High Capacity and Long Cycle Life High Voltage Spinel Cathode Materials for Lithium-Ion Batteries

Date of Award

12-2025

Degree Name

Doctor of Philosophy

Department

Chemical and Paper Engineering

First Advisor

Qingliu Wu, Ph.D.

Second Advisor

Kecheng Li, Ph.D.

Third Advisor

Wenquan Lu, Ph.D.

Keywords

Co-precipitation synthesis, elemental doping, lithium-ion batteries, material characterization, material science, renewable energy

Abstract

The rapidly growing electric vehicle (EV) market necessitates cobalt-free Lithium-Ion Batteries (LIBs) with high energy density and long cycle life. The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material due to its ~4.7 V operating potential, three-dimensional Li+ diffusion, and cobalt-free composition. However, its practical application is limited by capacity fading arising from Mn dissolution, oxygen vacancies, and bulk degradation. Elemental doping is widely recognized as a modification strategy, yet conventional uniform doping presents inherent trade-offs: while it strengthens the lattice, suppresses Mn3+-related degradation and offers limited surface passivation, it can also induce lattice distortions and phase transitions that impair electrochemical performance of LNMO cathodes.

To address this challenge, we innovatively developed a novel co-precipitation process to incorporate elements with large ionic radii and strong affinity to oxygen as dopants into LNMO cathode material to simultaneously improve surficial stability and preserve a disordered bulk. This work systematically established a process–structure–property relationship for synthesizing LNMO cathode materials with various dopants and through different doping strategies. To identify optimized co-precipitation conditions, Chapter 2 systematically investigated the effects of ammonia concentration, stirring speed, and calcination temperature, thereby isolating their effects on precursor chemistry, particle morphology, and cation ordering in LNMO cathode materials. Under optimized conditions (1 M NH3·H2O, 500 rpm stirring, and 900 ℃ calcination), LNMO cathode materials with uniform particle size and high crystallinity were obtained, delivering a specific capacity of ~131 mAh/g at 0.2 C with ~73% capacity retention after 500 cycles. With optimized conditions, Chapter 3 investigated the effect of uniform Ca doping on LNMO cathodes and its role in improving structural stability and electrochemical performance. Moderate substitution (Ca 0.05) expanded the lattice, suppressed high-energy {100} facets, and preserved a disordered spinel framework, resulting in ~121 mAh/g at 0.2 C with ~94% retention after 500 cycles, whereas excessive doping (Ca 0.1) induced partial ordering and lattice strain that impaired rate capability and cycling stability. To address the limitations of uniform doping, Chapter 4 developed a concentration gradient strategy. By enriching Ca at the particle surface while maintaining a disordered bulk, this approach coupled interfacial stability with preserved bulk disorder, leading to higher capacity than uniform doping at all doping levels, improved formation efficiency (~94–95% vs. ~88% undoped, ~92% uniform), enhanced rate capability (~113 mAh/g at 10 C), and superior cycling stability (~95% retention after 500 cycles vs. ~73% undoped).

In summary, this work established a new co-precipitation process to synthesize cathode materials with new doping strategies, developed high capacity, high rate, and long cycle life high voltage spinel cathode materials, and shed light on the mechanisms involved in the precursor chemistry, crystal nucleation/growth, and cell failure. Together, these findings provide both mechanistic insight and practical design principles for the development of robust, Co-free spinel cathodes to support next-generation lithium-ion batteries.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

12-1-2027

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