Syntheses and electrochemical properties of the Na-doped LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Recent Progress of High Voltage Spinel LiMn1.5Ni0.5O4 Cathode Material for Lithium-Ion Battery: Surface Modification, Doping, Electrolyte, and Oxygen Deficiency

High voltage spinel LiMn1.5Ni0.5O4 (LMNO) is a promising energy storage material for the next generation lithium batteries with high energy densities. However, due to the major controversies in synthesis, structure, and interfacial properties of LMNO, its unsatisfactory performance is still a challenge hindering the technology's practical applications. Herein, this paper provides general characteristics of LiMn1.5Ni0.5O4 such as spinel structure, electrochemical properties, and phase transition. In addition, factors such as electrolyte decomposition and morphology of LMNO that influence the electrochemical performances of LMNO are introduced. The strategies that enhance the electrochemical performances including coating, doping, electrolytes, and oxygen deficiency are comprehensively discussed. Through the discussion of the present research status and presentation of our perspectives on future development, we provide the rational design of LMNO in realizing lithium-ion batteries with improved electrochemical performances.

Synthesizing high performance LNMO cathode materials with porous structure by manipulating reynolds number in a microreactor

The demand for Lithium-ion batteries (LIBs) has significantly grown in the last decade due to their extensive use electric vehicles. To further advance the commercialization of LIBs for various applications, there is a pressing need to develop electrode materials with enhanced performance. The porous microsphere morphology LiNixMn2-xO4(LNMO) is considered to be an effective material with both high energy density and excellent rate performance. Nevertheless, LNMO synthesis technology still has problem such as long reaction time, high energy consumption and environmental pollution. Herein, LNMO microsphere was successfully synthesized with short precursors reaction time (18 s) at 40 °C without using chelating agent by microreaction technology combined solid-state lithiation. The optimized LNMO cathode shows microsphere (∼8μm) morphology stacked by nano primary particles, with abundant mesoporous and fully exposed low-energy plane. The electrochemical analysis indicates that the optimized LNMO cathode demonstrates 97.33% capacity retention even after 200 cycles at 1C. Additionally, the material shows a highly satisfactory discharge capacity of 92.3 mAh·g-1at 10C. Overall, microreaction technology is anticipated to offer a novel approach in the synthesis of LNMO cathode materials with excellent performance.

Improving Fast-Charging Capability of High-Voltage Spinel LiNi0.5 Mn1.5 O4 Cathode under Long-Term Cyclability through Co-Doping Strategy

Co-free spinel LiNi0.5 Mn1.5 O4 (LNMO) is emerging as a promising contender for designing next generation high-energy-density and fast-charging Li-ion batteries, due to its high operating voltage and good Li+ diffusion rate. However, further improvement of the Li+ diffusion ability and simultaneous resolution of Mn dissolution still pose significant challenges for their practical application. To tackle these challenges, a simple co-doping strategy is proposed. Compared to Pure-LNMO, the extended lattice in resulting LNMO-SbF sample provides wider Li+ migration channels, ensuring both enhanced Li+ transport kinetics, and lower energy barrier. Moreover, Sb creating structural pillar and stronger TM─F bond together provides a stabilized spinel structure, which stems from the suppression of detrimental irreversible phase transformation during cycling related to Mn dissolution. Benefiting from the synergistic effect, the LNMO-SbF material exhibits a superior reversible capacity (111.4 mAh g-1 at 5C, and 70.2 mAh g-1 after 450 cycles at 10C) and excellent long-term cycling stability at high current density (69.4% capacity retention at 5C after 1000 cycles). Furthermore, the LNMO-SbF//graphite full cell delivers an exceptional retention rate of 96.9% after 300 cycles, and provides a high energy density at 3C even with a high loading. This work provides valuable insight into the design of fast-charging cathode materials for future high energy density lithium-ion batteries.

Ge-Regulated Ordered Phase in Pseudosphere-Structured LiNi0.5Mn1.5O4 Spinel Effectively Inhibits Mn Dissolution

Due to the higher energy density, high thermal stability, and low cost, LiNi_0.5Mn_1.5O₄ (LNMO) spinel, with a large voltage operating window, has been one of the most promising cathode materials for lithium-ion batteries (LIBs). However, the interfacial reaction between the cathode and electrolyte and the two-phase reaction within the bulk of LNMO would destroy the original structure and lead to capacity deterioration, posing a significant challenge. Therefore, the way to suppress the transition-metal (TM) dissolution in LNMO has attracted much attention. However, the ordered/disordered phase regulation by metal atom doping to prohibit TM dissolution has not been extensively explored. Herein, a Ge-doping strategy is proposed to adjust the ratio of disordered/ordered phases in LNMO, resulting in exceptional structural stability. For the modified spinel cathode, there is almost no voltage drop and the capacity retention is up to 92.2% over 1000 cycles at 1C. These results demonstrate that incorporating Ge into LNMO forms a robust structure that effectively increases the amount of Mn⁴⁺ while blocking the diffusion of TM ions. In addition, Ge-doping also protects the bulk from further reactions with electrolytes, significantly enhancing the interfacial stability and relieving voltage decay in cycling. This approach can also be applied to design other high-stability cathodes through ordered/disordered phase regulation.

Enhanced Electrochemical Performance of LiNi0.5Mn1.5O4 Composite Cathodes for Lithium-Ion Batteries by Selective Doping of K+/Cl- and K+/F. NANOMATERIALS 2021;11:nano11092323. [PMID: 34578639 PMCID: PMC8466396 DOI: 10.3390/nano11092323]

K⁺/Cl^- and K⁺/F^- co-doped LiNi_0.5Mn_1.5O₄ (LNMO) materials were successfully synthesized via a solid-state method. Structural characterization revealed that both K⁺/Cl^- and K⁺/F^- co-doping reduced the Li_xNi_1-xO impurities and enlarged the lattice parameters compared to those of pure LNMO. Besides this, the K⁺/F^- co-doping decreased the Mn³⁺ ion content, which could inhibit the Jahn-Teller distortion and was beneficial to the cycling performance. Furthermore, both the K⁺/Cl^- and the K⁺/F^- co-doping reduced the particle size and made the particles more uniform. The K⁺/Cl^- co-doped particles possessed a similar octahedral structure to that of pure LNMO. In contrast, as the K⁺/F^- co-doping amount increased, the crystal structure became a truncated octahedral shape. The Li⁺ diffusion coefficient calculated from the CV tests showed that both K⁺/Cl^- and K⁺/F^- co-doping facilitated Li⁺ diffusion in the LNMO. The impedance tests showed that the charge transfer resistances were reduced by the co-doping. These results indicated that both the K⁺/Cl^- and the K⁺/F^- co-doping stabilized the crystal structures, facilitated Li⁺ diffusion, modified the particle morphologies, and increased the electrochemical kinetics. Benefiting from the unique advantages of the co-doping, the K⁺/Cl^- and K⁺/F^- co-doped samples exhibited improved rate and cycling performances. The K⁺/Cl^- co-doped Li_0.97K_0.03Ni_0.5Mn_1.5O_3.97Cl_0.03 (LNMO-KCl0.03) exhibited the best rate capability with discharge capacities of 116.1, 109.3, and 93.9 mAh g^-1 at high C-rates of 5C, 7C, and 10C, respectively. Moreover, the K⁺/F^- co-doped Li_0.98K_0.02Ni_0.5Mn_1.5O_3.98F_0.02 (LNMO-KF0.02) delivered excellent cycling stability, maintaining 85.8% of its initial discharge capacity after circulation for 500 cycles at 5C. Therefore, the K⁺/Cl^- or K⁺/F^- co-doping strategy proposed herein will play a significant role in the further construction of other high-voltage cathodes for high-energy LIBs.

Advances and Prospects of High-Voltage Spinel Cathodes for Lithium-Based Batteries

Insertion compounds have been dominating the cathodes in commercial lithium-ion batteries. In contrast to layered oxides and polyanion compounds, the development of spinel-structured cathodes is a little behind. Owing to a series of advantageous properties, such as high operating voltage (≈4.7 V), high capacity (≈135 mAh g^-1 ), low environmental impact, and low fabrication cost, the high-voltage spinel LiNi_0.5 Mn_1.5 O₄ represents a high-power cathode for advancing high-energy-density Li⁺ -ion batteries. However, the wide application and commercialization of this cathode are hampered by its poor cycling performance. Recent progress in both the fundamental understanding of the degradation mechanism and the exploration of strategies to enhance the cycling stability of high-voltage spinel cathodes have drawn continuous attention toward this promising insertion cathode. In this review article, the structure-property correlations and the failure mode of high-voltage spinel cathodes are first discussed. Then, the recent advances in mitigating the cycling stability issue of high-voltage spinel cathodes are summarized, including the various approaches of structural design, doping, surface coating, and electrolyte modification. Finally, future perspectives and research directions are put forward, aiming at providing insightful information for the development of practical high-voltage spinel cathodes.

Synthesis and Characterization of a Multication Doped Mn Spinel, LiNi0.3Cu0.1Fe0.2Mn1.4O4, as 5 V Positive Electrode Material

The suitability of multication doping to stabilize the disordered Fd3̅m structure in a spinel is reported here. In this work, LiNi0.3Cu0.1Fe0.2Mn1.4O4 was synthesized via a sol-gel route at a calcination temperature of 850 °C. LiNi0.3Cu0.1Fe0.2Mn1.4O4 is evaluated as positive electrode material in a voltage range between 3.5 and 5.3 V (vs Li+/Li) with an initial specific discharge capacity of 126 mAh g-1 at a rate of C/2. This material shows good cycling stability with a capacity retention of 89% after 200 cycles and an excellent rate capability with the discharge capacity reaching 78 mAh g-1 at a rate of 20C. In operando X-ray diffraction (XRD) measurements with a laboratory X-ray source between 3.5 and 5.3 V at a rate of C/10 reveal that the (de)lithiation occurs via a solid-solution mechanism where a local variation of lithium content is observed. A simplified estimation based on the in operando XRD analysis suggests that around 17-31 mAh g-1 of discharge capacity in the first cycle is used for a reductive parasitic reaction, hindering a full lithiation of the positive electrode at the end of the first discharge.

Role of Al-doping with different sites upon the structure and electrochemical performance of spherical LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Al-doped spinel LiNi_0.5Mn_1.5O₄ materials with different sites and contents were synthesized by rapid precipitation combined with hydrothermal treatment and calcination. The roles of Al on structural stability and electrochemical performance were studied by utilizing a series of techniques. XRD patterns indicated lower ion diffusion and no impure phased in doped samples. FT-IR and CV results reveal that Al-doped materials possess a Fd3̄m space group with increased disorder and increasing amounts of Mn³⁺. SEM and TEM equipped with EDS were used to characterize the regular morphology accompanied by a complete crystal structure and homogeneous distribution of elements. The Al content at the Ni, Mn, and Ni/Mn sites was optimized to be 5%, 3% and 5% (in total), respectively. The cycling stability was considerably enhanced at an ambient temperature (25 °C) and high temperature (55 °C). A typical Al dual-doped sample at Ni/Mn sites with 5% content delivered a reversible capacity of 113.5 mA h g^-1 after 200 cycles at 0.5C. The discharge capacity at 5, 10 and 20C was 127.3, 125.5 and 123.1 mA h g^-1, respectively. The discharge capacity remained at 126 mA h g^-1 after 50 cycles (55 °C, 0.5C). Subsequent EIS and analytical results of the cycled electrode showed improved structural stability with a lower resistance, stable cathode/electrolyte interface, and reduced dissolution of Mn. These data further demonstrated the feasibility and reliability of preparing high-performance spinel LiNi_0.5Mn_1.5O₄ cathode materials by doping with a suitable amount of Al.

Synthesis and Electrochemical Properties of LiNi0.5Mn1.5O4 Cathode Materials with Cr3+ and F- Composite Doping for Lithium-Ion Batteries

A Cr³⁺ and F^- composite-doped LiNi_0.5Mn_1.5O₄ cathode material was synthesized by the solid-state method, and the influence of the doping amount on the material's physical and electrochemical properties was investigated. The structure and morphology of the cathode material were characterized by XRD, SEM, TEM, and HRTEM, and the results revealed that the sample exhibited clear spinel features. No Cr³⁺ and F^- impurity phases were found, and the spinel structure became more stable. The results of the charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) test results suggested that LiCr_0.05Ni_0.475Mn_1.475O_3.95F_0.05 in which the Cr³⁺ and F^- doping amounts were both 0.05, had the optimal electrochemical properties, with discharge rates of 0.1, 0.5, 2, 5, and 10 C and specific capacities of 134.18, 128.70, 123.62, 119.63, and 97.68 mAh g^-1 , respectively. After 50 cycles at a rate of 2 C, LiCr_0.05Ni_0.475Mn_1.475O_3.95F_0.05 showed extremely good cycling performance, with a discharge specific capacity of 121.02 mAh g^-1 and a capacity retention rate of 97.9%. EIS test revealed that the doping clearly decreased the charge-transfer resistance.

Effect of Chromium and Niobium Doping on the Morphology and Electrochemical Performance of High-Voltage Spinel LiNi(0.5)Mn(1.5)O4 Cathode Material

Undoped, Cr-doped, and Nb-doped LiMn(1.5)Ni(0.5)O4 (LNMO) is synthesized via a PVP (polyvinylpyrrolidone)-combustion method by calcinating at 1000 °C for 6 h. SEM images show that the morphology of LNMO particles is affected by Cr and Nb doping. Cr doping results in sharper edges and corners and smaller particle size, and Nb doping leads to smoother edges and corners and more rounded and larger particles. The crystal and electron structure is investigated by XRD- and synchrotron-based soft X-ray absorption spectroscopy (sXAS). Cr doping and light Nb doping (LiNb(0.02)Ni(0.49)Mn(1.49)O4) improve the rate performance of LNMO. To explore the reason for rate-performance improvement, we conducted potential intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) tests. The Li(+) chemical diffusion coefficient at different state of charge (SOC) is calculated and suggests that both Cr and light Nb doping speeds up Li(+) diffusion in LNMO particles. The impedance spectra show that both R(SEI) and R(ct) are reduced by Cr and light Nb doping. The cycling performance is improved by Cr or Nb doping, and Cr doping increases both Coulombic efficiency and energy efficiency of LNMO at 1 C cycling. The LiCr(0.1)Ni(0.45)Mn(1.45)O4 remains at 94.1% capacity after 500 cycles at 1 C, and during the cycling, the Coulombic efficiency and energy efficiency remain at over 99.7% and 97.5%, respectively.

Enhanced fast charge–discharge performance of Li4Ti5O12 as anode materials for lithium-ion batteries by Ce and CeO2 modification using a facile method

Ce and CeO₂in situ modified Li₄Ti₅O₁₂ with fast charge–discharge performance for lithium-ion batteries were prepared by a solid-state method. The improved performance are found to be due to the increased ionic and electronic conductivity.