Patent Application
20240282996
The present invention relates to electrochemical energy storage devices and in particular to the batteries which contain chromic and bromide ions in aqueous acidic electrolytes.
There is an ever-increasing demand for advanced battery technologies with high safety and low cost for applications in large-scale renewable energy storage. The currently commercialized rechargeable batteries, such as Li-ion batteries, have attracted much attention in recent years. However, the safety issues associated with flammable organic electrolytes and the growing concerns about the high cost and availability of Li resources impede their large-scale deployment.
Unlike traditional batteries, flow-based electrochemical energy storage systems separate the energy storage and power generation by storing the electro-active species in externally flowing electrolytes, while maintaining the redox reactions at the electrode surface inside a stack. This unique architecture permits the flow batteries to independently scale the power and energy and enables high safety for intermittent renewable energy integration and other grid services. The most commercialized flow battery up to now is the all-vanadium redox flow battery (VRFB). However, despite continuous progress, the high cost of vanadium makes the installation cost of VRFB much higher than that of Li-ion batteries.
The purpose of this patent is to invent a chromium bromine flow battery to replace VRFB with similar performance characteristics but as low cost as Li-ion batteries. Chromium bromine flow battery (CBFB) was first patented in 1984 (U.S. Pat. No. 4,469,760) but has not been commercialized since then, probably because this CBFB was developed from the zinc-bromine flow battery (ZBFB) and inherited the drawbacks of ZBFB, including the low current and power densities. The bromine complexing agents were used in the CBFB to reduce bromine's vapor pressure in cathodic electrolyte and an anion exchange membrane was used to allow bromide and chloride ions to pass through. The use of organic bromine complexing agents can reduce the concentration of bromine in the cathodic electrolyte and prevent bromine from crossing over the membrane but make the cathodic and anodic electrolytes asymmetric with different ingredients of the complexing agents. The CBFB of this patent uses symmetric electrolytes with high concentration hydrobromic acid but without any complexing agents and uses a cation exchange membrane to allow hydrogen ions to pass through.
It is, therefore, an object of the present invention to provide a rechargeable electrochemical battery with similar performances to the VRFB but with lower costs.
This object is achieved in accordance with the present invention by providing a chromium bromine flow battery with a carbon anode, a carbon cathode, a cation exchange membrane for separating anodic electrolyte and cathodic electrolyte, and aqueous acidic electrolytes with 1-3M chromic ions and hydrobromic acid of high concentration greater than 4M.
The said carbon anode and carbon cathode comprise carbon (such as graphite felt, carbon felt, carbon cloth, carbon paper, carbon fiber, and graphite paper).
The invention may be more readily understood by reference to the following drawing wherein:
The referenced drawing is only for the purpose of illustrated embodiments and is not to be construed as limiting the present invention.
The invention discloses a rechargeable chromium bromine flow battery which comprises a carbon anode 1, a carbon cathode 2, a proton exchange membrane 3, and symmetric acidic aqueous 17 electrolytes.
As shown in
The hydrogen ions in the anodic electrolyte cross through the proton exchange membrane to enter the cathodic electrolyte during the discharging process. During the charging process, the hydrogen ions come back to the anodic electrolyte.
An energy density of 35 Wh/L has been achieved at the current density of 100 mA/cm2. This is higher than 25 Wh/L of the all-vanadium flow battery and 15 Wh/L of the iron-chromium redox flow battery (ICRFB). The energy efficiency reaches 82%, higher than 75% of ICRFB, and close to 85% of VRFB. The columbic efficiency can reach 99%, indicating the crossovers of bromine and Cr2+ are low and no organic complexing agents are necessary. The capacity decay rate during cycling is only 0.2% per cycle, lower than 0.6% of ICRFB and 0.3% of VRFB. The capacity can be easily restored by mixing the anodic and cathodic electrolytes after a long time of cycling. The costs of chromium and hydrobromic acid are much lower than vanadium. Chromium Cr3+/Cr2+ is low toxic and the aqueous solution is inflammable, which makes the system safe and environmentally friendly. Although bromine is easy to volatilize, it can be safely sealed in a container without emission.
Although the invention has been described in detail for the purpose of illustration based on the currently considered embodiment, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiment, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of claims.
