Lithium ion solid state battery – introduction and its future

Table of Contents

Nowadays, electric vehicles have gradually become the mainstream of the automobile market. In addition to paying attention to the product intelligence, mileage range and technical capabilities, automobile consumers are most concerned about the power battery of electric vehicles. After all, the power battery is the heart of electric vehicles. So that major manufacturers are investing a lot in the research and development of batteries, especially lithium ion solid state battery technology.

Lithium ion solid state battery market status

In the past three years, with the expansion of demand in the electric vehicle market, the power lithium battery industry has been dominated by the upstream lithium mining companies. And the price of lithium ore has risen sharply from less than 40,000 RMB/ton in 2020 to the highest 570,000 RMB/ton, becoming the “white oil” in the era of new energy.

Earlier this year,the production capacity of lithium mining, notably in Australia, has accelerated, and the battery material recycling industry has ushered in new opportunities due to price increases, and recycled resources have largely replaced the original resource demand.

At the same time, after the energy vehicle upsurge, downstream demand has languished to a certain extent. Under the double blow of demand and supply, lithium ore also experienced a harsh hit, and its price fell to 150,000 RMB/ton in just three months.

At the same time as the price of lithium ore falls, the economy of lithium ion power battery is highlighted again. Lithium ion solid state batteries, which have been underestimated in the past two years, have been recognized by people again under the double benefits of the market and technology.

What is a lithium ion solid state battery?


If lithium ion batteries are classified according to the form of the electrolyte, they can be divided into liquid batteries and solid state batteries according to the amount of liquid in them, and solid-state batteries can be divided into three types: semi-solid batteries, quasi-solid state batteries and all-solid state batteries.

The electrolyte in the liquid battery is composed of liquid, while the electrolyte mass percentage of semi-solid state battery is <10%, the electrolyte mass percentage of quasi-solid state battery is <5%, and all solid state battery does not contain any liquid electrolyte.

Differences between solid state battery and liquid battery


Solid state battery and liquid battery are different in the following three ways.

Energy density

Liquid batteries are about to reach the bottleneck of energy density, while solid-state batteries have a higher upper limit of it.
According to statistical data, the energy density of lithium ion batteries has increased by three times from 1991 to 2015, and the GAGR was about 3%. According to linear calculations, the energy density in 2020 and 2025 can only reach 300Wh/kg and 320Wh/kg.

However, from a practical technical point of view, due to the extremely strong activity and poor stability of the lithium metal anode, it is extremely difficult to be compatible with the liquid electrolyte. Thus, the advantages of its lowest electrochemical potential and extremely high capacitance cannot be brought into play, which directly limits the development of the energy density of the whole battery

In addition, it is difficult for the electrolyte to match the high voltage cathode. The current mainstream electrolyte voltage does not exceed 4.5V, which directly restricts the optional range of cathode materials and thus limits the development of energy density.

In other words, the growth rate of energy density of lithium ion batteries has slowed down significantly and is getting close to the theoretical limit. Without updating materials, it is difficult to make new breakthroughs.

Solid electrolytes solve these problems well. Compared with liquid electrolyte, solid electrolyte has more stable electrochemical performance and can be compatible with highly active lithium metal anode. At the same time, solid electrolyte can inhibit the precipitation of lithium dendrites, which meets the necessary conditions for the application of lithium metal anode.

At the same time, some solid-state electrolytes have a larger voltage range, which can be adapted to high-voltage cathode materials. If lithium metal anode are used, theoretically, the cathode can be made of lithium-free materials, and the energy density and cost reduction space are expected to be greatly improved. Volumetric energy density is more expected to exceed 100Wh/L.


Liquid batteries are difficult to solve the problem of safety, while solid state batteries fundamentally prevent the occurrence of problems.

Electrolyte is the biggest driver of liquid lithium ion battery safety accidents. The thermal runaway of lithium batteries is mainly due to the internal short circuit or high operating temperature, which leads to the initial temperature rise and cause the decomposition of the SEI film. At the same time, the continuous temperature rise of the electrolyte releases a variety of combustible gases and oxygen, and then burns.

At present, the lithium battery industry mainly relies on mitigating thermal runaway to deal with safety accidents, such as adding flame retardants or inert gases into the battery cells, and adding anti-puncture design or thermal barriers at the pack surface. However, the high-risk electrolyte is still the essence which causes LIB safety problems, and as it is a necessary material of LIB, safety problem cannot be solved in theory.

Meanwhile, the runaway initial temperature of solid electrolytes exceeds that of liquid electrolytes (120°C), and oxide solid electrolytes are the safest, with thermal runaway temperatures exceeding 600°C, theoretically eliminating safety issues such as battery combustion.

Process optimization

The space for process optimization of liquid batteries is far smaller than that of solid state batteries.

At present, the telecommunications manufacturing process of liquid batteries mainly includes electrode preparation (wet method mainly)→winding→packaging→liquid injection→chemical formation→sorting→assembling. While high-speed slurry mixing, coating and winding/stacking technologies and Large-capacity battery technology promotes the continuous expansion of single-line production capacity.

Manufacturing process of solid state battery

However, due to the low efficiency coating and drying, and the need to stop the wire and insert the pole piece in the winding process in the process of wet electrode preparation, even Tesla’s upgraded 4680 technology still involves complicated laser welding processes, so there is still a big bottleneck in the improvement of battery manufacturing efficiency.

In addition, the traditional process of assembling a CTM as a cell- module- battery pack-body uses a large number of components and adds overall mass, as well as involving complex connections and battery management systems.

Solid state batteries can use dry electrode technology, which is a solvent-free production technology. The method is to mix cathode and anode materials with binder, and then directly form a electrode of sheet shape or thin film shape through the way of calendering, spraying, extrusion or vapor deposition.

Compared with wet electrode preparation, the advantages of dry technology are mainly reflected as below:
Skip the steps of slurry mixing, drying, and recovery of harmful solvents, which saves the production costs such as materials, time, workshops, and labor.
In terms of performance, the electrode is thicker and the energy density is higher.
More environmentally friendly without toxic solvent.

In addition, in the process of assembly, the solid state battery cell with multi-layer bipolar structure itself can be regarded as a packing process. The serial-connected dense packing can greatly improve the utilization rate of space, achieve lower internal resistance, higher energy density and current output. In the subsequent packaging process, there is no need for complex connection, which means a great space for improving efficiency and reducing cost after mass production.

The optimization of solid state battery


The optimization of solid state battery can be started from the following three aspects.


At present, there are three mainstream routes for the selection of electrolyte materials for solid-state batteries, including polymers, oxides, and sulfides. The three technical systems are different, and each one has its own advantages and disadvantages.

Polymer: The advantage of polymer as electrolyte is that it is easy to process, compatible with the existing production equipment and process of liquid electrolyte, and has good mechanical properties. However, its conductivity is too low, and it needs to be heated to 60°C to work normally, and it cannot be adapted to high voltage cathode materials.

Sulfide: Sulfide is just the opposite of polymer.It has the highest conductivity and wide electrochemical stability, makes it the most potential technical route. But the preparation process of sulfide is very complex, and easy to react with water and oxygen in the air to produce hydrogen sulfide highly toxic gas.

Oxide: Oxide has the advantages of both the above two. It has relatively good conductivity, stability and electrochemical performance, makes it the fastest moving technology at the moment. Due to its relatively low development cost and difficulty, Chinese manufacturers are focusing on oxide solid electrolytes.It is expected to scale up in semi-solid state batteries.

From a long-term perspective, although the research and development of sulfide solid electrolytes is difficult, due to its excellent performance and great potential, it attracts powerful and well-capitalized battery companies to continuously invest in research and development. Many industry leaders with more than ten years of technological accumulation choose it as the main technology path, once a breakthrough is achieved, it is much likely to form high technical barriers.

Electrode material

Solid-state batteries could stick with the existing anode system, but it would do little to improve energy density. If you want to greatly increase the capacity, you need to apply lithium metal anode more efficiently.

Lithium metal anode has the advantage of high energy density, which is directly related to the capacity of battery. Therefore, we can say that the company which has mastered the application technology of lithium metal anode will be able to obtain the dual advantages of product performance and cost, and occupy the strategic heights of the market.

However, at present, lithium metal anode needs to solve the problem of stability, and there’s a great potential to reduce the cost of lithium metal anode mass production.

Semi-solid state battery

All-solid-state batteries still have technical difficulties to be overcome. For example, the ionic conductivity of solid-state electrolytes is much lower than that of liquid electrolytes, which leads to a significant increase in battery internal resistance, poor battery cycle performance, and poor rate performance.
On the other hand, the high cost is also a factor restricting the commercialization of all-solid-state batteries. At present, the industrial chain of liquid lithium batteries is very mature, and lithium batteries with better performance can be produced at low cost, while the industrial chain of all-solid-state batteries is still not mature enough. At this time, semi-solid battery the best choice as a compromise.

The manufacturing process and equipment of semi-solid state battery are highly common with the current lithium battery, only some key process links, such as in situ solid-state, mixing and liquid injection are different from the current liquid battery. However, semi-solid state battery has many characteristics such as high energy density, small size, higher safety and better flexibility. It has become the first choice of the next mainstream battery technology route for automobile manufacturers.

At the same time, semi-solid state battery is also seen as a transition route to all-solid state. After all, no new technology can be achieved overnight, they all need to be researched and developed step by step.

Global development status of solid state battery


The gradual transition from liquid batteries to solid-state batteries is an important trend in the progress of lithium battery technology. Globally, major car companies, battery companies, investment institutions, and scientific research institutions are actively deploying capital, technology, and talents to accelerate the industrialization of solid-state batteries.

Leading car manufacturers and governments around the world are entering the solid-state battery race. From a global perspective, it can be roughly divided into three camps: China, Japan and South Korea, Europe and the United States.

In terms of technology direction, Japan and South Korea started the earliest and chose the sulfide solid-state electrolyte route. At present, Japanese and South Korean companies are holding the world’s leading number of solid-state battery patents.

The South Korean government announced on April 20 that it will jointly invest 20 trillion KRW before 2030, led by the government and its leading battery companies, to develop advanced battery technologies, including solid-state batteries, and start commercial production in 2025 , to maintain South Korea’s strength in the field of power batteries.

In Europe and the United States, the oxide solid electrolyte route is mostly chosen for development of lithium metal anode applications. In China, all the three solid-state electrolyte routes have been laid out. While developing all-solid-state batteries, China is also vigorously developing semi-solid-state batteries that are more friendly to existing industries.


As an upgrade of traditional lithium batteries, solid-state batteries obtain higher energy density, better safety, greater space for process optimization, and stronger flexibility by replacing electrolytes and electrode materials, becoming the ideal form of next-generation lithium batteries.

Up to now, the three solid electrolytes have their own advantages and disadvantages, and none of them are as good as in theory. In addition, the lack of large-scale production has greatly increased the cost of solid-state batteries.

But with the passage of time and technological breakthroughs, we can believe that solid-state batteries will gradually spread, and gradually replace the traditional liquid lithium batteries in various fields.

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