What is a solid-state battery? What are the advantages and disadvantages of solid-state batteries?

NIO has announced the official launch of a 150kWh battery pack that utilizes a new battery concept: the solid-state battery. This might lead some to wonder, what exactly is a solid-state battery? How does it compare to previous batteries, and what are its advantages and disadvantages? Let's explore these questions.
 

1. What is a solid-state battery?

The primary difference between solid-state batteries and the currently mainstream traditional lithium-ion batteries lies in the electrolyte. Solid-state batteries use solid electrolytes to replace the liquid electrolytes and separators found in traditional lithium-ion batteries. Traditional lithium-ion batteries are composed mainly of positive and negative electrode materials, electrolytes, and separators. The positive and negative electrode materials determine the battery's capacity, while the electrolyte and separator act as the medium for transmitting lithium ions. This difference in electrolyte type is the essential distinction.
 

2. What are the advantages and disadvantages of solid-state batteries?

Solid-state batteries offer several advantages, including enhanced safety, higher energy density, and better cycle performance. However, they also come with drawbacks such as high impedance and increased cost. Let's examine these in detail:

Advantages:

1. Enhanced Safety: Batteries with liquid electrolytes are flammable and explosive, posing significant safety risks. In contrast, solid electrolytes can inhibit the formation of lithium dendrites, are less prone to catching fire or exploding, do not leak electrolytes, and are resistant to side reactions at high temperatures. When operating under high current, lithium dendrites are less likely to puncture the separator and cause short circuits, reducing the risk of fire due to gas generation.
    

2. High Energy Density: It is considered nearly impossible for liquid electrolyte batteries to achieve an energy density of more than 500Wh/kg. With solid electrolytes, the battery can forgo the use of lithium-embedded graphite anodes and instead use metallic lithium directly as the anode. This greatly reduces the amount of anode material needed and significantly increases the energy density of the entire battery, which in solid-state batteries can reach 300-400Wh/kg.
    

3. Long Cycle Life: Solid electrolytes address the issue of solid electrolyte interface (SEI) film formation by liquid electrolytes during charging and discharging, as well as the problem of lithium dendrites. This results in greatly improved cycle life and durability for lithium batteries, potentially reaching about 45,000 cycles in ideal conditions.
    

   

Disadvantages:

1. High Interface Impedance: The solid electrolyte and electrode material are connected in a solid state, which can lead to weak effective contact between the electrode and electrolyte. Additionally, ion transport dynamics within solid materials are relatively low, contributing to the problem of high interface impedance.
    

2. High Cost: It is estimated that the cost of liquid lithium batteries ranges from $120 to $200 per kWh. This price point is difficult to lower, prompting many battery manufacturers to develop cheaper but still energy-dense semi-solid batteries as an interim solution.