The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "This invention generally relates to electrochemical cells and, more particularly, to a reactive separator to prevent the formation of metal dendrites in metal-ion. batteries.
"Lithium-ion batteries (LIBs) are widely used in a vast number of applications such as power sources for electronic devices, electric vehicles, and energy storage devices for wind and solar power. However, one of the major safety issues for LIBs is lithium plating and dendrite formation during the charge process. Although graphite is used as a non-lithium-metal anode in state-of-the-art LIBs, lithium plating can still occur when the battery is subjected to abuse such as fast-charging, low-temperature environments, and overcharging.
"Lithium plating results in the formation of lithium dendrites that penetrate through the porous separator and short the battery. Serious consequences such as fire and explosions can be caused by such lithium dendrite formation and growth. Dendrite formation is worse when a lithium metal anode is used in the battery. However, the substitution of lithium metal for graphite is desirable in light of the resulting increase in energy density of LIBs and in the development of batteries beyond LIBs, such as lithium-sulfur and lithium-air batteries.
"Other alkali and alkaline earth metal-ion batteries, especially the rechargeable sodium-ion battery (SIB), have attracted a lot of research attention because of their low-cost and comparable energy density as compared to LIBs. Unlike LIBs, graphite is incapable of sodium accommodation in a sodium battery. Hard carbon is considered to be the most likely non-sodium-metal anode for SIBS in the foreseeable future. However, the potential for sodium intercalation into hard carbon is mainly below 100 millivolts (mV) and the sodium diffusion is slow between different sites in a hard carbon anode. These characteristics lead to the hazard of sodium dendrites when hard carbon is used in a SIB. Since the ionic radius becomes larger and larger in the elements of lithium to sodium, potassium, and cesium, and since few non-metal anodes have been reported for these metal-ion batteries, it is reasonable to conclude that the dendrite issue will remain as a major obstacle in the development of novel rechargeable metal-ion batteries.
"In order to prevent metal dendrite growth/penetration, several strategies have been developed in the past decades. Electrolyte additives are proven to be helpful to form a uniform solid electrolyte interface (SEI) layer on the anode surface, which is beneficial both to suppressing electrolyte decomposition and dendrite growth, but no reported additive can eliminate dendrite growth completely. A dense solid state electrolyte membrane, which can be either ceramic or polymer, is considered to be the most efficient dendrite penetration blocker, but the low conductivity and high fabrication cost of these membranes prevent their large-scale application. Gel-like polymer electrolytes without inorganic fillers have also demonstrated the ability to block dendrite growth at certain level, but the instability of these electrolytes at the anode electrode surface and the unstable structure of the gel-electrolyte remain as unsolved problems for practical applications.
"It would be advantageous if a structure existed that would react with lithium, sodium, or any other alkali and alkaline (earth) metal dendrite and therefore protect a battery from an internal short circuit, enabling a battery to achieve ultra-long cycle life with improved safety."
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors' summary information for this patent application: "Different from all of the aforementioned strategies, a separator is disclosed herein that is made up of a reactive layer that can react with lithium, sodium, or any other alkali and alkaline (earth) metal dendrite, to protect a battery from an internal short circuit. Although a reactive polymer separator containing a polytetrafluoroethylene layer was proposed in the 1990s for the prevention of dendrites in lithium-ion batteries (LIBs), the reaction between lithium and polytetrafluoroethylene is quite slow and therefore it cannot protect the cell from an internal short in most circumstance. Herein, a sandwich structure separator is described that includes a layer of reactive chemical agent, such as hexacyanometallate, that reacts with metal dendrite tips faster than polytetrafluoroethylene and, therefore, enables the battery to achieve ultra-long cycle life with improved safety.
"In one aspect, a sandwich structure separator includes two layers of non-reactive layers respectively adjacent to the cathode and anode, and one reactive layer between the non-reactive layers that chemically reacts with alkali or alkaline earth metals. The reactive layer may include organic or inorganic components that react with metal dendrites, such as lithium, sodium, potassium and cesium, which might otherwise form and grow on the anode. The metal dendrites are either consumed or passivated locally within the reactive layer so that they do not reach the cathode, protecting the battery from shorting by dendrite penetration.
"The multi-layered separator can be either a porous solid membrane or a gel-like polymer that contains reactive components, such as (but not limited to) benzoquinone, ferrocene derivates, metal ferricyanides/ferrocyanides, tetrathiafulvalene derivates, sulfides, metal hexacyanoferrate, and polyvinylpyrrolidone. These materials react with alkali or alkaline earth metal dendrites in the temperature range between -30 and 180 .degree. C. The non-reactive layers can be porous polymer or ceramic membranes, or gel-like polymer layers that are inactive, or they can be passivated at the interface to adjacent cathode or anode electrodes. The separator is itself ionically conductive, or is permeable to an ionic conductive electrolyte. The reactive layer can be either electronically conductive or insulating.
"Accordingly, a reactive separator is provided for a metal-ion battery. As noted above, the reactive separator is made up of a reactive layer that is chemically reactive to alkali or alkaline earth metals, and has a first side and a second side. A first non-reactive layer, chemically non-reactive with alkali or alkaline earth metals, is adjacent to the reactive layer first side. A second non-reactive layer, also chemically non-reactive with alkali or alkaline earth metals, is adjacent to the reactive layer second side. More explicitly, the first and second non-reactive layers are defined as having less than 5 percent by weight (wt %) of materials able to participate in electrochemical reactions with alkali or alkaline earth metals.
"The reactive layer may be formed as a porous membrane embedded with the above-mentioned reactive components, where the porous membrane is carbon or a porous polymer. Alternatively, the reactive layer is formed as a polymer gel embedded with reactive components. The first and second non-reactive layers may be a porous polymer, ceramic membrane, or polymer gel. The reactive and non-reactive layers may be made with the same material. In one aspect, the reactive separator includes a liquid electrolyte, and the combination of the first non-reactive layer, reactive layer, and second non-reactive layer is permeable to the liquid electrolyte. In another aspect, the reactive separator includes a plurality reactive layers and/or a plurality of non-reactive layers (more than two).
"Additional details of the above-described reactive separator and a battery made using a reactive separator are presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 is a partial cross-sectional view of a reactive separator for a metal-ion battery.
"FIG. 2 is a partial cross-sectional view of a first variation of the reactive separator of FIG. 1.
"FIG. 3 is a partial cross-sectional view of a second variation of the reactive separator of FIG. 1.
"FIG. 4 is a partial cross-sectional view of a metal-ion battery with a reactive separator.
"FIG. 5 is a partial cross-sectional view of a first variation of the metal-ion battery with reactive separator.
"FIG. 6 is a partial cross-sectional view of a second variation of the metal-ion battery using the reactive separator described by FIG. 2.
"FIG. 7 is a partial cross-sectional view of a third variation of the metal-ion battery using the reactive separator described by FIG. 3.
"FIG. 8 is an alternate depiction of the reactive separator of FIG. 4.
"FIG. 9 is a graph depicting the capacity retention of a conventional half-cell with a Prussian blue analogue (PBA) cathode, a layer of
"FIG. 10 is a graph depicting cycling performance of a PBA/Na battery with a KNiFe(CN).sub.6-carbon-PTFE reactive layer in a sandwich structured separator.
"FIG. 11 is a graph depicting the cycling performance of a PBA/Na battery with a PVDF-KNiFe(CN).sub.6 composite membrane reactive layer in a sandwich structured separator."
For additional information on this patent application, see: Wang, Long; Lu, Yuhao. Reactive Separator for a Metal-Ion Battery. Filed
Keywords for this news article include: Neurons, Chemistry, Dendrites, Electrolytes, Electrochemical, Inorganic Chemicals, Alkaline Earth Metals, Cell Surface Extensions,
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