Binder-Free Intertwined Si and MnO2 Composite Electrode for High-Performance Li-Ion Battery Anode.

Silicon is considered as the most felicitous anode material candidate for lithium-ion batteries on account of abundant availability, suitable operating potential, and high specific capacity. Nevertheless, drastic volume expansion during the cycle impedes its practical utilization. Herein, Si and MnO2 (Si-MO) constructed the binder-free intertwined electrode that is reported to effectively improve upon the cycling stability of Si-based materials. The Si-based electrode without a binder has good electrical conductivity, strong adhesion to the substrate, and ample space for mitigating volume expansion. The incorporation of MnO2 establishes a multiphase interface, which mitigates the electrode volume expansion, and supports the electrode structure. Furthermore, MnO2 (∼1230 mAh g-1 theoretical capacity) synergistically enhances the overall capacity of the composite electrodes. Consequently, the Si-MO composite electrode exhibits a reversible specific capacity of 1300 mAh g-1 at 420 mA g-1 and remarkable cycling performance with a specific capacity of 830 mAh g-1 after 500 cycles. In particular, a reversible specific capacity of 837 mAh g-1 at 4200 mA g-1 is achieved and remains stable during 200 cycles. This work provides a potentially feasible way to achieve the Si-based anode commercialization for LIBs.

Improving Electrochemical Performance of Thick Silicon Film Anodes with Implanted Solid Lithium Source Electrolyte.

Silicon is a potential next-generation anode material for a lithium-ion battery. However, the large-scale application of silicon is restricted by poor electrical conductivity, large volume change, and high irreversible capacity during the charge/discharge process. Here, we proposed a simple strategy by preimplanting a solid lithium source electrolyte (Li2CO3 and Li2O) into Si thick film to improve the electrochemical properties of Si materials. The implanted solid lithium source electrolyte participates in and induces the formation of SEI not only on the top surface of Si film but also in the interface of Si particles. The thick Si film with the implanted solid lithium electrolyte (a thickness of ∼10 µm) delivers above 2000 mAh g-1 specific capacity, >92% initial Coulombic efficiency, and ∼87% capacity retention over 150 cycles at 400 mA g-1. The present work sheds light on the design of high capacity and long cycle life electrode materials for other batteries.

Combining Surface Holistic Ge Coating and Subsurface Mg Doping to Enhance the Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 Cathodes.

Nickel-rich layered cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) is the most promising cathode material due to its high specific capacity and lower cost than lithium cobalt oxides. However, NCM811 suffers from structural instability and capacity degradation during charge-discharge cycles. Herein, we report a strategy to construct a conductive network by employing a holistic Ge coating, which interconnects Mg-doped NCM811 particles. Dopant Mg ions, serving as a "pillar" in the Li slab of NCM811, substantially enhance the structural reversibility. The Ge particles are not only coated on the electrode surface but also enter into the electrode pores to form a multidimensional conductive structure, which improves the conductivity of the electrode and slows down the interface side reaction, thus minimizing the irreversible loss of NCM811 upon long cycling. The modified NCM811 electrode delivers a high discharge capacity (∼204 mAh g-1 at 0.1C), excellent rate performance (∼155 mAh g-1 at 10C), and high capacity retention (83% after 200 cycles) even at 4.4 V. Additionally, a cylindrical full battery with graphite/modified NCM811 undergoes 1000 cycles with 86% capacity retention at 2C.

Ternary Si-SiO-Al Composite Films as High-Performance Anodes for Lithium-Ion Batteries.

Silicon (Si) is a promising anode material for lithium-ion batteries but has long been suffering from low conductivity, drastic volume change, poor cycling performance, etc. Adding SiO, Al, etc. to form Si-based binary composite films can improve some properties but have to give up others. Here, we prepared a ternary Si-SiO-Al composite film anode by adding SiO and Al together into Si using magnetron sputtering. This film has an extraordinary combination of conductivity, specific capacity, cycling stability, rate performance, etc., when compared with its binary and unary counterparts. While both SiO and Al can separately mitigate anode cracking resulting from the huge volume expansion during the lithiation/delithiation cycling process, the synergetic effect of adding SiO and Al together to form a ternary composite film can produce much better results. This film maintains an island structure that can efficiently buffer the volume expansion during the cycling process, giving rise to superior cycling performance and excellent rate performance. In addition, the cosputtered Al improves the electrical conductivity of the anode at the same time. This unique combination of anode properties, together with the low cost, suggests that the Si-SiO-Al composite film has the potential to be commercialized as a binder-free anode for lithium-ion batteries. This work also provides an efficient means to modulate the anode properties with more degrees of freedom.

Synergistic Effect of Salinized Quinone for Entrapment of Polysulfides for High-Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries have attracted considerable attention in the energy storage field due to their high theoretical energy density and low price. However, the dissolution of polysulfides and the "shuttle effect" lead to serious capacity degradation, which greatly hinders the industrial application of Li-S batteries. Herein, we propose a bifunctional quinone-type salt to anchor polysulfides and suppress their dissolution for use in high-performance Li-S batteries. We find that the tetrahydroxy-1,4-benzoquinone disodium salt dimer (TBS-dimer) does not dissolve in organic electrolytes and can be generated at 400 °C. The abundant reactive keto groups and double bonds result in the TBS-dimers having numerous "hot spots" for capturing sulfur (TBS/S-400) in the three-dimensional space of the molecule. The insolubility and abundant active sites of the organic salt remarkably suppress the dissolution of lithium polysulfides. As a result, the TBS/S-400 composite delivers a capacity decay rate of only 0.023% per cycle over 600 cycles at 2 C. The use of organic salts to effectively suppress the dissolution of lithium polysulfides opens a new avenue for the practical applications of high-performance Li-S batteries.

Lithium Titanate Matrix-Supported Nanocrystalline Silicon Film as an Anode for Lithium-Ion Batteries.

A facile preparation method of a Si-based anode with excellent cycling property is urgently required in the process of preparing lithium-ion batteries (LIBs). Here, lithium titanate (LTO) matrix-supported nanocrystalline Si film is prepared by radio frequency (RF) magnetron cosputtering utilizing LTO and silicon (Si) targets as the sputtering source. LTO-supported nanocrystalline Si film electrodes revealed a repeatable specific capacity of 1200 mA h g-1 at 150 mA g-1 with a maintenance of more than 75% even after 800 cycles. The remarkable electrochemical properties of the LTO-Si composite films could be attributed to the LTO matrix, preventing the electrolyte from directly making contact with the nanocrystalline Si materials, alleviating the stress of the periodic volume change and further providing efficient and rapid pathways for lithium-ion transport. The results suggest that Si-based LTO composite films are prospective anodes for LIBs, with high capacities and long cycling stabilities.