Enhancement of the Rate Capability of LiFePO4 by a New Highly Graphitic Carbon-Coating Method

LFP via Nanoscale Surface Reforming with a Tiny Minimal Amount of Conductivity-Enhancing Material

LiFePO4 (LFP) typically requires a conductive additive to improve its low ion and electron conductivity. In this study, we achieved significant enhancements in Li+ and electron mobility by applying a minimal amount of conductive material through a new coating process. The coin cell demonstrated an excellent capacity of 157.57 mA h g-1 at 0.1 C/25 °C, while the pouch cell exhibited excellent long-term cycling stability, maintaining 99.33% capacity after 150 cycles at 1 C/45 °C. Compared to pristine LFP, the rate capacities increased by 30%, reaching 130.9 mA h g-1 at 3 C. After 100 cycles, the RCT resistance value decreased by 10% compared to pristine. The uniform coating layer not only improved electronic conductivity but also enhanced the rate performance. DCIR testing of the pouch cell showed a 17.7% reduction in resistance values compared to that of pristine LFP with increasing cycles. This new coating method, using a very small amount of conductive material, forms a uniform coating layer that optimizes electrochemical performance while maintaining the economic benefits of the LFP cathode material.

Optimizing the Structure and Electrochemical Properties of Benzoquinone-Embedded COF via Heat Treatment for a High-Energy Organic Cathode

A benzoquinone-embedded aza-fused covalent organic framework (BQ COF) with the maximum loading of redox-active units per molecule was employed as a cathode for lithium-ion batteries (LIBs) to achieve high energy and power densities. The synthesis was optimized to obtain high crystallinity and improved electrochemical performance. Synthesis at moderate temperature followed by a solid-state reaction was found to be particularly useful for achieving good crystallinity and the activation of the COF. When used as a cathode for LIBs, very high discharge capacities of 513, 365, and 234 mAh g-1 were obtained at 0.1C, 1C, and 10C, respectively, showing a remarkable rate performance. More than 70% of the initial capacity was retained after 1000 cycles when the cathode was investigated for cyclic performance at 2.5C. We demonstrated that a straightforward heat treatment led to enhanced crystallinity, an optimized structure, and favorable morphology, resulting in enhanced electrode kinetics and an improved overall electrochemical behavior. A comparative study was conducted involving an aza-fused COF lacking carbonyl groups (TAB COF) and a small molecule containing phenazine and carbonyl (3BQ), providing useful insights into new material design. A full cell was assembled with graphite as the anode to assess the commercial feasibility of BQ COF, and a discharge capacity of 240 mAh g-1 was obtained at 0.5C. Furthermore, a pouch-type cell with a high discharge capacity and an excellent rate performance was assembled, demonstrating the practical applicability of our designed cathode. Considering the entire mass of the working electrode, a specific energy density of 492 Wh kg-1 and a power density of 492 W kg-1 were achieved at the high current density of 1C, which are comparable to those of commercially available cathodes. These results highlight the promise of organic electrode materials for next-generation lithium-ion batteries. Furthermore, this study provides a systematic approach for simultaneously designing organic materials with high power and energy densities.

A Layered Organic Cathode for High-Energy, Fast-Charging, and Long-Lasting Li-Ion Batteries

Eliminating the use of critical metals in cathode materials can accelerate global adoption of rechargeable lithium-ion batteries. Organic cathode materials, derived entirely from earth-abundant elements, are in principle ideal alternatives but have not yet challenged inorganic cathodes due to poor conductivity, low practical storage capacity, or poor cyclability. Here, we describe a layered organic electrode material whose high electrical conductivity, high storage capacity, and complete insolubility enable reversible intercalation of Li+ ions, allowing it to compete at the electrode level, in all relevant metrics, with inorganic-based lithium-ion battery cathodes. Our optimized cathode stores 306 mAh g-1cathode, delivers an energy density of 765 Wh kg-1cathode, higher than most cobalt-based cathodes, and can charge-discharge in as little as 6 min. These results demonstrate the operational competitiveness of sustainable organic electrode materials in practical batteries.

Construction of a Preoxidation and Cation Doping Regeneration Strategy to Improve Rate Performance Recycling Spent LiFePO4 Materials

Efficient recycling of spent lithium-ion batteries (LIBs) is significant for solving environmental problems and promoting resource conservation. Economical recycling of LiFePO4 (LFP) batteries is extremely challenging due to the inexpensive production of LFP. Herein, we report a preoxidation combine with cation doping regeneration strategy to regenerate spent LiFePO4 (SLFP) with severely deteriorated. The binder, conductive agent, and residual carbon in SLFP are effectively removed through preoxidation treatment, which lays the foundation for the uniform and stable regeneration of LFP. Mg2+ doping is adopted to promote the diffusion efficiency of lithium ions, reduces the charge-transfer impedance, and further improves the electrochemical performance of the regenerated LFP. The discharge capacity of SLFP with severe deterioration recovers successfully from 43.2 to 136.9 mA h g-1 at 0.5 C. Compared with traditional methods, this technology is simple, economical, and environment-friendly. It provided an efficient way for recycling SLFP materials.

Efficient Reduction of Selenite to Elemental Selenium by Liquid-Phase Catalytic Hydrogenation Using a Highly Stable Multiwalled Carbon Nanotube-Supported Pt Catalyst Coated by N-Doped Carbon

A stable catalyst, Pt/carbon nanotube (CNT) coated with N-doped carbon (Pt/CNT@CN), was designed to reduce selenite (Se(IV)) in water to elemental selenium by liquid-phase catalytic hydrogenation. Commercial Pt/C, pristine Pt/CNT, and carbon-coated Pt/CNT (Pt/CNT@C) were used for benchmarking. The Pt particles in Pt/CNT@CN were completely embedded beneath the coatings to minimize leaching and were not easily accessible to Se(IV). However, Schottky-Mott-type metal-carbon junctions that activate H2 were formed on the coated catalyst, facilitating effective reduction of Se(IV). The initial activity of Pt/CNT@CN (900.5 mg L-1 gcat-1 h-1) was two times higher than that of commercial Pt/C (448.6 mg L-1 gcat-1 h-1). The commercial Pt/C and uncoated Pt/CNT lost their initial activities during reuse and were almost inactive after 10 cycles due to significant Pt leaching (>90%) during the reaction and acid-washing regeneration processes. Pt/CNT@CN maintained 33% of the initial activity after the first cycle and stabilized over the following 9 cycles due to effective protection of Pt particles by carbon coatings. After 10 cycles, the activity of Pt/CNT@CN was over 20 times higher than that of Pt/C and uncoated Pt/CNT. Overall, catalytic hydrogenation using carbon-coated-supported Pt catalysts is an effective and promising approach to remove Se(IV) in water.

Controlled Hydrothermal/Solvothermal Synthesis of High-Performance LiFePO4 for Li-Ion Batteries

The sluggish Li-ion diffusivity in LiFePO₄ , a famous cathode material, relies heavily on the employment of a broad spectrum of modifications to accelerate the slow kinetics, including size and orientation control, coating with electron-conducting layer, aliovalent ion doping, and defect control. These strategies are generally implemented by employing the hydrothermal/solvothermal synthesis, as reflected by the hundreds of publications on hydrothermal/solvothermal synthesis in recent years. However, LiFePO₄ is far from the level of controllable preparation, due to the lack of the understanding of the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ . In this paper, the recent progress in controlled hydrothermal/solvothermal synthesis of LiFePO₄ is first summarized, before an insight into the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ is obtained. Thereafter, a review over surface decoration, lattice substitution, and defect control is provided. Moreover, new research directions and future trends are also discussed.

Clean Block Copolymer Microparticles from Supercritical CO2: Universal Templates for the Facile and Scalable Fabrication of Hierarchical Mesostructured Metal Oxides

Metal oxide microparticles with well-defined internal mesostructures are promising materials for a variety of different applications, but practical routes to such materials that allow the constituent structural length scales to be precisely tuned have thus far been difficult to realize. Herein, we describe a novel platform methodology that utilizes self-assembled block copolymer (BCP) microparticles synthesized by dispersion polymerization in supercritical CO₂ (scCO₂) as universal structure directing agents for both hydrolytic and nonhydrolytic sol-gel routes to metal oxides. Spherically structured poly(methyl methacrylate- block-4-vinylpyridine) (PMMA- b-P4VP) BCP microparticles are translated into a series of the corresponding organic/inorganic composites and pure inorganic derivatives with a high degree of fidelity for the metal oxides TiO₂ and LiFePO₄. The final products are comprised of particles close to 1 μm in size with a highly ordered internal morphology of interconnected spheres between 20-40 nm in size. Furthermore, our approach is readily scalable, enabling grams of pure or carbon-coated TiO₂ and LiFePO₄, respectively, to be fabricated in a facile two step route involving ambient temperature mixing and drying stages. Given that both length scales within these BCP microparticles can be controlled independently by minor variations in the reagent quantities used, the present general strategy could represent a milestone in the design and synthesis of hierarchical metal oxides with completely tunable dimensions.

Polyethylene oxide film coating enhances lithium cycling efficiency of an anode-free lithium-metal battery

The practical implementation of an anode-free lithium-metal battery with promising high capacity is hampered by dendrite formation and low coulombic efficiency. Most notably, these challenges stem from non-uniform lithium plating and unstable SEI layer formation on the bare copper electrode. Herein, we revealed the homogeneous deposition of lithium and effective suppression of dendrite formation using a copper electrode coated with a polyethylene oxide (PEO) film in an electrolyte comprising 1 M LiTFSI, DME/DOL (1/1, v/v) and 2 wt% LiNO3. More importantly, the PEO film coating promoted the formation of a thin and robust SEI layer film by hosting lithium and regulating the inevitable reaction of lithium with the electrolyte. The modified electrode exhibited stable cycling of lithium with an average coulombic efficiency of ∼100% over 200 cycles and low voltage hysteresis (∼30 mV) at a current density of 0.5 mA cm-2. Moreover, we tested the anode-free battery experimentally by integrating it with an LiFePO4 cathode into a full-cell configuration (Cu@PEO/LiFePO4). The new cell demonstrated stable cycling with an average coulombic efficiency of 98.6% and capacity retention of 30% in the 200th cycle at a rate of 0.2C. These impressive enhancements in cycle life and capacity retention result from the synergy of the PEO film coating, high electrode-electrolyte interface compatibility, stable polar oligomer formation from the reduction of 1,3-dioxolane and the generation of SEI-stabilizing nitrite and nitride upon lithium nitrate reduction. Our result opens up a new route to realize anode-free batteries by modifying the copper anode with PEO to achieve ever more demanding yet safe interfacial chemistry and control of dendrite formation.

Polymer-Templated LiFePO4/C Nanonetworks as High-Performance Cathode Materials for Lithium-Ion Batteries

Lithium iron phosphate (LFP) is currently one of the main cathode materials used in lithium-ion batteries due to its safety, relatively low cost, and exceptional cycle life. To overcome its poor ionic and electrical conductivities, LFP is often nanostructured, and its surface is coated with conductive carbon (LFP/C). Here, we demonstrate a sol-gel based synthesis procedure that utilizes a block copolymer (BCP) as a templating agent and a homopolymer as an additional carbon source. The high-molecular-weight BCP produces self-assembled aggregates with the precursor-sol on the 10 nm scale, stabilizing the LFP structure during crystallization at high temperatures. This results in a LFP nanonetwork consisting of interconnected ∼10 nm-sized particles covered by a uniform carbon coating that displays a high rate performance and an excellent cycle life. Our "one-pot" method is facile and scalable for use in established battery production methodologies.

Crystal growth kinetics, microstructure and electrochemical properties of LiFePO4/carbon nanocomposites fabricated using a chelating structure phosphorus source

LiFePO4/carbon (LFP/C) nanocomposites were fabricated using bis(hexamethylene triamine penta (methylene phosphonic acid)) (BHMTPMPA) as a new and environment-friendly phosphorus source. The activation energy of the fabricated LFP/C was first investigated in depth based on the theoretical Arrhenius equation and experimental results of the LFP/C composite particle size distribution to explore the grain growth dynamics of the LFP/C particles during the sintering process. The results indicate that the activation energy is lower than 3.82 kJ mol-1 when the sintering temperature is within the range of 600-800 °C, which suggests that the crystal growth kinetics of the LFP/C particles is diffusion-controlled. The diffusion-controlled mechanism results from the mutual effects of chelation with Fe2+ cations, in situ formation of carbon layers and high concentration of hard aggregates due to the use of an organic phosphorous source (BHMTPMPA). The diffusion-controlled mechanism of the LFP/C effectively reduces the LFP particle size and hinders the growth of anomalous crystals, which may further result in nanosized LFP particles and good electrochemical performances. SEM and TEM analyses show that the prepared LFP/C has a uniform particle size of about 300 nm, which further confirms the effects of the diffusion-controlled mechanism of the LFP/C particle crystal growth kinetics. Electrochemical tests also verify the significant influence of the diffusion-controlled mechanism. The electrical conductivity and Li-ion diffusion coefficient (D Li +) of the fabricated LFP/C nanocomposite are 1.56 × 10-1 S cm-1 and 6.24 × 10-11 cm2 s-1, respectively, due to the chelating structure of the phosphorus source. The fabricated LFP/C nanocomposite exhibits a high reversible capacity of 166.9 mA h g-1 at 0.2C rate, and presents an excellent rate capacity of 134.8 mA h g-1 at 10C.

Facile Synthesis of Carbon-Coated Spinel Li4Ti5O12/Rutile-TiO2 Composites as an Improved Anode Material in Full Lithium-Ion Batteries with LiFePO4@N-Doped Carbon Cathode

The spinel Li₄Ti₅O₁₂/rutile-TiO₂@carbon (LTO-RTO@C) composites were fabricated via a hydrothermal method combined with calcination treatment employing glucose as carbon source. The carbon coating layer and the in situ formed rutile-TiO₂ can effectively enhance the electric conductivity and provide quick Li⁺ diffusion pathways for Li₄Ti₅O₁₂. When used as an anode material for lithium-ion batteries, the rate capability and cycling stability of LTO-RTO@C composites were improved in comparison with those of pure Li₄Ti₅O₁₂ or Li₄Ti₅O₁₂/rutile-TiO₂. Moreover, the potential of approximately 1.8 V rechargeable full lithium-ion batteries has been achieved by utilizing an LTO-RTO@C anode and a LiFePO₄@N-doped carbon cathode.

Improved Electrochemical Performance of LiFePO4@N-Doped Carbon Nanocomposites Using Polybenzoxazine as Nitrogen and Carbon Sources

Polybenzoxazine is used as a novel carbon and nitrogen source for coating LiFePO₄ to obtain LiFePO₄@nitrogen-doped carbon (LFP@NC) nanocomposites. The nitrogen-doped graphene-like carbon that is in situ coated on nanometer-sized LiFePO₄ particles can effectively enhance the electrical conductivity and provide fast Li⁺ transport paths. When used as a cathode material for lithium-ion batteries, the LFP@NC nanocomposite (88.4 wt % of LiFePO₄) exhibits a favorable rate performance and stable cycling performance.

Reducing Li-diffusion pathways via “adherence” of ultra-small nanocrystals of LiFePO4 on few-layer nanoporous holey-graphene sheets for achieving high rate capability

A unique 3D configuration comprising ultra-small LFP particles “adhered” to few-layer reduced holey-graphene oxide sheets allows Li⁺-ions to traverse shorter non-tortuous pathways leading to excellent battery performance.