In situ formation of ionically conductive nanointerphase on Si particles for stable battery anode

Boosting Sodium Compensation Efficiency via a CNT/MnO2 Catalyst toward High-Performance Na-Ion Batteries

The formation of a solid electrolyte interphase on carbon anodes causes irreversible loss of Na+ ions, significantly compromising the energy density of Na-ion full cells. Sodium compensation additives can effectively address the irreversible sodium loss but suffer from high decomposition voltage induced by low electrochemical activity. Herein, we propose a universal electrocatalytic sodium compensation strategy by introducing a carbon nanotube (CNT)/MnO2 catalyst to realize full utilization of sodium compensation additives at a much-reduced decomposition voltage. The well-organized CNT/MnO2 composite with high catalytic activity, good electronic conductivity, and abundant reaction sites enables sodium compensation additives to decompose at significantly reduced voltages (from 4.40 to 3.90 V vs Na+/Na for sodium oxalate, 3.88 V for sodium carbonate, and even 3.80 V for sodium citrate). As a result, sodium oxalate as the optimal additive achieves a specific capacity of 394 mAh g-1, almost reaching its theoretical capacity in the first charge, increasing the energy density of the Na-ion full cell from 111 to 158 Wh kg-1 with improved cycle stability and rate capability. This work offers a valuable approach to enhance sodium compensation efficiency, promising high-performance energy storage devices in the future.

Three-dimensionally multiple protected silicon anode toward ultrahigh areal capacity and stability

Silicon (Si) is considered as one of the most promising candidates for next-generation lithium-ion battery (LIB) anode due to its high theoretical capacity. However, the drastic volume change of Si anodes during lithiation/delithiation processes leads to rapid capacity fade. Herein, a three-dimensional Si anode with multiple protection strategy is proposed, including citric acid-modification of Si particles (CA@Si), GaInSn ternary liquid metal (LM) addition, and porous copper foam (CF) based electrode. The CA modified supports strong adhesive attraction of Si particles with binder and LM penetration maintains good electrical contact of the composite. The CF substrate constructs a stable hierarchical conductive framework, which could accommodate the volume expansion to retain integrity of the electrode during cycling. As a result, the obtained Si composite anode (CF-LM-CA@Si) demonstrates a discharge capacity of 3.14 mAh cm^-2 after 100 cycles at 0.4 A g^-1, corresponding to 76.1% capacity retention rate based on the initial discharge capacity and delivers comparable performance in full cells. The present study provides an applicable prototype of high-energy density electrodes for LIBs.

In Situ Prepared Three-Dimensional Covalent and Hydrogen Bond Synergistic Binder to Boost the Performance of SiOx Anodes for Lithium-Ion Batteries

Polymer binders play an important role in enhancing the electrochemical performance of silicon-based anodes to alleviate the volume expansion for lithium-ion batteries. It is difficult for common one-dimensional (1D) linear binders to limit the volume expansion of a silicon-based electrode when combined with silicon-based particles with scant binding points. Therefore, it is necessary to design a three-dimensional (3D) network structure, which has multiple binding points with the silicon particles to dissipate the mechanical stress in the continuous charge and discharge circulation. Here, a covalent and hydrogen bond synergist 3D network green binder (poly(acrylic acid) (PAA)-dextrin 9 (Dex₉)) was prepared by the simple in situ thermal condensation of a one-dimensional liner binder PAA and Dex in the electrode fabrication process. The optimized SiO_x@PAA-Dex₉ electrode exhibits an initial Coulombic efficiency (ICE) of 82.4% at a current density of 0.2 A g^-1. At a high current density of 1 A g^-1, it retains a capacity of 607 mAh g^-1 after 300 cycles, which is approximately twice as high as that of the SiO_x@PAA electrode. Furthermore, the results of in situ electrochemical dilatometry (ECD) and characterization of electrode structures demonstrate that the PAA-Dex₉ binder can effectively buffer the huge volume change and maintain the integrity of the SiO_x electrodes. The research overcomes the low electrochemical stability difficulty of the 3D binder and sheds light on developing the simple fabrication procedure of an electrode.

Functionally Gradient Silicon/Graphite Composite Electrodes Enabling Stable Cycling and High Capacity for Lithium-Ion Batteries

Silicon (Si) is regarded as one of the most promising anode materials for high-energy-density lithium (Li)-ion batteries (LIBs). However, Li insertion/extraction induced large volume change, which can lead to the fracture of the Si material itself and the delamination/pulverization of electrodes, is the major challenge for the practical application of Si-based anodes. Herein, a facile and scalable multilayer coating approach was proposed for the large-scale fabrication of functionally gradient Si/graphite (Si/Gr) composite electrodes to simultaneously mitigate the volume change-caused structural degradation and realize high capacity by regulating the spatial distributions of Si and Gr particles in the electrodes. Both our experimental characterizations and chemomechanical simulations indicated that, with a parabolic gradient (PG) distribution of Si through the thickness direction that the two Si-poor surface layers guarantee the major mechanical support and the middle Si-rich layer ensures the high capacity, the as-prepared PG-Si/Gr electrode can not only effectively improve the stability of the electrode structure but also efficiently enable high capacity and stable electrochemical reactions. Consequently, the PG-Si/Gr electrode with a mass loading of 3.15 mg cm^-2 exhibited a reversible capacity of 579.2 mAh g^-1 (1.82 mAh cm^-2) after 200 cycles at 0.2C. Even with a mass loading of 8.45 mg cm^-2, the PG-Si/Gr anodes still delivered a high reversible capacity of 4.04 mAh cm^-2 after 100 cycles and maintained excellent cycling stability. Moreover, when paired with a commercial LiNi_0.5Mn_0.3Co_0.2O₂ (NCM532) cathode (9.56 mg cm^-2), the PG-Si/Gr||NCM532 full cell revealed an initial reversible areal capacity of 1.64 mAh cm^-2 and sustained a stable areal capacity of 0.94 mAh cm^-2 at 0.2C after 100 cycles.

Boosting Interfacial Ion Transfer in Potassium-Ion Batteries via Synergy Between Nanostructured Bi@NC Bulk Anode and Electrolyte

Using high-capacity alloy-type anodes can greatly advance potassium-ion batteries (PIBs). However, the primary limits are unstable solid electrolyte interphase (SEI) and tough interfacial ion transfer associated with large-size K⁺ during electrochemical (de)alloy reactions. Here, we achieve excellent energy storage performance of PIBs via the synergy between a nanostructured Bi@N-doped carbon (Bi@NC) bulk anode and a KPF₆-dimethoxyethane (DME) electrolyte. The Bi@NC material with a high tap density of 3.81 g cm^-3 is prepared by simply pyrolyzing a commercial Bi salt yet affords a favorable nano/microstructure consisting of Bi nanograins confined in 3D ultrathin N-doped carbon shells, facilitating electron/ion transport and structural integrity. Detailed impedance spectroscopy investigation unveils that K⁺ transport through SEI at the Bi@NC anode, rather than the desolvation of K⁺, dominates the interfacial K⁺ transfer. More importantly, spectroscopic and microscopic characterizations provide clear evidence that the interplay between Bi@NC anode and optimized KPF₆-DME electrolyte can produce a unique SEI layer containing Bi³⁺-solvent complex that enables the activation energy of interfacial K⁺ transfer as low as 25.9 kJ mol^-1, thereby ultrafast charge transfer at Bi@NC. Consequently, the Bi@NC anode in half cells achieves exceptional rate capability (206 mAh g^-1 or 784 mAh cm^-3 at 120C) accompanied by high specific capacity (331 mAh g^-1 or 1261 mAh cm^-3) and long cycle life (running 1400 cycles at 15C with a tiny capacity fading rate of 0.013% per cycle). Moreover, the Bi@NC anode and KPF₆-DME electrolyte are also compatible with a potassium Prussian blue cathode and assembled full PIBs achieve stable cyclability (87.3% capacity retention after 100 cycles at 2.5C) and excellent rate performance (65.1% capacity retention upon increasing rates from 1 to 20C).

High Lithium Ion Flux of Integrated Organic Electrode/Solid Polymer Electrolyte from In Situ Polymerization

The high interface impedance between inorganic material electrodes and solid electrolytes results in a high Li⁺ diffusion energy barrier, which limits the electrochemical performance of active materials. To solve this issue, an integrated configuration of organic active material electrode-solid polymer electrolyte (SPE) is synthesized via in situ polymerization. In the integrated aminoanthraquinone-solid polymer electrolyte (AQ-SPE), the naphthalene urethane bond acts as a bridge that links the organic material electrode and the SPE and acts as a channel for Li⁺ transport at the electrode/SPE interface. Compared to the activation energy of the conventional aminoanthraquinone/solid polymer electrolyte (AQ/SPE), the activation energy of the charge transfer process for the integrated AQ-SPE decreases from 71.2 to 42.1 kJ mol^-1, and the charge transfer impedance decreases from 1140 to 198 Ω at 50 °C. The first and 625th discharge capacity densities of AQ in the integrated AQ-SPE at 0.1 mA cm^-1 and 50 °C are 139.7 and 125.3 mAh g^-1, respectively. Moreover, pouch batteries with the integrated AQ-SPE show excellent safety performance. The in situ fabrication of integrated electrode-SPE provides an enlightening and extended method for realizing efficient, safe, and environmentally friendly batteries.

Realizing Sub-5 nm Red Phosphorus Dispersion in a SiOx/C Matrix for Enhanced Lithium Storage

With high capacity and suitable working plateau, silicon oxide (SiOx) has become a promising lithium-ion battery (LIB) anode material. However, bare SiOx usually suffers from sluggish electron transport and unsatisfactory cyclability. Composting SiOx with a second phase has become an efficient strategy to tackle the current drawbacks. Herein, a P/SiOx/C ternary composite, featuring sub-5 nm red phosphorus (P) clusters uniformly dispersed in a dense SiOx/C matrix has been constructed through an "inside-out" synthesis strategy. The nanosizing of bulk red P sealed in an organosilica matrix is realized by the high-temperature treatment-driven sublimation/diffusion. With the red P amount of ∼7.53 wt %, the P/SiOx/C ternary composite provides a stable discharge capacity of ∼950 mAh g-1 and also manifests a decent rate capability (510 mAh g-1 at 5 A g-1). This study affords a ternary compositing strategy for designing SiOx-based anode materials with desirable electrochemical performance for the next-generation LIBs.