Solvent-Free Solid-State Lithium Battery Based on LiFePO4 and MWCNT/PEO/PVDF-HFP for High-Temperature Applications
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ABSTRACT:
SUBMITTER: Yu H
PROVIDER: S-EPMC8567355 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Low ionic conductivity at room temperature and limited electrochemical window of poly(ethylene oxide) (PEO) are the bottlenecks restricting its further application in high-energy density lithium metal battery. Herein, a differentiated salt designed multilayered PEO-based solid polymer electrolyte (DSM-SPE) is exploited to achieve excellent electrochemical performance toward both the high-voltage LiCoO2 cathode and the lithium metal anode. The LiCoO2/Li metal battery with DSM-SPE displays a capacity retention of 83.3% after 100 cycles at 60 °C with challenging voltage range of 2.5 to 4.3 V, which is the best cycling performance for high-voltage (≥4.3 V) LiCoO2/Li metal battery with PEO-based electrolytes up to now. Moreover, the Li/Li symmetrical cells present stable and low polarization plating/stripping behavior (less than 80 mV over 600 h) at current density of 0.25 mA cm-2 (0.25 mAh cm-2). Even under a high-area capacity of 2 mAh cm-2, the profiles still maintain stable. The pouch cell with DSM-SPE exhibits no volume expansion, voltage decline, ignition or explosion after being impaled and cut at a fully charged state, proving the excellent safety characteristic of the DSM-SPE-based lithium metal battery.
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Project description:The typical lithium-ion-battery positive electrode of "lithium-iron phosphate (LiFePO4) on aluminum foil" contains a relatively large amount of inactive materials of 29 wt% (22 wt% aluminum foil + 7 wt% polymeric binder and graphitic conductor) which limits its maximum specific capacity to 120.7 mA h g-1 (71 wt% LiFePO4) instead of 170 mA h g-1 (100 wt% LiFePO4). We replaced the aluminum current-collector with a multi-walled carbon nanotube (MWCNT) network. We optimized the specific capacity of the "freestanding MWCNT-LiFePO4" positive electrode. Through the optimization of our unique surface-engineered tape-cast fabrication method, we demonstrated the amount of LiFePO4 active materials can be as high as 90 wt% with a small amount of inactive material of 10 wt% MWCNTs. This translated to a maximum specific capacity of 153 mA h g-1 instead of 120.7 mA h g-1, which is a significant 26.7% gain in specific capacity compared to conventional cathode design. Experimental data of the freestanding MWCNT-LiFePO4 at a low discharge rate of 17 mA g-1 show an excellent specific capacity of 144.9 mA h g-1 which is close to its maximum specific capacity of 153 mA h g-1. Furthermore, the freestanding MWCNT-LiFePO4 has an excellent specific capacity of 126.7 mA h g-1 after 100 cycles at a relatively high discharge rate of 170 mA g-1 rate.
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Project description:Lithium battery materials can be advantageously used for the selective sequestration of lithium ions from natural resources, which contain other cations in high excess. However, for practical applications, this new approach for lithium production requires the battery host materials to be stable over many cycles while retaining the high lithium selectivity. Here, a nearly symmetrical cell design was employed to show that LiFePO4 shows good capacity retention with cycling in artificial lithium brines representative of brines from Chile, Bolivia and Argentina. A quantitative correlation was identified between brine viscosity and capacity degradation, and for the first time it was demonstrated that the dilution of viscous brines with water significantly enhanced capacity retention and rate capability. The electrochemical and X-ray diffraction characterisation of the cycled electrodes also showed that the high lithium selectivity was preserved with cycling. Raman spectra of the cycled electrodes showed no signs of degradation of the carbon coating of LiFePO4 , while scanning electron microscopy images showed signs of particle cracking, thus pointing towards interfacial reactions as the cause of capacity degradation.
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Project description:Safety concerns related to the use of potentially explosive, liquid organic electrolytes in commercial high-power lithium-ion batteries are constantly rising. One promising alternative is to use thermally stable ionic liquids (ILs) as conductive media, which are however, limited by low ionic conductivity at room temperature. This can be improved by adding fillers, such as silica or alumina nanoparticles (NPs), in the polymer matrix that hosts the IL. To maximize the effect of such NPs, they have to be uniformly dispersed in the matrix while keeping their size as small as possible. In this work, starting from a water dispersion of silica NPs, we present a novel method to incorporate silica NPs at the nanoscale level (<200 nm) into PVdF-HFP polymer clusters, which are then blended with the IL solution and hot-pressed to form separators suitable for battery applications. The effect of different amounts of silica in the polymer matrix on the ionic conductivity and cyclability of the separator is investigated. A membrane containing 10 wt.% of silica (with respect to the polymer) was shown to maximize the performance of the separator, with a room temperature ionic conductivity of of 1.22 mS cm - 1 . The assembled half-coin cell with LiFePO 4 and Li as the cathode and the anode exhibited a capacity retention of more than 80% at a current density of 2C and 60 ∘ C.
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