(A) Schematic of the effect of recharging Ni–Zn (conventional powder zinc anodes) versus Ni–3D Zn in which the anode is redesigned as a monolithic aperiodic sponge ensuring persistent 3D wiring of the metallic Zn core. Dendrites that form at powder composite Zn anodes can reach hundreds of micrometers in length. (B) The calculated specific energy of a fully packaged Ni–Zn cell as a function of increasing Zn depth of discharge versus a capacity-matched NiOOH electrode. The shaded areas highlight the specific energy range of common battery chemistries. For example, at =40% DODZn (percentage of theoretical utilization), Ni–Zn becomes competitive with Li-ion at the single-cell level.
Researchers at the US Naval Research Laboratory’s (NRL) Chemistry Division have demonstrated that the use of zinc formed into three-dimensional sponges for use as an anode boosts the performance of nickel–zinc alkaline cells in three areas: (i) > 90% theoretical depth of discharge (DODZn) in primary (single-use) cells; (ii) > 100 high-rate cycles at 40% DODZn at lithium-ion–commensurate specific energy; and (iii) the tens of thousands of power-demanding duty cycles required for start-stop microhybrid vehicles.
Joseph Parker, Jeffrey Long, and Debra Rolison from NRL’s Advanced Electrochemical Materials group are leading the effort to create an entire family of safer, water-based, zinc batteries. With 3-D Zn, the battery provides an energy content and rechargeability that rival lithium-ion batteries while avoiding the safety issues that continue to plague lithium. The research appears in the journal Science.
The present energy-storage landscape continues to be dominated by lithium-ion batteries despite numerous safety incidents and obstacles, including transportation restrictions, constrained resource supply (lithium and cobalt), high cost, limited recycling infrastructure, and balance-of-plant requirements—the last of which constrains the energy density of Li-ion stacks. Despite these disadvantages, Li-ion batteries are widely used because they provide high energy density, high specific power, and long cycle life—attributes that must also be met by any alternative battery system in order to compete for market share.
The family of zinc-based alkaline batteries (Zn anode versus a silver oxide, nickel oxyhydroxide, or air cathode) is expected to emerge as the front-runner to replace not only Li-ion but also leadacid and nickel–metal hydride batteries. This projection arises because Zn is globally available and inexpensive, with two-electron redox (Zn0/2+) and low polarizability that respectively confer high specific capacity and power. The long-standing limitation that has prevented implementing Zn in next-generation batteries lies in its poor rechargeability due to dendrite formation.
We bypass this obstacle to cycling durability by redesigning the Zn electrode as a monolithic, porous, aperiodic architecture in which an inner core of electron-conductive metallic Zn persists even to deep levels of discharge...In primary 3D Zn–air cells, this “sponge” form factor (3D Zn) discharges >90% of the Zn, a 50% improvement over conventional powder-bed composites. When cycling Zn sponges at the demanding current densities that otherwise induce dendrite formation in alkaline electrolyte—typically greater than 10 mA cm–2—the 3D Zn restructures uniformly without generating separator-piercing dendrites.
Zinc-based batteries are widely used for single-use applications, but are not considered rechargeable in practice due to their tendency to grow conductive dendrites inside the battery, which can grow long enough to cause short circuits.
The key to realizing rechargeable zinc-based batteries lies in controlling the behavior of the zinc during cycling. Electric currents are more uniformly distributed within the sponge, making it physically difficult to form dendrites.
With the benefits of rechargeability, the 3-D Zn sponge is ready to be deployed within the entire family of Zn-based alkaline batteries across the civilian and military sectors.