Towards a stable Li–CO2 battery: The effects of CO2 to the Li metal anode
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The primary objectives of this project were to develop the anode and cathode materials for high-energy density cells for use in plug-in hybrid electric vehicles (PHEVs) and in electric vehicles (EV) that offer substantially enhanced performance over current batteries used in PHEVs and with reduced cost. This was accomplished by performing research on both the anode and cathode components to improve their volumetric (and gravimetric) capacity. On the anode side the goal of doubling the capacity of today's graphite based anodes was accomplished, using a tin-iron composite anode. This anode was found to have a coulombic efficiency greater than silicon allowing for more than 500 cycles. It shows the technical viability of alternative anodes. On the cathode side, two materials were investigated, both of which can react with two lithium ions. The intercalation cathode, LixVOPO4, where 0≤x≤2, was shown to be highly reversible over two voltage plateaus, one at around 3.8 volts and the other at 2.5 volts. The total capacity exceeded 300 Ah/kg at low rates. The SnFe//LixVOPO4 couple was effectively cycled in full cells; the lifetime was limited by side-reactions on the cathode, which limited the overal cell coulombic efficiency to 98-99%. The conversion cathode, CuF2, had an initial capacity of 500 Ah/kg, but that fell rapidly due to transport of cuprous ions through all electrolytes studied. Summarizing, a new alternative anode for graphitic carbon was found that shows the technicla feasibility of using metal-based hosts for advanced anodes.
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Lithium-ion batteries (LIB) with both high volumetric and gravimetric specific capacities are desirable for power sources in microsystems. Si is a promising anode material for the above LIBs. However, its huge volume change combined with strict constraint by the bulky current collector (and/or the substrate) during lithiation/delithiation causes a severe stress and thus rapid capacity fading. Strategies in the literatures help suppress the capacity fading but degrade the anode initial Coulombic efficiency and specific capacities. This work presents a freestanding Si anode with an ultrathin current collector. Unlike those in the literatures whose current collector (and/or the substrate) accounts for the main part, the Si film dominates in this freestanding anode. This causes weak constraint from the current collector, therefore, the Si film can expand/shrink easily and stress induced by Si volume change can be effectively released, thus resulting in good anode cyclability (98.6% retention over 150 cycles). Moreover, the dominant role of the Si film in this anode ensures the anode to have high volumetric (6989 mAh cm−3) and gravimetric (2107 mAh g−1) specific capacities even when both the Si and current collector are included for calculations. This freestanding anode also displays a high initial Coulombic efficiency of 92.8% due to its small surface area.
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Current methods for extending the cycle life of volume-expanded anode materials for lithium-ion batteries mainly focus on development of nanosize three-dimensional structures and composite materials. We propose a novel anode material of GeO2–Sn30Co30C40 that is synthesized by high energy ball milling (SPEX). This material depends on the nanosized and composite concept, which combines the advantageous properties of Sn–Co–C (long cycle life) and GeO2 (high capacity). The composite anode shows a reversible capacity over 800 mAh/g with good capacity retention. Furthermore, the first-cycle Coulombic efficiency is 80%, much higher than the 34.6% obtained for pure GeO2. Pair distribution function measurements indicated the reversible reaction of GeO2 and SnO2, which is the key factor in the improved Coulombic efficiency. This reversibility can be explained by the catalytic role of Co3Ge2 phase, which facilities the conversion reactions of metal oxides and acts as an electronic conductive component for the composite anode.
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Anode‐free rechargeable lithium (Li) batteries (AFLBs) are phenomenal energy storage systems due to their significantly increased energy density and reduced cost relative to Li‐ion batteries, as well as ease of assembly because of the absence of an active (reactive) anode material. However, significant challenges, including Li dendrite growth and low cycling Coulombic efficiency (CE), have prevented their practical implementation. Here, an anode‐free rechargeable lithium battery based on a Cu||LiFePO 4 cell structure with an extremely high CE (>99.8%) is reported for the first time. This results from the utilization of both an exceptionally stable electrolyte and optimized charge/discharge protocols, which minimize the corrosion of the in situly formed Li metal anode.
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SiO x coating is an effective strategy to prolong the cycling stability of Si-based anodes due to the robust interaction between Si and the SiO x layer. However, the SiO x layer-protected Si anode is limited by the relatively low initial Coulombic efficiency and sluggish Li+ diffusion ability induced by the SiO x layer. Herein, we present the preparation of selectively prelithiated Si@SiO x (Si@Li2SiO3) anode by using a facile strategy to resolve the above issues. As the anode for lithium ion batteries, Si@Li2SiO3 exhibits a high initial Coulombic efficiency (ICE) of 89.1%, an excellent rate performance (959 mA h g-1 at 30 A g-1), and a superior capacity retention (3215 mA h g-1). The full cell with LiFePO4 cathode and Si@Li2SiO3 anodes is successfully assembled, disclosing a high ICE of 91.1% and excellent long cycling stability. The superior electrochemical performance of Si@Li2SiO3 can be attributed to the coating layer, which can strengthen the integrity of the electrode, decrease irreversible reactions, and provide efficient Li+ diffusion channels.
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