Investigations on structural and electrochemical analysis of high-capacity and stable anodes for lithium-ion batteries.

Abstract

The advent of lithium-ion batteries (LIBs) in the 1990s marked a transformative milestone in energy storage, driven by reversible intercalation chemistry enabling lithium-ion transport between cathodes and anodes via an electrolyte. Renowned for their superior energy density, LIBs have become indispensable across diverse applications, from portable electronics to electric vehicles (EVs) and grid-scale storage systems. However, to meet the escalating demands of EVs and sustainable energy infrastructure, the development of cost-effective, safe anode materials with significantly higher energy density remains critical.<br /> <br /> Oxide-based anode materials have emerged as a promising frontier for next-generation LIBs due to their high theoretical capacities, structural tunability, and potential for multi-electron redox reactions. Transition metal oxides (TMOs) such as Fe₃O₄, SnO₂, Co₃O₄, and TiO₂ exhibit conversion and alloying mechanisms capable of achieving lithium storage capacities far exceeding that of conventional graphite anodes (~372 mA h g^-1). For instance, SnO₂ demonstrates a reversible capacity exceeding 780 mA h g^-1, attributed to lithium insertion/extraction and alloying with lithium to form LixSn phases, while Fe₃O₄ undergoes a conversion reaction that reduces the metal oxide to its metallic state with simultaneous Li₂O formation, enhancing energy storage potential.<br /> <br /> Despite their advantages, oxide-based anodes face significant challenges, including substantial volumetric expansion during cycling (up to 300%), which can lead to electrode pulverization and rapid capacity degradation, as well as intrinsically low electrical conductivity that limits rate capability. Addressing these issues has necessitated advancements in material engineering, including nanostructuring, doping, and the integration of oxide materials with conductive carbonaceous frameworks such as graphene. These approaches enhance structural stability, improve conductivity, and mitigate degradation, enabling better ion/electron transport and electrochemical performance. Innovative strategies such as the synthesis of one-dimensional (1D) and two-dimensional (2D) nanostructures have further enhanced the performance of oxide-based anodes by increasing surface area, reducing ion diffusion pathways, and maintaining electrode integrity during cycling. Electrolyte engineering and composite formation with carbon materials also contribute to improved initial Coulombic efficiency and long-term stability. Oxide-based anodes represent a pivotal research direction for advancing LIB technology, offering a pathway to meet the increasing energy density requirements of portable electronics, EVs, and grid-scale energy systems. A comprehensive understanding of their reaction mechanisms, coupled with continued innovations in material design and synthesis, will be instrumental in overcoming current limitations and achieving their successful integration into commercial battery technologies.<br /> <br /> Graphite, with a theoretical capacity of 372 mA h g^-1, has been widely used as the anode material in commercial lithium-ion batteries (LIBs). Its flat voltage profile and low operating voltage, approximately 0 V versus Li⁺/Li, are advantageous for maximizing the energy density of full-cell batteries. However, significant challenges are associated with its use: the low electrode potential promotes the formation of lithium dendrites on the anode surface, raising critical safety concerns, it also facilitates the development of passivating solid-electrolyte interphase (SEI) layers, which result in reduced initial Coulombic efficiency and impaired rate capacity and the commonly used N-Methyl-2-pyrrolidone (NMP)-based solvent for graphite anodes poses severe environmental and health risks due to its toxicity.<br /> <br /> We systematically designed and evaluated three configurations to study the influence of binder type and electrolyte composition on the performance of BiFeO₃(BFO)-based anodes: (1) a PVDF binder combined with a conventional carbonate electrolyte (1 M LiPF₆ in EC-DMC); (2) a PVDF binder paired with a carbonate electrolyte containing 10% fluoroethylene carbonate (FEC) as an additive (1 M LiPF₆ in EC-DMC + 10% FEC); and (3) a sodium carboxymethyl cellulose (CMC) binder used alongside the FEC-modified carbonate electrolyte (1 M LiPF₆ in EC-DMC + 10% FEC).<br /> <br /> The configuration employing the CMC binder in conjunction with the FEC-containing electrolyte demonstrated superior electrochemical performance, emerging as the optimal choice for BFO-based anodes. This enhanced performance is attributed to the role of FEC in improving the stability and elasticity of the solid electrolyte interphase (SEI) formed at the BFO-lithium interface.<br /> <br /> Herein also to mitigate aforementioned issues, we explored an alternative approach using a sodium carboxymethyl cellulose (CMC) water-based binder combined with a carbonate electrolyte containing fluoroethylene carbonate (FEC) additives. Specifically, we investigated the combination of 1M LiPF₆/EC-DMC with 10% FEC on Bi₂O₃ anodes. Key findings include: The CMC binder (20%) with FEC additive (10%) demonstrated superior performance and proved to be the optimal choice for Bi₂O₃-based anodes. And the FEC additive enhanced the stability and elasticity of the SEI layer on the Bi₂O₃ anode, improving its compatibility with lithium.<br /> <br /> For the first time, we report on the integration of high-purity, commercially available ferroelectric SrTiO₃ (STO) with silicon nanopowder and multi-walled carbon nanotubes (CNTs) using a simple and scalable solid-state planetary ball-milling technique. The resulting STO@Si@CNT composite was systematically evaluated for its electrochemical performance in Li⁺ ion intercalation, revealing significant enhancements in battery performance. The CNT matrix effectively mitigates mechanical stress by transferring the volumetric expansion strain of Si to STO while maintaining the conductive pathways essential for Li⁺ ion transport. Meanwhile, STO nanoparticles generate a localized ferroelectric potential, induced through deformation during lithiation, which influences Li⁺ mobility. Furthermore, by optimizing a water-based sodium carboxymethyl cellulose (CMC) binder and utilizing a standard carbonate-based electrolyte (1M LiPF₆ in EC: DMC, 1:1 wt% with 10% FEC additive), the composite anode delivers an impressive specific capacity of ~1500 mA h g^-1, exceptional high-rate performance (~1400 mA h g^-1), and remarkable cycling stability exceeding 1000 cycles. These results highlight the critical role of STO in addressing the volumetric expansion challenges of silicon anodes while enhancing lithium-ion transport. This work underscores STO's untapped potential for advancing next-generation silicon-based anode technologies in lithium-ion batteries.<br /> <br /> We also investigated perovskite-based oxide nanoparticles, specifically barium titanate (BaTiO₃) (BTO) and strontium titanate (SrTiO₃) (STO), as innovative anode materials for lithium-ion batteries. These materials were evaluated using a straightforward carbonate-based electrolyte system enhanced with 10% fluoroethylene carbonate (FEC) [1M LiPF₆ (1:1 EC: DEC) + 10% FEC]. The STO and BTO electrodes demonstrated exceptional performance, delivering a specific capacity of approximately 80 mA h g^-1; at a safe and low iv average operating potential of ~0.6 V versus Li/Li⁺. Furthermore, they exhibited remarkable high-rate capability with a consistent capacity of ~80 mA h g^-1; and outstanding cycling stability, retaining performance over 500 cycles at a high current density of 100 mA g^-1;.These findings underscore the feasibility of perovskite-type materials as advanced anodes for lithium-ion batteries, highlighting their significant potential for lithium-ion storage.