Conformal Prelithiation Nanoshell on LiCoO2 Enabling High-Energy Lithium-Ion Batteries

Energy band modulation of Li2O-rGO core-shell as cathode sacrificial additive enables capacity enhancement of hard carbon anode in Li-ion batteries

Lithium oxides (Li2O) possess a considerable theoretical capacity, rendering them highly promising as cathodic pre-lithiation additives. However, its decomposition voltage exceeds the charging cut-off voltage of most cathode materials, hindering its direct use as a cathode sacrificial additive. Herein, we design a facile and safe method to reduce the decomposition energy of Li2O at room temperature to offset the irreversible capacity loss by using a core-shell structured Li2O-reduced graphene oxide (rGO)-polyethylene glycol (PEG) composite (denoted as Li2O-rGO-PEG). The graphene oxide (GO) was heat-treated to remove oxygen functional groups to synthesize rGO, and then reacted with Li2O to form a Li2O-rGO composite. According to the DFT calculations, the density of states at the Fermi level of Li2O-rGO becomes continuous and features a metallic nature, which significantly improves the electrical conductivity of Li2O and facilitates electron conduction that modify the delithiation potential of Li2O. PEG was used to enhance the cohesive force between rGO and Li2O and to protect Li2O from atmospheric contamination. Moreover, in order to demonstrate the excellent pre-lithiation ability of Li2O-rGO-PEG composite, hard carbon (HC) with low initial coulombic efficiency (ICE) was used as the anode. In the application of LFP (Li2O)/HC full cell, Li2O was decomposed to Li+ to effectively improve the initial charge capacity from 149.7 to 200 mAh/g and discharge capacity from 104.2 to 147.5 mAh/g, which are 33.6 % and 41.6 % higher than those of the pristine LFP/HC full cell, respectively. The cathode pre-lithiation method proposed in this work is simple and environmentally friendly. The successful utilization of Li2O as a pre-lithiation additive effectively addressed the issue of low initial coulombic efficiency of the HC, indicating excellent prospects for practical applications.

Origin of electrochemical voltage range and voltage profile of insertion electrodes

This study evaluates electrochemical voltage-range and voltage-profile regarding electrodes of insertion (intercalation) batteries. The phrase "voltage-range" expresses the difference between obtained maximum and minimum potential for the cells. It also can be called as operating voltage-range, working voltage-range, electrochemical voltage-range, or voltage window. This paper proposes a new notion regarding electron density of states, i.e. trans-band, which can be implemented to justify the voltage -range and -profile, by means of Fermi levels' alignment. Voltage -range and -profile of a number of insertion electrode materials are clarified by the proposed theoretical approach, namely LiMn2O4, Li2Mn2O4, ZnMn2O4, LiFePO4, LiCoO2, Li2FeSiO4, LiFeSO4F, and TiS2. Moreover, the probable observed difference between charge and discharge profile is explained by the approach. The theoretical model/approach represents a number of important concepts, which can meet some scientific fields, e.g. electrochemistry, energy storage devices, solid state physics (DFT), and phase diagrams. By means of DFT calculations, this paper deals with quantizing the energy of electrochemical reactions, justifying the configuration of voltage-profile, and explaining the origin of the voltage-range. Accordance with the experimental observations suggests that this paper can extend boundary of quantum mechanics toward territories of classical thermodynamics, and boundary of the modern thermodynamics toward kinetics. Opening a new horizon in the related fields, this paper can help tuning, engineering, and predicting cell-voltage behavior.

Advances of LiCoO2 in Cathode of Aqueous Lithium-Ion Batteries

Aqueous lithium-ion batteries offer promising advantages such as low cost, enhanced safety, high rate capability, and the ability to deliver considerable capacity at 1.8 V, making them ideal candidates for large-scale reserve power sources for renewable energy. However, the practical application of aqueous lithium-ion batteries has been hindered by the poor cycle stability of layered cathode materials, including LiCoO2, in neutral aqueous electrolytes. This review examines the working principles, material limitations, and research progress of aqueous lithium-ion batteries. The types and characteristics of materials used in the cathode of aqueous lithium-ion batteries are summarized, with a primary focus on the attenuation mechanisms of LiCoO2 when used as the cathode material in aqueous electrolytes. Furthermore, this review explores the advancements in utilizing LiCoO2 in the cathode of aqueous lithium-ion batteries, as well as the combination with machine learning. By addressing these critical aspects, this review aims to provide a comprehensive understanding of aqueous lithium-ion batteries and shed light on future development and application prospects.

Electrolyte-assisted low-voltage decomposition of Li2C2O4 for efficient cathode pre-lithiation in lithium-ion batteries

Lithium oxalate (Li2C2O4) is an attractive cathode pre-lithiation additive for lithium-ion batteries (LIBs), but its application is hindered by its high decomposition potential (>4.7 V). Due to the liquid-solid synergistic effect of the NaNO2 additive and the LiNi0.83Co0.07Mn0.1O2 (NCM) cathode material, the decomposition efficiency of micro-Li2C2O4 reaches 100% at a low charge cutoff voltage of 4.3 V. Our work boosts the widespread practical application of Li2C2O4 by a simple and promising electrolyte-assisted cathode pre-lithiation strategy.

Controllable synthesis of a Na-enriched Na4V2(PO4)3 cathode for high-energy sodium-ion batteries: a redox-potential-matched chemical sodiation approach

Exploring a sodium-enriched cathode (i.e. Na4V2(PO4)3, which differs from its traditional stoichiometric counterpart Na3V2(PO4)3 that can provide extra endogenous sodium reserves to mitigate the irreversible capacity loss of the anode material (i.e. hard carbon), is an intriguing presodiation method for the development of high energy sodium-ion batteries. To meet this challenge, herein, we first propose a redox-potential-matched chemical sodiation approach, utilizing phenazine-sodium (PNZ-Na) as the optimal reagent to sodiate the Na3V2(PO4)3 precursor into Na-enriched Na4V2(PO4)3. The spontaneous sodiation reaction enables a fast reduction of one-half V ions from V3+ to V2+, followed by the insertion of one Na+ ion into the NASICON framework, which only takes 90 s to obtain the phase-pure Na4V2(PO4)3 product. When paired with a hard carbon anode, the resulting Na4VP‖HC full cell exhibits a high energy density of 251 W h kg-1, which is 58% higher than that of 159 W h kg-1 for the Na3VP‖HC control cell. Our chemical sodiation methodology provides an innovative approach for designing sodium-rich cathode materials and could serve as an impetus to the development of advanced sodium-ion batteries.

Probing Hybrid LiFePO4/FePO4 Phases in a Single Olive LiFePO4 Particle and Their Recovering from Degraded Electric Vehicle Batteries

The recycling of LiFePO4 from degraded lithium-ion batteries (LIBs) from electric vehicles (EVs) has gained significant attention due to resource, environment, and cost considerations. Through neutron diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, we revealed continuous lithium loss during battery cycling, resulting in a Li-deficient state (Li1-xFePO4) and phase separation within individual particles, where olive-shaped FePO4 nanodomains (5-10 nm) were embedded in the LiFePO4 matrix. The preservation of the olive-shaped skeleton during Li loss and phase change enabled materials recovery. By chemical compensation for the lithium loss, we successfully restored the hybrid LiFePO4/FePO4 structure to pure LiFePO4, eliminating nanograin boundaries. The regenerated LiFePO4 (R-LiFePO4) exhibited a high crystallinity similar to the fresh counterpart. This study highlights the importance of topotactic chemical reactions in structural repair and offers insights into the potential of targeted Li compensation for energy-efficient recycling of battery electrode materials with polyanion-type skeletons.

Synthesis and modification mechanism of vanadium oxide coated LiFePO4cathode materials with excellent electrochemical performance

In an era of rapid industrial development, such that the demand for energy is increasing daily, lithium-ion batteries are playing a dominant role in energy storage devices due to their high safety and low cost. However, it is still a challenge for the preparation of advanced cathodes, which can determine the battery performance, with stable structures and fast diffusion of Li+. This is especially the case for lithium iron phosphate (LFP), a cathode material with severe limitations due to its low conductive efficiency. To improve its conductivity, LFP was compounded with defect-modified V2O5to prepare LFP/V/C materials with excellent electrochemical properties, which exhibited an initial capacity of 138.85 mAh g-1and 95% retention after 500 charge/discharge cycles at a current density of 5 C. Also, the effect of defects on ionic diffusion was discussed in detail by means of density function theor (DFT) calculations, confirming that the improvement of electrochemical performance is closely related to the introduction of hybrid conductive layers of surface cladding.

The Proof-of-Concept of Anode-Free Rechargeable Mg Batteries

The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less-prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof-of-concept of anode-free Mg₂ Mo₆ S₈ -MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg₂ Mo₆ S₈ and MgS acts as the active material to reversibly provide high capacities. Besides, Mg₂ Mo₆ S₈ shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode-free Mg₂ Mo₆ S₈ -MgS/Cu batteries deliver a high reversible capacity of 190 mAh g^-1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L^-1 . The proposed anode-free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice.

All-Solid-State Garnet-Based Lithium Batteries at Work-In Operando TEM Investigations of Delithiation/Lithiation Process and Capacity Degradation Mechanism

Li₇ La₃ Zr₂ O₁₂ (LLZO)-based all-solid-state Li batteries (SSLBs) are very attractive next-generation energy storage devices owing to their potential for achieving enhanced safety and improved energy density. However, the rigid nature of the ceramics challenges the SSLB fabrication and the afterward interfacial stability during electrochemical cycling. Here, a promising LLZO-based SSLB with a high areal capacity and stable cycle performance over 100 cycles is demonstrated. In operando transmission electron microscopy (TEM) is used for successfully demonstrating and investigating the delithiation/lithiation process and understanding the capacity degradation mechanism of the SSLB on an atomic scale. Other than the interfacial delamination between LLZO and LiCoO₂ (LCO) owing to the stress evolvement during electrochemical cycling, oxygen deficiency of LCO not only causes microcrack formation in LCO but also partially decomposes LCO into metallic Co and is suggested to contribute to the capacity degradation based on the atomic-scale insights. When discharging the SSLB to a voltage of ≈1.2 versus Li/Li⁺ , severe capacity fading from the irreversible decomposition of LCO into metallic Co and Li₂ O is observed under in operando TEM. These observations reveal the capacity degradation mechanisms of the LLZO-based SSLB, which provides important information for future LLZO-based SSLB developments.

Prelithiation Bridges the Gap for Developing Next-Generation Lithium-Ion Batteries/Capacitors

The ever-growing market of portable electronics and electric vehicles has spurred extensive research for advanced lithium-ion batteries (LIBs) with high energy density. High-capacity alloy- and conversion-type anodes are explored to replace the conventional graphite anode. However, one common issue plaguing these anodes is the large initial capacity loss caused by the solid electrolyte interface formation and other irreversible parasitic reactions, which decrease the total energy density and prevent further market integration. Prelithiation becomes indispensable to compensate for the initial capacity loss, enhance the full cell cycling performance, and bridge the gap between laboratory studies and the practical requirements of advanced LIBs. This review summarizes the various emerging anode and cathode prelithiation techniques, the key barriers, and the corresponding strategies for manufacturing-compatible and scalable prelithiation. Furthermore, prelithiation as the primary Li⁺ donor enables the safe assembly of new-configured "beyond LIBs" (e.g., Li-ion/S and Li-ion/O₂ batteries) and high power-density Li-ion capacitors (LICs). The related progress is also summarized. Finally, perspectives are suggested on the future trend of prelithiation techniques to propel the commercialization of advanced LIBs/LICs.

Prelithiation Reagents and Strategies on High Energy Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely employed in energy-storage applications owing to the relatively higher energy density and longer cycling life. However, they still need further improvement especially on the energy density to satisfy the increasing demands on the market. In this respect, the irreversible capacity loss (ICL) in the initial cycle is a critical challenge due to the lithium loss during the formation of solid electrolyte interphase (SEI) layer on the anode surface. The strategy of prelithiation was then proposed to compensate for the ICL in the anode and recover the energy density. Here, various methods of the prelithiation are summarized and classified according to the basic working mechanism. Further, considering the critical importance and promising progress of prelithiation in both fundamental research and real applications, this Review article is intended to discuss the considerations involved in the selection of prelithiation reagents/strategies and the electrochemical performance in full-cells. Moreover, insights are provided regarding the practical application prospects and the challenges that still need to be addressed.

Energy-Saving Synthesis of Functional CoS2/rGO Interlayer With Enhanced Conversion Kinetics for High-Performance Lithium-Sulfur Batteries

Lithium sulfur (Li-S) battery has exhibited great application potential in next-generation high-density secondary battery systems due to their excellent energy density and high specific capacity. However, the practical industrialization of Li-S battery is still affected by the low conductivity of sulfur and its discharge product (Li₂S₂/Li₂S), the shuttle effect of lithium polysulfide (Li₂S_n, 4 ≤ n ≤ 8) during charging/discharging process and so on. Here, cobalt disulfide/reduced graphene oxide (CoS₂/rGO) composites were easily and efficiently prepared through an energy-saving microwave-assisted hydrothermal method and employed as functional interlayer on commercial polypropylene separator to enhance the electrochemical performance of Li-S battery. As a physical barrier and second current collector, the porous conductive rGO can relieve the shuttle effect of polysulfides and ensure fast electron/ion transfer. Polar CoS₂ nanoparticles uniformly distributed on rGO provide strong chemical adsorption to capture polysulfides. Benefitting from the synergy of physical and chemical constraints on polysulfides, the Li-S battery with CoS₂/rGO functional separator exhibits enhanced conversion kinetics and excellent electrochemical performance with a high cycling initial capacity of 1,122.3 mAh g⁻¹ at 0.2 C, good rate capabilities with 583.9 mAh g⁻¹ at 2 C, and long-term cycle stability (decay rate of 0.08% per cycle at 0.5 C). This work provides an efficient and energy/time-saving microwave hydrothermal method for the synthesis of functional materials in stable Li-S battery.

A Review on Recent Advances for Boosting Initial Coulombic Efficiency of Silicon Anodic Lithium Ion batteries

Rechargeable silicon anode lithium ion batteries (SLIBs) have attracted tremendous attention because of their merits, including a high theoretical capacity, low working potential, and abundant natural sources. The past decade has witnessed significant developments in terms of extending the lifespan and maintaining high capacities of SLIBs. However, the detrimental issue of low initial Coulombic efficiency (ICE) toward SLIBs is causing more and more attention in recent years because ICE value is a core index in full battery design that profoundly determines the utilization of active materials and the weight of an assembled battery. Herein, a comprehensive review is presented of recent advances in solutions for improving ICE of SLIBs. From design perspectives, the strategies for boosting ICE of silicon anodes are systematically categorized into several aspects covering structure regulation, prelithiation, interfacial design, binder design, and electrolyte additives. The merits and challenges of various approaches are highlighted and discussed in detail, which provides valuable insights into the rational design and development of state-of-the-art techniques to deal with the deteriorative issue of low ICE of SLIBs. Furthermore, conclusions and future promising research prospects for lifting ICE of SLIBs are proposed at the end of the review.

Ultra-Low-Dose Pre-Metallation Strategy Served for Commercial Metal-Ion Capacitors

Interfacial bonding strategy has been successfully applied to address the high overpotential issue of sacrificial additives, which reduced the decompositon potential of Na₂C₂O₄ from 4.50 to 3.95 V. Ultra-low-dose technique assisted commercial sodium ion capacitor (AC//HC) could deliver a remarkable energy density of 118.2 Wh kg^-1 as well as excellent cycle stability. In-depth decomposition mechanism of sacrificial compound and the relative influence after pre-metallation were revealed by advanced in situ and ex situ characterization approaches. Sacrificial pre-metallation strategy could compensate for the irreversible consumption of metal ions and reduce the potential of anode, thereby elevating the cycle performance as well as open-circuit voltage for full metal ion capacitors (MICs). However, suffered from massive-dosage abuse, exorbitant decomposition potential, and side effects of decomposition residue, the wide application of sacrificial approach was restricted. Herein, assisted with density functional theory calculations, strongly coupled interface (M-O-C, M = Li/Na/K) and electron donating group have been put forward to regulate the band gap and highest occupied molecular orbital level of metal oxalate (M₂C₂O₄), reducing polarization phenomenon and Gibbs free energy required for decomposition, which eventually decrease the practical decomposition potential from 4.50 to 3.95 V. Remarkably, full sodium ion capacitors constituted of commercial materials (activated carbon//hard carbon) could deliver a prominent energy density of 118.2 Wh kg^-1 as well as excellent cycle stability under an ultra-low dosage pre-sodiation reagent of 15-30 wt% (far less than currently 100 wt%). Noteworthily, decomposition mechanism of sacrificial compound and the relative influence on the system of MICs after pre-metallation were initially revealed by in situ differential electrochemical mass spectrometry, offering in-depth insights for comprehending the function of cathode additives. In addition, this breakthrough has been successfully utilized in high performance lithium/potassium ion capacitors with Li₂C₂O₄/K₂C₂O₄ as pre-metallation reagent, which will convincingly promote the commercialization of MICs.

Tailoring Co3d and O2p Band Centers to Inhibit Oxygen Escape for Stable 4.6 V LiCoO2 Cathodes

High-voltage LiCoO₂ delivers a high capacity but sharp fading is a critical issue, and the capacity decay mechanism is also poorly understood. Herein, we clarify that the escape of surface oxygen and Li-insulator Co₃ O₄ formation are the main causes for the capacity fading of 4.6 V LiCoO₂ . We propose the inhibition of the oxygen escape for achieving stable 4.6 V LiCoO₂ by tailoring the Co3d and O2p band center and enlarging their band gap with MgF₂ doping. This enhances the ionicity of the Co-O bond and the redox activity of Co and improves cation migration reversibility. The inhibition of oxygen escape suppresses the formation of Li-insulator Co₃ O₄ and maintains the surface structure integrity. Mg acts as a pillar, providing a stable and enlarged channel for fast Li⁺ intercalation/extraction. The modulated LiCoO₂ shows almost zero strain and achieves a record capacity retention at 4.6 V: 92 % after 100 cycles at 1C and 86.4 % after 1000 cycles at 5C.

Commercialization-Driven Electrodes Design for Lithium Batteries: Basic Guidance, Opportunities, and Perspectives

Current lithium-ion battery technology is approaching the theoretical energy density limitation, which is challenged by the increasing requirements of ever-growing energy storage market of electric vehicles, hybrid electric vehicles, and portable electronic devices. Although great progresses are made on tailoring the electrode materials from methodology to mechanism to meet the practical demands, sluggish mass transport, and charge transfer dynamics are the main bottlenecks when increasing the areal/volumetric loading multiple times to commercial level. Thus, this review presents the state-of-the-art developments on rational design of the commercialization-driven electrodes for lithium batteries. First, the basic guidance and challenges (such as electrode mechanical instability, sluggish charge diffusion, deteriorated performance, and safety concerns) on constructing the industry-required high mass loading electrodes toward commercialization are discussed. Second, the corresponding design strategies on cathode/anode electrode materials with high mass loading are proposed to overcome these challenges without compromising energy density and cycling durability, including electrode architecture, integrated configuration, interface engineering, mechanical compression, and Li metal protection. Finally, the future trends and perspectives on commercialization-driven electrodes are offered. These design principles and potential strategies are also promising to be applied in other energy storage and conversion systems, such as supercapacitors, and other metal-ion batteries.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes

Rechargeable Li-based battery technologies utilising silicon, silicon-based, and Si-derivative anodes coupled with high-capacity/high-voltage insertion-type cathodes have reaped significant interest from both academic and industrial sectors. This stems from their practically achievable energy density, offering a new avenue towards the mass-market adoption of electric vehicles and renewable energy sources. Nevertheless, such high-energy systems are limited by their complex chemistry and intrinsic drawbacks. From this perspective, we present the progress, current status, prevailing challenges and mitigating strategies of Li-based battery systems comprising silicon-containing anodes and insertion-type cathodes. This is accompanied by an assessment of their potential to meet the targets for evolving volume- and weight-sensitive applications such as electro-mobility.

Molecularly Compensated Pre-Metallation Strategy for Metal-Ion Batteries and Capacitors

The use of a sacrificial cathode additive as a pre-metallation method could ensure adequate metal sources for advanced energy storage devices. However, this pre-metallation technique suffers from the precise regulation of decomposition potential of additive. Herein, a molecularly compensated pre-metallation (Li/Na/K) strategy has been achieved through Kolbe electrolysis, in which the electrochemical oxidation potential of a metal carboxylate is manipulated by the bonding energy of the oxygen-metal (O-M) moiety. The electron-donating effect of the substituent and the low charge density of the cation can dramatically weaken the O-M bond strength, further bringing out the reduced potential. Thus, sodium acetate exhibits a superior pre-sodiation feature for sodium-ion battery accompanied with a large irreversible specific capacity of 301.8 mAh g^-1 , remarkably delivering 70.6 % enhanced capacity retention in comparison to the additive-free system after 100 cycles. This methodology has been extended to construct a high-performance lithium-ion battery and a lithium/sodium/potassium-ion capacitor.

Ultrafine Sodium Sulfide Clusters Confined in Carbon Nano-polyhedrons as High-Efficiency Presodiation Reagents for Sodium-Ion Batteries

Sodium loss at the anode in the initial sodiation process significantly reduces the energy density of sodium-ion batteries (SIBs). Here, a high-capacity Na₂S/C nanocomposite featuring ultrafine Na₂S nanoclusters (<2 nm) confined in ZIF-8-derived microporous N-doped carbon is fabricated and employed as a cathode presodiation reagent to compensate for this sodium loss and increase the energy density of SIBs. The ultrafine size of Na₂S enables fast reaction kinetics for sodium extraction and the carbon matrix provides good electronic conductivity. Also, the overall particle size of the Na₂S/C nanocomposite (∼40 nm) is close to that of conductive additive. The above features enable it to replace a partial amount of conductive additive and compensate for the sodium loss at the anode concurrently. As a demonstration, the Na₃V₂(PO₄)₃ electrode with 5 wt % Na₂S/C and 5 wt % carbon black was fabricated, and it displayed a 19 mAh g^-1 higher initial charge specific capacity than that of the counterpart with 10% carbon black without the addition of Na₂S/C, realizing an increased energy density from 178 to 263 Wh kg^-1 in the full cell configuration pairing with a hard carbon anode. Moreover, a stable cycling performance up to 200 cycles with an average capacity loss of 0.024 mAh g^-1 per cycle was achieved for the presodiated Na₃V₂(PO₄)₃ electrode.

The Electrolysis of Anti-Perovskite Li2 OHCl for Prelithiation of High-Energy-Density Batteries

Anti-perovskite type Li₂ OHCl was previously studied as a solid-state Li⁺ conductor. Here, we report that the Li₂ OHCl can be electrolyzed at 3.3 V or 4.0 V, with the creation of O₂ /HCl gases and the release of 2 equiv. Li⁺ via two different decomposition routes, depending on the acidity of electrolyte. In the electrolyte with trace acid, the Li₂ OHCl is oxidized at a constant voltage of 3.3 V. In neutral electrolyte, the oxidization of Li₂ OHCl starts at 4.0 V, but the produced HCl will increase the acidity of electrolyte and lead to a voltage drop to 3.3 V for the electrolysis of Li₂ OHCl. The electrolysis of Li₂ OHCl delivers a lithium releasing capacity as high as 810 mAh g^-1 , with an equivalent Li-deposition or Li-intercalation on anode, making it a promising candidate as a Li reservoir for prelithiation of anode. Using Li₂ OHCl as the lithium source, silicon-carbon (Si@C) composite anode can be effectively prelithiated. The full cells composed of LiNi_0.8 Mn_0.1 Co_0.1 O₂ (NMC811) cathode and prelithiated Si@C anode exhibited increased capacities with the increment of prelithiation dosages.

Recent Advances in Silicon-Based Electrodes: From Fundamental Research toward Practical Applications

The increasing demand for higher-energy-density batteries driven by advancements in electric vehicles, hybrid electric vehicles, and portable electronic devices necessitates the development of alternative anode materials with a specific capacity beyond that of traditional graphite anodes. Here, the state-of-the-art developments made in the rational design of Si-based electrodes and their progression toward practical application are presented. First, a comprehensive overview of fundamental electrochemistry and selected critical challenges is given, including their large volume expansion, unstable solid electrolyte interface (SEI) growth, low initial Coulombic efficiency, low areal capacity, and safety issues. Second, the principles of potential solutions including nanoarchitectured construction, surface/interface engineering, novel binder and electrolyte design, and designing the whole electrode for stability are discussed in detail. Third, applications for Si-based anodes beyond LIBs are highlighted, specifically noting their promise in configurations of Li-S batteries and all-solid-state batteries. Fourth, the electrochemical reaction process, structural evolution, and degradation mechanisms are systematically investigated by advanced in situ and operando characterizations. Finally, the future trends and perspectives with an emphasis on commercialization of Si-based electrodes are provided. Si-based anode materials will be key in helping keep up with the demands for higher energy density in the coming decades.

Role of free volumes and segmental dynamics on ion conductivity of PEO/LiTFSI solid polymer electrolytes filled with SiO2 nanoparticles: a positron annihilation and broadband dielectric spectroscopy study

The limited ionic conductivity of polymer electrolytes is a major issue for their industrial application. Enhancement of ionic conductivity in the poly(ethylene oxide), PEO, based electrolyte has been achieved by loading passive nanofillers such as SiO₂ nanoparticles (NPs). To investigate the role of modifications in free volume characteristics and the polymer chain dynamics induced by the loading of passive fillers on the ionic conductivity of the PEO based ternary electrolyte, a systematic investigation has been carried out using positron annihilation and broadband dielectric spectroscopy. As a result of interfacial interactions, the loading of SiO₂ NPs alters the semi-crystalline morphology of PEO resulting in a higher crystallinity at lower loadings due to the surface confinement of PEO chains, and the formation of smaller PEO crystallites at higher loadings due to interparticle nanoconfinement. These modifications are accompanied by a decrease in free volume fraction at the lowest loading (0.5 wt%) followed by an increase at higher loadings (≥2.0 wt%). The Almond-West formalism considering two different universalities in different temperature and frequency ranges has been used to explain the ion-conduction process at different NP loadings. The Li ion conductivity is observed to be maximum for a 5.0 wt% loading of SiO₂ NPs. The enhancement in ionic conductivity is observed to be directly correlated with the free volume characteristics and segmental dynamics of the PEO matrix, confirming their role in ion transport in polymer electrolytes.

A Scalable Cathode Chemical Prelithiation Strategy for Advanced Silicon-Based Lithium Ion Full Batteries

A silicon anode with ultra-high specific capacity has motivated tremendous exploration for high-energy-density lithium ion batteries while it still faces serious issues of irreversible lithium loss, unstable electrode electrolyte interface (SEI), and huge volume expansion. Prelithiation is a crucial technology to alleviate the harm of active lithium loss of silicon-based full-cell systems. Herein, we reported a cathode prelithiation method using Li₂S-PAN as a lithium "donor", which was synthesized via chemical reaction between sulfurized polyacrylonitrile and Li-biphenyl complex. The Li₂S-PAN with an initial charging capacity of 668 mAh g^-1 (2.5-4.0 V) is loaded on the LiFePO₄ electrode, and the LiFePO₄/Li₂S-PAN composite electrode displays a high initial charge capacity of 206 mAh g^-1, which is 22.3% higher than the pristine LiFePO₄. With a silicon/graphite/carbon (Si/G/C) composite anode, the Si/G/C||LiFePO₄/Li₂S-PAN full cell exhibits a reversible capacity of 123 and 107 mAh g^-1 in the 1st and 10th cycle, which is 15.5 and 24.5% higher than the Si/G/C||LiFePO₄ battery, respectively. The SEI layer of the silicon anode in the Si/G/C||LiFePO₄/Li₂S-PAN cell contains abundant conductive LiF species, which can enhance the interfacial stability and reaction kinetics of the cells. The proposed cathode prelithiation process is compatible with the industrial roll-to-roll electrode preparation process, exhibiting a promising application prospect.

Prelithiation: A Crucial Strategy for Boosting the Practical Application of Next-Generation Lithium Ion Battery

With the urgent market demand for high-energy-density batteries, the alloy-type or conversion-type anodes with high specific capacity have gained increasing attention to replace current low-specific-capacity graphite-based anodes. However, alloy-type and conversion-type anodes have large initial irreversible capacity compared with graphite-based anodes, which consume most of the Li⁺ in the corresponding cathode and severely reduces the energy density of full cells. Therefore, for the practical application of these high-capacity anodes, it is urgent to develop a commercially available prelithiation technique to compensate for their large initial irreversible capacity. At present, various prelithiation methods for compensating the initial irreversible capacity of the anode have been reported, but due to their respective shortcomings, large-scale commercial applications have not yet been achieved. In this review, we have systematically summarized and analyzed the advantages and challenges of various prelithiation methods, providing enlightenment for the further development of each prelithiation strategy toward commercialization and thus facilitating the practical application of high-specific-capacity anodes in the next-generation high-energy-density lithium-ion batteries.