Research Progress on Negative Electrodes for Practical Li‐Ion Batteries: Beyond Carbonaceous Anodes

Research activities related to the development of negative electrodes for construction of high‐performance Li‐ion batteries (LIBs) with conventional cathodes such as LiCoO₂, LiFePO₄, and LiMn₂O₄ are described. The anode materials are classified in to three main categories, insertion, conversion, and alloying type, based on their reactivity with Li. Although numerous materials have been proposed (i.e., for half‐cell assembly), few of them have reached commercial applications, apart from graphite, Li₄Ti₅O₁₂, Si, and Sn‐Co‐C. This clearly demonstrates that full‐cell studies are desperately needed rather than just characterizing materials in half‐cell assemblies. Additionally, the performance of such anodes in practical Li‐ion configurations (full‐cell) is much more important than merely proposing materials for LIBs. Irreversible capacity loss, huge volume variation, unstable solid electrolyte interface layer formation, and poor cycleability are the main issues for conversion and alloy type anodes. This review addresses how best to circumvent the mentioned issues during the construction of Li‐ion cells and the future prospects of such anodes are described in detail.     

Best Practices for Mitigating Irreversible Capacity Loss of Negative Electrodes in Li‐Ion Batteries

Development of high performance lithium‐ion (Li‐ion) power packs is a topic receiving significant attention in research today. Future development of the Li‐ion power packs relies on the development of high capacity and high rate anodes. More specifically, materials undergo either conversion or an alloying mechanism with Li. However, irreversible capacity loss (ICL) is one of the prime issues for this type of negative electrode. Traditional insertion‐type materials also experience ICL, but it is considered negligible. Therefore, eliminating ICL is crucial before the fabrication of practical Li‐ion cells with conventional cathodes such as LiFePO₄, LiMn₂O₄, etc. There are numerous methods for eliminating ICL such as pre‐treating the electrode, usage of stabilized Li metal powder, chemical and electrochemical lithiation, sacrificial salts for both anode and cathode, etc. The research strategies that have been explored are reviewed here in regards to the elimination of ICL from the high capacity anodes as described. Additionally, mitigating ICL observed from the carbonaceous anodes is discussed and compared.     

“Water‐in‐Salt” Electrolyte Makes Aqueous Sodium‐Ion Battery Safe,Green, and Long‐Lasting

Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium‐ion chemistry of practical energy density and cycle life. The sodium‐ion water‐in‐salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na⁺‐conducting solid‐electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na‐ion battery constructed on Na_0.66[Mn_0.66Ti_0.34]O₂ as cathode and NaTi₂(PO₄)₃ as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li‐ion and Na‐ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin.     

Nature‐Inspired Tri‐Pathway Design Enabling High‐Performance Flexible Li–O2 Batteries

Trees have an abundant network of channels for the multiphase transport of water, ions, and nutrients. Recent studies have revealed that multiphase transport of ions, oxygen (O₂) gas, and electrons also plays a fundamental role in lithium–oxygen (Li–O₂) batteries. The similarity in transport behavior of both systems is the inspiration for the development of Li–O₂ batteries from natural wood featuring noncompetitive and continuous individual pathways for ions, O₂, and electrons. Using a delignification treatment and a subsequent carbon nanotube/Ru nanoparticle coating process, one is able to convert a rigid and electrically insulating wood membrane into a flexible and electrically conductive material. The resulting cell walls are comprised of cellulose nanofibers with abundant nanopores, which are ideal for Li⁺ ion transport, whereas the unperturbed wood lumina act as a pathway for O₂ gas transport. The noncompetitive triple pathway design endows the wood‐based cathode with a low overpotential of 0.85 V at 100 mA g^?1, a record‐high areal capacity of 67.2 mAh cm^?2, a long cycling life of 220 cycles, and superior electrochemical and mechanical stability. The integration of such excellent electrochemical performance, outstanding mechanical flexibility, and renewable yet cost‐effective starting materials via a nature‐inspired design opens new opportunities for developing portable energy storage devices.     

Efficient Li‐Ion‐Conductive Layer for the Realization of Highly Stable High‐Voltage and High‐Capacity Lithium Metal Batteries

Recently, a consensus has been reached that using lithium metal as an anode in rechargeable Li‐ion batteries is the best way to obtain the high energy density necessary to power electronic devices. Challenges remain, however, with respect to controlling dendritic Li growth on these electrodes, enhancing compatibility with carbonate‐based electrolytes, and forming a stable solid–electrolyte interface layer. Herein, a groundbreaking solution to these challenges consisting in the preparation of a Li₂TiO₃ (LT) layer that can be used to cover Li electrodes via a simple and scalable fabrication method, is suggested. Not only does this LT layer impede direct contact between electrode and electrolyte, thus avoiding side reactions, but it assists and expedites Li‐ion flux in batteries, thus suppressing Li dendrite growth. Other effects of the LT layer on electrochemical performance are investigated by scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique analyses. Notably, LT layer‐incorporating Li cells comprising high‐capacity/voltage cathodes with reasonably high mass loading (LiNi_0.8Co_0.1Mn_0.1O₂, LiNi_0.5Mn_1.5O₄, and LiMn₂O₄) show highly stable cycling performance in a carbonate‐based electrolyte. Therefore, it is believed that the approach based on the LT layer can boost the realization of high energy density lithium metal batteries and next‐generation batteries.     

Recent Progress on Stability Enhancement for Cathode in Rechargeable Non‐Aqueous Lithium‐Oxygen Battery

The pressing demand on the electronic vehicles with long driving range on a single charge has necessitated the development of next‐generation high‐energy‐density batteries. Non‐aqueous Li‐O₂ batteries have received rapidly growing attention due to their higher theoretical energy densities compared to those of state‐of‐the‐art Li‐ion batteries.To make them practical for commercial applications, many critical issues must be overcome, including low round‐trip efficiency and poor cycling stability, which are intimately connected to the problems resulting from cathode degradation during cycling. Encouragingly, during the past years, much effort has been devoted to enhancing the stability of the cathode using a variety of strategies and these have effectively surmounted the challenges derived from cathode deteriorations,thus endowing Li‐O₂ batteries with significantly improved electrochemical performances. Here, a brief overview of the general development of Li‐O₂ battery is presented. Then, critical issues relevant to the cathode instability are discussed and remarkable achievements in enhancing the cathode stability are highlighted. Finally, perspectives towards the development of next generation highly stable cathode are also discussed.     

Iron‐Based Supercapacitor Electrodes: Advances and Challenges

Supercapacitors (SCs) have great promise as the state‐of‐the‐art power source in portable electronics and hybrid vehicles. The performance of SCs is largely determined by the properties of the electrode material, and numerous efforts have been devoted to the explorations of novel electrode materials. Recently, iron‐based materials, including Fe₂O₃, Fe₃O₄, FeOOH, FeO_x, CoFe₂O₄, and MnFe₂O₄, have received considerable attention as very promising electrode materials for SCs due to their high theoretical specific capacitances, natural abundance, low cost, and non‐toxicity. However, most of these Fe‐based SC electrodes suffer from poor conductivity and/or electrochemical instability, which seriously impede their implementation as high‐performance electrodes for SCs. To settle these issues, substantial efforts have been made in improving their conductivity and cycling stability, and great processes have been achieved. Here, recent research advances in the rational design and synthesis of diverse Fe‐based nanostructured electrodes and their capacitive performance for SCs are presented. Besides, challenges and prospects of Fe‐based materials as advanced negative electrodes for SCs are also discussed.     

Surface Engineering Strategies of Layered LiCoO2 Cathode Material to Realize High‐Energy and High‐Voltage Li‐Ion Cells

Battery industries and research groups are further investigating LiCoO₂ to unravel the capacity at high‐voltages (>4.3 vs Li). The research trends are towards the surface modification of the LiCoO₂ and stabilize it structurally and chemically. In this report, the recent progress in the surface‐coating materials i.e., single‐element, binary, and ternary hybrid‐materials etc. and their coating methods are illustrated. Further, the importance of evaluating the surface‐coated LiCoO₂ in the Li‐ion full‐cell is highlighted with our recent results. Mg,P‐coated LiCoO₂ full‐cells exhibit excellent thermal stability, high‐temperature cycle and room‐temperature rate capabilities with high energy‐density of ≈1.4 W h cc^?1 at 10 C and 4.35 V. Besides, pouch‐type full‐cells with high‐loading (18 mg cm^?2) electrodes of layered‐Li(Ni,Mn)O₂ ‐coated LiCoO₂ not only deliver prolonged cycle‐life at room and elevated‐temperatures but also high energy‐density of ≈2 W h cc^?1 after 100 cycles at 25 °C and 4.47 V (vs natural graphite). The post‐mortem analyses and experimental results suggest enhanced electrochemical performances are attributed to the mechanistic behaviour of hybrid surface‐coating layers that can mitigate undesirable side reactions and micro‐crack formations on the surface of LiCoO₂ at the adverse conditions. Hence, the surface‐engineering of electrode materials could be a viable path to achieve the high‐energy Li‐ion cells for future applications.     

Enhanced Cyclability of Lithium–Oxygen Batteries with Electrodes Protected by Surface Films Induced via In Situ Electrochemical Process

Although the rechargeable lithium–oxygen (Li–O₂) batteries have extremely high theoretical specific energy, the practical application of these batteries is still limited by the instability of their carbon‐based air‐electrode, Li metal anode, and electrodes, toward reduced oxygen species. Here a simple one‐step in situ electrochemical precharging strategy is demonstrated to generate thin protective films on both carbon nanotubes (CNTs), air‐electrodes and Li metal anodes simultaneously under an inert atmosphere. Li–O₂ cells after such pretreatment demonstrate significantly extended cycle life of 110 and 180 cycles under the capacity‐limited protocol of 1000 mA h g^?1 and 500 mA h g^?1, respectively, which is far more than those without pretreatment. The thin‐films formed from decomposition of electrolyte during in situ electrochemical precharging processes in an inert environment, can protect both CNTs air‐electrode and Li metal anode prior to conventional Li–O₂ discharge/charge cycling, where reactive reduced oxygen species are formed. This work provides a new approach for protection of carbon‐based air‐electrodes and Li metal anodes in practical Li–O₂ batteries, and may also be applied to other battery systems.     

Blood‐Capillary‐Inspired,Free‐Standing,Flexible, and Low‐Cost Super‐Hydrophobic N‐CNTs@SS Cathodes for High‐Capacity,High‐Rate,and Stable Li‐Air Batteries

With the rising demand for flexible and wearable electronic devices, flexible power sources with high energy densities are required to provide a sustainable energy supply. Theoretically, rechargeable, flexible Li‐O₂/air batteries can provide extremely high specific energy densities; however, the high costs, complex synthetic methods, and inferior mechanical properties of the available flexible cathodes severely limit their practical applications. Herein, inspired by the structure of human blood capillary tissue, this study demonstrates for the first time the in situ growth of interpenetrative hierarchical N‐doped carbon nanotubes on the surface of stainless‐steel mesh (N‐CNTs@SS) for the fabrication of a self‐supporting, flexible electrode with excellent physicochemical properties via a facile and scalable one‐step strategy. Benefitting from the synergistic effects of the high electronic conductivity and stable 3D interconnected conductive network structure, the Li‐O₂ batteries obtained with the N‐CNTs@SS cathode exhibit superior electrochemical performance, including a high specific capacity (9299 mA h g^?1 at 500 mA g^?1), an excellent rate capability, and an exceptional cycle stability (up to 232 cycles). Furthermore, as‐fabricated flexible Li‐air batteries containing the as‐prepared flexible super‐hydrophobic cathode show excellent mechanical properties, stable electrochemical performance, and superior H₂O resistibility, which enhance their potential to power flexible and wearable electronic devices.     

High Energy Density Aqueous Li‐Ion Flow Capacitor

High energy density Li‐ion hybrid flow capacitors are demonstrated by employing LiMn₂O₄ and activated carbon slurry electrodes. Compared to the existing aqueous flow electrochemical capacitors, the hybrid one exhibits much higher energy densities due to the introduction of high capacity Li‐insertion materials (e.g., LiMn₂O₄ in the present work) as the flowable electrode with asymmetrical cell configuration. A record energy density, i.e., 23.4 W h kg^?1 at a power of 50.0 W kg^?1 has been achieved for aqueous flow capacitors tested at static condition reported to date. A full operational Li‐ion flow capacitor tested in an intermittent‐flow mode has also been demonstrated. The Li‐ion hybrid flow capacitor shows great promise for high‐rate grid applications.     

Superior Lithium Storage Properties of β‐FeOOH

Several crystal forms of FeOOH are recently reported to be highly promising for lithium storage due to their high capacity, low cost, and environmental friendliness. In particular, β‐FeOOH has shown a capacity of ≈1000 mAh g^?1, which is comparable to other promising iron‐based anodes, such as Fe₂O₃ and Fe₃O_4. However, its storage mechanisms are unclear and the potential for further improvement remains unexplored. Here, it is shown that this material can have a very high reversible capacity of ≈1400 mAh g^?1, which is 20%–40% higher than Fe₂O₃ and Fe₃O₄. Such a high capacity is delivered from a series of reactions including intercalation and conversion reactions, formation/deformation of solid‐state electrolyte interface layers and interfacial storage. The mechanisms are studied by a combination of electrochemical and X‐ray absorption near edge spectroscopic approaches. Moreover, very long cycling performance, that is, after even more than 3000 cycles the material still has a significant capacity of more than 800 mAh g^?1, is obtained by a simple electrode design involving introducing a rigid support into porous electrodes. Such long cycling performance is for the first time achieved for high‐capacity materials based on conversion reactions.     

A New P2‐Type Layered Oxide Cathode with Extremely High Energy Density for Sodium‐Ion Batteries

Herein, a new P2‐type layered oxide is proposed as an outstanding intercalation cathode material for high energy density sodium‐ion batteries (SIBs). On the basis of the stoichiometry of sodium and transition metals, the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode is synthesized without impurities phase by partially substituting Ni and Fe into the Mn sites. The partial substitution results in a smoothing of the electrochemical charge/discharge profiles and thus greatly improves the battery performance. The P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode delivers an extremely high discharge capacity of 221.5 mAh g^?1 with a high average potential of ≈2.9 V (vs Na/Na⁺) for SIBs. In addition, the fast Na‐ion transport in the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode structure enables good power capability with an extremely high current density of 2400 mA g^?1 (full charge/discharge in 12 min) and long‐term cycling stability with ≈80% capacity retention after 500 cycles at 600 mA g^?1. A combination of electrochemical profiles, in operando synchrotron X‐ray diffraction analysis, and first‐principles calculations are used to understand the overall Na storage mechanism of P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂.     

Elucidating the Effect of Iron Doping on the Electrochemical Performance of Cobalt‐Free Lithium‐Rich Layered Cathode Materials

The eco‐friendly and low‐cost Co‐free Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ is investigated as a positive material for Li‐ion batteries. The electrochemical performance of the 3 at% Fe‐doped material exhibits an optimal performance with a capacity and voltage retention of 70 and 95%, respectively, after 200 cycles at 1C. The effect of iron doping on the electrochemical properties of lithium‐rich layered materials is investigated by means of in situ X‐ray diffraction spectroscopy and galvanostatic intermittent titration technique during the first charge–discharge cycle while high‐resolution transmission electron microscopy is used to follow the structural and chemical change of the electrode material upon long‐term cycling. By means of these characterizations it is concluded that iron doping is a suitable approach for replacing cobalt while mitigating the voltage and capacity degradation of lithium‐rich layered materials. Finally, complete lithium‐ion cells employing Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ and graphite show a specific energy of 361 Wh kg^?1 at 0.1C rate and very stable performance upon cycling, retaining more than 80% of their initial capacity after 200 cycles at 1C rate. These results highlight the bright prospects of this material to meet the high energy density requirements for electric vehicles.     

Iron‐Oxide‐Based Advanced Anode Materials for Lithium‐Ion Batteries

Iron oxides, such as Fe₂O₃ and Fe₃O₄, have recently received increased attention as very promising anode materials for rechargeable lithium‐ion batteries (LIBs) because of their high theoretical capacity, non‐toxicity, low cost, and improved safety. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, recent research progress in the rational design and synthesis of diverse iron oxide‐based nanomaterials and their lithium storage performance for LIBs, including 1D nanowires/rods, 2D nanosheets/flakes, 3D porous/hierarchical architectures, various hollow structures, and hybrid nanostructures of iron oxides and carbon (including amorphous carbon, carbon nanotubes, and graphene). By focusing on synthesis strategies for various iron‐oxide‐based nanostructures and the impacts of nanostructuring on their electrochemical performance, novel approaches to the construction of iron‐oxide‐based nanostructures are highlighted and the importance of proper structural and compositional engineering that leads to improved physical/chemical properties of iron oxides for efficient electrochemical energy storage is stressed. Iron‐oxide‐based nanomaterials stand a good chance as negative electrodes for next generation LIBs.     

Spinel‐Layered Core‐Shell Cathode Materials for Li‐Ion Batteries

In an attempt to overcome the problems associated with LiNiO₂, the solid solution series of lithium nickel‐metal oxides, Li[Ni_1–xM_x]O₂ (with M = Co, Mn, Al, Ti, Mg, etc.), have been investigated as favorable cathode materials for high‐energy and high‐power lithium‐ion batteries. However, along with the improvement in the electrochemical properties in Ni‐based cathode materials, the thermal stability has been a great concern, and thus violent reaction of the cathode with the electrolyte needs to be avoided. Here, we report a heterostructured Li[Ni_0.54Co_0.12Mn_0.34]O₂ cathode material which possesses both high energy and safety. The core of the particle is Li[Ni_0.54Co_0.12Mn_0.34]O₂ with a layered phase (R3‐m) and the shell, with a thickness of < 0.5 μm, is a highly stable Li_1+x[CoNi_xMn_2–x]₂O₄ spinel phase (Fd‐3m). The material demonstrates reversible capacity of 200 mAhg‐1 and retains 95% capacity retention under the most severe test condition of 60 °C. In addition, the amount of oxygen evolution from the lattice in the cathode with two heterostructures is reduced by 70%, compared to the reference sample. All these results suggest that the bulk Li[Ni_0.54Co_0.12Mn_0.34]O₂ consisting of two heterostructures satisfy the requirements for hybrid electric vehicles, power tools, and mobile electronics.     

Insights into Ionic Transport and Structural Changes in Magnetite during Multiple‐Electron Transfer Reactions

Metal oxides, such as Fe₃O₄, hold promise for future battery applications due to their abundance, low cost, and opportunity for high lithium storage capacity. In order to better understand the mechanisms of multiple‐electron transfer reactions leading to high capacity in Fe₃O₄, a comprehensive investigation on local ionic transport and ordering is made by probing site occupancies of anions (O^2?) and cations (Li⁺, Fe³⁺/Fe²⁺) using multiple synchrotron X‐ray and electron‐beam techniques, in combination with ab‐initio calculations. Results from this study provide the first experimental evidence that the cubic‐close‐packed (ccp) O‐anion array in Fe₃O₄ is sustained throughout the lithiation and delithiation processes, thereby enabling multiple lithium intercalation and conversion reactions. Cation displacement/reordering occurs within the ccp O‐anion framework, which leads to a series of phase transformations, starting from the inverse spinel phase and turning into intermediate rock‐salt‐like phases (Li_xFe₃O₄; 0 < x < 2), then into a cation‐segregated phase (Li₂O?FeO), and finally converting into metallic Fe and Li₂O. Subsequent delithiation and lithiation processes involve interconversion between metallic Fe and FeO‐like phases. These results may offer new insights into the structure‐determined ionic transport and electrochemical reactions in metal oxides, and those of other compounds sharing a ccp anion framework, reminiscent of magnetite.     

Ni‐Rich Layered Cathode Materials with Electrochemo‐Mechanically Compliant Microstructures for All‐Solid‐State Li Batteries

While Ni‐rich cathode materials combined with highly conductive and mechanically sinterable sulfide solid electrolytes are imperative for practical all‐solid‐state Li batteries (ASLBs), they suffer from poor performance. Moreover, the prevailing wisdom regarding the use of Li[Ni,Co,Mn]O₂ in conventional liquid electrolyte cells, that is, increased capacity upon increased Ni content, at the expense of degraded cycling stability, has not been applied in ASLBs. In this work, the effect of overlooked but dominant electrochemo‐mechanical on the performance of Ni‐rich cathodes in ASLBs are elucidated by complementary analysis. While conventional Li[Ni_0.80Co_0.16Al_0.04]O₂ (NCA80) with randomly oriented grains is prone to severe particle disintegration even at the initial cycle, the radially oriented rod‐shaped grains in full‐concentration gradient Li[Ni_0.75Co_0.10Mn_0.15]O₂ (FCG75) accommodate volume changes, maintaining mechanical integrity. This accounts for their different performance in terms of reversible capacity (156 vs 196 mA h g^?1), initial Coulombic efficiency (71.2 vs 84.9%), and capacity retention (46.9 vs 79.1% after 200 cycles) at 30 °C. The superior interfacial stability for FCG75/Li₆PS₅Cl to for NCA80/Li₆PS₅Cl is also probed. Finally, the reversible operation of FCG75/Li ASLBs is demonstrated. The excellent performance of FCG75 ranks at the highest level in the ASLB field.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

ZnFe2O4‐C/LiFePO4‐CNT: A Novel High‐Power Lithium‐Ion Battery with Excellent Cycling Performance

An innovative and environmentally friendly battery chemistry is proposed for high power applications. A carbon‐coated ZnFe₂O₄ nanoparticle‐based anode and a LiFePO₄‐multiwalled carbon nanotube‐based cathode, both aqueous processed with Na‐carboxymethyl cellulose, are combined, for the first time, in a Li‐ion full cell with exceptional electrochemical performance. Such novel battery shows remarkable rate capabilities, delivering 50% of its nominal capacity at currents corresponding to ≈20C (with respect to the limiting cathode). Furthermore, the pre‐lithiation of the negative electrode offers the possibility of tuning the cell potential and, therefore, achieving remarkable gravimetric energy and power density values of 202 Wh kg^?1 and 3.72 W kg^?1, respectively, in addition to grant a lithium reservoir. The high reversibility of the system enables sustaining more than 10 000 cycles at elevated C‐rates (≈10C with respect to the LiFePO₄ cathode), while retaining up to 85% of its initial capacity.