Introduction
Batteries are one of the most ubiquitous technologies powering our increasingly digital world. From consumer electronics to electric vehicles and the electric grid, advancements in battery technology hold great potential to transform how we power our lives. Researchers around the world are working tirelessly to improve existing battery chemistries and develop novel solutions to increase energy densities, lifespan, safety and more. This review paper aims to discuss cutting edge research on lithium-ion batteries, the current dominant battery technology, as well as emerging technologies that could surpass lithium-ion in the future.
Lithium-Ion Battery Research
Lithium-ion batteries are currently the best commercial option for many applications due to their high energy density. Further improvements are still needed to fully enable electric vehicles and renewable energy integration. Researchers are pursuing multiple avenues to enhance lithium-ion performance and lifetime.
Anode Materials
The most widely used anode material in current lithium-ion batteries is graphite, which provides good cycle life but relatively low theoretical capacity. Silicon is a highly promising alternative anode material due to its extremely high specific capacity that is about 10 times greater than graphite. Silicon anodes experience severe volume expansion and contraction during charge/discharge which leads to capacity fade. To mitigate this problem, researchers have tried embedding silicon nanoparticles in flexible carbon matrices or alloying silicon with metals like tin and copper. Prelithiation is another technique to form a protective solid electrolyte interphase on the silicon surface. Promising results show silicon anodes can now cycle stably for hundreds of cycles instead of tens.
Cathode Materials
The majority of commercial lithium-ion batteries employ lithium cobalt oxide (LiCoO2) cathodes due to their high energy density. Cobalt is expensive, toxic and provides inadequate thermal stability. Manganese-rich and nickel-rich lithium metal oxides have emerged as safer, lower cost alternatives to LiCoO2 while maintaining good specific capacities. Layered transition metal oxides like lithium nickel cobalt aluminum oxide (NCA) and lithium nickel cobalt manganese oxide (NMC) are now commonly used in electric vehicle batteries. Perovskites and polyanionic compounds are cutting-edge cathode materials under investigation that could boost energy densities even further.
Solid-State Electrolytes
Conventional lithium-ion batteries use liquid organic electrolytes which are volatile and flammable. Solid-state electrolytes made of ceramics or polymers could enable safer, longer lasting batteries by replacing the liquid electrolyte. Interface issues between the solid electrolyte and electrode materials often lead to high impedance. Researchers are developing new solid electrolyte compositions and surface treatments to address these challenges. Promising candidates include lithium phosphorus oxynitride (LiPON), lithium lanthanum zirconate (LLZO) and sulfide-based glasses. Fully solid-state batteries may finally realize the promise of lithium metal anodes.
Beyond Lithium-Ion
While lithium-ion remains the top commercial battery technology, the future of energy storage likely involves next-generation battery systems beyond lithium-ion:
Lithium-Sulfur Batteries – Sulfur cathodes provide a much higher specific capacity than lithium-ion but face issues with polysulfide dissolution. Nanostructured sulfur composites and ion selective membranes are being investigated to stabilize cycling.
Lithium-Air Batteries – Theoretical energy densities comparable to gasoline. Difficult to commercialize due to complex cathode chemistry and moisture sensitivity. Dry cell designs and catalytically-active protective layers show promise.
Solid-State Lithium Batteries – As mentioned, solid electrolytes could enable lithium metal anodes for very high energy densities. Interfacial engineering is critical to optimize ionic conductivity and stability.
Sodium-Ion Batteries – Similar chemistry to lithium-ion but utilizes more abundant sodium instead of lithium. Research focuses on developing high capacity electrode materials compatible with sodium. May compete for stationary storage applications.
Flow Batteries – Rechargeable batteries that separate energy storage from power generation. Long lifetime and scalable energy capacity makes them suitable for the electric grid. Many chemistries under investigation including vanadium, zinc-bromine and all-vanadium.
Conclusion
Decades of research have established lithium-ion batteries as the dominant energy storage solution. Continued improvements to lithium-ion materials and manufacturing will surely enhance the technology. In parallel, research into next-generation battery systems holds promise to bring the next big leap in battery capabilities. A diverse portfolio of battery technologies tailored for different applications will likely power our energy needs into the future. With worldwide focus and investments, battery innovations could significantly accelerate the adoption of renewable energy and electric mobility.