Porous LiFePO4 Research Articles

Integrating Aperiodic 3D Porous Electrodes into 3D Batteries through Spray‐Deposited Polymer Electrolytes

AbstractDue to their exceptional energy and power densities, 3D micro‐batteries emerge as highly promising candidates for miniaturized power sources. However, fabricating a complete and uniform electrolyte/separator membrane to separate 3D electrodes in assembled 3D batteries remains a significant challenge. Herein, the study presents a straightforward approach to preparing 3D electrolyte membranes via a modified spray‐deposition method. This 3D electrolyte membrane effectively isolates the 3D porous LiFePO4 cathode from the Li anode with a ionic conductivity of 9.6 × 10−4 S cm−1, facilitating the creation of an integrated aperiodic 3D battery. The 3D battery exhibits a specific capacity of up to 8.8 mAh cm−2 (29.1 mWh cm−2) and attains a maximum power density of 12.7 mW cm−2. The characteristic time is 0.17 s for 3D battery while 0.73 s for traditional 2D batteries. The enhanced rate performance with thick electrode is primarily attributed to the reduced ionic diffusion pathway. These results represent the highest peak power and energy density among all reported aperiodic 3D batteries. The utilization of spray‐deposited electrolytes for 3D electrode separation promises significant advancements in developing 3D batteries and demonstrates great potentials for practical applications.

Lithium recovery from brine by PEG-modified porous LiFePO4/FePO4 electrode system

Lithium recovery from high Mg/Li brine through the electrochemical intercalation /de-intercalation technology has attracted great attention due to its good selectivity. To obtain higher equipment capacity, the LiFePO4/FePO4 electrodes with higher coating density are applied for lithium extraction. Unfortunately, it also brings a problem of slow diffusion of Li+ within the electrode, which limits the intercalation rate of lithium. To solve the problem of Li+ diffusion, a PEG-modified porous LiFePO4 electrode was prepared for lithium recovery. After modification, a “microcracks-microporosity” composite structure appears on the electrode, and the agglomeration of electrode materials reduces due to the dispersing effect of PEG. Therefore, the diffusion resistance of Li+ within the electrode decreases, and the electrode polarization reduces. Using the PEG-modified porous LiFePO4/FePO4 system to recover lithium, the Li+ intercalation rate reaches 4.45 g(Li)·m−2·h−1, while that of unmodified electrode is only 2.10 g(Li)·m−2·h−1. Besides, the intercalation of Na+ was significantly reduced from 0.28 to 0.07 of Na/Fe ratio in FePO4 cathode, which means better selectivity and circularity. Therefore, the application of PEG-modified porous electrode systems can efficiently recover lithium from brines.

An inexpensive preparation of unique nano-micro porous LiFePO4 cathode with excellent rate capability for lithium-ion batteries

The application of LiFePO4 cathode material in the field of power lithium-ion batteries is seriously hampered by its poor rate performance that is triggered by its inherent poor electrical conductivity and low ion diffusion coefficient. Herein, an inexpensive and facile preparation method is developed to fabricate a novel nano-micro porous structural LiFePO4 cathode using 30 nm carbon black and iron powder as direct raw materials. It is found that the added amount of carbon black is an important factor affecting the phase and morphology of the products. Optimizing the amount of carbon black, the LiFePO4 cathode with the unique nano-micro porous structure and high specific surface area could be obtained. Such unique porous architecture with a high specific surface area can accelerate lithium-ion diffusion during charge/discharge to promote its rate performance. Meanwhile, the residual graphitized carbon derived from carbon black can not only enlarge the surface pseudocapacitance under high C rates but also enhance its electronic conductivity. Benefit from the suitable pseudocapacitive behavior and high Li+ diffusion coefficient, the LFP-1.5 electrode exhibits a discharge specific capacity of 166.27 mAh/g at 0.1C and 124.95 mAh/g at 20C, indicating prominent discharge specific capacity and excellent high-rate charge/discharge capability.

A new strategy for the preparation of highly stable and high-capacity electrodes for green electrochemical extraction of lithium

Electrochemical method is a green lithium extraction method, but this technology is limited by the stability and capacity of the electrodes. Herein, a new strategy for the preparation of highly stable and high-capacity electrodes by in-situ polymerization and synchronous conversion was developed. It was found that when resorcinol and formaldehyde containing soluble Li, Fe, and P sources were polymerized in-situ and then carbonized at 700 °C, the Li, Fe, and P sources were successfully converted into LiFePO4 and uniformly dispersed in the carbon matrix. The carbon in the material formed a three-dimensional (3D) skeleton in the form of interconnected carbon spheres, and the LiFePO4 was grown in-situ on the 3D carbon skeleton. Since no polymer binder was used, the electrode exhibited high hydrophilicity and stability. Especially, the unique hierarchical porous structure of the electrode makes it have high electrochemical and lithium extraction performance. Even for Li+ with a concentration of only 100 mg·L−1, the intercalation capacity reached 5.13 mg·cm−3, which was nearly twice that of the electrode prepared by the traditional method. The equilibrium time for Li+ intercalation was only 45 min, and the dissolution loss rate of Fe3+ was no more than 0.23 % after 50 CV cycles. Based on these excellent properties, the porous carbon-supported LiFePO4 electrode prepared will has a broad application prospect for lithium recovery from aqueous solutions by the green electrochemical technology, and the preparation strategy developed in this work also provides a new prospective for the preparation of high-performance lithium extraction electrodes.

All 3D printing lithium metal batteries with hierarchically and conductively porous skeleton for ultrahigh areal energy density

The revival of Li metal batteries (LMBs) is revolutionizing current Li-ion battery technology. However, their practical applications are prevented by the bottlenecks like Li dendrite growth, low Coulombic efficiency, and mismatched cathodes with limited mass loading and sluggish kinetics, resulting in poor cyclability and low energy density. Here, 3D printed conductive Ti3C2Tx MXene scaffolds and porous LiFePO4 lattices are proposed to construct high-mass-loading LMBs with prolonged lifespan and high energy density. The exceptional lithiophilic feature of Ti3C2Tx regulates the uniform deposition of metallic Li, allowing the stable MXene scaffold to achieve an outstanding areal capacity of 30 mAh/cm2 at 30 mA/cm2 and ultralong cycle lifespan of 4800 h. The full battery is assembled by rationally matching this dendrite-free MXene based Li anode with a hierarchically conductive LiFePO4 framework at an ultrahigh mass loading of 171 mg/cm2. The as-assembled LMBs deliver unprecedented areal capacity of 25.3 mAh/cm2, record-high areal energy density of 81.6 mWh/cm2 and improved cycling stability of 500 cycles, breaking through the limitation of thick-film cathodes. Thereby, this work offers a viable strategy for the reasonable fabrication of advanced LMBs.

Mechanical properties of heterogeneous, porous LiFePO4 cathodes obtained using statistical nanoindentation and micromechanical simulations

Among cathode materials for Li-ion batteries, LiFePO4 (LFP) is one of the most relevant for commercial batteries in electric vehicle applications. In this work, the Young’s modulus and the indentation hardness of a commercial composite LiFePO4 cathode are measured using statistical nanoindentation. The influence of the surface roughness, a substrate effect, as well as particle size effect and densification on the measurement are discussed in detail. A focus lies on the analysis of the mechanical properties of the porous secondary LiFePO4 particles and the porosity dependence of the Young’s modulus. The measurements are validated via finite element simulations on reconstructed real microstructures. It was found that the mechanical properties of the secondary LiFePO4 particles are significantly lower than those of bulk LiFePO4 and a porosity dependence of the Young’s modulus was established. The experimental Young’s modulus of the porous LiFePO4 is 47.3GPa and the indentation hardness is 2.5GPa. For porous ceramics such as these, this results in an estimation of the yield strength of 1.5GPa.

Solution combustion synthesis of hierarchical porous LiFePO4 powders as cathode materials for lithium-ion batteries

Hierarchical porous LiFePO4 powders were prepared by solution combustion method using a mixture of cetyltrimethylammonium bromide (CTAB) and glycine as fuel. The effects of fuel contents on structural, microstructural, and electrochemical properties were studied by various characterization methods such as X-ray diffraction, infrared spectroscopy, scanning electron microscopy, N2 adsorption–desorption isotherms, and galvanostatic charge/discharge. Single phase LiFePO4 powders were crystallized by calcination at 700 °C. Phase evolution was depended on the nature and amount of intermediate phases. The hierarchical porous microstructure was obtained at an appropriate amount of mixed fuels. LiFePO4 powders showed the high specific discharge capacity of 110 mAh g−1 and high capacity retention of 98% at 1C which were attributed to their high crystallinity and high specific surface areas. The porous microstructure and small particle size were benefitted for the electrode kinetics, as indicated by electrochemical impedance spectroscopy.

Porous carbon-coated LiFePO4 nanocrystals prepared by in situ plasma-assisted pyrolysis as superior cathode materials for lithium ion batteries

The porous carbon-coated LiFePO4 (LFP) nanocrystals synthesized by in situ plasma-assisted pyrolysis are reported. The particle size of LFP nanoparticles is well controlled through the coating of polyaniline (PANI) on FePO4. The effect of PANI content in FePO4/PANI on the morphology and electrochemical performance of LiFePO4 particles is extensively investigated. Results show that the optimized amount of PANI in FePO4/PANI is 10.16% and the corresponding carbon content in activated porous carbon-coated LiFePO4 (LFP/AC-P4) is 9.27%. The primary particle size of LFP/AC-P4 is 20~50 nm which are wrapped and connected homogeneously and loosely by activated porous carbon. The LFP/AC-P4 composite delivers a capacity of 166.9 mAh g−1 at 0.2 C, which is much higher than carbon-encapsulated LiFePO4 nanocomposite (LFP/C) synthesized without the assistance of plasma pyrolysis (163.5 mAh g−1). Even at high rate of 5 C, a specific capacity of 128.4 mAh g−1 is achievable with no obvious capacity fading after 250 cycles.

Sputtered Porous Li-Fe-P-O Film Cathodes Prepared by Radio Frequency Sputtering for Li-ion Microbatteries

The increasing demands from micro-power applications call for the development of the electrode materials for Li-ion microbatteries using thin-film technology. Porous Olivine-type LiFePO4 (LFP) and NASICON-type Li3Fe2(PO4)3 have been successfully fabricated by radio frequency (RF) sputtering and post-annealing treatments of LFP thin films. The microstructures of the LFP films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the LFP films were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements. The deposited and annealed thin film electrodes were tested as cathodes for Li-ion microbatteries. It was found that the electrochemical performance of the deposited films depends strongly on the annealing temperature. The films annealed at 500 °C showed an operating voltage of the porous LFP film about 3.45 V vs. Li/Li+ with an areal capacity of 17.9 µAh cm−2 µm−1 at C/5 rate after 100 cycles. Porous NASICON-type Li3Fe2(PO4)3 obtained after annealing at 700 °C delivers the most stable capacity of 22.1 µAh cm−2 µm−1 over 100 cycles at C/5 rate, with an operating voltage of 2.8 V vs. Li/Li+. The post-annealing treatment of sputtered LFP at 700 °C showed a drastic increase in the electrochemical reactivity of the thin film cathodes vs. Li+, leading to areal capacity ~9 times higher than as-deposited film (~27 vs. ~3 µAh cm−2 µm−1) at C/10 rate.

Porous spherical LiFePO4·LiMnPO4·Li3V2(PO4)3@C@rGO composites as a high-rate and long-cycle cathode for lithium ion batteries

Abstract The porous spherical LiFePO4·LiMnPO4·Li3V2(PO4)3@C@rGO (Sample-G) composites are prepared via a spray drying process. The results show that the composites consist of orthorhombic olivine-type LiFe0.5Mn0.5PO4 and monoclinic Li3V2(PO4)3, which are evenly distributed. In particular, nanoparticles are embedded in graphene nanosheets, which are interconnected and stacked to form a porous sphere structure with an interior three-dimensional conductive network, resulting in the huge improvement on electrochemical performance and structural stability. Due to the increased Li+ diffusion coefficient, the composite possesses 98.6 and 82.9 mAh g−1 with capacities retention of 81.6% and 71.8% at 10 and 20C after 1000 cycles, respectively. The mutual cross-doping effect between LFP·LMP·LVP and a porous sphere structure with a 3D conductive network inside provides a practical method for improving the cycling and rate performance.

High-performance 3D directional porous LiFePO4/C materials synthesized by freeze casting

The directional freeze casting technology has received increasing attention as a processing method to fabricate the aligned porous materials due to the advantages of easy operation and free of byproduct. Here, we innovatively applied the directional freezing technology to synthesize the 3D directional porous LiFePO4 materials. The distinctive 3D directional porous structure of LiFePO4 is templated from the aligned ice crystals frozen under the temperature gradient in liquid nitrogen. When used as a positive electrode material in lithium-ion batteries, the directional porous LiFePO4/C composite exhibits high reversible capacities of 162 mA h g−1 at 0.1 C and 72 mA h g−1 at 10 C, and a high capacity retention of 93.3% after 800 cycles at 1 C. The 3D directional porous LiFePO4/C is promising for application in lithium-ion batteries and the synthesis strategy could be potentially extended to prepare other high performance electrode materials.

Electrochemical Oscillation in Li-Ion Batteries

Summary Two-phase reactions are prevalent in Li-ion batteries, whereas the underlying dynamics of phase separation in a real electrode still remain elusive, since numerous electrode particles constitute a formidably complex system for existing experimental techniques. Here we present an intriguing oscillatory phenomenon in the typical phase-separating electrode material Li 4 Ti 5 O 12 . During galvanostatic processes, the voltage oscillates due to the discrete nature of multi-particle phase-separating reactions, and the subtle oscillatory signals allow us to evaluate the fraction of actively phase-separating particles in real time. Through the analysis of oscillatory phenomena, we unveil the dependence of the active fraction on the depth of charge/discharge, cycling current, and working temperature, considerably deepening our understanding of the multi-particle phase-separation reaction. Moreover, it is the first time that electrochemical oscillations have been identified in rechargeable battery systems, opening up a new frontier for both theoretical and experimental researchers.

Thick Binder-Free Electrodes for Li-Ion Battery Fabricated Using Templating Approach and Spark Plasma Sintering Reveals High Areal Capacity

The templating approach is a powerful method for preparing porous electrodes with interconnected well-controlled pore sizes and morphologies. The optimization of the pore architecture design facilitates electrolyte penetration and provides a rapid diffusion path for lithium ion, which becomes even more crucial for thick porous electrodes. In the present work, we used NaCl micro-size particles as templating agent for the fabrication of 1 mm-thick porous LiFePO4 (LFP) and Li4Ti5O12 (LTO) composite electrodes using Spark Plasma Sintering (SPS) technique. These sintered binder-free electrodes are self-supported and present a large porosity (40%) with relatively uniform pores. The electrochemical performances of half and full batteries reveals a remarkable specific areal capacity (20 mAh/cm2), which is four times higher than those of 100 µm thick electrodes present in conventional tape-casted Li-ion batteries (5 mAh/cm2). 3D morphological study of both electrode types was carried out using µCT full field TXM technique to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results also demonstrate that the coupling between salt templating method and SPS technique turn out to be a promising way to reach the ultimate goal in the fabrication of thick electrodes with high energy density.

Development of Low Cost Printable All Solid State Lithium Microbatteries Incorporating Photo-Polymerized Ionogel As Electrolyte

With the advent of the microelectronics and the "smart-devices", the need for micro-sources of energy has risen. To meet these needs, a massive production of microbatteries is required in the next decades. Physical vapor deposition (PVD) is the process commonly used to fabricate thin film all solid state microbatteries. Commercially, LiCoO2 and lithium are used respectively as positive and negative electrodes. LiPON is commonly used as solid electrolyte because of its good ionic conductivity, good thermal and electrochemical stability and also for its good interfacial stability with the electrodes. However, the PVD process requires very expensive deposition machineries, with a high energy cost, which impact consequently the price and the development of the microbatteries. Processes involving liquid step, such as ink jet printing or screen printing propose cheaper machinery and much higher production rate. Moreover, these techniques are precise enough to deposit any pattern either by located drop jetting or by use of specific mask fitting the desired shape. In this communication, we will report our efforts to develop all or partially printed microbatteries. We have worked on replacing LiPON by another solid electrolyte which could be deposited by printing. Ionogels are solid electrolyte in which an ionic liquid (IL) is confined within a solid host network. Although solid like electrolytes, ionogels are formed from a liquid precursor, and are thus appropriate materials for the purpose. The liquid precursor is obtained by mixing the IL with organic, inorganic or hybrid monomers that are then polymerized to build in-situ the confining network. Furthermore, ionogels show good ionic conductivity and also good thermal and electrochemical stability, thus making them attractive solid electrolyte for lithium batteries. The time required to form a fully solidified material can vary depending on the nature of the confining network and the polymerization process. By using photo-polymerization, which is very fast, the manufacturing time is lesser than an hour, while for LiPON it can last more than ten hours. We have identified a promising printable photo-polymerizable ionogel composition with high ionic conductivity, pressure-sensitive-adhesive character, low interface resistance with lithium electrode, which allows stable cycling of LiFePO4/lithium cells, at least up to 1200 cycles at ambient temperature, C/5 rate and for surface capacities typical of microbatteries, e.g. 0.15 mAh cm-2. This ionogel is based on short molecular weight monomers with high content of polymerizable functionalities (triacrylate and diacrylate) and ILs composed of fluorinated sulfonylimide anions combined with alkylated pyrrolidinium cations [1]. We have evaluated the feasibility of making all or partially printed microbatteries with this printable solid electrolyte, not starting from the ground but trying to fit in an existing industrial process that uses PVD for manufacturing microbatteries. Microbatteries assembled from a dense PVD made LiCoO2 layer, a printed photo-polymerized ionogel, and a lithium layer exhibit good performance. However, the photo-polymerized ionogel showed very low compatibility when the lithium electrode is directly deposited by PVD on the top of it. Thus the lithium electrode must be mechanically assembled with the ionogel electrolyte. Microbatteries assembled from a printed porous LiFePO4 composite layer [2], a printed photo-polymerized ionogel, and lithium layer (an already made foil or evaporated layer and mechanically pressed on the ionogel surface) also demonstrated good performance. Acknowledgements Financial funding from the project TOURS 2015 n° O12590-418393 (Programme d’Investissement d’Avenir – FSN – AAP Nanoélectronique n°1) is acknowledged.

Graphene foam supported LiFePO4 nanosheets composite as advanced cathode for lithium ion batteries

Smart design of advanced cathode plays a significantly important role for the development of high-performance lithium ion batteries (LIBs). In this work, we synthesized a new kind of LiFePO4/Graphene foam (LFP/GF) integrated binder-free cathode via chemical vapor deposition (CVD) + hydrothermal method. The LFP is composed of interconnected LiFePO4 nanosheets with numerous nanopores of 50–500 nm. High porosity and good adhesion endow LiFePO4/GF film superior electrochemical properties with remarkable high-rate capacities, small polarization and stable cycling life. A high-rate capacity of 110 mAh g−1 at 24 C is obtained for the LiFePO4/GF composite. Moreover, a high capacity retention of 95% is acquired after 160 cycles. This enhancement is due to the unique integrated porous LiFePO4 nanosheets and good support of graphene foam providing fast ion/electron transfer. Our work displays a new insight in constructing integrated cathode for application in high-performance LIBs.

Thick Binder‐Free Electrodes for Li–Ion Battery Fabricated Using Templating Approach and Spark Plasma Sintering Reveals High Areal Capacity

AbstractThe templating approach is a powerful method for preparing porous electrodes with interconnected well‐controlled pore sizes and morphologies. The optimization of the pore architecture design facilitates electrolyte penetration and provides a rapid diffusion path for lithium ions, which becomes even more crucial for thick porous electrodes. Here, NaCl microsize particles are used as a templating agent for the fabrication of 1 mm thick porous LiFePO4 and Li4Ti5O12 composite electrodes using spark plasma sintering technique. These sintered binder‐free electrodes are self‐supported and present a large porosity (40%) with relatively uniform pores. The electrochemical performances of half and full batteries reveal a remarkable specific areal capacity (20 mA h cm−2), which is 4 times higher than those of 100 µm thick electrodes present in conventional tape‐casted Li–ion batteries (5 mA h cm−2). The 3D morphological study is carried out using full field transmission X‐ray microscopy in microcomputed tomography mode to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results also demonstrate that the coupling between the salt templating method and the spark plasma sintering technique turns out to be a promising way to fabricate thick electrodes with high energy density.

Carbon Fiber Reinforced LiFePO4-Based Three-Dimensional Bulk Electrodes with Metal-Current-Collector- and Binder-Free Design

Conductive hierarchically porous LiFePO4 blocks enhanced by carbon fiber were successfully obtained, which is benefited from nice sinter-activity of hydrothermal synthesized LiFePO4. In combination with hierarchically porous and carbon-fiber-reinforced electric-conductive topologies, metal-current-collector- and binder-free design, the as-prepared bulk electrodes present excellent rate capability and cycle life. Our proofof- concept study on LiFePO4-based bulk electrodes shows facile approach to improve energy density and lower cost of Li-ion batteries.

Self-Assembled Porous Micro-Spherical LiFePO4 Synthesized by Spray-Drying for Pouch-Typed Cell

Self-Assembled porous micro-spherical LiFePO4 have been successfully obtained through spray drying route. The prepared LiFePO4 is higher tap of 1.4 g cm–3 thank to its self-assembled porous structure. The studies of electrochemical performances were conducted at full cell level. The results show that the assembled pouch-typed full-cells with as-obtained LiFePO4 are of excellent rate capability and cycle life. As a result, the as-prepared LiFePO4 cathode material with self-assembled porous structure is capable of large-scale applications.

Fabrication of Porous Electrodes with a Picosecond Pulsed Laser and Improvement of the Rate Performance of a Porous Graphite Anode and LiFePO4 Cathode

To improve the rate performance of graphite anodes and lithium iron phosphate (LiFePO4) cathodes, micrometer-sized through-holes were formed on the electrode surface with a picosecond pulsed laser. The through-holes with 20 mm diameters were uniformly arranged with an opening rate of 1%. Compared with that of non-porous electrodes, the discharge capacities of the porous anode and cathode electrodes did not degrade even at a high current density at a 10 C rate. The formation of through-holes on the electrodes provides a remarkable improvement in the rate performance by enhancing the ability of Li+ ions to reach the active material surfaces.

Controllable synthesis of porous LiFePO4 for tunable electrochemical Li-insertion performance

A templated freeze-drying method is developed to prepare the porous LiFePO4 materials with the controlled pore size and porosity, by conveniently adjusting the size and content of the template in the precursor solution. The morphology and structure of the porous LiFePO4 materials are characterized and the relavant electrochemical lithium-insertion performances are systematically studied. It’s found that the porous characteristics play a critical role in the lithium-ion intercalation processes and significantly affect the power capability of LiFePO4. The optimized porous LiFePO4 material presents remarkable specific capacity (167mAhg−1 at 0.1 C), rate capability (151mAhg−1 at 1 C and 110mAhg−1 at 10 C) and cycling stability (99.3% retention after 300 cycles at 1 C). These findings demonstrate that the electrochemical performance of the electrode material can be purposely tuned and remarkably improved by the rational design and introduction of the suitable pores, which open up new strategies for the synthesis of advanced porous materials for the lithium-ion power battery applications.