Microstructure Engineered Ni‐Rich Layered Cathode for Electric Vehicle Batteries

Abstract

density and long service life. General electromobility, which is considered necessary for the reduction of carbon emissions, requires the current EV market to grow exponentially; however, EV technology is confronted with significant performance and economic challenges, such as, limited driving range and battery durability and high battery costs, respectively. [1][2][3] These issues are directly related to the limitations of the LIBs powering EVs. Hence, improvements in the energy density and cycling stability of LIBs, as well as cost reduction, are prerequisites for envisioned general electromobility. Efforts have focused on developing high-capacity cathode materials because the overall performance of current LIBs is dictated by their cathodes. The capacity and cycle life of cathodes are generally inferior to those of graphite anodes (e.g., Li[Ni 0.8 Co 0.15 Al 0.05 ] O 2 and graphite have capacities of 200 and 360 mAh g -1 , respectively). Among the viable cathode materials for LIBs, layered Ni-rich lithium-nickel-cobalt-aluminum oxides, Li[Ni x Co y Al z ]O 2 (NCA), are the most promising materials for EV LIBs owing to their high theoretical capacity (278 mAh g -1 ) and good rate performance. [4,5] Recently, Tesla Motors adopted NCA materials in LIBs to power their Models S, X, and 3, which are capable of operating for 400-550 km per single full charge. However, to compete against internal combustion engine vehicles, EVs should have a driving range exceeding 600 km per single charge, which can be achieved by increasing the energy density of the cathode. Increasing the energy density of an NCA cathode requires increasing its relative fraction of Ni. [6] However, a highly delithiated NCA cathode, when charged to 4.3 V, suffers from structural degradation at the cathode particle surfaces owing to reaction between unstable Ni 4+ and the electrolyte that forms a deleterious NiOlike rock salt impurity phase. [7][8][9] Furthermore, Ni-rich layered cathodes (relative Ni fraction ≥ 0.8) undergo abrupt lattice contractions in the c-axis direction caused by H2→H3 phase transitions (at ≈4.15 V), which generate microcracks. [9][10][11][12][13][14][15] The severity of the microcracking increases with increasing Ni content. [14] The microcracks cause the electrolyte to penetrate the particle interior and attack inner primary particles, causing structural degradation, which leads to capacity fading and eventually to catastrophic mechanical failure. [6,7,[12][13][14][15] Moreover, this degradation triggers oxygen release from the host structure, giving riseThe Nb doping of Li[Ni 0.855 Co 0.13 Al 0.015 ]O 2 (NCA85) modifies its primary particle morphology to allow precise tailoring of its microstructure. The Nb dopant (1 mol%) elongates the primary particles and aligns them in the radial direction, creating a configuration that effectively dissipates the abrupt internal strain caused by H2↔H3 phase transitions near the charge end. The negation of the internal strain substantially improves the long-term cycling stability achieved...

Leveraging Advanced X-ray Imaging for Sustainable Battery Design

“…Furthermore, multiple coexisting TM (Ni, Mn, and Co) cations could experience a complicated electrochemical reaction, which may distort their electronic structures during battery cycling . In fact, it is the change in electronic structure that leads to particle cracking, voltage hysteresis, reaction heterogeneities, and chemo-mechanical degradation. ,− …”

Fast‐Charging Strategies for Lithium‐Ion Batteries: Advances and Perspectives

“…Element doping has been reported to change the lattice size, expand the Li + diffusion channels, suppress the strain caused by the change of lattice volume during cycling, and improve the mechanical stability. In Figure 3c, Sun's group [44] changed the morphology of the primary particles by doping Nb during the lithiation of the Li(Ni 0.855 Co 0.13 Al 0.015 )O 2 (P-NCA85) cathode, so that its microstructure can be precisely adjusted. Nb doping elongates and radially aligns primary particles to form 1-Nb NCA85, which effectively eliminates the abrupt internal strain caused by the H2 $ H3 phase transition, enabling excellent fast-charging capability.…”

Lattice Engineering to Refine Particles and Strengthen Bonds of the LiNi0.9Co0.05Mn0.05O2 Cathode toward Efficient Lithium Ion Storage

“…Horribly, these locally accumulated stresses will be released along the grain boundaries, which lead to mechanical fatigue of the bulk structure and the formation of microcracks. 19,20 These microcracks will further allow electrolytes to penetrate inside particles and attack newly exposed interfaces, 21 which triggers the continuous irreversible phase transition (H2 ↔ H3 phase transition) and damaged cathode− electrolyte interface, 22 thus resulting in a slowdown in the kinetics of Li + de-/intercalation. Subsequently, an abundant existence of highly unstable Ni 4+ on the newly exposed interface will cause the electrolyte decomposition at a highly delithiated state, 23,24 mixing in the octahedral site is another critical issue because the exchange of similar ionic radii Li + (0.76 Å) and Ni 2+ (0.69 Å) within the (003) plane would generate some deformed structure.…”