New aqueous rechargeable lithium battery shows good safety, high reliability, high energy density and low cost; another post Li-ion alternative
|Schematic illustration of the aqueous rechargeable lithium battery (ARLB) using the coated lithium metal as anode, LiMn2O4 as cathode and 0.5 mol l-1 Li2SO4 aqueous solution as electrolyte. Wang et al. Click to enlarge.|
Researchers from Fudan University in China and Technische Universität Chemnitz in Germany have developed an aqueous rechargeable lithium battery (ARLB) using coated Li metal as the anode. In a paper published in Scientific Reports, the open access journal from the Nature Publishing Group, the team reports that the ARLB delivers an output voltage of about 4V.
The battery shows an energy density of up to 446 Wh kg-1—about 80% higher than conventional Li-ion batteries, and much higher than energy densities reported for earlier ARLBs (30–45 Wh kg-1). The battery, which can be low cost and reliable in terms of safety, provides another chemistry for post Li-ion batteries, they suggest, and with higher practical energy densities than Li-air systems for supporting applications including electric vehicles and large-scale grid energy storage.
Aqueous rechargeable lithium batteries (ARLBs), which use aqueous electrolytes and lithium intercalation compounds as electrode(s) based on redox reactions, were invented in 1994 and have attracted wide attentions since 2007 as a promising system because of their low capital investment, high reliability and good safety. Recent breakthroughs show clearly that they can present very good cycling performance and super-fast charge performance, which can be comparable with filling gasoline for engine cars.
Although several attempts have been made on the anode materials, the main disadvantages is that their energy density is still much lower than that of conventional lithium ion batteries due to the narrow electrochemical window of water. If anode materials of lower redox potentials can be stable in aqueous electrolytes, high energy density systems will be feasible.
Here we introduce a coating layer on lithium metal. The coated lithium metal is stable in aqueous electrolytes. Combining with the coated lithium metal as anode, LiMn2O4 as cathode and 0.5 mol l-1 Li2SO4 aqueous solution as electrolyte, an ARLB is built up. Its average discharge voltage is about 4.0 V, much higher than the theoretic stable window of water, 1.229 V. It presents an energy density of 446 Wh kg-1 together with excellent cycling performance.—Wang et al.
In conventional lithium metal rechargeable batteries, the use of Li metal as anode material is restricted due to the safety issues caused by the formation of lithium dendrites during repeated charge-discharge cycles, leading to short circuiting. In the new ARLB, the coating prevents dendrite formation.
The coating of the Li metal consists of a home-made gel polymer electrolyte (GPE) and a LISICON film. LISICON film is a solid electrolyte which can also act as a separator; due to its solid structure, protons, water, hydrated and solvated ions cannot pass through. The GPE ensures the good electrochemical stability of the LISICON film, and only Li+ ions can transfer between Li metal and the outside.
The coated lithium metal is also very stable in the aqueous solution, with no hydrogen evolution observed. (Lithium metal reacts rapidly with water to produce hydrogen and lithium hydroxide, LiOH.)
Due to the “cross-over” effect, lithium ions at the higher potential side in the aqueous electrolyte can pass through the coating and arrive at the lower potential side of lithium metal. As a result, the coated lithium metal is very stable in the aqueous electrolyte and the average output voltage of this ARLB is 4.0 V.—Wang et al.
In addition to its capacity and cycling performance, the ARLB offers another benefit, the researchers note: thermal management.
In this ARLB system, the aqueous electrolyte has high thermal capacitance and can absorb large amounts of heat. During the same charge and discharge process, the temperature of this system will be much lower than that for conventional lithium ion batteries. In addition, water or aqueous electrolyte is in direct contact with both of the Li metal anode and the LiMn2O4 cathode, and the cooling effects will be very efficient. The cooling system, which is usually needed for large capacity battery modules, is not needed for the application in electric vehicles. The safety and reliability is greatly improved when compared with conventional lithium ion batteries.—Wang et al.
Compared with Lithium/air batteries, the ARLB offers the following advantages, the researchers said:
- Much better cycling performance.
- Higher practical energy density.
- Higher energy efficiency.
- Lower cost of production, using well-known materials.
Furthermore, they noted, the cycling performance of the ARLB is much better than that of lithium-ion batteries.
Replacing LiMn2O4 with LiCoO2 or Li[NixCoyMn1-x-y]O2 can deliver higher energy density in the ARLB, they suggested. Using LiCoO2 in the ARLB design could result in an energy density—on the basis of the electrode materials—above 570 Wh kg-1, with an estimated practical energy density above 285 Wh kg-1.
With Li[NixCoyMn1-x-y]O2, the estimated practical energy density would be above 300 Wh kg-1.
Based on these data, it means that this new ARLB chemistry can ensure electric vehicles to run above 300 km [186 miles] for one charge, which presents great promise.—Wang et al.
Xujiong Wang, Yuyang Hou, Yusong Zhu, Yuping Wu & Rudolf Holze (2013) An Aqueous Rechargeable Lithium Battery Using Coated Li Metal as Anode. Scientific Reports 3, Article number: 1401 doi: 10.1038/srep01401