Surface Modification of the LiFePO4 Cathode for the Aqueous Rechargeable Lithium Ion Battery

The Development and Prospect of Stable Polyanion Compound Cathodes in LIBs and Promising Complementers

Cathode materials are usually the key to determining battery capacity, suitable cathode materials are an important prerequisite to meet the needs of large-scale energy storage systems in the future. Polyanionic compounds have significant advantages in metal ion storage, such as high operating voltage, excellent structural stability, safety, low cost, and environmental friendliness, and can be excellent cathode options for rechargeable metal-ion batteries. Although some polyanionic compounds have been commercialized, there are still some shortcomings in electronic conductivity, reversible specific capacity, and rate performance, which obviously limits the development of polyanionic compound cathodes in large-scale energy storage systems. Up to now, many strategies including structural design, ion doping, surface coating, and electrolyte optimization have been explored to improve the above defects. Based on the above contents, this paper briefly reviews the research progress and optimization strategies of typical polyanionic compound cathodes in the fields of lithium-ion batteries (LIBs) and other promising metal ion batteries (sodium ion batteries (SIBs), potassium ion batteries (PIBs), magnesium ion batteries (MIBs), calcium ion batteries (CIBs), zinc ion batteries (ZIBs), aluminum ion batteries (AIBs), etc.), aiming to provide a valuable reference for accelerating the commercial application of polyanionic compound cathodes in rechargeable battery systems.

Interfacial Chemistry in Aqueous Lithium-Ion Batteries: A Case Study of V2O5 in Dilute Aqueous Electrolytes

Aqueous lithium-ion batteries (ALIBs) are promising for large-scale energy storage systems because of the cost-effective, intrinsically safe, and environmentally friendly properties of aqueous electrolytes. Practical application is however impeded by interfacial side-reactions and the narrow electrochemical stability window (ESW) of aqueous electrolytes. Even though higher electrolyte salt concentrations (e.g., water-in-salt electrolyte) enhance performance by widening the ESW, the nature and extent of side-reaction processes are debated and more fundamental understanding thereof is needed. Herein, the interfacial chemistry of one of the most popular electrode materials, V2O5, for aqueous batteries is systematically explored by a unique set of operando analytical techniques. By monitoring electrode/electrolyte interphase deposition, electrolyte pH, and gas evolution, the highly dynamic formation/dissolution of V2O5/V2O4, Li2CO3 and LiF during dis-/charge is demonstrated and shown to be coupled with electrolyte decomposition and conductive carbon oxidation, regardless of electrolyte salt concentration. The study provides deeper understanding of interfacial chemistry of active materials under variable proton activity in aqueous electrolytes, hence guiding the design of more effective electrode/electrolyte interfaces for ALIBs and beyond.

Selective recovery of lithium from spent lithium iron phosphate batteries

The recovery of lithium from spent lithium iron phosphate (LiFePO4) batteries is of great significance to prevent resource depletion and environmental pollution. In this study, through active ingredient separation, selective leaching and stepwise chemical precipitation develop a new method for the selective recovery of lithium from spent LiFePO4 batteries by using sodium persulphate (Na2S2O8) to oxidize LiFePO4 to FePO4. The impact of various variables on the efficiency of lithium leaching was investigated. Moreover, a combination of thermodynamic analysis and characterization techniques such as X-ray diffraction and X-ray photoelectron spectroscopy was employed to elucidate the leaching mechanism. It was found that 98.65% of lithium could be selectively leached in just 35 minutes at 60°C with only 0.2 times excess of Na2S2O8. This high leaching efficiency can be attributed to the stability and lack of structural damage during the oxidation leaching process. The proposed process is economically viable and environmentally friendly, thus showing great potential for the large-scale recycling of spent LiFePO4 batteries.

Modification of mixed-nitrogen anions configuration for accelerating lithium ions transport in the LiFePO4 electrode

Olivine-type LiFePO4 (LFP) is considered a promising cathode material for lithium-ion batteries (LIBs) owing to its abundance, high specific capacity, and cycling performance. However, its poor electronic and ionic transportation properties degrade the high rate capability, which limits its use in high-energy-density LIBs for applications such as electric vehicles. Therefore, in this study, we propose a modification of the anion configuration through nitrogen substitution using ion implantation to improve electronic and ionic transport during lithiation/delithiation. We found that nitrogen substitution at the oxygen sites effectively improved the electrochemical properties through surface modification and charge-transfer kinetics. In particular, the increased amount of nitrogen substitution at the surface regions resulted in reduced ionic and electronic resistances. These modified characteristics led to a remarkable rate capability with a high capacity (128.2 mA h g-1 at 10C). We expect that these modified anion effects on the electrochemical properties can be effective in the design of cathode materials for LIBs.

Enhanced charge transport properties of an LFP/C/graphite composite as a cathode material for aqueous rechargeable lithium batteries

Electrodes that offer quick ion transport, a large surface area, and excellent electrical conductivity support high performance aqueous rechargeable lithium batteries. LiFePO4 (LFP) nanoparticles have been successfully coated with carbon by a chemical sol-gel route, and assembled on graphite by an ultrasonication method to acquire LFP/C/graphite. This LFP/C/graphite composite exhibits exceptional electrochemical performance at various current densities (1C to 20C). LFP/C/graphite delivers better capacity that is higher than that of LFP/C particles and high stability after 60 cycles at a current density of 1C for aqueous rechargeable lithium batteries as a cathode material. The graphite serves as a good volume buffer in improving the lithium performance of LFP/C/graphite during the charge/discharge process. The LFP/C/graphite composite shows high rate capability at 20C that returned to the initial capacity at 1C after 25 cycles with coulombic efficiency of 97%. Therefore, this effort presents a super low-cost route to fabricate high performance cathode materials in aqueous rechargeable lithium batteries and other energy storage appliances.

Charge Carriers for Aqueous Dual-Ion Batteries

Environmental and safety concerns of energy storage systems call for application of aqueous battery systems which have advantages of low cost, environmental benignity, safety, and easy assembling. Among the aqueous battery systems, aqueous dual-ion batteries (ADIBs) provide high possibility for achieving excellent battery performance. Compared with the "rocking chair" batteries with only one type of carrier involved in the charging and discharging, ADIBs with both cations and anions as charge carriers possess diverse selections of electrodes and electrolytes. Charge carriers are the basis of the configuration of ADIBs. In this Review, cations and anions that could be applied in ADIBs are demonstrated with corresponding electrode materials and favorable electrolytes. Some insertion mechanisms are emphasized to provide insights for the possibilities to enhance the practical performances of ADIBs.

Electrolytes with Micelle-Assisted Formation of Directional Ion Transport Channels for Aqueous Rechargeable Batteries with Impressive Performance

Low-cost and ecofriendly electrolytes with suppressed water reactivity and raised ionic conductivity are desirable for aqueous rechargeable batteries because it is a dilemma to decrease the water reactivity and increase the ionic conductivity at the same time. In this paper, Li₂SO₄–Na₂SO₄–sodium dodecyl sulfate (LN-SDS)-based aqueous electrolytes are designed, where: (i) Na⁺ ions dissociated from SDS increase the charge carrier concentration, (ii) DS⁻/SO₄²⁻ anions and Li⁺/Na⁺ cations are capable of trapping water molecules through hydrogen bonding and/or hydration, resulting in a lowered melting point, (iii) Li⁺ ions reduce the Krafft temperature of LN-SDS, (iv) Na⁺ and SO₄²⁻ ions increase the low-temperature electrolyte ionic conductivity, and (v) SDS micelle clusters are orderly aggregated to form directional ion transport channels, enabling the formation of quasi-continuous ion flows without (r.t.) and with (≤0 °C) applying voltage. The screened LN-SDS is featured with suppressed water reactivity and high ionic conductivity at temperatures ranging from room temperature to −15 °C. Additionally, NaTi₂(PO₄)₃‖LiMn₂O₄ batteries operating with LN-SDS manifest impressive electrochemical performance at both room temperature and −15 °C, especially the cycling stability and low-temperature performance.

Recent Progress and Future Advances on Aqueous Monovalent-Ion Batteries towards Safe and High-Power Energy Storage

Aqueous monovalent-ion batteries have been rapidly developed recently as promising energy storage devices in large-scale energy storage systems owing to their fast charging capability and high power densities. In recent years, Prussian blue analogues, polyanion-type compounds, and layered oxides have been widely developed as cathodes for aqueous monovalent-ion batteries because of their low cost and high theoretical capacity. Furthermore, many design strategies have been proposed to expand their electrochemical stability window by reducing the amount of free water molecules and introducing an electrolyte addictive. This review highlights the advantages and drawbacks of cathode and anode materials, and summarizes the correlations between the various strategies and the electrochemical performance in terms of structural engineering, morphology control, elemental compositions, and interfacial design. Finally, this review can offer rational principles and potential future directions in the design of aqueous monovalent-ion batteries.

Development and Future Scope of Renewable Energy and Energy Storage Systems

 This review study attempts to summarize available energy storage systems in order to accelerate the adoption of renewable energy. Inefficient energy storage systems have been shown to function as a deterrent to the implementation of sustainable development. It is therefore critical to conduct a thorough examination of existing and soon-to-be-developed energy storage technologies. Various scholarly publications in the fields of energy storage systems and renewable energy have been reviewed and summarized. Data and themes have been further highlighted with the use of appropriate figures and tables. Case studies and examples of major projects have also been researched to gain a better understanding of the energy storage technologies evaluated. An insightful analysis of present energy storage technologies and other possible innovations have been discovered with the use of suitable literature review and illustrations. This report also emphasizes the critical necessity for an efficient storage system if renewable energy is to be widely adopted. 

LiFePO4 Battery Material for the Production of Lithium from Brines: Effect of Brine Composition and Benefits of Dilution

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.

Sustainable Battery Materials from Biomass

Sustainable sources of energy have been identified as a possible way out of today's oil dependency and are being rapidly developed. In contrast, storage of energy to a large extent still relies on heavy metals in batteries. Especially when built from biomass-derived organics, organic batteries are promising alternatives and pave the way towards truly sustainable energy storage. First described in 2008, research on biomass-derived electrodes has been taken up by a multitude of researchers worldwide. Nowadays, in principle, electrodes in batteries could be composed of all kinds of carbonized and noncarbonized biomass: On one hand, all kinds of (waste) biomass may be carbonized and used in anodes of lithium- or sodium-ion batteries, cathodes in metal-sulfur or metal-oxygen batteries, or as conductive additives. On the other hand, a plethora of biomolecules, such as quinones, flavins, or carboxylates, contain redox-active groups that can be used as redox-active components in electrodes with very little chemical modification. Biomass-based binders can replace toxic halogenated commercial binders to enable a truly sustainable future of energy storage devices. Besides the electrodes, electrolytes and separators may also be synthesized from biomass. In this Review, recent research progress in this rapidly emerging field is summarized with a focus on potentially fully biowaste-derived batteries.

Selective recovery of lithium and iron phosphate/carbon from spent lithium iron phosphate cathode material by anionic membrane slurry electrolysis

A simple, green and effective method, which combined lithium iron phosphate battery charging mechanism and slurry electrolysis process, is proposed for recycling spent lithium iron phosphate. Li and FePO₄ can be separation in anionic membrane slurry electrolysis without the addition of chemical reagent. The leaching efficiency of Li can reach to 98% and over 96% of Fe are recycled as FePO₄/C. Kinetics analysis indicates that the surface chemical reaction is the control step during the slurry electrolysis. Additionally, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Electrochemical Impedance Spectroscopy (EIS) characterization and thermodynamic analysis are employed to investigate the leaching mechanism. It is found that the spent LiFePO₄ is delithiated and oxidized to FePO₄ by the function of e^-, which is similar as the LiFePO₄ battery charging process. EIS analysis also verify the kinetics results, the charge transfer resistance controlled the leaching process. Finally, a novel process for recovery of spent LiFePO₄ is proposed. The recovered Li₂CO₃ and FePO₄/C can be used for resynthesize LiFePO₄, and the resynthesized LiFePO₄ exhibits reversible capacities of 143.6 mAh g^-1 at 1C and high current efficiency, stable cycle performances at 0.1 and 0.5C which meets the basic requirements for reuse.

Thermal conductivity of V2O5 nanowires and their contact thermal conductance

Vanadium pentoxide (V2O5)-based composites show outstanding performances as cathode materials in lithium-ion batteries. However, their inferior thermal conductivity restricts the heat dissipation through the cathode electrode. In this study, we measured the thermal conductivity of V2O5 nanowires using the thermal bridge method and found that their thermal conductivity is 3.84 ± 0.38 W m-1 K-1 at T = 300 K. The contact thermal resistance between two nanowires with the same size was measured to be up to 50%-80% of the total thermal resistance in the measured samples, indicating that their contact is the bottleneck for thermal dissipation.

Voltage issue of aqueous rechargeable metal-ion batteries

Over the past two decades, a series of aqueous rechargeable metal-ion batteries (ARMBs) have been developed, aiming at improving safety, environmental friendliness and cost-efficiency in fields of consumer electronics, electric vehicles and grid-scale energy storage. However, the notable gap between ARMBs and their organic counterparts in energy density directly hinders their practical applications, making it difficult to replace current widely-used organic lithium-ion batteries. Basically, this huge gap in energy density originates from cell voltage, as the narrow electrochemical stability window of aqueous electrolytes substantially confines the choice of electrode materials. This review highlights various ARMBs with focuses on their voltage characteristics and strategies that can effectively raise battery voltage. It begins with the discussion on the fundamental factor that limits the voltage of ARMBs, i.e., electrochemical stability window of aqueous electrolytes, which decides the maximum-allowed potential difference between cathode and anode. The following section introduces various ARMB systems and compares their voltage characteristics in midpoint voltage and plateau voltage, in relation to respective electrode materials. Subsequently, various strategies paving the way to high-voltage ARMBs are summarized, with corresponding advancements highlighted. The final section presents potential directions for further improvements and future perspectives of this thriving field.

Atomic-Scale Direct Identification of Surface Variations in Cathode Oxides for Aqueous and Nonaqueous Lithium-Ion Batteries

The electrochemical (de)intercalation reactions of lithium ions are initiated at the electrode surface in contact with an electrolyte solution. Therefore, substantial structural degradation, which shortens the cycle life of cells, is frequently observed at the surface of cathode particles, including lithium-metal intermixing, phase transitions, and dissolution of lithium and transition metals into the electrolyte. Furthermore, in contrast to the strict restriction of moisture in lithium-ion cells with nonaqueous organic electrolytes, electrode materials in aqueous-electrolyte cells are under much more reactive environments with water and oxygen, thereby leading to serious surface chemical reactions on the cathode particles. The present article presents key results regarding structural and composition variations at the surface of oxide-based cathodes in both high-performance nonaqueous and recently proposed aqueous lithium-ion batteries; in particular, focusing on direct atomic-scale observations preformed by means of scanning transmission electron microscopy. Precise identification of surface degradation at the atomic level is thus emphasized because it can provide significant insights into overcoming the limitations of current lithium-ion batteries.

High-Capacity and Long-Cycle Life Aqueous Rechargeable Lithium-Ion Battery with the FePO4 Anode

Aqueous lithium-ion batteries are emerging as strong candidates for a great variety of energy storage applications because of their low cost, high-rate capability, and high safety. Exciting progress has been made in the search for anode materials with high capacity, low toxicity, and high conductivity; yet, most of the anode materials, because of their low equilibrium voltages, facilitate hydrogen evolution. Here, we show the application of olivine FePO₄ and amorphous FePO₄·2H₂O as anode materials for aqueous lithium-ion batteries. Their capacities reached 163 and 82 mA h/g at a current rate of 0.2 C, respectively. The full cell with an amorphous FePO₄·2H₂O anode maintained 92% capacity after 500 cycles at a current rate of 0.2 C. The acidic aqueous electrolyte in the full cells prevented cathodic oxygen evolution, while the higher equilibrium voltage of FePO₄ avoided hydrogen evolution as well, making them highly stable. A combination of in situ X-ray diffraction analyses and computational studies revealed that olivine FePO₄ still has the biphase reaction in the aqueous electrolyte and that the intercalation pathways in FePO₄·2H₂O form a 2-D mesh. The low cost, high safety, and outstanding electrochemical performance make the full cells with olivine or amorphous hydrated FePO₄ anodes commercially viable configurations for aqueous lithium-ion batteries.

Piperidinium-based ionic liquid electrolyte with linear solvent and LiODFB for LiFePO4/Li cells at room and high temperature

Lithium difluoro(oxalato)borate (LiODFB) combines the advantages of the salts LiBOB and LiBF₄ when used in electrolytes for lithium ion cells.