Controlling Ni²⁺from the Surface to the Bulk by a New Cathode Electrolyte Interphase Formation on a Ni-Rich Layered Cathode in High-Safe and High-Energy-Density Lithium-Ion Batteries

Abstract

Ni-rich high-energy-density lithium ion batteries pose great risks to safety due to internal short circuits and overcharging; they also have poor performance because of cation mixing and disordering problems. For Ni-rich layered cathodes, these factors cause gas evolution, the formation of side products, and life cycle decay. In this study, a new cathode electrolyte interphase (CEI) for Ni2+ self-oxidation is developed. By using a branched oligomer electrode additive, the new CEI is formed and prevents the reduction of Ni3+ to Ni2+ on the surface of Ni-rich layered cathode; this maintains the layered structure and the cation mixing during cycling. In addition, this new CEI ensures the stability of Ni4+ that is formed at 100% state of charge in the crystal lattice at high temperature (660 K); this prevents the rock-salt formation and the over-reduction of Ni4+ to Ni2+. These findings are obtained using in situ X-ray absorption spectroscopy, operando X-ray diffraction, operando gas chromatography–mass spectroscopy, and X-ray photoelectron spectroscopy. Transmission electron microscopy reveals that the new CEI has an elliptical shape on the material surface, which is approximately 100 nm in length and 50 nm in width, and covers selected particle surfaces. After the new CEI was formed on the surface, the Ni2+ self-oxidation gradually affects from the surface to the bulk of the material. It found that the bond energy and bond length of the Ni–O are stabilized, which dramatically inhibit gas evolution. The new CEI is successfully applied in a Ni-rich layered compound, and the 18650- and the punch-type full cells are fabricated. The energy density of the designed cells is up to 300 Wh/kg. Internal short circuit and overcharging safety tests are passed when using the standard regulations of commercial evaluation. This new CEI technology is ready and planned for future applications in electric vehicle and energy storage.

Coating of a Novel Lithium-Containing Hybrid Oligomer Additive on Nickel-Rich LiNi0.8Co0.1Mn0.1O2 Cathode Materials for High-Stability and High-Safety Lithium-Ion Batteries

“…Therefore, we can consider that the BTJ-L polymer coating layer functions also as an artificial CEI layer, impairing TM dissolution from the cathode active materials in the carbonatebased electrolytes. 5,10,41 Figure 9a,b present the Nyquist plots of the coin cells incorporating the pristine NCM811 and 1 wt % BTJ-L@ NCM811 electrodes, conducted at 1C before and after 100 cycles, respectively. Prior to cycling (see Figure 9a), the bulk resistance (R b ) and charge transfer resistance (R ct ) values of the cells containing the 1 wt % BTJ-L@NCM811 electrode (2.5 and 102.2 Ω, respectively) were slightly lower than those of the cells with the pristine NCM811 electrode (3.1 and 122.1 Ω, respectively), likely enabling faster charge carrier transport at high C rates, as revealed in Figure 8a and Table S2.…”

“…We conclude that the NCM811 electrode modified with the BTJ-L oligomer additive could effectively alleviate the side reactions between the electrolyte and the electrode, resulting from the inhibition of CEI layer formation in the presence of the BTJ-L protective layer, as revealed in Table S5. 5,10,41,43 Consequently, the electrochemical performance was greatly enhanced.…”

“…The BTJ-L oligomer layer modifying the NCM811 active materials apparently protected the core materials against HF attack (it functioned as a protection layer), even at elevated temperature. Therefore, we can consider that the BTJ-L polymer coating layer functions also as an artificial CEI layer, impairing TM dissolution from the cathode active materials in the carbonate-based electrolytes. ,, …”

In Situ Co–O Bond Reinforcement of the Artificial Cathode Electrolyte Interphase in Highly Delithiated LiCoO2 for High-Energy-Density Applications

“…R-Si-O-LiCoO 2 was produced through in situ Co–O bond reinforcement on the surface of LiCoO 2 when LiCoO 2 was in a highly delithiated state. Several studies have indicated that branched oligomers have high potential for absorbing heat during thermal runaway. − Thus, in the present study, the amino groups in APTES were made to react with a branched oligomer through the aza-Michael addition reaction to produce an artificial cathode electrolyte interphase (ACEI).…”

In Situ Co-modification Strategy for Achieving High-Capacity and Durable Ni-Rich Cathodes for High-Temperature Li-Ion Batteries

“…Nevertheless, with the accumulation of heat upon long-term and high-power operation, the temperature inside the batteries will exceed 40 °C, leading to the performance decay of batteries. , This places higher demands for the thermal stability of cathodes in LIBs . Currently, Ni-rich layered oxides are the preferred cathodes for high-power LIBs in virtue of their high-energy density. , However, they often undergo inferior thermal stability and rapid resistance growth at high temperatures. − Specifically, the electron transfer from O 2 to strong oxidizing Ni 4+ induces lattice oxygen escape, which is further exacerbated by a high temperature. − Meanwhile, released oxygen from the lattice framework prefers to react with the electrolytes, thereby exacerbating the interfacial adverse reactions and increasing the resistance. − Therefore, synchronously constructing a stable structure and robust cathode–electrolyte interface is crucial for a Ni-rich cathode with enhanced cycling and thermal stability at high temperatures.…”