In Situ Developed Si@Polymethyl Methacrylate Capsule as a Li-Ion Battery Anode with High-Rate and Long Cycle-Life

Bionic Capsule Lithium-Ion Battery Anodes for Efficiently Inhibiting Volume Expansion

Magnetite (Fe3O4) has a large theoretical reversible capacity and rich Earth abundance, making it a promising anode material for LIBs. However, it suffers from drastic volume changes during the lithiation process, which lead to poor cycle stability and low-rate performance. Hence, there is an urgent need for a solution to address the issue of volume expansion. Taking inspiration from how glycophyte cells mitigate excessive water uptake/loss through their cell wall to preserve the structural integrity of cells, we designed Fe3O4@PMMA multi-core capsules by microemulsion polymerization as a kind of anode materials, also proposed a new evaluation method for real-time repair effect of the battery capacity. The Fe3O4@PMMA anode shows a high reversible specific capacity (858.0 mAh g-1 at 0.1 C after 300 cycles) and an excellent cycle stability (450.99 mAh g-1 at 0.5 C after 450 cycles). Furthermore, the LiNi0.8Co0.1Mn0.1O2/Fe3O4@PMMA pouch cells exhibit a stable capacity (200.6 mAh) and high-capacity retention rate (95.5 %) after 450 cycles at 0.5 C. Compared to the original battery, the capacity repair rate of this battery is as high as 93.4 %. This kind of bionic capsules provide an innovative solution for improving the electrochemical performance of Fe3O4 anodes to promote their industrial applications.

Bio-Inspired Electrodes with Rational Spatiotemporal Management for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are currently the predominant energy storage power source. However, the urgent issues of enhancing electrochemical performance, prolonging lifetime, preventing thermal runaway-caused fires, and intelligent application are obstacles to their applications. Herein, bio-inspired electrodes owning spatiotemporal management of self-healing, fast ion transport, fire-extinguishing, thermoresponsive switching, recycling, and flexibility are overviewed comprehensively, showing great promising potentials in practical application due to the significantly enhanced durability and thermal safety of LIBs. Taking advantage of the self-healing core-shell structures, binders, capsules, or liquid metal alloys, these electrodes can maintain the mechanical integrity during the lithiation-delithiation cycling. After the incorporation of fire-extinguishing binders, current collectors, or capsules, flame retardants can be released spatiotemporally during thermal runaway to ensure safety. Thermoresponsive switching electrodes are also constructed though adding thermally responsive components, which can rapidly switch LIB off under abnormal conditions and resume their functions quickly when normal operating conditions return. Finally, the challenges of bio-inspired electrode designs are presented to optimize the spatiotemporal management of LIBs. It is anticipated that the proposed electrodes with spatiotemporal management will not only promote industrial application, but also strengthen the fundamental research of bionics in energy storage.

Enabling Uniform and Stable Lithium-Ion Diffusion at the Ultrathin Artificial Solid-Electrolyte Interface in Siloxene Anodes

Constructing a stable and robust solid electrolyte interphase (SEI) has a decisive influence on the charge/discharge kinetics of lithium-ion batteries (LIBs), especially for silicon-based anodes which generate repeated destruction and regeneration of unstable SEI films. Herein, a facile way is proposed to fabricate an artificial SEI layer composed of lithiophilic chitosan on the surface of two-dimensional siloxene, which has aroused wide attention as an advanced anode for LIBs due to its special characteristics. The optimized chitosan-modified siloxene anode exhibits an excellent reversible cyclic stability of about 672.6 mAh g-1 at a current density of 1000 mA g-1 after 200 cycles and 139.9 mAh g-1 at 6000 mA g-1 for 1200 cycles. Further investigation shows that a stable and LiF-rich SEI film is formed and can effectively adhere to the surface during cycling, redistribute lithium-ion flux, and enable a relatively homogenous lithium-ion diffusion. This work provides constructive guidance for interface engineering strategy of nano-structured silicon anodes.

Si Single-Atom Sites Anchored Carbon Anode Achieving the Zero-Strain Feature and Superior Li+ Storage Performance

Overcoming the significant volume strain in silicon-based anodes has been the focus of research for decades. The strain/stress in silicon-based anodes is inversely proportional to their size. In this study, we design atomic Si sites to achieve the ultimate size effect, which indeed exhibits a zero-strain feature. Compared with conventional silicon-based anodes with alloying addition reactions, the lithium-ion storage mechanism of atomic Si sites is solid-solution reactions, which brings about the zero-strain feature. Additionally, the ligand structure of atomic Si sites remains constant during cycling. This zero-strain feature results in excellent cycling stability. Furthermore, the exposed atomic Si sites enhance the electrochemical reaction kinetics, leading to outstanding rate performance. Moreover, the anode inherits the advantages of silicon-based anodes, including a low working voltage (~0.21 V) and high specific capacity (~2300 mAh g-1 or ~1203 mAh cm-3). This work establishes a novel pathway for designing low/zero-strain anodes.

Rational Design of Ion-Conductive Layer on Si Anode Enables Superior-Stable Lithium-Ion Batteries

Silicon (Si) is considered a promising commercial material for the next-generation of high-energy density lithium-ion battery (LIB) due to its high theoretical capacity. However, the severe volume changes and the poor conductivity hinder the practical application of Si anode. Herein, a novel core-shell heterostructure, Si as the core and V3 O4 @C as the shell (Si@V3 O4 @C), is proposed by a facile solvothermal reaction. Theoretical simulations have shown that the in-situ-formed V3 O4 layer facilitates the rapid Li+ diffusion and lowers the energy barrier of Li transport from the carbon shell to the inner core. The 3D network structure constructed by amorphous carbon can effectively improve electronic conductivity and structural stability. Benefiting from the rationally designed structure, the optimized Si@V3 O4 @C electrode exhibits an excellent cycling stability of 1061.1 mAh g-1 at 0.5 A g-1 over 700 cycles (capacity retention of 70.0%) with an average Coulombic efficiency of 99.3%. In addition, the Si@V3 O4 @C||LiFePO4 full cell shows a superior capacity retention of 78.7% after 130 cycles at 0.5 C. This study opens a novel way for designing high-performance silicon anode for advanced LIBs.

Rational design of hollow Ti2Nb10O29 nanospheres towards High-Performance pseudocapacitive Lithium-Ion storage

Ti2Nb10O29, as one of the most promising anode materials for lithium-ion batteries (LIBs), possesses excellent structural stability during lithiation/delithiation cycling and higher theoretical capacity. However, Ti2Nb10O29 faces some challenges, such as insufficient ion diffusion coefficient and poor electronic conductivity. To overcome these problems, this study investigates the effect of applying nanostructure engineering on Ti2Nb10O29 and the lithium storage behaviors. We successfully synthesized hollow Ti2Nb10O29 nanospheres (h-TNO NSs) via solvothermal method using phenolic resin nanospheres as the template. The effects of using a template or not and the annealing atmospheres on the microstructures of the as-prepared Ti2Nb10O29 are investigated. Different nanostructures (porous Ti2Nb10O29 nanoaggregates (p-TNO NAs) without a template and core-shelled Ti2Nb10O29@C nanospheres (cs-TNO@C NSs)) were formed through annealing in Ar. When examined as anodes for LIBs, the h-TNO NSs electrode with hollow spherical structure displayed a better lithium storage performance. Compared to its counterparts, p-TNO NAs and cs-TNO@C NSs, h-TNO NSs electrode exhibited a higher reversible capacity of 282.5 mAh g-1 at 1C, capacity retention of 79.5% (i.e., 224.6 mAh g-1) after 200 cycles, and a higher rate capacity of 173.1 mAh g-1 at 10C after 600 cycles. The excellent electrochemical performance of h-TNO NSs is attributed to the novel structure. The hollow nanospheres with cavities and thin shells not only exposed more active sites and improved ion diffusion, but also buffered the volume variation upon cycling and facilitated electrolyte penetration. This consequently enhanced the lithium storage performance of the electrode and its high pseudocapacitive contribution (90% at 1.0 mV s-1).

Sponge-Like Porous-Conductive Polymer Coating for Ultrastable Silicon Anodes in Lithium-Ion Batteries

Urgent calls for reversible cycling performance of silicon (Si) requires an efficient solution to maintain the silicon-electrolyte interface stable. Herein, a conductive biphenyl-polyoxadiazole (bPOD) layer is coated on Si particles to enhance the electrochemical process and prolong the cells lifespan. The conformal bPOD coatings are mixed ionicelectronic conductors, which not only inhibit the infinite growth of solid electrolyte interphase (SEI) but also endow electrodes with outstanding ion/electrons transport capacity. The superior 3D porous structure in the continuous phase allows the bPOD layers to act like a sponge to buffer volume variation, resulting in high structural stability. The in situ polymerized bPOD coating and it-driven thin LiF-rich SEI layer remarkably improve the lithium storage performance of Si anodes, showing a high reversible specific capacity of 1600 mAh g-1 even after 500 cycles at 1 A g-1 along with excellent rate capacity of over 1500 mAh g-1 at 3 A g-1 . It should be noticed that a long cycle life of 800 cycles with 1065 mAh g-1 at 3 A g-1 can also be achieved with a capacity retention of more than 80%. Therefore,  we  believe this unique polymer coating design paves the way for the widespread adoption of next-generation lithium-ion batteries.

A Uniform Self-Reinforced Organic/Inorganic Hybrid SEI Chelation Strategy on Microscale Silicon Surfaces for Stable-Cycling Anodes in Lithium-Ion Batteries

A promising anode material for Li-ion batteries, silicon (Si) suffers from volume expansion-induced pulverization and solid electrolyte interface (SEI) instability. Microscale Si with high tap density and high initial Coulombic efficiency (ICE) has become a more anticipated choice, but it will exacerbate the above issues. In this work, the polymer polyhedral oligomeric silsesquioxane-lithium bis (allylmalonato) borate (PSLB) is constructed by in situ chelation on microscale Si surfaces via click chemistry. This polymerized nanolayer has an "organic/inorganic hybrid flexible cross-linking" structure that can accommodate the volume change of Si. Under the stable framework formed by PSLB, a large number of oxide anions on the chain segment preferentially adsorb LiPF6 and further induce the integration of inorganic-rich, dense SEI, which improves the mechanical stability of SEI and provides accelerated kinetics for Li+ transfer. Therefore, the Si4@PSLB anode exhibits significantly enhanced long-cycle performance. After 300 cycles at 1 A g-1 , it can still provide a specific capacity of 1083 mAh g-1 . Cathode-coupled with LiNi0.9 Co0.05 Mn0.05 O2 (NCM90) in the full cell retains 80.8% of its capacity after 150 cycles at 0.5 C.

Prefabrication of "Trinity" Functional Binary Layers on a Silicon Surface to Develop High-Performance Lithium-Ion Batteries

The silicon (Si) anode is widely recognized as the most prospective next-generation anode. To promote the application of Si electrodes, it is imperative to address persistent interface side reactions caused by the huge volume expansion of Si particles. Herein, we introduce beneficial groups of the optimized binder and electrolyte on the Si surface by a co-dissolution method, realizing a "trinity" functional layer composed of azodicarbonamide and 4-nitrobenzenesulfonyl fluoride (AN). The "trinity" functional AN interfacial layer induces beneficial reductive decomposition reactions of the electrolyte and forms a hybrid solid-electrolyte interphase (SEI) skin layer with uniformly distributed organic/inorganic components, which can enhance the mechanical strength of the overall electrode, restrain harmful electrolyte depletion reactions, and maintain efficient ion/electron transport. Hence, the optimized Si@AN11 electrode retains 1407.9 mAh g^-1 after 500 cycles and still delivers 1773.5 mAh g^-1 at 10 C. In stark contrast, Si anodes have almost no reserved capacity at the same test conditions. Besides, the LiNi_0.5Co_0.2Mn_0.3O₂//Si@AN11 full-cell maintains 141.2 mAh g^-1 after 350 cycles. This work demonstrates the potential of developing multiple composite artificial layers to modulate the SEI properties of various next-generation electrodes.

Mechanics-based design of lithium-ion batteries: a perspective

From the overall framework of battery development, the battery structures have not received enough attention compared to the chemical components in batteries. The mechanical-electrochemical coupling behavior is a starting point for investigation on battery structures and the subsequent battery design. This perspective systematically reviews the efforts on the mechanics-based design for lithium-ion batteries (LIBs). Two typical types of mechanics-based LIB designs, namely the design at the preparation stage and that at the cycling stage, have been discussed, respectively. The former systemizes the structure design of multiscale battery components from the particle level to the cell level. The latter focuses on the external mechanics-related control, including external pressures and charge-discharge protocols, of in-service LIBs. Moreover, the general problems currently being faced in the mechanics-based LIB design are summarized, followed by the outlook of possible solutions.

Construction of a LiF-Rich and Stable SEI Film by Designing a Binary, Ion-, and Electron-Conducting Buffer Interface on the Si Surface

Stabilizing a solid electrolyte interface (SEI) film on the Si surface is a prerequisite for realizing silicon (Si) anode applications. Interfacial engineering is one of the effective strategies to construct stable SEI films on Si surfaces and improve the electrochemical performance of the Si anodes. This work develops a silver (Ag)-decorated mucic acid (MA) buffer interface on the Si surface and the obtained Si@MA*Ag anode retains 1567 mAh g^-1 after 500 cycles at 2.1 A g^-1 and exhibits 1740 mAh g^-1 at 126 A g^-1, which are significantly higher than those of the bare Si anode of 247 and 145 mAh g^-1 under the same conditions, respectively. Analysis indicates that the improved electrochemical performance is because of the depressed volume effect of the Si particles and the sustained integrity of the electrode laminate during cycling, the enhanced lithium diffusion on the Si surface, and the improved electronic conductivity of the Si anode, as well as the facilitated formation of inorganic components in the SEI film.

Robust Multiscale Electron/Ion Transport and Enhanced Structural Stability in SiOx Semi-Solid Anolytes Enabled by Trifunctional Artificial Interfaces for High-Performance Li-Ion Slurry Flow Batteries

SiO_x suspension is regarded as an attractive anolyte for high-energy-density Li-ion slurry flow batteries. However, the poor electronic conductivity and non-negligible volume variation of SiO_x greatly hinder its practical applications. Herein, these issues are successfully addressed by rationally designing a trifunctional interface with mixed electron/ion and hard/soft modulated properties on SiO_x surface via H-bonding interactions. The interface comprises a lithiated polymer layer (LiPN) interfused with functionalized single-walled carbon nanotubes. Carbon nanotubes work as electrical tentacles to enhance the multiscale electron conduction. The LiPN layer with transferable Li-ions facilitates ion transport. In addition, the LiPN layer employs lithiated rigid polyacrylic acid as a framework to provide mechanical support and soft nafion as a buffer to accommodate volume change, which maintains the structural integrity of SiO_x . Hence, SiO_x @LiPN/S anolytes exhibit significantly improved rate and cycle performances. Specially, the interface enables the anolytes to load more active particles (30 wt%) or less conductive additives (0.4 wt%). The semi-solid pouch cells based on high-active-content anolytes with stable cyclability are first demonstrated and the flow cell using low-conductive-content anolytes displays a high volumetric capacity of 207 Ah L^-1 . This strategy paves a novel approach for optimizing semi-solid electrodes for high-performance Li-ion slurry flow batteries.

Integrating SEI into Layered Conductive Polymer Coatings for Ultrastable Silicon Anodes

Tackling the huge volume expansion of silicon (Si) anode desires a stable solid electrolyte interphase (SEI) to prohibit the interfacial side reactions. Here, a layered conductive polyaniline (LCP) coating is built on Si nanoparticles to achieve high areal capacity and long lifespan. The conformal LCP coating stores electrolyte in interlamination spaces and directs an in situ formation of LCP-integrated hybrid SEI skin with uniform distribution of organic and inorganic components, enhancing the flexibility of the SEI to buffer the volume changes and maintaining homogeneous ion transport during cycling. As a result, the Si anode shows a remarkable cycling stability under high areal capacity (≈3 mAh cm^-2 ) after 150 cycles and good rate performance of 942 mAh g^-1 at 5 A g^-1 . This work demonstrates the great potential of regulating the SEI properties by a layered polymer-directing SEI formation for the mechanical and electrochemical stabilization of Si anodes.

Bioinspired Thermal Runaway Retardant Capsules for Improved Safety and Electrochemical Performance in Lithium-Ion Batteries

Vigorous development of electric vehicles is one way to achieve global carbon reduction goals. However, fires caused by thermal runaway of the power battery has seriously hindered large-scale development. Adding thermal runaway retardants (TRRs) to electrolytes is an effective way to improve battery safety, but it often reduces electrochemical performance. Therefore, it is difficult to apply in practice. TRR encapsulation is inspired by the core-shell structures such as cells, seeds, eggs, and fruits in nature. In these natural products, the shell isolates the core from the outside, and has to break as needed to expose the core, such as in seed germination, chicken hatching, etc. Similarly, TRR encapsulation avoids direct contact between the TRR and the electrolyte, so it does not affect the electrochemical performance of the battery during normal operation. When lithium-ion battery (LIB) thermal runaway occurs, the capsules release TRRs to slow down and even prevent further thermal runaway. This review aims to summarize the fundamentals of bioinspired TRR capsules and highlight recent key progress in LIBs with TRR capsules to improve LIB safety. It is anticipated that this review will inspire further improvement in battery safety, especially for emerging LIBs with high-electrochemical performance.

Electronic Structure Reconfiguration of Self-Supported Polyoxometalate-Based Lithium-Ion Battery Anodes for Efficient Lithium Storage

Polyoxometalate (POM)-based materials are considered as promising candidates for lithium-ion batteries (LIBs) due to their stable and well-defined molecular structure and reversible multielectron redox properties. Currently, POM-based electrode materials suffer from high interfacial resistance and low uniformity. Herein, we reported a self-supported POM-based anode material for LIBs by electrodepositing H₃PMo₁₂O₄₀ (PMo₁₂) and aniline on carbon cloth (CC) for the first time. The as-prepared polyaniline (PANi)-PMo₁₂/CC composite exhibited an excellent reversible capacity of 1092 mA h g^-1 for 200 cycles at 1 A g^-1. Such an outstanding performance was attributed to the rapid electron transfer and Li⁺ diffusion stemming from the exposure of more active sites by the self-supported structure, the strong electrostatic interaction, and electronic structure reconfiguration between the active PMo₁₂ cluster and conductive PANi polymer. This work provides insight into the electronic structure engineering of highly efficient LIB anode materials.

A Novel Tin-Bonded Silicon Anode for Lithium-Ion Batteries

Poor cyclic stability and low rate performance due to dramatic volume change and low intrinsic electronic conductivity are the two key issues needing to be urgently solved in silicon (Si)-based anodes for lithium-ion batteries. Herein, a novel tin (Sn)-bonded Si anode is proposed for the first time. Sn, which has a high electronic conductivity, is used to bond the Si-anode material and copper (Cu) current collector together using a hot-pressed method with a temperature slightly above the melting point of Sn. The cycling performance of the electrode is studied using a galvanostatic method. Nanoindentation and peeling tests are conducted to measure the mechanical strength of the electrodes. Direct current polarization and galvanostatic intermittent titration techniques are applied to assess the conductivity of the composites. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy are conducted to evaluate the effect of the coating layer on the cycling ability of the composites. The Sn-bonded Si anodes show superior cycling stability and high rate performance with an improved initial Coulombic efficiency. Analyses reveal that the low-melting-point Sn helps to markedly improve the electronic conductivity of the electrodes and serves as a metallic binder as well to enhance the adhesive strength of the electrode. It is hopeful that this novel Sn-bonded Si anode provides a new insight for the development of advanced Si-based anodes for LIBs.

Enveloping a Si/N-doped carbon composite in a CNT-reinforced fibrous network as flexible anodes for high performance lithium-ion batteries

A CNT-reinforced carbonaceous fibers network anchored with N-doped carbon-coated Si (C/Si/CNTs) has been fabricated. Utilized as flexible anodes for lithium-ion batteries, the C/Si/CNT delivers excellent cycling performance and rate capabilities.