LiFePO4 Research Articles

In Situ Inorganic/Organic Protective Layer on Carbon Paper as Advanced Current Collector for Robust Li Metal Anode.

Lithium (Li) metal is regarded as the most promising anode for next-generation batteries with high energy density. However, the uncontrolled dendrite growth and infinite volume expansion during cycling seriously hinder the application of Li metal batteries (LMBs). Herein, an inorganic/organic protective layer (labeled as BPH), composed of in situ formed inorganic constituents and PVDF-HFP, is designed on the 3D carbon paper (CP) surface by hot-dipping method. The BPH layer can effectively improve the mechanical strength and ionic conductivity of the SEI layer, which is beneficial to expedite the Li-ion transfer of the entire framework and achieve stable Li plating/stripping behavior. As a result, the modified 3D CP (BPH-CP) exhibits an ultrahigh average Coulombic efficiency (CE) of ≈99.7% over 400 cycles. Further, the Li||LiFePO4 (LFP) cell exhibits an extremely long-term cycle life of over 3000 cycles at 5 C. Importantly, the full cell with high mass loading LiFePO4 (20mgcm-2) or LiNi0.8Co0.1Mn0.1O2 (NCM, 16mgcm-2) cathode exhibits stable cycling for 100 or 150 cycles at 0.5 C with high-capacity retention of 86.5% or 82.0% even at extremely low N/P ratio of 0.88 or 0.94. believe that this work enlightens a simple and effective strategy for the application of high-energy-density and high-rate-C LMBs.

Cathode-Electrolyte Interphase Engineering toward Fast-Charging LiFePO4 Cathodes by Flash Carbon Coating.

Lithium iron phosphate (LiFePO4, LFP) batteries are widely used in electric vehicles and energy storage systems due to their excellent cycling stability, affordability and safety. However, the rate performance of LFP remains limited due to its low intrinsic electronic and ionic conductivities. In this work, an ex situ flash carbon coating method is developed to enhance the interfacial properties for fast charging. A continuous, amorphous carbon layer is achieved by rapidly decomposing the precursors and depositing carbon species in a confined space within 10 s. Simultaneously, different heteroatoms can be introduced into the surface carbon matrix, which regulates the irregular growth of cathode-electrolyte interphase (CEI) and selectively facilitates the inorganic region formation. The inorganic-rich, hybrid conductive CEI not only promotes electron and ion transport but also restricts parasitic side reactions. Consequently, LFP cathodes with fluorinated carbon coatings exhibited the highest capacity of 151 mAh g-1 at 0.2 C and 96mAhg-1 at 10 C, indicating their excellent rate capability over commercial LFP (58mAh g-1 at 10 C). This solvent-free, versatile surface modification is shown for other electrode materials, providing an efficient platform for electrode-electrolyte interphase engineering through a surface post-treatment.

Selective leaching of lithium from mixed spent lithium iron phosphate powder

In recent years, lithium iron phosphate (LFP) batteries have been widely used in the electric vehicle industry. The recycling of spent LFP will be propitious to conserving resources and alleviating the environmental risks it poses. In this study, a selective extraction method for lithium from spent LFP was proposed using nitric acid. Lithium leached into the liquid phase, while P and Fe remained in the leaching residue. Under the conditions of 120°C, HNO3/Li molar ratio of 2, and time of 2 h, the leaching efficiency of lithium reached 99.5 %, with a selectivity reaching 82.1 %. Initially, LFP was decomposed to liberate Li, Fe, and P in the liquid phase. Subsequently, ferrous ions were oxidized to trivalent, high-valent iron ions re-precipitated as FePO4·2 H2O. Thermodynamic calculations indicate that the temperature and pH value of the extraction system have significant influence on both the oxidation and reprecipitation steps. An imbalance of Fe/P ratio (<1) in the raw material hinders the selectivity of lithium extraction, and supplementing this portion of Fe can enhance the selectivity to over 90 %. Additionally, LiCO3 and anhydrous FePO4 were effectively regenerated from the leachate and residue. This study provides a novel approach for the recycling of spent LFP and probably contributes to the sustainability of the lithium ion battery industry.

Laser-Generated Au nanoparticles as lithophilic sites in self-supported film host for anode-free lithium metal battery

Anode-free lithium metal batteries (AFLMBs) are considered to have greater application potential than traditional LMBs because of their higher energy density and safety. Unfortunately, their poor cycling performances originated from the unsatisfactory reversibility of Li plating/stripping remains a big challenge. A rational designed host for lithium deposition is an effective solving strategy. Herein, pure Au nanoparticles (NPs) without any impurities are prepared by a liquid-phase laser irradiation technology to construct and develop a self-supported Au/reduced graphene oxide (Au/rGO) film as lithium deposition host for AFLMBs. The densely and uniformly distributed Au NPs provide abundant lithiophilic sites that significantly reduce the nucleation barrier of lithium. Attributed to the precise regulation of Au sites towards lithium nucleation/growth, dendrites-free anode and improved electrochemical performance are obtained by using the Au/rGO film host. It keeps stable for 30 min of lithiation at 6 mA cm−2 without dendrite formation. Additionally, the Li||Au/rGO half-cell shows an overpotential close to 0 mV and maintains a Coulombic efficiency exceeding 97 % after 500 cycles at 1 mA cm−2. Moreover, a symmetric Au/rGO-Li cell can operate for 700 h without short-circuit. When paired with LiFePO4 (LFP) to assemble a full battery, the Au/rGO-Li achieves 96 % capacity retention rate after 100 cycles. This work not only develops an efficient host for lithium, but also provides a unique strategy to the safety concerns associated with LMBs’ anodes.

Toxicity Assessment of Gas, Solid and Liquid Emissions from Li-Ion Cells of Different Chemistry Subjected to Thermal Abuse

Lithium-ion batteries (LIBs) are employed in a range of devices due to their high energy and power density. However, the increased power density of LIBs raises concerns regarding their safety when subjected to external abuse. The thermal behavior is influenced by a number of factors, i.e., the state of charge (SoC), the cell chemistry and the abuse conditions. In this study, three distinct cylindrical Li-ion cells, i.e., lithium nickel cobalt aluminum oxide (NCA), lithium titanate oxide (LTO), and lithium iron phosphate (LFP), were subjected to thermal abuse (heating rate of 5 °C/min) in an air flow reactor, with 100% SoC. Venting and thermal runaway (TR) were recorded in terms of temperature and pressure, while the emitted products (gas, solid, and liquid) were subjected to analysis by FT-IR and ICP-OES. The concentrations of the toxic gases (HF, CO) are significantly in excess of the Immediate Danger to Life or Health Limit (IDLH). Furthermore, it is observed that the solid particles are the result of electrode degradation (metallic nature), whereas the liquid aerosol is derived from the electrolyte solvent. It is therefore evident that in the event of a LIB fire, in order to enhance the safety of the emergency responders, it is necessary to use appropriate personal protective equipment (PPE) in order to minimize exposure to toxic substances, i.e., particles and aerosol.

Carbon and MXene Dual Confinement and Dense Structural Engineering Toward Construct High Performance Micron‐SiOx Anode for Li‐Ion Batteries

AbstractThe intrinsic low conductivity, low tap density, and huge volume expansion during lithium storage severely restrict the practicality of micron‐silicon suboxide (m‐SiOx). Here, a carbon and MXene dual confinement and dense structural engineering strategy is proposed to construct m‐SiOx composites (m‐SiOx@C/MXene) through in situ carbon coating and electrostatic self‐assembly process. This integrated structural achieves a conductivity of 157 S cm−1 for m‐SiOx@C/MXene, which is 7 and 2 orders of magnitude higher than m‐SiOx (5.3 × 10−5 S cm−1) and m‐SiOx@C (2.9 S cm−1), respectively. The tap density of m‐SiOx@C/MXene reaches 1.35 g cm−3, significantly greater than that of m‐SiOx (0.82 g cm−3) and m‐SiOx@C (0.75 g cm−3). The 29% volume expansion of m‐SiOx@C/MXene during lithium storage is much lower than the 228% and 162% of m‐SiOx and m‐SiOx@C. The synergistic effect of the above advantages enables m‐SiOx@C/MXene to exhibit excellent rate performance and cycle stability. When assembled into a full cell with the LiFePO4 (LFP) cathode, it features high capacity retention and energy density of 99.1% and 380 Wh kg−1 after 100 cycles at 0.2 C. This work provides new reference for the stable structural design of m‐SiOx or other materials with huge volume expansion during energy storage.

Pathway decisions for reuse and recycling of retired lithium-ion batteries considering economic and environmental functions

Reuse and recycling of retired electric vehicle (EV) batteries offer a sustainable waste management approach but face decision-making challenges. Based on the process-based life cycle assessment method, we present a strategy to optimize pathways of retired battery treatments economically and environmentally. The strategy is applied to various reuse scenarios with capacity configurations, including energy storage systems, communication base stations, and low-speed vehicles. Hydrometallurgical, pyrometallurgical, and direct recycling considering battery residual values are evaluated at the end-of-life stage. For the optimized pathway, lithium iron phosphate (LFP) batteries improve profits by 58% and reduce emissions by 18% compared to hydrometallurgical recycling without reuse. Lithium nickel manganese cobalt oxide (NMC) batteries boost profit by 19% and reduce emissions by 18%. Despite NMC batteries exhibiting higher immediate recycling returns, LFP batteries provide superior long-term benefits through reuse before recycling. Our strategy features an accessible evaluation framework for pinpointing optimal pathways of retired EV batteries.

High-surface area active boron nitride nanofiber rich in oxygen vacancies enhanced the interface stability of all-solid-state composite electrolytes

Solid electrolytes are the most promising candidate for replacing liquid electrolytes due to their safety and chemical stability advantages. However, a single inorganic or organic solid electrolyte cannot meet the requirements of commercial all-solid-state batteries (ASSBs), which motivates the composite polymer electrolyte (CPE). Herein, a CPE of boron nitride nanofiber (BNNF) with a high specific surface area, rich pore structure, and poly (ethylene oxide) (PEO) are reported. Anions strongly adsorb on the surface of BNNF through electrostatic interactions based on oxygen vacancies, promoting the dissociation of lithium salts at the two-phase interface. The three-dimensional (3D) BNNF network provides three advantages in the CPE, including (i) improving ionic conductivity through strong interaction between polymers and fillers, (ii) improving mechanical properties through weaving a robust skeleton, and (iii) improving stability through a rapid and uniform thermal dispersion pathway. Therefore, the CPE with BNNF delivers high ionic conduction of 4.21 × 10−4 S cm−1 at 60°C and excellent cycling stability (plating/stripping cycles for 2000 h with a low overpotential of ∼40 mV), which results in excellent electrochemical performance of LiFePO4 (LFP) full cell assembled with CPE-5BNNF-1300 (152.7 mAh g−1 after 200 cycles at 0.5 C, and 134.8 mAh g−1 at 2.0 C). Furthermore, when matched with high-voltage LiNi0.6Co0.2Mn0.2O2 (NCM622), it also exhibits an outstanding rate capacity of 120.4 mAh g−1 at 1.0 C. This work provides insight into the BNNF composite electrolyte and promotes its practical application for ASSBs.

Multifunctional quasi-solid state electrolytes based on “reverse” plant cell structure for high-performance lithium metal batteries

Quasi-solid state electrolytes (QSSEs) combine the benefits of both solid and liquid electrolytes, making them promising for high-performance lithium metal batteries (LMBs). However, developing QSSEs that achieve high ionic conductivity, a continuous electrode/electrolyte interface, and significant mechanical robustness remains challenging. Plant cell walls provide mechanical strength, while the cell membrane offers excellent material transport capabilities, making them effective models for quasi-solid electrolytes. However, using plant cells as a model can result in poor interface contacts due to the rigid components on the exterior. To address this, a “reverse” plant cell QSSE with a multifunctional bilayer architecture has been proposed. The outer layer acts as a functional reaction interface to enhance Li⁺ transmission, improve interfacial contact, and significantly reduce interfacial impedance. Meanwhile, the inner layer is designed to provide mechanical robustness and shorten ion transport distances. The QSSE inspired by “reverse” plant cells has an ionic conductivity of 4.26 × 10−3 S cm−1, a Li+ transference number (tLi+) of 0.91, and an electrochemical stability window (ESW) of 4.83 V. Li−LiFePO4 (LFP) full cells based on the “reverse” plant cell QSSE can maintain a cycling capacity of 137 mAh g−1 after 500 cycles at 1 C, with 95 % retention.

Approach towards the Purification Process of FePO4 Recovered from Waste Lithium-Ion Batteries

The rapid development of new energy vehicles and Lithium-Ion Batteries (LIBs) has significantly mitigated urban air pollution. However, the disposal of spent LIBs presents a considerable threat to the environment. Recycling these waste LIBs not only addresses the environmental issues but also compensates for resource shortages and generates substantial economic benefits. Current recycling processes primarily focus on the extraction of valuable metals, often overlooking the treatment of residual waste post-extraction. This project targets the iron phosphate (FePO4) derived from waste lithium iron phosphate (LFP) battery materials, proposing a direct acid leaching purification process to obtain high-purity iron phosphate. This purified iron phosphate can then be used for the preparation of new LFP battery materials, aiming to establish a complete regeneration cycle that recovers lithium carbonate and iron phosphate from waste LFP materials for the production of LFP. The study investigates process parameters such as acid types and concentrations, leaching time, and the number of leaching cycles. The results demonstrate that, after purification, the levels of impurity metals decrease while the iron content increases correspondingly. Under optimized experimental conditions, the dilute sulfuric acid leaching rates of Al, Cu, Ca, and Ni reached 36.0%, 51.4%, 89.5%, and 90.9%, respectively. Furthermore, hydrothermal treatment in dilute phosphoric acid achieved leaching rates of 87.9%, 85.8%, 98.4%, and 99.1% for Al, Ca, Cu, and Ni, respectively. The microstructure characterization revealed significant changes in phase and grain morphology during the leaching process in dilute phosphoric acid, which are likely associated with the liberation of impurity atoms from the lattice. These findings indicate that acid leaching is highly effective in removing impurities from the iron phosphate recycled from waste LIBs.

Stress and Strain Characterization for Evaluating Mechanical Safety of Lithium-Ion Pouch Batteries under Static and Dynamic Loadings

The crashworthiness of electric vehicles depends on the response of lithium-ion cells to significant deformation and high strain rates. This study thoroughly explores the mechanical behavior due to damage of lithium-ion battery (LIB) cells, focusing on Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) types during both quasi-static indentation and dynamic high-velocity penetration tests. Employing a novel approach, a hemispherical indenter addresses gaps in stress–strain data for pouch cells, considering crucial factors like strain rate/load rate and battery cell type. In the finite element method (FEM) analysis, the mechanical response is investigated in two stages. First, a viscoplastic model is developed in Abaqus/Standard to predict the indentation test. Subsequently, a thermomechanical model is formulated to predict the high-speed-impact penetration test. Considering the high plastic strain rate of the LIB cell, adiabatic heating effects are incorporated into this model, eliminating heat conduction between elements. Addressing a notable discrepancy from prior research, this work explores the substantial reduction in force observed when transitioning from a single cell to a stack of two cells. The study aims to unveil the underlying reasons and provide insights into the mechanical behavior of stacked cells.

In-situ formed Li2O and an artificial protective layer on copper current collectors to enhance the cycling stability of lithium metal anode batteries

In this study, we present a facile one-step method for the thermal treatment of commercial Cu foils, leading to the growth of Cu2O and CuO nanoparticles in an air atmosphere, resulting in the coating of an artificial protective layer on the copper foil surface. The as-prepared CuO/Cu2O nanoparticles exhibit a spherical morphology, providing ample active sites to improve uniform lithium plating and cyclic stability by building a highly stable In-situ Li2O-rich solid-electrolyte interphase (ISEI). The artificial solid-electrolyte interphase (ASEI) protective layer contains graphene oxide (GO) as a filler with PVDF-HFP and lithium Nafion polymers, enhances Li+ ion migration, which reduces volume expansion and stabilizes the interface, preventing unwanted side reactions between active lithium and electrolytes by facilitating controlled lithium deposition underneath. For integration into an anode-less full cell based on a 2032-type coin cell, alongside a lithium iron phosphate (LFP) cathode, the ISEI oxide layer was grown on a Cu foil electrode (denoted as Cu-30) via a thermal treatment at 320 °C in air for 30 min and coated ASEI (denoted as GO@Cu-30). This cell demonstrated remarkable electrochemical performance. After 250 cycles at 0.5C, it exhibited an outstanding capacity retention of 93.12 % with 99.92 % CE, significantly surpassing the performance of a bare Cu foil, which showed a capacity retention of only 9.54 % with CE of 98.77 %. This work highlights the potential of a simple thermally treated Cu foil as a current collector to overcome the Anode-less lithium metal battery (ALMB) challenges associated with high-energy-density demand.

Mechanical methods for materials concentration of lithium iron phosphate (LFP) cells and product potential evaluation for recycling.

The production and sales of lithium-ion batteries (LIB) are rapidly expanding nowadays, causing a significant impact on the consumption of critical raw materials, such as lithium. Thus, developing and improving methods for the separation and recovery of materials from LIBs is necessary to ensure the supply of critical raw materials, as well as to meet the recycling targets set by some countries. This study evaluated and compared two mechanical routes to concentrate materials of LiFePO4 (LPF) cells. In addition, the economic, environmental, and scarcity risk potential of the products obtained through the best mechanical route were evaluated. The first route involved 6 grinding cycles in a knife mill, followed by particle size separation into 3 fractions. The second route involved a single grinding cycle (knife and hammer mill were tested), followed by particle size separation into 6 fractions. The second route showed more promise, with obtaining fractions rich in (1) iron, (2) aluminum and copper, and (3) cathode materials. Additionally, less operating time and energy consumption were necessary. The hammer mill offered a better separation for the iron and the cathodic materials (LiFePO4), while the knife mill proved to be more effective in concentrating the aluminum and copper. The product potential evaluation of the best route revealed that the priority fractions for recycling in economic and environmental assessment in LFP2 are 2 < n < 9.5mm (due Cu and Al) and n < 0.5mm (due Li). Considering the scarcity risk, priority should be assigned to the recycling of the fraction n < 0.5 due to lithium.

A Comprehensive Review of Functional Gel Polymer Electrolytes and Applications in Lithium-Ion Battery.

The rapid expansion of flexible and wearable electronics has necessitated a focus on ensuring their safety and operational reliability. Gel polymer electrolytes (GPEs) have become preferred alternatives to traditional liquid electrolytes, offering enhanced safety features and adaptability to the design requirements of flexible lithium-ion batteries. This review provides a comprehensive and critical overview of recent advancements in GPE technology, highlighting significant improvements in its physicochemical properties, which contribute to superior long-term cycling stability and high-rate capacity compared with traditional organic liquid electrolytes. Special attention is given to the development of smart GPEs endowed with advanced functionalities such as self-protection, thermotolerance, and self-healing properties, which further enhance battery safety and reliability. This review also critically examines the application of GPEs in high-energy cathode materials, including lithium nickel cobalt manganese (NCM), lithium nickel cobalt aluminum (NCA), and thermally stable lithium iron phosphate (LiFePO4). Despite the advancements, several challenges in GPE development remain unresolved, such as improving ionic conductivity at low temperatures and ensuring mechanical integrity and interfacial compatibility. This review concludes by outlining future research directions and the remaining technical hurdles, providing valuable insights to guide ongoing and future efforts in the field of GPEs for lithium-ion batteries, with a particular emphasis on applications in high-energy and thermally stable cathodes.

Improving Lithium-Ion Battery Performance: Nano Al2O3 Coatings on High-Mass Loading LiFePO4 Cathodes via Atomic Layer Deposition

Lithium iron phosphate (LiFePO4 or LFP) is a promising cathode material for lithium-ion batteries (LIBs), but side reactions between the electrolyte and the LFP electrode can degrade battery performance. This study introduces an innovative coating strategy, using atomic layer deposition (ALD) to apply a thin (5 nm and 10 nm) Al2O3 layer onto high-mass loading LFP electrodes. Galvanostatic charge–discharge cycling and electrochemical impedance spectroscopy (EIS) were used to assess the electrochemical performance of coated and uncoated LFP electrodes. The results show that Al2O3 coatings enhance the cycling performance at room temperature (RT) and 40 °C by suppressing side reactions and stabilizing the cathode–electrolyte interface (CEI). The coated LFP retained 67% of its capacity after 100 cycles at 1C and RT, compared to 57% for the uncoated sample. Post-mortem analyses, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), were conducted to investigate the mechanisms behind the improved performance. These analyses reveal that Al2O3 coatings are highly effective in reducing LFP electrode degradation during cycling, demonstrating the potential of ALD Al2O3 coatings to enhance the durability and performance of LFP electrodes in LIBs.

Nondestructive diagnosis technique for LiFePO4/graphite cells based on the internal resistance curve analysis

To explain the degradation mechanism of lithium-ion batteries, a nondestructive diagnosis technology to estimate the degree of degradation of the cell components is required. A technology that satisfies that requirement is widely used to analyze the open-circuit voltage (OCV) curve of a cell and estimate the positive-electrode and negative-electrode capacities and the amount of deactivated lithium. However, it has been difficult to estimate the degradation of electrodes composed of active materials with flat electrode potentials, such as lithium iron phosphate (LFP). The novel nondestructive method developed in this study can estimate the degradation state of battery components using LFP by analyzing the “internal resistance curve” of the battery. This method is used to determine the degradation parameters that explain both the measured OCV curve and the measured internal resistance curves of the cell by comparing the internal resistance curves of the cells with those of the positive and negative electrodes. The results of calendar life tests of lithium-ion batteries using LFP at elevated temperature and high voltage were analyzed by using this method, and the results of the analysis show that the degradation of the LFP positive electrode was progressing.

Characterization of Lithium-Ion Battery Fire Emissions—Part 1: Chemical Composition of Fine Particles (PM2.5)

Lithium-ion batteries (LIB) pose a safety risk due to their high specific energy density and toxic ingredients. Fire caused by LIB thermal runaway (TR) can be catastrophic within enclosed spaces where emission ventilation or occupant evacuation is challenging or impossible. The fine smoke particles (PM2.5) produced during a fire can deposit in deep parts of the lung and trigger various adverse health effects. This study characterizes the chemical composition of PM2.5 released from TR-driven combustion of cylindrical lithium iron phosphate (LFP) and pouch-style lithium cobalt oxide (LCO) LIB cells. Emissions from cell venting and flaming combustion were measured in real time and captured by filter assemblies for subsequent analyses of organic and elemental carbon (OC and EC), elements, and water-soluble ions. The most abundant PM2.5 constituents were OC, EC, phosphate (PO43−), and fluoride (F−), contributing 7–91%, 0.2–40%, 1–44%, and 0.7–3% to the PM2.5 mass, respectively. While OC was more abundant during cell venting, EC and PO43− were more abundant when flaming combustion occurred. These freshly emitted particles were acidic. Overall, particles from LFP tests had higher OM but lower EC compared to LCO tests, consistent with the higher thermal stability of LFP cells.

Enabling room temperature solid-state lithium batteries by blends of copolymers and ionic liquid electrolytes

High lithium-concentration phosphonium ionic liquids electrolytes have shown outstanding properties even overcoming ammonium derivatives in terms of viscosity and transport properties. Consequently, they have been also combined with fluorinated polymers, such as poly(vinylidene fluoride) (PVDF) or poly(ionic liquids), for solid-state batteries with satisfying performance at 50 °C. The aim of this work is to develop highly lithium conducting solid-state electrolyte (≥0.1 mS cm−1) at room temperature but maintaining solid-state properties. For this, polymer electrolytes based on ISOBAM alternating copolymer (isobutylene and maleic anhydride) and ionic liquid (P111i4FSI) were developed. The composition-dependent behavior of the solid electrolytes was studied in terms of electrochemical impedance spectroscopy (EIS), reaching σLi+ of 0.52 mS cm−1; differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) under different ionic liquid electrolyte loadings and salt concentration. The polymer electrolytes presented a solid-like behavior in the range of 25 to 90 °C with a storage modulus of 2.3·104 Pa. Finally, the best free-standing membrane electrolytes were tested and compared electrochemically in lithium symmetrical cells and lithium iron phosphate full cells exhibiting an excellent cycling at room temperature.

Concentrated precipitation electrolyte for reviving ultrathin lithium metal anode

Realizing high-performance lithium metal batteries requires the presence of a robust solid-electrolyte interphase (SEI) on the Li metal surface that forms before or during operation. Herein, high concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrite (LiNO3) are employed to create a novel concentrated precipitation electrolyte (CPE) and form an inorganic-rich SEI. It is found that an ultrathin Li metal anode (thickness of 25 μ m) in the CPE remains highly reversible over 300 cycles with an average Coulombic efficiency (CE) of 97.21 % in an asymmetric Cu|Li cell. The CPE enables superior stability to the LiFePO4 (LFP) cathode at a high mass loading of ∼15 mg cm−2 and reaches a capacity retention of 82.8 % after 100 cycles with an average CE of 99.94 %. This study elucidates the mechanism of LiTFSI and LiNO3 in enhancing the physiochemical properties of the SEI surface layer. It is believed that this design concept and the findings can be broadened to optimize SEIs via electrolyte engineering for practical Li metal batteries.

In-situ repair of failed LiFePO4 cathode using residual Li- and C-containing impurities from active material separation process

Effectively recovering spent lithium-ion batteries can reduce resource waste and environmental pollution. LiFePO4 (LFP) batteries have been widely used in new energy vehicles. The main reason for the performance degradation of LFP cathodes is the loss of Li, oxidation of Fe, and the destruction of crystal structure and surface carbon layer. Here, an in-situ repair strategy of high-temperature calcination, using impurities remaining in cathode blackmass (e.g., LiPF6, LiPO3, Fe2O3, acetylene black, binder, and electrolyte) as raw materials, was proposed. During the calcination process, the residual LiPF6 is converted into Li, acting as a lithium source to fill the vacancies. The residual binder and electrolyte are pyrolyzed into amorphous carbon and carbon nanotubes, which deposit on the LFP particles to repair the missing carbon layer and enhance the conductivity of the electrode material. The pyrolytic carbon and residual acetylene black can provide a reducing atmosphere, converting Fe3+ to Fe2+. Additionally, the residual LiPO3 and Fe2O3 impurities undergo recrystallization forming new LFP. The failed LFP was restored to the same level as commercial LFP by calcining at 750 °C for 3 h. This in-situ repair strategy reduces the input of raw materials, providing a valuable reference for large-scale recycling of lithium batteries.