High-Performance and Industrially Feasible Ni-Rich Layered Cathode Materials by Integrating Coherent Interphase

For developing the industrially feasible Ni-rich layered oxide cathode with extended cycle life, it is necessary to mitigate both the mechanical degradation due to intergranular cracking between primary particles and gas generation from the reaction between the electrolyte and residual Li in the cathode. To simultaneously resolve these two issues, we herein propose a simple but novel method to reinforce the primary particles in LiNi_0.91Co_0.06Mn_0.03O₂ by providing a Li-reactive material, whose spinel interphase is coherent with the surface of the cathode. The modified structure significantly outperforms analogous bare samples: they conserve more than 90% of the initial capacity after 50 cycles and also exhibit a greater rate capability. By tracking the same particle location during cycling, we confirmed that the current method significantly reduces crack generation because the provided coating material can penetrate inside the grain boundary of the secondary particle and help maintain the volume of the primary particle. Finally, first-principles calculations were implemented to determine the role of this spinel material, i.e., having intrinsically isotropic lattice parameters, superior mechanical properties, and only a small volume change during delithiation. We believe that the proposed method is straightforward and cost-effective; hence, it is directly applicable for the mass production of Ni-rich cathode material to enable its commercialization

Overview of the Oxygen Behavior in the Degradation of Li₂MnO₃ Cathode Material

The Li₂MnO₃ cathode material is vulnerable to complex degradation behaviors during the operation of battery although it has attracted much attention recently due to its potentially large capacity. In this study, we comprehensively examined the degradation process in Li₂MnO₃, using theoretical density functional computations as well as experimental techniques (<i>in situ</i> X-ray absorption near edge structure spectroscopy, X-ray diffraction, and Raman spectroscopy). Our study reveals that during the delithiation process, the Li ions mixed in the Mn layer are removed together with those in the Li layer, thereby inducing the release of oxygen atoms. The oxygen loss reaction is energetically favorable at the highly delithiated states, and it can reduce the plateau voltage in the charging curve. Such oxygen loss was observed during or even before the second cycle and furthermore it accelerates the phase transformation of the layered structure to a spinel one. Our results also suggest that oxygen release can be prevented when H ions are exchanged with Li ions during the charging process

Silicon/Carbon Nanotube/BaTiO₃ Nanocomposite Anode: Evidence for Enhanced Lithium-Ion Mobility Induced by the Local Piezoelectric Potential

We report on the synergetic effects of silicon (Si) and BaTiO₃ (BTO) for applications as the anode of Li-ion batteries. The large expansion of Si during lithiation was exploited as an energy source <i>via</i> piezoelectric BTO nanoparticles. Si and BTO nanoparticles were dispersed in a matrix consisting of multiwalled carbon nanotubes (CNTs) using a high-energy ball-milling process. The mechanical stress resulting from the expansion of Si was transferred <i>via</i> the CNT matrix to the BTO, which can be poled, so that a piezoelectric potential is generated. We found that this local piezoelectric potential can improve the electrochemical performance of the Si/CNT/BTO nanocomposite anodes. Experimental measurements and simulation results support the increased mobility of Li-ions due to the local piezoelectric potential

Dendrite-Free Lithium Deposition for Lithium Metal Anodes with Interconnected Microsphere Protection

A lithium (Li) metal anode is required to achieve a high-energy-density battery, but because of an undesirable growth of Li dendrites, it still has safety and cyclability issues. In this study, we have developed a microsphere-protected (MSP) Li metal anode to suppress the growth of Li dendrites. Microspheres could guide Li ions to selective areas and pressurize dendrites during their growth. Interconnections between microspheres improved the pressurization. By using an MSP Li metal anode in a 200 mAh pouch-type Li/NCA full cell at 4.2 V, dendrite-free Li deposits with a density of 0.4 g/cm³, which is 3 times greater than that in the case of bare Li metal, were obtained after charging at 2.9 mAh/cm². The MSP Li metal enhanced the cyclability to 190 cycles with a criterion of 90% capacity retention of the initial discharge capacity at a current density of 1.45 mA/cm²