Operando Quantification of (De)Lithiation Behavior of Silicon–Graphite Blended Electrodes for Lithium‐Ion Batteries

Due to the high lithium capacity of silicon, the composite (blended) electrodes containing silicon (Si) and graphite (Gr) particles are attractive alternatives to the all‐Gr electrodes used in conventional lithium‐ion batteries. In this Communication, the lithiation and delithiation in the Si and Gr particles in a 15 wt% Si composite electrode is quantified for each component using energy dispersive X‐ray diffraction. This quantification is important as the components cycle in different potential regimes, and interpretation of cycling behavior is complicated by the potential hysteresis displayed by Si. The lithiation begins with Li alloying with Si; lithiation of Gr occurs at later stages when the potential dips below 0.2 V (all potentials are given vs Li/Li⁺). In the 0.2–0.01 V range, the relative lithiation of Si and Gr is ≈58% and 42%, respectively. During delithiation, Li⁺ ion extraction occurs preferentially from Gr in the 0.01–0.23 V range and from Si in the 0.23–1.0 V range; that is, the delithiation current is carried sequentially, first by Gr and then by Si. These trends can be used for rational selection of electrochemical cycling windows that limits volumetric expansion in Si particles, thereby extending cell life.     

Solid‐State Prelithiation Enables High‐Performance Li‐Al‐H Anode for Solid‐State Batteries

Lithium alanates exhibit high theoretical specific capacities and appropriate lithiation/delithiation potentials, but suffer from poor reversibility, cycling stability, and rate capability due to their sluggish kinetics and extensive side reactions. Herein, a novel and facile solid‐state prelithiation approach is proposed to in situ prepare a Li₃AlH₆‐Al nanocomposite from a short‐circuited electrochemical reaction between LiAlH₄ and Li with the help of fast electron and Li‐ion conductors (C and P6₃mc LiBH₄). This nanocomposite consists of dispersive Al nanograins and an amorphous Li₃AlH₆ matrix, which enables superior electrochemical performance in solid‐state cells, as much higher specific capacity (2266 mAh g^?1), Coulombic efficiency (88%), cycling stability (71% retention in the 100th cycle), and rate capability (1429 mAh g^?1 at 1 A g^?1) are achieved. In addition, this nanocomposite works well in the solid‐state full cell with LiCoO₂ cathode, demonstrating its promising application prospects. Mechanism analysis reveals that the dispersive Al nanograins and amorphous Li₃AlH₆ matrix can dramatically enhance the lithiation and delithiation kinetics without side reactions, which is mainly responsible for the excellent overall performance. Moreover, this solid‐state prelithiation approach is general and can also be applied to other Li‐poor electrode materials for further modification of their electrochemical behavior.     

High‐Performance All‐Solid‐State Lithium–Sulfur Batteries Enabled by Amorphous Sulfur‐Coated Reduced Graphene Oxide Cathodes

Safety and the polysulfide shuttle reaction are two major challenges for liquid electrolyte lithium–sulfur (Li–S) batteries. Although use of solid‐state electrolytes can overcome these two challenges, it also brings new challenges by increasing the interface resistance and stress/strain. In this work, the interface resistance and stress/strain of sulfur cathodes are significantly reduced by conformal coating ≈2 nm sulfur (S) onto reduced graphene oxide (rGO). An Li–S full cell consisting of an rGO@S‐Li₁₀GeP₂S₁₂‐acetylene black (AB) composite cathode is evaluated. At 60 °C, the all‐solid‐state Li–S cell demonstrates a similar electrochemical performance as in liquid organic electrolyte, with high rate capacities of 1525.6, 1384.5, 1336.3, 903.2, 502.6, and 204.7 mA h g^?1 at 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 C, respectively. It can maintain a high and reversible capacity of 830 mA h g^?1 at 1.0 C for 750 cycles. The uniform distribution of the rGO@S nanocomposite in the Li₁₀GeP₂S₁₂‐AB matrix generates uniform volume changes during lithiation/delithiation, significantly reducing the stress/strain, thus extending the cycle life. Minimization of the stress/strain of solid cells is the key for a long cycle life of all‐solid‐state Li–S batteries.     

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.     

Vanadate‐Based Materials for Li‐Ion Batteries: The Search for Anodes for Practical Applications

While the practical application of electrode materials depends intensively on the Li⁺ ion storage mechanisms correlating ultimately with the coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling, only intercalation‐type electrode materials have proven viable for commercialization up to now. This paper reviews the promising anode materials of metal vanadates (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni, Li) that have high capacity, low cost, and abundant resource, and also discusses the related Li⁺ ion storage mechanism. It is concluded that most of these (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni) exhibit irreversible redox reactions upon lithiation/delithiation accompanied by large volume expansion, which is not favorable for industrial applications. In particular, Li₃VO₄ with specific intercalation Li⁺ ion storage mechanism and compatible merits of safety and energy density exhibits great potential for practical application. This review systematically summarizes the latest progress in Li₃VO₄ research, including the representative fabrication approaches for advanced morphology and state‐of‐the‐art technologies to boost performance and the morphology variation associated with Li⁺ ion storage mechanisms. Furthermore, an outlook on where breakthroughs for Li₃VO₄ may be most likely achieved will be provided.     

Influence of Oxides on the Stress Evolution and Reversibility during SnOx Conversion and Li‐Sn Alloying Reactions

The effect of varying the oxygen content in Sn and SnO_x films during potential dependent SnO_x conversion reactions and Li_ySn alloying relevant to Li ion battery anodes is examined. For metallic Sn films, the stresses and stability of the films are controlled by Li alloying reactions. Small, non‐contacting separated Sn particles exhibit higher electrochemical stability relative to more continuous polycrystalline films with larger particles. Metallic Sn particles develop tensile stress during Li_ySn de‐alloying as porous structures are formed. The amount of stress associated with lithiation and delithiation of well‐separated metallic particles decreases as a porous, easy to lithiate, material forms with cycling. During the lithiation of oxides, conversion reactions (SnO_x → Sn) and the lithiation of the metallic Sn control the stress responses of the films, leading to highly potential‐dependent stress development. In particular, evidence for a multistep electrochemical mechanism, in which partially reversible lithiation of the oxygen‐containing phases is conjoined with a fully reversible lithiation of the metallic phases of the Sn, is found. The electrochemical stress analysis provides new insight into these mechanisms and delineates the extent of the reversibility of lithiation and conversion reactions of oxides.     

Atomic Structure of Li2MnO3 after Partial Delithiation and Re‐Lithiation

Li₂MnO₃ is the parent compound of the well‐studied Li‐rich Mn‐based cathode materials xLi₂MnO₃·(1‐x)LiMO₂ for high‐energy‐density Li‐ion batteries. Li₂MnO₃ has a very high theoretical capacity of 458 mA h g^?1 for extracting 2 Li. However, the delithiation and lithiation behaviors and the corresponding structure evolution mechanism in both Li₂MnO₃ and Li‐rich Mn‐based cathode materials are still not very clear. In this research, the atomic structures of Li₂MnO₃ before and after partial delithiation and re‐lithiation are observed with spherical aberration‐corrected scanning transmission electron microscopy (STEM). All atoms in Li₂MnO₃ can be visualized directly in annular bright‐field images. It is confirmed accordingly that the lithium can be extracted from the LiMn₂ planes and some manganese atoms can migrate into the Li layer after electrochemical delithiation. In addition, the manganese atoms can move reversibly in the (001) plane when ca. 18.6% lithium is extracted and 12.4% lithium is re‐inserted. LiMnO₂ domains are also observed in some areas in Li_1.63MnO₃ at the first cycle. As for the position and occupancy of oxygen, no significant difference is found between Li_1.63MnO₃ and Li₂MnO₃.     

Redox Targeting of Anatase TiO2 for Redox Flow Lithium‐Ion Batteries

Anatase TiO₂ is an extensively studied anode material for lithium‐ion batteries because of its superior capability of storing Li⁺ electrochemically. Here reversible lithium storage of TiO₂ is achieved chemically using redox targeting reactions. In the presence of a pair of redox mediators, bis(pentamethylcyclopentadienyl)cobalt (CoCp^* ₂) and cobaltocene (CoCp₂) in an electrolyte, TiO₂ and its lithiated form Li _x TiO₂ can be reduced and oxidized by CoCp^* ₂ and CoCp₂ ⁺, respectively, which accompany Li⁺ insertion and extraction, albeit without attaching the TiO₂ onto the electrode. The reversible chemical lithiation/delithiation and the involved phase transitions are unambiguously confirmed using density functional theory (DFT) calculations, UV‐vis spectroscopy, X‐ray photoelectron spectoscopy (XPS), and Raman spectroscopy. A redox flow lithium‐ion battery (RFLB) half‐cell is assembled and evaluated, which is a critical step towards the development of RFLB full cells.     

On the Capacity Losses Seen for Optimized Nano‐Si Composite Electrodes in Li‐Metal Half‐Cells

While the use of silicon‐based electrodes can increase the capacity of Li‐ion batteries considerably, their application is associated with significant capacity losses. In this work, the influences of solid electrolyte interphase (SEI) formation, volume expansion, and lithium trapping are evaluated for two different electrochemical cycling schemes using lithium‐metal half‐cells containing silicon nanoparticle–based composite electrodes. Lithium trapping, caused by incomplete delithiation, is demonstrated to be the main reason for the capacity loss while SEI formation and dissolution affect the accumulated capacity loss due to a decreased coulombic efficiency. The capacity losses can be explained by the increasing lithium concentration in the electrode causing a decreasing lithiation potential and the lithiation cut‐off limit being reached faster. A lithium‐to‐silicon atomic ratio of 3.28 is found for a silicon electrode after 650 cycles using 1200 mAhg^?1 capacity limited cycling. The results further show that the lithiation step is the capacity‐limiting step and that the capacity losses can be minimized by increasing the efficiency of the delithiation step via the inclusion of constant voltage delithiation steps. Lithium trapping due to incomplete delithiation consequently constitutes a very important capacity loss phenomenon for silicon composite electrodes.     

Electrochemical Reaction of Lithium with Nanostructured Silicon Anodes: A Study by In‐Situ Synchrotron X‐Ray Diffraction and Electron Energy‐Loss Spectroscopy

Silicon‐based anodes are an appealing alternative to graphite for lithium‐ion batteries because of their extremely high capacity. However, poor cycling stability and slow kinetics continue to limit the widespread use of silicon in commercial batteries. Performance improvement has been often demonstrated in nanostructured silicon electrodes, but the reaction mechanisms involved in the electrochemical lithiation of nanoscale silicon are not well understood. Here, in‐situ synchrotron X‐ray diffraction is used to monitor the subtle structural changes occurring in Si nanoparticles in a Si‐C composite electrode during lithiation. Local analysis by electron energy‐loss spectroscopy and transmission electron microscopy is performed to interrogate the nanoscale morphological changes and phase evolution of Si particles at different depths of discharge. It is shown that upon lithiation, Si nanoparticles behave quite differently than their micrometer‐sized counterparts. Although both undergo an electrochemical amorphization, the micrometer‐sized silicon exhibits a linear transformation during lithiation, while a two‐step process occurs in the nanoscale Si. In the first half of the discharge, lithium reacts with surfaces, grain boundaries and planar defects. As the reaction proceeds and the cell voltage drops, lithium consumes the crystalline core transforming it into amorphous Li_xSi with a primary particle size of just a few nanometers. Unlike the bulk silicon electrode, no Li₁₅Si₄ or other crystalline Li_xSi phases were formed in nanoscale Si at the fully‐lithiated state.     

Cascade‐Type Prelithiation Approach for Li‐Ion Capacitors

An industry‐relevant method for pre‐lithiation of lithium‐ion capacitors to balance the first charge irreversibility is demonstrated, which addresses the prime bottleneck for their market integration. Based on a composite positive electrode that integrates pyrene monomers and an insoluble lithiated base, Li₃PO₄, a “cascade‐type” process involving two consecutive irreversible reactions is proposed: i) oxidative electropolymerization of the pyrene moieties releases electrons and protons; ii) protons are captured by Li₃PO₄ and exchanged for a stoichiometric amount of Li⁺ into the electrolyte. (¹H, ¹⁹F, and ³¹P) NMR spectroscopy, operando X‐ray diffraction, and Raman spectroscopy support this mechanism. By decoupling the irreversible source of lithium ions from electrons, the cascade‐type pre‐lithiation allows the simultaneous enhancement of the capacity of the positive electrode, thanks to p‐doping of the resulting polymer. Remarkably, the proton scavenging properties of Li₃PO₄ also boost the polymerization process, which enables a 16% increase in capacity without detrimental effect on power properties and cyclability. Full cells integrating a cheap carbon black based negative electrode, show much‐improved capacity of 17 mAh g^‐1_electrodes (44 F g^‐1_electrodes, 3–4.4 V) and excellent stability over 2200 cycles at 1 A g^‐1. Thanks to its versatile chemistry and flexibility this approach in principle can be applied to any kind of ion‐battery.     

Cu3P Binary Phosphide: Synthesis via a Wet Mechanochemical Method and Electrochemical Behavior as Negative Electrode Material for Lithium‐Ion Batteries

Mechanochemical synthesis of Cu₃P in the presence of n‐dodecane results in a material with a secondary particle size distribution of 10 μm, secondary particles which consist of homogeneously agglomerated 20 nm primary particles. The electrochemical performance of Cu₃P with lithium is influenced by the reaction depth, in other words by the lower potential cut‐off. During the electrochemical reaction, the displacement of copper by lithium from the Cu₃P structure until the formation of Li₃P and Cu deteriorates the capacity retention. Improved performance was obtained when the charge potential was limited to 0.50 V (vs. Li/Li⁺) and the formation of the Li_xCu_3‐xP phase (0 ≤ × ≤ 2). In this case, when the potential is limited to 0.5 V, the capacity is stable for more than 50 cycles. Acceptable electrochemical performances in Li‐ion cells within the voltage range 0.50–2.0 V (vs. Li/Li⁺) were shown when Cu₃P was used as an anode and Li_1.2(Ni_0.13Mn_0.54Co_0.13)O₂ and LiNi_0.5Mn_1.5O₄ as positive electrode materials.     

Storage Capacity and Cycling Stability in Ge Anodes: Relationship of Anode Structure and Cycling Rate

Operando X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li₁₅Ge₄ (c‐Li₁₅Ge₄) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g^?1 can be attained up to 100 cycles at a slow C‐rate of C/21 when there is complete conversion of Ge anode into c‐Li₁₅Ge₄. When the C‐rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g^?1 is achieved with poorer electrochemical reversibility. An increase in C‐rate to C/5 and higher reduces the capacity (≈500 mAh g^?1) due to an impeded transformation from amorphous Li_xGe to c‐Li₁₅Ge₄, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C‐rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high‐capacity anodes.     

Advanced Energy‐Storage Architectures Composed of Spinel Lithium Metal Oxide Nanocrystal on Carbon Textiles

Current battery technologies are known to suffer from kinetic problems associated with the solid‐state diffusion of Li⁺ in intercalation electrodes materials. Not only the use of nanostructure materials but also the design of electrode architectures can lead to more advanced properties. Here, advanced electrode architectures consisting of carbon textiles conformally covered by Li₄Ti₅O₁₂ nanocrystal are rationally designed and synthesized for lithium ion batteries. The efficient two‐step synthesis involves the growth of ultrathin TiO₂ nanosheets on carbon textiles, and subsequent conversion into spinel Li₄Ti₅O₁₂ through chemical lithiation. Importantly, this novel approach is simple and general, and it is used to successfully produce LiMn₂O₄/carbon composites textiles, one of the leading cathode materials for lithium ion batteries. The resulting 3D textile electrode, with various advantages including the direct electronic pathway to current collector, the easy access of electrolyte ions, the reduced Li⁺/e^? diffusion length, delivers excellent rate capability and good cyclic stability over the Li‐ion batteries of conventional configurations.     

Single Nanostructure Electrochemical Devices for Studying Electronic Properties and Structural Changes in Lithiated Si Nanowires

Nanostructured Si is a promising anode material for the next generation of Li‐ion batteries, but few studies have focused on the electrical properties of the Li‐Si alloy phase, which are important for determining power capabilities and ensuring sufficient electrical conduction in the electrode structure. Here, we demonstrate an electrochemical device framework suitable for testing the electrical properties of single Si nanowires (NWs) at different lithiation states and correlating these properties with structural changes via transmission electron microscopy (TEM). We find that single Si NWs usually exhibit Ohmic I–V response in the lithiated state, with conductivities two to three orders of magnitude higher than in the delithiated state. After a number of sequential lithiation/delithiation cycles, the single NWs show similar conductivity after each lithiation step but show large variations in conductivity in the delithiated state. Finally, devices with groups of NWs in physical contact were fabricated, and structural changes in the NWs were observed after lithiation to investigate how the electrical resistance of NW junctions and the NWs themselves affect the lithiation behavior. The results suggest that electrical resistance of NW junctions can limit lithiation. Overall, this study shows the importance of investigating the electronic properties of individual components of a battery electrode (single nanostructures in this case) along with studying the nature of interactions within a collection of these component structures.     

A Hybrid Mg2+/Li+ Battery Based on Interlayer‐Expanded MoS2/Graphene Cathode

The hybrid Mg²⁺/Li⁺ battery (MLIB) is a very promising energy storage technology that combines the advantage of the Li and Mg electrochemistry. However, previous research has shown that the battery performance is limited due to the strong dependence on the Li content in the dual Mg²⁺/Li⁺ electrolyte. This limitation can be circumvented by significantly improving the diffusion kinetics of Mg²⁺ in the electrode, so that both Li⁺ and Mg²⁺ ions can be utilized as charge carriers. Herein, a free‐standing interlayer expanded MoS₂/graphene composite (E‐MG) is demonstrated as a cathode for MLIB. The key advantage of this cathode is to enable the efficient intercalation of both Mg²⁺ and Li⁺. The E‐MG electrode displays a reversible capacity of ≈300 mA h g^?1 at 20 mA g^?1 in an MLIB cell, corresponding to a specific energy density up to ≈316.9 W h kg^?1, which is comparable to that of the state‐of‐the‐art Li‐ion batteries (LIBs) and has no dendrite formation. The composite electrode is stable against cycling with a coulombic efficiency close to 100% at 500 mA g^?1. This new electrode design represents a significant step forward for building a safe and high‐density electrochemical energy storage system.     

Conductive Li3.08Cr0.02Si0.09V0.9O4 Anode Material: Novel “Zero‐Strain” Characteristic and Superior Electrochemical Li+ Storage

“Zero‐strain” compounds are ideal energy‐storage materials for long‐term cycling because they present negligible volume change and significantly reduce the mechanically induced deterioration during charging–discharging. However, the explored “zero‐strain” compounds are very limited, and their energy densities are low. Here, γ phase Li_3.08Cr_0.02Si_0.09V_0.9O₄ (γ‐LCSVO) is explored as an anode compound for lithium‐ion batteries, and surprisingly its “zero‐strain” Li⁺ storage during Li⁺ insertion–extraction is found through using various state‐of‐the‐art characterization techniques. Li⁺ sequentially inserts into the 4c(1) and 8d sites of γ‐LCSVO, but its maximum unit‐cell volume variation is only ≈0.18%, the smallest among the explored “zero‐strain” compounds. Its mean strain originating from Li⁺ insertion is only 0.07%. Consequently, both γ‐LCSVO nanowires (γ‐LCSVO‐NW) and micrometer‐sized particles (γ‐LCSVO‐MP) exhibit excellent cycling stability with 90.1% and 95.5% capacity retention after as long as 2000 cycles at 10C, respectively. Moreover, γ‐LCSVO‐NW and γ‐LCSVO‐MP respectively deliver large reversible capacities of 445.7 and 305.8 mAh g^?1 at 0.1C, and retain 251.2 and 78.4 mAh g^?1 at 10C. Additionally, γ‐LCSVO shows a suitably safe operating potential of ≈1.0 V, significantly lower than that of the famous “zero‐strain” Li₄Ti₅O₁₂ (≈1.6 V). These merits demonstrate that γ‐LCSVO can be a practical anode compound for stable, high‐energy, fast‐charging, and safe Li⁺ storage.     

Mechanism of Na+ Insertion in Alkali Vanadates and Its Influence on Battery Performance

Sodium‐ion batteries may become an alternative to the widespread lithium‐ion technology due to cost and kinetic advantages provided that cyclability is improved. For this purpose, the interplay between electrochemical and structural processes is key and is demonstrated in this work for Na_2.46V₆O₁₆ (NVO) and Li_2.55V₆O₁₆ employing operando synchrotron X‐ray diffraction. When NVO is cycled between 4.0 and 1.6 V, Na‐ions reversibly occupy two crystallographic sites, which results in remarkable cyclability. Upon discharge to 1.0 V, however, Na‐ions occupy also interstitial sites, inducing irreversible structural change with some loss of crystallinity concomitant with a decrease in capacity. Capacity fading increases with the ionic radius of the alkali ions (K⁺ > Na⁺ > Li⁺), suggesting that smaller ions stabilize the structure. This correlation of structural variation and electrochemical performance suggests a route toward improving cycling stability of a sodium‐ion battery. Its essence is a minor Li⁺‐retention in the A_2+xV₆O₁₆ structure. Even though the majority of Li‐ions are replaced by the abundant Na⁺, the residual Li‐ions (≈10%) are sufficient to stabilize the layered structure, diminishing the irreversible structural damage. These results pave the way for further exploitation of the role of small ions in lattice stabilization that increases cycling performance.     

Electrochemical and Structural Investigation of Calcium Substituted Monoclinic Li3V2(PO4)3 Anode Materials for Li‐Ion Batteries

In this work, the effect of Li⁺ substitution in Li₃V₂(PO₄)₃ with a large divalent ion (Ca²⁺) toward lithium insertion is studied. A series of materials, with formula Li_3?2xCa_xV₂(PO₄)₃/C (x = 0, 0.5, 1, and 1.5) is synthesized and studied in the potential region 3–0.01 V versus Li⁺/Li. Synchrotron diffraction demonstrates that Li₃V₂(PO₄)₃/C has a monoclinic structure (space group P2₁/n), while Ca_1.5V₂(PO₄)₃/C possesses a rhombohedral structure (space group R‐3c). The intermediate compounds, Li₂Ca_0.5V₂(PO₄)₃/C and LiCaV₂(PO₄)₃/C, are composed of two main phases, including monoclinic Li₃V₂(PO₄)₃/C and rhombohedral Ca_1.5V₂(PO₄)₃/C. Cyclic voltammetry reveals five reduction and oxidation peaks on Li₃V₂(PO₄)₃/C and Li₂Ca_0.5V₂(PO₄)₃/C electrodes. In contrast, LiCaV₂(PO₄)₃/C and Ca_1.5V₂(PO₄)₃/C have no obvious oxidation and reduction peaks but a box‐type voltammogram. This feature is the signature for capacitive‐like mechanism, which involves fast electron transfer on the surface of the electrode. Li₃V₂(PO₄)₃/C undergoes two solid‐solution and a short two‐phase reaction during lithiation and delithiation processes, whereas Ca_1.5V₂(PO₄)₃/C only goes through capacitive‐like mechanism. In operando X‐ray absorption spectroscopy confirms that, in both Li₃V₂(PO₄)₃/C and Ca_1.5V₂(PO₄)₃/C, V ions are reduced during the insertion of the first three Li ions. This study demonstrates that the electrochemical characteristic of polyanionic phosphates can be easily tuned by replacing Li⁺ with larger divalent cations.     

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li+ Conductors

All‐solid‐state Li‐ion batteries based on Li₇La₃Zr₂O₁₂ (LLZO) garnet structures require novel electrode assembly strategies to guarantee a proper Li⁺ transfer at the electrode–electrolyte interfaces. Here, first stable cell performances are reported for Li‐garnet, c‐Li_6.25Al_0.25La₃Zr₂O₁₂, all‐solid‐state batteries running safely with a full ceramics setup, exemplified with the anode material Li₄Ti₅O₁₂. Novel strategies to design an enhanced Li⁺ transfer at the electrode–electrolyte interface using an interface‐engineered all‐solid‐state battery cell based on a porous garnet electrolyte interface structure, in which the electrode material is intimately embedded, are presented. The results presented here show for the first time that all‐solid‐state Li‐ion batteries with LLZO electrolytes can be reversibly charge–discharge cycled also in the low potential ranges (≈1.5 V) for combinations with a ceramic anode material. Through a model experiment, the interface between the electrode and electrolyte constituents is systematically modified revealing that the interface engineering helps to improve delivered capacities and cycling properties of the all‐solid‐state Li‐ion batteries based on garnet‐type cubic LLZO structures.