Superior Stability Secured by a Four-Phase Cathode Electrolyte Interface on a Ni-Rich Cathode for Lithium Ion Batteries

Abstract

A multifunctional coating with high ionic and electronic conductivity is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM) to boost the battery stability upon cycling and during storage as well. Phosphoric acid reacts with residual lithium species on the pristine NCM to form a Li3PO4 coating with extra carbon nanotubes (CNTs) penetrating through, which shows high ionic and electronic conductivity. NCM, Li3PO4, CNTs, and the electrolyte jointly form a four-phase cathode electrolyte interface, which plays a key role in the great enhancement of capacity retention, from 50.3% for pristine NCM to 84.8% for the modified one after 500 cycles at 0.5C at room temperature. The modified NCM also delivers superior electrochemical performances at a high cut-off voltage (4.5 V), high temperature (55 °C), and high rate (10C). Furthermore, it can deliver 154.2 mA h g–1 at the 500th cycle after exposed to air with high humidity for 2 weeks. These results demonstrate that the well-constructed multifunctional coating can remarkably enhance the chemical and electrochemical performances of NCM. The improved cycling, storage, and rate performance are attributed to the four-phase cathode electrolyte interface delivering high electron and ionic conductivity and securing the cathode against attack. This work broadens the horizon for constructing effective electrode/electrolyte interfaces for electrochemical energy storage and conversion.

Rational Design of a Piezoelectric BaTiO3 Nanodot Surface‐Modified LiNi0.6Co0.2Mn0.2O2 Cathode Material for High‐Rate Lithium‐Ion Batteries

“…Meanwhile, the peaks of 529.2 eV and 531.1 eV in the O 1s spectra correspond to the lattice oxygen and residual lithium in Figure 2d. [36] The area of residual lithium in O 1s is similar to that in C 1s, confirming that the modification process of BTO reduces the content of residual lithium compounds.…”

Effect of LiTFSI and LiFSI on Cycling Performance of Lithium Metal Batteries Using Thermoplastic Polyurethane/Halloysite Nanotubes Solid Electrolyte

“…The three pairs of oxidation and reduction peaks on their second and third cycles are originated from three-phase transitions of NCM during the charge-discharge process. In comparison with TPU-HNTs-LiFSI-PE, the smaller overlaps of TPU-HNTs-LiTFSI-PE represented the improvement of electrochemical reversibility [52]. It was worth noting that there were significant differences in oxidation-reduction potentials during the first cycle, which is different from that of a recent research [53].…”

The Formation, Detriment and Solution of Residual Lithium Compounds on Ni-Rich Layered Oxides in Lithium-Ion Batteries

“…(B) Schematic diagrams of the working mechanism of CNT& Li 3 PO 4 coating layer and cycling stability of CNT& Li 3 PO 4 coated sample compared to pristine and (C and D) SEM images of the CNT& Li 3 PO 4 coated sample. Adapted from [Yang et al, 2019c] with permission from American Chemical Society. (E) Schematic views of the sublimation-induced gas-reacting process on the surface and inside of the secondary particles and (F) The improved cycling performance of surface Li x S y O z coated sample.…”

“…Moreover, the coating layers can be formed in-situ on the surface of Ni-rich cathode materials via chemical reactions between coating media and residual lithium compounds, which could eliminate surface impurities as well as form a functional film on the surface. For example, H 3 PO 4 (Jo et al, 2014a;Min et al, 2017;Yang et al, 2019c), an acidic coating media, can react with the residual lithium compounds, such as LiOH and Li 2 CO 3 to form a Li 3 PO 4 coating layer, which has been verified to effectively enhance the surface stability of Ni-rich cathode materials. Due to the reduced surface insulating impurities and high ionic conductivity of newly generated Li 3 PO 4 , the capacity retention and rate capability of Li 3 PO 4 -coated NCM622 are greatly improved (Jo et al, 2014a).…”

“…As shown in Figure 4A, metal phosphates could effectively reduce both LiOH and Li 2 CO 3 , whereas metal oxides tend to react with LiOH more, in which P 2 O 5 may be an optimal choice. In a further step, Yang et al constructed a four-phase cathode electrolyte interface on NCM811, as described in Figure 4B ( Yang et al, 2019c). The phosphoric acid reacted with surface FIGURE 6 | (A) Cycling performance curves of pristine and Al doping modified material before and after air storage for 30 days and (B) Concentration of residual lithium species on Ni-rich cathode with various Ni contents before and after air exposure for 30 days and (C) Schematic illustration of the mechanism of Al-doping in improving air stability of Ni-rich cathode.…”