present, there are more than 50 companies in the world including top 10 lithium battery companies in the world devoted to the technical development of solid state lithium battery. Generally speaking, Japan and South Korea are in a leading position in technology, European and American companies are widely deployed, and a small number of Chinese companies have mastered some core technologies, but there is still a gap compared with the world's leading technologies.

At the same time, major car companies around the world are also deploying solid-state lithium batteries, including many traditional fuel vehicle leading companies and new car manufacturers. Volkswagen has invested in Quantum Scape to lay out solid-state batteries, while BMW has actively invested in self-developed solid-state batteries, and has launched in-depth cooperation with Solid Power in the United States.

4. Future development trend of solid state lithium battery

Solid state lithium battery is considered to be the next generation of power battery technology. Once the industrialization barrier is broken through, it is expected to subvert the traditional lithium-ion battery industry. Despite decades of development, some key scientific issues, some core materials and technologies of all solid state lithium battery have not yet been broken through, which restricts their large-scale mass production and application. The main problems and challenges include:

• The ionic conductivity of the electrolyte at room temperature is too low;
• The electrolyte does not match the electrode material, and the electrolyte/electrode interface impedance is too high;
• The technology and equipment suitable for large-scale production are not yet available;
• The matching battery management system solution is not mature yet.

In the short to medium term, semi-solid and quasi-solid batteries are a more realistic development path, which provides buffer space for some links of traditional lithium-ion batteries (such as diaphragms). Once semi-solid batteries are installed in large quantities, if their cost level is the same as that of the existing lithium-ion battery system, it will have a huge impact on the traditional power battery industry.

At present, there is a certain degree of uncertainty in the development prospects of the three solid electrolyte technology routes.

● Oxide electrolytes have the fastest progress due to their high room temperature ionic conductivity, good chemical stability, low requirements on the preparation environment, and ease of large-scale production and application. Semi-solid and quasi-solid batteries are expected to be mass-produced and loaded into vehicles in the short to medium term;

● Sulfide electrolytes have high room temperature ionic conductivity and good mechanical properties, and are easy to construct all-solid-state batteries, but have poor air stability, complex synthesis processes, and high environmental requirements that lead to high production costs. Although the technical difficulty is very high, the battery performance is excellent. Leading companies have accumulated technology for decades. Once a breakthrough will form a high technical barrier, the potential is huge in the long run;

● The polymer electrolyte route is likely to be a supplement to the first two routes, and it is compounded with oxides and sulfides to improve the electrolyte/electrode interface flexibility and improve battery cycle performance.

From the perspective of the solid state lithium battery material system, the short-term high probability is that the semi-solid electrolyte system will replace the traditional liquid electrolyte system, and the cathode and anode materials will most likely maintain the ternary cathode and silicon carbon anode system.

With the further improvement of battery energy density requirements and technological progress, in the medium term, silicon-rich and lithium-rich anode materials will be used in top 10 lithium ion battery anode material companies, and the cathode material system will remain unchanged. In the long run, the cathode material system will be replaced by lithium-rich materials with higher specific capacity, the anode will be metal lithium, and the electrolyte will be all solid.

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