Solid-State Batteries. A brief review on the current stage of…
By: Basudhrity Banerjee
Tags: Electrolyte, Technology, Battery, Energy Storage

Introduction

Solid-state batteries or SSB is one of the upcoming technologies in the battery space which is taking the world by a storm. Solid-state batteries are basically batteries which have all its component in solid-state. Conventional batteries have solid cathode, anode pasted on solid current collectors and liquid electrolyte sandwiched in between, where the active materials are separated by a separator. Whereas in solid-state battery construction all the components are solid, this includes the solid electrolyte. A separator is not used in this type of battery constructions. The construction remains fairly same and in order of:

Current Collector | Cathode | Solid Electrolyte | Anode | Current Collector

The need of Solid-state batteries

Safety of lithium-ion batteries has been always a concern for the scientific society. In fact safety is a parameter due to which the transportation of the batteries is restricted. Most of the batteries with liquids electrolytes are prone to flammability which makes them risky for handheld electronic equipment. To attain higher working potential window, most of the liquid electrolytes use organic solvents which are mostly flammable. Mishandling, overcharging and leaking are some of the common problems associated with normal batteries. Quality of the separator and its ability to withstand high voltages and also formation of dendrites puncturing the separator often causes short circuit which results in failure of the battery.

All of the above-stated problem have one common link, liquid electrolyte and separators. In order to fix this issue, researcher have come up with the concept of solid electrolytes. The solution is fairly simple. The flammable liquid electrolytes are replaced by solid electrolytes which are primarily made out of ceramics, glass, or polymers.

This solid battery being inflammable are less likely to burst into flames and the omission of separator serves as the answer for a safer battery technology.

Variants

The major categories in which solid-state electrolyte batteries can be divided are mainly glass, ceramic and polymers. Ceramic and glass electrolytes tends to be brittle which lowers down its mechanical strength. When fabricated in a battery pack, special care is required so as to avoid any fractures. This types of batteries are also difficult to synthesis in bulk quantity due to their complex processes. The basic precursors are often costly which increases its price.

Ceramics type solid electrolytes are of great interest for SSB, as it is a bit more mature technology in comparison to others. They mainly consist of oxides, sulfides and phosphates. They can be used in LIB, NIB and many more. Ceramic type solid electrolytes are often layered to give it a backbone. Ceramic electrolytes often allows substitution of certain elements with other elements which leads to Na+ vacancies in the interlayer gaps.

Few combinations are Li7La3Zr2O12, Li3P7S11, Li10GeP2S12, Na3PS4 Li2S–P2S5 glasses have exhibited high ionic conductivities. Few of these solid electrolytes are as good as liquid electrolytes in terms of conductivity. Sulphides based solid electrolytes are favourable for their cold press techniques whereas certain oxides based requires sintering over 1000 °C. Traditional sodium ion conductor Na-β″- Al2O3 ceramic pellet is also a very popular choice.

Polymer types solid-state batteries are also a very interesting choice as some polymers can conduct ions effectively. They are often flame retardant. Some of the components used in the synthesis are easily available and inexpensive. The method of synthesis is also fairly simple. The polymer matrix is often made using some of the common polymer bases such as polyvinylidene flouride(PVdF) or poly(acrylonitrile)(PAN), poly(ethylene oxide)(PEO), poly(ethylene glycol)(PEG), dimethacrylate (PEGDMA). Conducting salts like LiPF6, NaPF6, NaClO4 etc are also introduced in solvent mediums such as carbonates and glymes. Few downfalls of gel polymer solid-state batteries is their low to moderate ionic conductivity. This types of battery combinations work well at high temperature which is again not safe to operate. The flow of ions from active materials through the solid electrolyte is also often restricted.

Applications

Solid-state batteries are slowly making advances, as of now they are widely used in wearable devices, Radio Frequency Identification, medical devices like pacemakers and etc. More in-depth research and innovation is required. When the cost of solid-state batteries will come at par with the conventional batteries, its applications will also increase.

The issues

The replacement may sound very easy but a lot of alteration are to be kept in mind. The construction techniques change when the electrolyte system is changed. It no longer remains the simple method of wetting the active materials into the electrolyte which allows an easy pathway for ion movement. In solid-state batteries, it’s harder for ions to move through the solids matrix, which means solid-state batteries are difficult to engineer. As the process changes it also increases the price and can have performance problems. The problem lies in creating a conductive and easy free-flowing interphase between the cathode, electrolyte and anode for easy flow of ions. Sintering is a good method by which the solid electrolyte is attached to the active materials.

Few other issues are physical and mechanical strength. Resistance at the interphase of electrodes and electrolytes causes less flow of ions and formation of dendrites which results in low energy density. Sometimes a high-temperature operation is also required. One of the major disadvantages is obviously their cost.

Conclusion

For the solid-state batteries to take over the energy sector, a lot of research and implementations are required at the manufacturing stage. Though a lot of research is going on, quite a few things remain to be improved upon. The solid-state batteries need to be at par with the traditional batteries in terms of energy density and price in order to make its mark in the EV sectors. The universal research teams and scientist have come a long way in terms of attaining the goal, however constant improvement is the key.