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- NSF-PAR ID:
- Date Published:
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- Journal of Applied Electrochemistry
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Applications of silicon as a high-performance anode material has been impeded by its low intrinsic conductivity and huge volume expansion (> 300%) during lithiation. To address these problems, nano-Si particles along with conductive coatings and engineered voids are often employed, but this results in high cost anodes. Here, we report a scalable synthesis method that can realize high specific capacity (~800 mAh g-1), ultrafast charge/discharge (at 8 A g-1 Si) and high initial Coulombic efficiency (~90%) with long cycle life (1000 cycles) at the same time. To achieve 1000 cycle stability, micron-sized Si particles are subjected to high-energy ball milling to create nanostructured Si building blocks with nano-channel shaped voids encapsulated inside a nitrogen (N)-doped carbon shell (termed as Si micro-reactor). The nano-channel voids inside a Si micro-reactor not only offer the space to accommodate the volume expansion of Si, but also provide fast pathways for Li ion diffusion into the center of the nanostructured Si core and thus ultrafast charge/discharge capability. The porous N-doped carbon shell helps to improve the conductivity while allowing fast Li ion transport and confining the volume expansion within the Si micro-reactor. Submicron-sized Si micro-reactors with limited specific surface area (35 m2 g-1) afford sufficient electrode/electrolyte interfacial area for fast lithiation/delithiation, leading to the specific capacity ranging from ~800 to 420 mAh g-1 under ultrafast charging conditions (8 A g-1), but not too much interfacial area for surface side reactions and thus high initial coulombic efficiency (~90%). Since Si micro-reactors with superior electrochemical properties are synthesized via an industrially scalable and eco-friendly method, they have the potential for practical applications in the future.more » « less
Silicon is regarded as one of the most promising anode materials for lithium-ion batteries. Its high theoretical capacity (4000 mAh/g) has the potential to meet the demands of high-energy density applications, such as electric air and ground vehicles. The volume expansion of Si during lithiation is over 300%, indicating its promise as a large strain electrochemical actuator. A Si-anode battery is multifunctional, storing electrical energy and actuating through volume change by lithium-ion insertion.
To utilize the property of large volume expansion, we design, fabricate, and test two types of Si anode cantilevers with bi-directional actuation: (a) bimorph actuator and (b) insulated double unimorph actuator. A transparent battery chamber is fabricated, provided with NCM cathodes, and filled with electrolyte. The relationship between state of charge and electrode deformation is measured using current integration and high-resolution photogrammetry, respectively. The electrochemical performance, including voltage versus capacity and Coulombic efficiency versus cycle number, is measured for several charge/discharge cycles. Both configurations exhibit deflections in two directions and can store energy. In case (a), the largest deflection is roughly 35% of the cantilever length. Twisting and unexpected bending deflections are observed in this case, possibly due to back-side lithiation, non-uniform coating thickness, and uneven lithium distribution. In case (b), the single silicon active coating layer can deflect 12 passive layers.
Germanium (Ge) is deemed as one of the most promising alloying anodes for rechargeable lithium‐ion batteries (LIBs) due to its large theoretical capacity, high electrical conductivity, fast lithium‐ion diffusivity, and mechanical robustness. However, Ge‐based anodes suffer from large volume changes during lithiation and delithiation, which can deteriorate their electrochemical performance rapidly. Herein, the large volume change issue is effectively addressed using an asymmetric membrane structure that is prepared using a phase‐inversion method in combination with hydrogen peroxide etching and surface coating. The asymmetric Ge membrane etched by ≈30 wt% H2O2at 90 °C for 30 s demonstrates a capacity retention higher than 80% in 50 cycles at 160 mA g−1. Coating the H2O2‐etched Ge membrane with carbonaceous membranes can further improve the retention up to 95% in 50 cycles at 160 mA g−1, whereas ≈100% capacity of 700 mAh g−1can be maintained in 170 cycles at 400 mA g−1. A combination of electron microscopy, spectrophotometry, and X‐ray analyses confirms the electrochemical performance of asymmetric Ge membranes as the LIB anode can be significantly affected by membrane geometry, the duration of hydrogen peroxide etching, carbonaceous membrane coating, and Ge concentration.
Si‐based anodes with a stiff diamond structure usually suffer from sluggish lithiation/delithiation reaction due to low Li‐ion and electronic conductivity. Here, a novel ternary compound ZnSi2P3with a cation‐disordered sphalerite structure, prepared by a facile mechanochemical method, is reported, demonstrating faster Li‐ion and electron transport and greater tolerance to volume change during cycling than the existing Si‐based anodes. A composite electrode consisting of ZnSi2P3and carbon achieves a high initial Coulombic efficiency (92%) and excellent rate capability (950 mAh g−1at 10 A g−1) while maintaining superior cycling stability (1955 mAh g−1after 500 cycles at 300 mA g−1), surpassing the performance of most Si‐ and P‐based anodes ever reported. The remarkable electrochemical performance is attributed to the sphalerite structure that allows fast ion and electron transport and the reversible Li‐storage mechanism involving intercalation and conversion reactions. Moreover, the cation‐disordered sphalerite structure is flexible to ionic substitutions, allowing extension to a family of Zn(Cu)Si2+
xP3solid solution anodes ( x= 0, 2, 5, 10) with large capacity, high initial Coulombic efficiency, and tunable working potentials, representing attractive anode candidates for next‐generation, high‐performance, and low‐cost Li‐ion batteries.
Pre-lithiation is the most effective method to overcome the initial capacity loss of high-capacity electrodes and has the potential to be used in beyond-conventional lithium-ion batteries. In this article we focus on two types of pre-lithiation: the first type can be applied to batteries in which the cathode has been fully lithiated but the anode has a large initial capacity loss, such as batteries made with lithium metal oxide cathode and silicon-carbon anode. The second type can be applied to batteries in which both electrodes are initially lithium-free and suffer a loss of lithium during the initial cycles, such as batteries made with sulfurized-polyacrylonitrile cathode and silicon-carbon anode. We describe the pre-lithiation procedures and electrode potential profiles during pre-lithiation corresponding to different pre-lithiation sources for both types of pre-lithiation. We also derive formulas for the theoretical specific energy and energy density that are based entirely on measurable parameters such as specific capacities, porosities, mass densities of two electrodes and extra lithium source, Coulombic efficiencies of electrodes, and the voltage of the cell. These formulas can be applied to different pre-lithiation sources to predict the specific energy of conventional and beyond-conventional lithium-ion batteries as a function of the type of pre-lithiation.more » « less