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Low ionic conductivity is one of the main hurdles for the practical application of advanced all‐solid‐state lithium‐ion batteries. Protein‐based solid electrolytes are recently proposed and can potentially provide both high ionic conductivity and high mechanical properties due to the decoupled ion transport mechanism. In this work, the effects of lithium salts and protein structures on the performance of protein‐based electrolytes through both ab initio density functional theory calculations and experiments are systematically investigated. The results show that the anions can be strongly locked by the charged amino acids, thus providing intermediate hopping sites for lithium‐ion, reducing energy barrier for lithium‐ion transport, and then enhancing the ionic conductivity. These calculations also demonstrate that need to be locked at appropriate positions by properly controlling the protein structures in order to provide bridging effects and facilitate lithium‐ion transport. The findings are consistent with the experimental observations and can provide guidance for design and optimization of protein‐based solid electrolytes.

 

Structural and compositional diversities of proteins generate a number of functions for fabricating novel and advanced materials. Recent progress in protein engineering endows flexible approaches and new functionalities, which makes the fabricated materials potentially applicable in a broad spectrum of fields. Such engineering strategies by applying proteins alone or together with other molecules derive numerous functional materials such as patterned nanometal materials/nanometallic compounds, well‐designed nanocomposites, etc. Advantages in materials’ tunability, property improvement (e.g., electronic and mechanical properties, etc.), functionalities, and biocompatibility have been demonstrated, thus providing alternatives to existing materials via conventional methods. This review summarizes and discusses the strategies of fabricating functional materials using proteins as the critical contributors. Benefiting from their versatility, proteins find their roles in engineering functional materials via acting as structure‐control agents, reaction agents, and battery components, which are emphasized in this review. The strategies of each group of functions are specifically detailed. Properties of protein‐engineered functional materials and their potential applications in the fields of microelectronics, energy storage and conversion, sensor devices, etc. are also reviewed.

 

Fe2O3 is an appealing anode material due to its high specific capacity (1007 mAh g− 1), low cost, natural abundance, and nontoxicity. However, its unstable structure during cycling processes has hindered its potential. In this study, we present a “green” synthesis method to fabricate stable porous Fe2O3 encapsulated in a buffering hollow structure (p-Fe2O3@h-TiO2) as an effective anode material for Li-ion batteries. The synthesis process only involves glucose as an “etching” agent, without the need for organic solvents or difficult-to-control environments. Characterizations of the nanostructures, chemical compositions, crystallizations, and thermal behaviors for the intermediate/final products confirm the formation of p-Fe2O3@h-TiO2. The synthesized Fe2O3 anode material effectively accommodates volume change, decreases pulverization, and alleviates agglomeration, leading to a high capacity that is over eleven times greater than that of the as-received commercial Fe2O3 after a long cycling process. This work provides an attractive, “green” and efficient method to convert commercially abundant resources like Fe2O3 into effective electrode materials for energy storage systems. 

Electrochemical energy storage devices (EESDs) are critical technologies in modern economy, covering numerous fields such as portable electronics, electric vehicles, etc. The expanding market of EESDs demands for extra requirements such as safety, environmental friendliness and low cost, in addition to increasingly enhanced electrochemical properties. Natural proteins are abundant, versatile bio-macromolecules involving tremendous amount of amino acids/functional groups/heteroatoms, which greatly benefit sustainable technologies for advancing performances of EESDs. Recent years, significant research on utilizing natural proteins including plant/animal proteins to fabricate active materials for enhancing performance of EESDs has been well reported. Therefore, it is important to comprehensively summarize the progress and achievements, analyze the advantages/challenges, and predict the prospective for future protein-based strategies toward high performance EESDs, which are the contents of this review. The protein-derived active materials include activated carbons, silicon, sulfur, metal alloys, transitional metal compounds, and nonprecious metal catalysts. The resulting EESDs are associated with Li-/Na-/K-ion batteries, metal–air batteries, and redox flow batteries, as well as supercapacitors. The contributions of proteins to stabilizing/protecting electrodes, and thus enhancing performance of EESDs are specifically emphasized. Furthermore, studies on genetical engineering of proteins for directing self-assembly of active material nanoparticles are introduced. 

With plenty of charges and rich functional groups, bovine serum albumin (BSA) protein provides effective transport for multiple metallic ions inside blood vessels. Inspired by the unique ionic transport function, we develop a BSA protein coating to stabilize Li anode, regulate Li+ transport, and resolve the Li dendrite growth for Li metal batteries (LMBs). The experimental and simulation studies demonstrate that the coating has strong interactions with Li metal, increases the wetting with electrolyte, reduces the electrolyte/Li side reactions, and significantly suppresses the Li dendrite formation. As a result, the BSA coating exhibits excellent stability in the electrolyte and improves the performance of Li|Cu and Li|Li cells as well as the LiFePO4|Li batteries. This work reveals that LMBs can benefit from the biological function of BSA, i.e., special transport capability of metallic ions, and lays an important foundation in design of protein-based materials for effectively enhancing the electrochemical performance of energy storage systems. 

Despite numerous reported lithium metal batteries (LMBs) with excellent cycling performance achieved in labs, transferring the high performing LMBs from lab-scale to industrial-production remains challenging. Therefore, via imitating the stand-still process in battery production, a conventional but important procedure, to investigate the formation and evolution of a solid electrolyte interface (SEI) is particularly important for LMBs. Our previous studies indicate that zein (corn protein)-modified carbonate-ester electrolyte (the most commercialized) effectively improves the performance of LMBs through guiding Li- ions and repairing cracked SEI. Herein, we investigate the formation and evolution of the protein-modified SEIs on Li anodes by imitating the stand-still temperature and duration. A simulation study on the protein denaturation in the electrolyte under different temperatures demonstrates a highly unfolded configuration at elevated temperatures. The experiments show that this heat-treated-zein (H-zein) modified SEI forms quickly and becomes stable after a stand-still process of less than 100 min. Moreover, the H-zein SEI exhibits excellent wetting behavior with the electrolyte due to the highly unfolded protein structures with more functional groups exposed. The Li|Li cell with the H-zein SEI achieves prolonged cycling performance (>360 h vs.
260 h of the cell with the untreated-zein (U-zein) modified SEI). The LiFePO4|Li cell with the H-zein SEI shows much stable long-term cycling performance of capacity retention (70% vs. 42% of the cell with U-zein SEI) after 200 cycles. This study confirms that the appropriately treated protein is able to effectively improve the performance of LMBs, and will inspire future studies for the production process of LMBs toward their commercialization. 

Suffering from critical instability of lithium (Li) anode, the most commercial electrolytes, carbonate-ester electrolytes, have been restrictedly used in high-energy Li metal batteries (LMBs) despite of their broad implementation in lithium-ion batteries. Here, abundant, natural corn protein, zein, is exploited as a novel additive to stabilize Li anode and effectively prolong the cycling life of LMBs based on carbonate-ester electrolyte. It is discovered that the denatured zein is involved in the formation of solid electrolyte interphase (SEI), guides Li+ deposition and repairs the cracked SEI. In specific, the zein-rich SEI benefits the anion immobilization, enabling uniform Li+ deposition to diminish dendrite growth; the preferential zein-Li reaction effectively repairs the cracked SEI, protecting Li from parasite reactions. The resulting symmetrical Li cell exhibits a prolonged cycling life to over 350 h from <200 h for pristine cell at 1 mA cm􀀀 2 with a capacity of 1 mAh cm^ 2. Paired with LiFePO4 cathode, zein additive markedly improves the electrochemical performance including a higher capacity of 130.1 mAh g^ 1 and a higher capacity retention of ~ 80 % after 200 cycles at 1 C. This study demonstrates a natural protein to be an effective additive for the most commercial electrolytes for advancing performance of LMBs. 

High-voltage lithium metal batteries (LMBs) are a promising high-energy density energy storage system. However, their practical implementations are impeded by short lifespan due to uncontrolled lithium dendrite growth, narrow electrochemical stability window, and safety concerns of liquid electrolytes. Here, a porous composite aerogel is reported as the gel electrolyte (GE) matrix, made of metal–organic framework (MOF)@bacterial cellulose (BC), to enable long-life LMBs under high voltage. The effectiveness of suppressing dendrite growth is achieved by regulating ion deposition and facilitating ion conduction. Specifically, two hierarchical mesoporous Zr-based MOFs with different organic linkers, that is, UiO-66 and NH2-UiO-66, are embedded into BC aerogel skeletons. The results indicate that NH2-UiO-66 with anionphilic linkers is more effective in increasing the Li+ transference number; the intermolecular interactions between BC and NH2-UiO-66 markedly increase the electrochemical stability. The resulting GE shows high ionic conductivity (≈1 mS cm−1), high Li+ transference number (0.82), wide electrochemical stability window (4.9 V), and excellent thermal stability. Incorporating this GE in a symmetrical Li cell successfully prolongs the cycle life to 1200 h. Paired with the Ni-rich LiNiCoAlO2 (Ni: Co: Al = 8.15:1.5:0.35, NCA) cathode, the NH2-UiO-66@BC GE significantly improves the capacity, rate performance, and cycle stability, manifesting its feasibility to operate under high voltage.