Alleviating Mn Ion Dissolution in LiMn2O4 by Activation of TiO2 Lewis Acid Sites in Electrospun PVA/TiO2 Quasi-Solid Polymer Electrolyte

The primary concern of interest in high-voltage cathodes such as spinel LiMn2O4 is transition metal dissolution. Though several techniques and structural modifications are continuously under examination, a crucial factor that could make a significant impact is the careful evaluation of electrolyte properties. In this regard, a PVA/TiO2 (PT) quasi-solid polymer electrolyte prepared using an electrospinning technique is employed to suppress HF scavengers, a main cause of manganese dissolution. Good electrochemical stability of 5.05 V, ionic conductivity of 0.26 × 10-5 S cm-1, stable plating-stripping, and tLi+ of 0.82 are evidence for good electrolyte performance. Lewis acid sites of TiO2 firmly hold the PF6- anions, and strong hydrogen bonding of carbonate solvents disrupts the cycle of electrolyte decomposition reactions. The capacity retention of 73% after 500 cycles at a 2C rate and post-mortem analysis of the LMO cathode provide evidence for the successful suppression of manganese dissolution using a PT electrolyte.

Alumina - Stabilized SEI and CEI in Potassium Metal Batteries

Aluminum oxide (Al2O3) nanopowder is spin-coated onto both sides of commercial polypropene separator to create artificial solid-electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm2-0.5 mAh/cm2 and 3.0 mA/cm2-0.5 mAh/cm2. Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo-stage focused ion beam (cryo-FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina-modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal - SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.

An in-situ polymerization strategy for gel polymer electrolyte Si||Ni-rich lithium-ion batteries

Coupling the Si-based anodes with nickel-rich LiNixMnyCo1-x-yO2 cathodes (x ≥ 0.8) in the energy-dense cell prototype suffers from the mechanical instability of the Li-Si alloys, cathode collapse upon the high-voltage cycling, as well as the severe leakage current at elevated temperatures. More seriously, the cathode-to-anode cross-talk effect of transitional metal aggravates the depletion of the active Li reservoir. To reconcile the cation utilization degree, stress dissipation, and extreme temperature tolerance of the Si-based anode||NMC prototype, we propose a gel polymer electrolyte to reinforce the mechanical integrity of Si anode and chelate with the transitional cations towards the stabilized interfacial property. As coupling the conformal gel polymer electrolyte encapsulation with the spatial arranged Si anode and NMC811 cathode, the 2.7 Ah pouch-format cell could achieve the high energy density of 325.9 Wh kg-1 (based on the whole pouch cell), 88.7% capacity retention for 2000 cycles, self-extinguish property as well as a wide temperature tolerance. Therefore, this proposed polymerization strategy provides a leap toward the secured Li batteries.

Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries.

Insights into the multi-functional lithium difluoro(oxalate)borate additive in boosting the Li-ion reaction kinetics for Li3VO4 anodes

The rational design of a solid electrolyte interphase (SEI) with high ionic conductivity and high electrochemical stability is significantly important in improving the electrochemical performance of anode materials. Herein, lithium difluoro(oxalate)borate (LiDFOB) is used as an electrolyte additive to generate protective SEI films on Li3VO4 (LVO) anodes. The addition of LiDFOB is beneficial to form a dense, uniform, stable and LiF-richer SEI, which is helpful to boost the Li-ion storage kinetics. In addition, the generated SEI can inhibit the further decomposition of electrolytes and maintain the morphology of LVO anodes during charge/discharge processes. As a result, LVO-based anodes exhibit a much higher capacity (769.5 mA h g-1 at 0.5 A g-1), enhanced rate performance (243.3 mA h g-1 at 5.0 A g-1) and excellent long-term cycling stability (209.9 mA h g-1 after 5000 cycles) when cycled in 1 wt% LiDFOB addition electrolyte. This work confirms that LiDFOB is a promising multi-functional additive for LiPF6 electrolytes and provides new insights into SEI construction towards high-performance LVO anodes.

Guaiacol as an Organic Superoxide Dismutase Mimics for Anti-ageing a Ru-based Li-rich Layered Oxide Cathode

High-capacity Li-rich layered oxides using oxygen redox as well as transition metal redox suffer from its structural instability due to lattice oxygen escaped from its structure during oxygen redox and the following electrolyte decomposition by the reactive oxygen species. Herein, we rescued a Li-rich layered oxide based on 4d transition metal by employing an organic superoxide dismutase mimics as a homogeneous electrolyte additive. Guaiacol scavenged superoxide radicals via dismutation or disproportionation to convert two superoxide molecules to peroxide and dioxygen after absorbing lithium superoxide on its partially negative oxygen of methoxy and hydroxyl groups. Additionally, guaiacol was decomposed to form a thin and stable cathode-electrolyte interphase (CEI) layer, endowing the cathode with the interfacial stability.

Carrageenan as a Sacrificial Binder for 5 V LiNi0.5 Mn1.5 O4 Cathodes in Lithium-Ion Batteries

5 V-class LiNi0.5 Mn1.5 O4 (LNMO) with its spinel symmetry is a promising cathode material for lithium-ion batteries. However, the high-voltage operation of LNMO renders it vulnerable to interfacial degradation involving electrolyte decomposition, which hinders long-term and high-rate cycling. Herein, this longstanding challenge presented by LNMO is overcome by incorporating a sacrificial binder, namely, λ-carrageenan (CRN), a sulfated polysaccharide. This binder not only uniformly covers the LNMO surface via hydrogen bonding and ion-dipole interaction but also offers an ionically conductive cathode-electrolyte interphase layer containing LiSOx F, a product of the electrochemical decomposition of the sulfate group. Taking advantage of these two auspicious properties, the CRN-based electrode exhibits cycling and rate performance far superior to that of its counterparts based on the conventional poly(vinylidene difluoride) and sodium alginate binders. This study introduces a new concept, namely "sacrificial" binder, for battery electrodes known to deliver superior electrochemical performance but be adversely affected by interfacial instability.

High-performance Li/LiNi0.8Co0.1Mn0.1O2 batteries enabled by optimizing carbonate-based electrolyte and electrode interphases via triallylamine additive

Lithium (Li) metal batteries (LMBs), paired with high-energy-density cathode materials, are promising to meet the ever-increasing demand for electric energy storage. Unfortunately, the inferior electrode-electrolyte interfaces and hydrogen fluoride (HF) corrosion in the state-of-art carbonate-based electrolytes lead to dendritic Li growth and unsatisfactory cyclability of LMBs. Herein, a multifunctional electrolyte additive triallylamine (TAA) is proposed to circumvent those issues. The TAA molecule exhibits strong nucleophilicity and contains three unsaturated carbon-carbon double bonds, the former for HF elimination, the later for in-situ passivation of aggressive electrodes. As evidenced theoretically and experimentally, the preferential oxidation and reduction of carbon-carbon double bonds enable the successful regulation of components and morphologies of electrode interfaces, as well as the binding affinity to HF effectively blocks HF corrosion. In particular, the TAA-derived electrode interfaces are packed with abundant lithium-containing inorganics and oligomers, which diminishes undesired parasitic reactions of electrolyte and detrimental degradation of electrode materials. When using the TAA-containing electrolyte, the cell configuration with Li anode and nickel-rich layered oxide cathode and symmetrical Li cell deliver remarkably enhanced electrochemical performance with regard to the additive-free cell. The TAA additive shows great potential in advancing the development of carbonate-based electrolytes in LMBs.

Electron and Ion Transport in Lithium and Lithium-Ion Battery Negative and Positive Composite Electrodes

Electrochemical energy storage systems, specifically lithium and lithium-ion batteries, are ubiquitous in contemporary society with the widespread deployment of portable electronic devices. Emerging storage applications such as integration of renewable energy generation and expanded adoption of electric vehicles present an array of functional demands. Critical to battery function are electron and ion transport as they determine the energy output of the battery under application conditions and what portion of the total energy contained in the battery can be utilized. This review considers electron and ion transport processes for active materials as well as positive and negative composite electrodes. Length and time scales over many orders of magnitude are relevant ranging from atomic arrangements of materials and short times for electron conduction to large format batteries and many years of operation. Characterization over this diversity of scales demands multiple methods to obtain a complete view of the transport processes involved. In addition, we offer a perspective on strategies for enabling rational design of electrodes, the role of continuum modeling, and the fundamental science needed for continued advancement of electrochemical energy storage systems with improved energy density, power, and lifetime.

Ni-Ion-Chelating Strategy for Mitigating the Deterioration of Li-Ion Batteries with Nickel-Rich Cathodes

Ni-rich cathodes are the most promising candidates for realizing high-energy-density Li-ion batteries. However, the high-valence Ni⁴⁺ ions formed in highly delithiated states are prone to reduction to lower valence states, such as Ni³⁺ and Ni²⁺ , which may cause lattice oxygen loss, cation mixing, and Ni ion dissolution. Further, LiPF₆ , a key salt in commercialized electrolytes, undergoes hydrolysis to produce acidic compounds, which accelerate Ni-ion dissolution and the interfacial deterioration of the Ni-rich cathode. Dissolved Ni ions migrate and deposit on the surface of the graphite anode, causing continuous electrolyte decomposition and threatening battery safety by forming Li dendrites on the anode. Herein, 1,2-bis(diphenylphosphino)ethane (DPPE) chelates Ni ions dissolved from the Ni-rich cathode using bidentate phosphine moieties and alleviates LiPF₆ hydrolysis via complexation with PF₅ . Further, DPPE reduces the generation of corrosive HF and HPO₂ F₂ substantially compared to the amounts observed using trimethyl phosphite and tris(trimethylsilyl) phosphite, which are HF-scavenging additives. Li-ion cells with Ni-rich cathodes and graphite anodes containing DPPE exhibit remarkable discharge capacity retentions of 83.4%, with high Coulombic efficiencies of >99.99% after 300 cycles at 45 °C. The results of this study will promote the development of electrolyte additives.

Synthesis of high-voltage cathode material using the Taylor-Couette flow-based co-precipitation method

LiNi_0.5Mn_1.5O₄ (LNMO), a next-generation high-voltage battery material, is promising for high-energy-density and power-density lithium-ion secondary batteries. However, rapid capacity degradation occurs due to problems such as the elution of transition metals and the generation of structural distortion during cycling. Herein, a new LNMO material was synthesized using the Taylor-Couette flow-based co-precipitation method. The synthesized LNMO material consisted of secondary particles composed of primary particles with an octahedral structure and a high specific surface area. In addition, the LNMO cathode material showed less structural distortion and cation mixing as well as a high cyclability and rate performance compared with commercially available materials.

Designing better electrolytes

Electrolytes and the associated interphases constitute the critical components to support the emerging battery chemistries that promise tantalizing energy but involve drastic phase and structure complications. Designing better electrolytes and interphases holds the key to the success of these batteries. As the only component that interfaces with every other component in the device, an electrolyte must satisfy multiple criteria simultaneously. These include transporting ions while insulating electrons between the electrodes and maintaining stability against electrodes of extreme chemical natures: the strongly oxidative cathode and the strongly reductive anode. In most advanced batteries, the two electrodes operate at potentials far beyond the thermodynamic stability limits of electrolytes, so the stability therein has to be realized kinetically through an interphase formed from the sacrificial reactions between electrolyte and electrodes.

Sulfated Alginate as an Effective Polymer Binder for High-Voltage LiNi0.5Mn1.5O4 Electrodes in Lithium-Ion Batteries

Although the increasing demand for high-energy-density lithium-ion batteries (LIBs) has inspired extensive research on high-voltage cathode materials, such as LiNi_0.5Mn_1.5O₄ (LNMO), their commercialization is hindered by problems associated with the decomposition of common carbonate solvent-based electrolytes at elevated voltages. To address these problems, we prepared high-voltage LNMO composite electrodes using five polymer binders (two sulfated and two nonsulfated alginate binders and a poly(vinylidene fluoride) conventional binder) and compared their electrochemical performances at ∼5 V vs Li/Li⁺. The effects of binder type on electrode performance were probed by analyzing cycled electrodes using soft/hard X-ray photoelectron spectroscopy and scanning transmission electron microscopy. The best-performing sulfated binder, sulfated alginate, uniformly covers the surface of LNMO and increased its affinity for the electrolyte. The electrolyte decomposition products generated in the initial charge-discharge cycle on the alginate-covered electrode participated in the formation of a protective passivation layer that suppressed further decomposition during subsequent cycles, resulting in enhanced cycling and rate performances. The results of this study provide a basis for the cost-effective and technically undemanding fabrication of high-energy-density LIBs.

Toward the Integration of a Silicon/Graphite Anode-Based Lithium-Ion Battery in Photovoltaic Charging Battery Systems

Solar photovoltaic (PV) energy generation is highly dependent on weather conditions and only applicable when the sun is shining during the daytime, leading to a mismatch between demand and supply. Merging PVs with battery storage is the straightforward route to counteract the intermittent nature of solar generation. Capacity (or energy density), overall efficiency, and stability at elevated temperatures are among key battery performance metrics for an integrated PV-battery system. The performance of high-capacity silicon (Si)/graphite (Gr) anode and LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) cathode cells at room temperature, 45, and 60 °C working temperatures for PV modules are explored. The electrochemical performance of both half and full cells are tested using a specially formulated electrolyte, 1 M LiPF₆ in ethylene carbonate: diethyl carbonate, with 5 wt % fluoroethylene carbonate, 2 wt % vinylene carbonate, and 1 wt % (2-cyanoethyl)triethoxysilane. To demonstrate solar charging, perovskite solar cells (PSCs) are coupled to the developed batteries, following the evaluation of each device. An overall efficiency of 8.74% under standard PV test conditions is obtained for the PSC charged lithium-ion battery via the direct-current-direct-current converter, showing the promising applicability of silicon/graphite-based anodes in the PV-battery integrated system.

Cationic Covalent Organic Framework with Ultralow HOMO Energy Used as Scaffolds for 5.2 V Solid Polycarbonate Electrolytes

Solid polymer electrolytes (SPEs) have become promising candidate to replace common liquid electrolyte due to highly improved security. However, the practical use of SPEs is still restricted by their decomposition and breakage at the electrode interfacial layer especially at high voltage. Herein, a new cationic covalent organic framework (COF) is designed and synthesized as a reinforced skeleton to resist the constant oxidative decomposition of solid polycarbonate electrolyte, which can stabilize cathode electrolyte interphase layer to develop long-term cycle solid lithium metal battery. The ultralow HOMO energy (-12.55 eV according to density functional theory (DFT) calculations), reflecting its oxidation resistance at positive potential, would be responsible for the high decomposition voltage of 5.2 V versus Li⁺ /Li of solid polycarbonate electrolyte. Furthermore, the smooth surface of interfacial layer and inhibited decomposition reaction at cathode side is confirmed in solid LiCoO₂ cell, which realizes high initial capacity up to 160.3 mAh g^-1 at 0.1 C and greatly improved stability in 4.5 V class solid polymer lithium metal battery with high capacity retention over 200 cycles. This new type of high-voltage resistant solid polymer electrolyte promotes the realization of high-voltage cathode materials and higher energy density lithium metal battery.

Controlling Gas Generation of Li-Ion Battery through Divinyl Sulfone Electrolyte Additive

The focus of mainstream lithium-ion battery (LIB) research is on increasing the battery’s capacity and performance; however, more effort should be invested in LIB safety for widespread use. One aspect of major concern for LIB cells is the gas generation phenomenon. Following conventional battery engineering practices with electrolyte additives, we examined the potential usage of electrolyte additives to address this specific issue and found a feasible candidate in divinyl sulfone (DVSF). We manufactured four identical battery cells and employed an electrolyte mixture with four different DVSF concentrations (0%, 0.5%, 1.0%, and 2.0%). By measuring the generated gas volume from each battery cell, we demonstrated the potential of DVSF additives as an effective approach for reducing the gas generation in LIB cells. We found that a DVSF concentration of only 1% was necessary to reduce the gas generation by approximately 50% while simultaneously experiencing a negligible impact on the cycle life. To better understand this effect on a molecular level, we examined possible electrochemical reactions through ab initio molecular dynamics (AIMD) based on the density functional theory (DFT). From the electrolyte mixture’s exposure to either an electrochemically reductive or an oxidative environment, we determined the reaction pathways for the generation of CO₂ gas and the mechanism by which DVSF additives effectively blocked the gas’s generation. The key reaction was merging DVSF with cyclic carbonates, such as FEC. Therefore, we concluded that DVSF additives could offer a relatively simplistic and effective approach for controlling the gas generation in lithium-ion batteries.

Dynamic Nuclear Polarization in battery materials

The increasing need for portable and large-scale energy storage systems requires development of new, long lasting and highly efficient battery systems. Solid state NMR spectroscopy has emerged as an excellent method for characterizing battery materials. Yet, it is limited when it comes to probing thin interfacial layers which play a central role in the performance and lifetime of battery cells. Here we review how Dynamic Nuclear Polarization (DNP) can lift the sensitivity limitation and enable detection of the electrode-electrolyte interface, as well as the bulk of some electrode and electrolyte systems. We describe the current challenges from the point of view of materials development; considering how the unique electronic, magnetic and chemical properties differentiate battery materials from other applications of DNP in materials science. We review the current applications of exogenous and endogenous DNP from radicals, conduction electrons and paramagnetic metal ions. Finally, we provide our perspective on the opportunities and directions where battery materials can benefit from current DNP methodologies as well as project on future developments that will enable NMR investigation of battery materials with sensitivity and selectivity under ambient conditions.

Effect of vinylene carbonate on SEI formation on LiMn2O4 in carbonate-based electrolytes

The electrochemical reaction of vinylene carbonate on the anode contributes to reduce the reaction of ROH and LiPF6 at LiMn2O4 cathode resulting in an increased LiF/MnF2 ratio of the SEI layer.

Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes

This study demonstrates the application of Al₂O₃ coatings for the high-voltage cathode material LiNi_0.5-x Mn_1.5+x O_4-δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6-1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al₂O₃ coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al₂O₃-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al₂O₃-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al₂O₃-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al₂O₃ coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al₂O₃ coatings could thus be verified, and the coating is not offering long-term protection from HF attack.

From Materials to Cell: State-of-the-Art and Prospective Technologies for Lithium-Ion Battery Electrode Processing

Electrode processing plays an important role in advancing lithium-ion battery technologies and has a significant impact on cell energy density, manufacturing cost, and throughput. Compared to the extensive research on materials development, however, there has been much less effort in this area. In this Review, we outline each step in the electrode processing of lithium-ion batteries from materials to cell assembly, summarize the recent progress in individual steps, deconvolute the interplays between those steps, discuss the underlying constraints, and share some prospective technologies. This Review aims to provide an overview of the whole process in lithium-ion battery fabrication from powder to cell formation and bridge the gap between academic development and industrial manufacturing.

High-voltage liquid electrolytes for Li batteries: progress and perspectives

Since the advent of the Li ion batteries (LIBs), the energy density has been tripled, mainly attributed to the increase of the electrode capacities. Now, the capacity of transition metal oxide cathodes is approaching the limit due to the stability limitation of the electrolytes. To further promote the energy density of LIBs, the most promising strategies are to enhance the cut-off voltage of the prevailing cathodes or explore novel high-capacity and high-voltage cathode materials, and also replacing the graphite anode with Si/Si-C or Li metal. However, the commercial ethylene carbonate (EC)-based electrolytes with relatively low anodic stability of ∼4.3 V vs. Li⁺/Li cannot sustain high-voltage cathodes. The bottleneck restricting the electrochemical performance in Li batteries has veered towards new electrolyte compositions catering for aggressive next-generation cathodes and Si/Si-C or Li metal anodes, since the oxidation-resistance of the electrolytes and the in situ formed cathode electrolyte interphase (CEI) layers at the high-voltage cathodes and solid electrolyte interphase (SEI) layers on anodes critically control the electrochemical performance of these high-voltage Li batteries. In this review, we present a comprehensive and in-depth overview on the recent advances, fundamental mechanisms, scientific challenges, and design strategies for the novel high-voltage electrolyte systems, especially focused on stability issues of the electrolytes, the compatibility and interactions between the electrolytes and the electrodes, and reaction mechanisms. Finally, novel insights, promising directions and potential solutions for high voltage electrolytes associated with effective SEI/CEI layers are proposed to motivate revolutionary next-generation high-voltage Li battery chemistries.

Research Progress of Single-Crystal Nickel-Rich Cathode Materials for Lithium Ion Batteries

Single-crystal nickel-rich cathode materials (SC-NRCMs) are the most promising candidates for next-generation power batteries which enable longer driving range and reliable safety. In this review, the outstanding advantages of SC-NRCMs are discussed systematically in aspects of structural and thermal stabilities. Particularly, the intergranular-crack-free morphology exhibits superior cycling performance and negligible parasitic reactions even under severe conditions. Besides, various synthetic methods are summarized and the relation between precursor, sintering process, and final single-crystal products are revealed, providing a full view of synthetic methods. Then, challenges of SC-NRCMs in fields of kinetics of lithium diffusion and the one particularly occurred at high voltage (intragranular cracks and aggravated parasitic reactions) are discussed. The corresponding mechanism and modifications are also referred. Through this review, it is aimed to highlight the magical morphology of SC-NRCMs for application perspective and provide a reference for following researchers.

A Comparative Review of Metal Oxide Surface Coatings on Three Families of Cathode Materials for Lithium Ion Batteries

In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.

Interphases, Interfaces, and Surfaces of Active Materials in Rechargeable Batteries and Perovskite Solar Cells

The ever-increasing demand for clean sustainable energy has driven tremendous worldwide investment in the design and exploration of new active materials for energy conversion and energy-storage devices. Tailoring the surfaces of and interfaces between different materials is one of the surest and best studied paths to enable high-energy-density batteries and high-efficiency solar cells. Metal-halide perovskite solar cells (PSCs) are one of the most promising photovoltaic materials due to their unprecedented development, with their record power conversion efficiency (PCE) rocketing beyond 25% in less than 10 years. Such progress is achieved largely through the control of crystallinity and surface/interface defects. Rechargeable batteries (RBs) reversibly convert electrical and chemical potential energy through redox reactions at the interfaces between the electrodes and electrolyte. The (electro)chemical and optoelectronic compatibility between active components are essential design considerations to optimize power conversion and energy storage performance. A focused discussion and critical analysis on the formation and functions of the interfaces and interphases of the active materials in these devices is provided, and prospective strategies used to overcome current challenges are described. These strategies revolve around manipulating the chemical compositions, defects, stability, and passivation of the various interfaces of RBs and PSCs.

A Surface Se-Substituted LiCo[O2- δ Seδ ] Cathode with Ultrastable High-Voltage Cycling in Pouch Full-Cells

Cycling LiCoO₂ to above 4.5 V for higher capacity is enticing; however, hybrid O anion- and Co cation-redox (HACR) at high voltages facilitates intrinsic O^{α -} (α < 2) migration, causing oxygen loss, phase collapse, and electrolyte decomposition that severely degrade the battery cyclability. Hereby, commercial LiCoO₂ particles are operando treated with selenium, a well-known anti-aging element to capture oxygen-radicals in the human body, showing an "anti-aging" effect in high-voltage battery cycling and successfully stopping the escape of oxygen from LiCoO₂ even when the cathode is cycled to 4.62 V. Ab initio calculation and soft X-ray absorption spectroscopy analysis suggest that during deep charging, the precoated Se will initially substitute some mobile O^{α -} at the charged LiCoO₂ surface, transplanting the pumped charges from O^{α -} and reducing it back to O^2- to stabilize the oxygen lattice in prolonged cycling. As a result, the material retains 80% and 77% of its capacity after 450 and 550 cycles under 100 mA g^-1 in 4.57 V pouch full-cells matched with a graphite anode and an ultralean electrolyte (2 g Ah^-1 ).

Unanticipated Mechanism of the Trimethylsilyl Motif in Electrolyte Additives on Nickel-Rich Cathodes in Lithium-Ion Batteries

The introduction of a trimethylsilyl (TMS) motif in electrolyte additives for lithium-ion batteries is regarded as an effectual approach to remove corrosive hydrofluoric acid (HF) that structurally and compositionally damages the electrode-electrolyte interface and gives rise to transition metal dissolution from the cathode. Herein, we present that electrolyte additives with TMS moieties lead to continued capacity loss of polycrystalline (PC)-LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes coupled with graphite anodes compared to additives without TMS as the cycle progresses. Through a comparative study using electrolyte additives with and without TMS moieties, it is revealed that the TMS group is prone to react with residual lithium compounds, in particular, lithium hydroxide (LiOH) on the PC-NCM811 cathode, and the resulting TMS-OH triggers the decomposition of PF₅ created by the autocatalytic decomposition of LiPF₆ that generates reactive species, namely, HF and POF₃. This work aims to offer a way to build favorable interface structures for Ni-rich cathodes covered with residual lithium compounds through a study to figure out the roles of TMS moieties of electrolyte additives.

A LiPO2F2/LiPF6 dual-salt electrolyte enabled stable cycling performance of nickel-rich lithium ion batteries

The LiPO₂F₂/LiPF₆ dual-salt electrolyte can significantly enhance the cycling performance of NCM811/Li cells.

Di(methylsulfonyl) Ethane: New Electrolyte Additive for Enhancing LiCoO2/Electrolyte Interface Stability under High Voltage

In the work reported in this article, di(methylsulfonyl) ethane (DMSE) was examined as a neoteric S-related electrolyte additive to elevate LiCoO₂/electrolyte interfacial stability at 3.0-4.5 V (compared to Li/Li⁺). DMSE, when added to the electrolyte, can significantly enhance the high-voltage performance of LiCoO₂/graphite cells. Meanwhile, capacity retention increased from 20.8 to 66.5% after 100 cycles owing to the adjunction of 0.5 wt % DMSE to the electrolyte (carbonate solvents and lithium salt). The density functional theory calculation results indicate that DMSE has a greater highest occupied molecular orbital energy in contrast to ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Differential capacity versus voltage analysis and linear sweep voltammetry result indicate that DMSE is decomposed in preference to the electrolyte solvents. DMSE's effects are distinguished by electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, X-ray-diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The outcomes indicate that the enhanced cycling performance is attributed to the involvement of DMSE in the generation of a thinner film on LiCoO₂, which results in lower interfacial impedance and it protects the electrolyte from decomposition at high voltage.

High-Energy and High-Power-Density Potassium Ion Batteries Using Dihydrophenazine-Based Polymer as Active Cathode Material

Polymeric aromatic amines were shown to be very promising cathodes for lithium-ion batteries. Surprisingly, these materials are scarcely used for designing post-lithium batteries. In this Letter, we investigate the application of the high-voltage poly(N-phenyl-5,10-dihydrophenazine) (p-DPPZ) cathodes for K-ion batteries. The designed batteries demonstrate an impressive specific capacity of 162 mAh g^-1 at the current density of 200 mA g^-1, operate efficiently at high current densities of 2-10 A g^-1, enabling charge and discharge within ∼1-4 min, and deliver the specific capacity of 125-145 mAh g^-1 with a retention of 96 and 79% after 100 and 1000 charge-discharge cycles, respectively. Finally, these K-ion batteries with polymeric p-DPPZ cathodes showed rather outstanding specific power of >3 × 10⁴ W kg^-1, thus paving a way to the design of ultrafast and durable high-capacity metal-ion batteries matching the increasing demand for high power and high energy density electrochemical energy storage devices.

Stabilizing a High-Voltage Lithium-Rich Layered Oxide Cathode with a Novel Electrolyte Additive

We report a novel electrolyte additive, bis(trimethylsilyl)carbodiimide, that effectively stabilizes high-voltage lithium-rich oxide cathode. Charge/discharge tests demonstrate that even trace amounts of bis(trimethylsilyl)carbodiimide in a baseline electrolyte improve the cycling stability of this cathode significantly, either in Li-based half cells or graphite-based full cells, where the capacity retention after 200 cycles between 2 and 4.8 V at 0.5C is enhanced from 40 to 72% and 49 to 77%, respectively. Analyses using physical characterization and theoretical calculations reveal that this additive not only builds a protective film on the cathode but also eliminates detrimental hydrogen fluoride via its strong coordination with hydrogen fluoride or protons.

Simplifying the Electrolyte Systems with the Functional Cosolvent

The state-of-the-art electrolytes utilized in lithium-ion batteries are based on liquid carbonates combining a number of additives to fulfill the practical requirements including safety and low temperature. The plenty of components result in the quadruple times of probable radical groups involved into the interfacial reactions, rendering it too difficult to control the surface layer. This work tends to simplify the system with the fluorine-substituted ether as the functional cosolvent to expand the functions of basic electrolytes. The incorporation of this solvent enables the electrolyte to self-extinguish, reduces its freezing point to ∼75 °C lower, and assists in the formation of LiF-rich protective interlayers, resulting in the improvement of the rate capability, cryogenic performance, and cyclic stability for the LiNi_1/3Co_1/3Mn_1/3O₂ cathode. This novel design could significantly diminish the amount of necessary additives and possess the acceptable cost, which provides a probability to revitalize the development of liquid electrolytes.

Fluorinated Cyclic Phosphorus(III)-Based Electrolyte Additives for High Voltage Application in Lithium-Ion Batteries: Impact of Structure-Reactivity Relationships on CEI Formation and Cell Performance

Two selected and designed fluorinated cyclic phosphorus(III)-based compounds, namely 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane (PFPOEPi) and 2-(2,2,3,3,3-pentafluoro-propoxy)-4-(trifluormethyl)-1,3,2-dioxaphospholane (PFPOEPi-1CF₃), were synthesized and comprehensively characterized for high voltage application in lithium-ion batteries (LIBs). Cyclic voltammetry (CV) and constant current cycling were conducted, followed by post mortem analysis of the NMC111 electrode surface via scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). To support and complement obtained experimental results, density functional theory (DFT) calculations and molecular dynamics (MD) simulations were performed. Theoretical and experimental findings show that the considered phospholane molecule class enables high voltage LIB application by sacrificial decomposition on the cathode surface and involvement in the formation of a cathode electrode interphase (CEI) via polymerization reaction. In addition, obtained results point out that the introduction of the CF₃ group has a significant influence on the formation and dynamics of the CEI as well as on the overall cell performance, as the cell impedance as well as the thickness of the CEI is increased compared to the cells containing PFPOEPi, which results in a decreased cycling performance. This systematic approach allows researchers to understand the structure-reactivity relationship of the newly synthesized compounds and helps to further tailor the vital physicochemical properties of functional electrolyte additives relevant for high voltage LIB application.

Scavenging Materials to Stabilize LiPF6 -Containing Carbonate-Based Electrolytes for Li-Ion Batteries

In conjunction with electrolyte additives used for tuning the interfacial structures of electrodes, functional materials that eliminate or deactivate reactive substances generated by the degradation of LiPF₆ -containing electrolytes in lithium-ion batteries offer a wide range of electrolyte formulation opportunities. Herein, the recent advancements in the development of: (i) scavengers with high selectivity and affinity toward unwanted species and (ii) promoters of ion-paired LiPF₆ dissociation are highlighted, showing that the utilization of the above additives can effectively mitigate the problem of electrolyte instability that commonly results in battery performance degradation and lifetime shortening. A deep mechanistic understanding of LiPF₆ -containing electrolyte failure and the action of currently developed additives is demonstrated to enable the rational design of effective scavenging materials and thus allow the fabrication of highly reliable batteries.

Synthesis and electrochemical properties of Li1.3Nb0.3Cr0.4O2 as a high-capacity cathode material for rechargeable lithium batteries

A cation-disordered Li-excess cathode material on the binary system xLi3NbO4-(1 - x)LiCrO2 (x = 0.43) has been successfully prepared by mechanical milling, and delivers a high reversible capacity of ∼362 mA h g-1, which originates from a highly reversible Cr3+/Cr6+ three-electron redox reaction with electrochemically inactive niobium ions.