Surface Modification Engineering Enabling 4.6 V Single‐Crystalline Ni‐Rich Cathode with Superior Long‐Term Cyclability

Abstract

Aiming for increased nickel and lower cobalt content in layered transition metal oxide cathodes (NCM) is a feasible strategy for achieving increased energy density and cost competitiveness in commercial lithium-ion batteries. However, the practical long-term cycling of NCM cathodes suffers from severe capacity degradation due to irreversible interface phase transformation and unavoidable crack formation. Herein, an in situ modification strategy is used to form a uniform and conformal Li 1.8 Sc 0.8 Ti 1.2 (PO 4 ) 3 (LSTP) protective layer by interconnecting the single-crystal-layered LiNi 0.6 Co 0.1 Mn 0.3 O 2 (SC-NCM) particles. LSTP surface modification helps to construct a robust cathode-electrolyte interphase thin film between the cathode and the electrolyte, which can prevent SC-NCM corrosion by electrolyte, and the stability of the mechanics can improve the intergranular cracks caused by long cycles under harsh conditions. Moreover, the LSTP conductive modification layer facilitates the lithium-ion transport among cathode particles, effectively enhancing the rate capability. Impressively, the LSTP modified SC-NCM exhibits a high reversible capacity of 144.3 mAh g −1 at the high discharge rate of 5 C and maintains a capacity retention of 90.27% even at the ultrahigh charge voltage of 4.6 V operation after 500 cycles. Moreover, in a pouch-type full battery, the graphite/LSTP modified SC-NCM maintains a capacity retention of 89.6% after 1700 cycles.

Challenges and Strategies towards Single‐Crystalline Ni‐Rich Layered Cathodes

“…), electrical conductors (e.g., carbon, [86] graphene, [87] polyaniline, [88] polypyrrole, [89] RuO 2 [90] etc. ), and lithium-ion conductors (e.g., Li 3 VO 4 , [91] LiV 2 O 4 , [92] Li 2 MoO 4 , [93] LiNbO 3 , [94] Li 2 SiO 3 , [95] Li 4 SiO 4 , [96] Li 2 TiO 3 , [97] Li 4 Ti 5 O 12 , [98] Li 2 MnO 3 , [99] Li 3 PO 4 , [100] LiAlO 2 , [5d,101] LiAlSiO 4 , [102] Li 2 ZrO 3 , [94b,103] Li 3.2 Zr 0.4 Si 0.6 O 3.6 , [104] Li 3x La 2/3−x TiO 3 , [105] Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 , [106] Li 1.8 Sc 0.8 Ti 1.2 (PO 4 ) 3 [107] etc.). The main modification mechanisms are as follows: 1) promote the interfacial ion/electron transportation by coating ion/ electron conductors; 2) inhibit the interfacial parasitic reactions acted as an electrolyte barrier; 3) alleviate the surface phase transformation and lattice oxygen evolution by providing chemical bonding and physical protective layer; 4) remove the surface residual lithium by reacting with Li compounds.…”

“…For single-crystalline cathodes, the main challenges are the sluggish Li diffusion kinetics and surface reconstruction, therefore the previously reported surface coating layers were majorly Li-ion conductors, such as LiV 2 O 4 , LiAlO 2 , LiBO 2 , Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 , and Li 1.8 Sc 0.8 Ti 1.2 (PO 4 ) 3 et al [72,92,[106][107][108] Fan et al [106] constructed a Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 (LYTP) ion/ electron conductive network to interconnect single-crystal LiNi 0.88 Co 0.09 Mn 0.03 O 2 , which effectively promoted the surface/ interfacial Li + transportation between the adjacent reactive particles (Table 1). Notably, Ti 4+ was also doped into the particle subsurface during the in situ synthesis (Figure 7g), which not only enhanced the electronic conductivity due to the increased electron concentration but also stabilized the lattice oxygen derived from the stronger TiO bond (evidenced by the DFT calculations).…”

“…Moreover, they further adopted similar coating strategy and modification mechanism to construct a Li 1.8 Sc 0.8 Ti 1.2 (PO 4 ) 3 (LSTP) protective layer to increase the structural stability and electrochemical performances of single-crystal LiNi 0.6 Co 0.1 Mn 0.3 O 2 , which showed a high reversible capacity of 144.3 mAh g −1 at 5 C and maintained superior capacity retention of 90.27% even at the ultrahigh cut-off voltage of 4.6 V after 500 cycles. [107] In addition, carbon-coated LiFePO 4 (LFP), benefited from its extraordinary chemical stability and ionic/electronic conductivity, [109] has also been proposed to enhance the cycling capability and thermal safety of single-crystalline NCM622 at high potential of 4.6 V. More importantly, the introduced PO 4 3− was preferentially adsorbed on TM site as indicated by DFT calculations, which could greatly prevent the surface TM and O ions from electrolyte corrosion, facilitating the remarkable capacity retention of 86.5% after 1000 cycles at 1 C between 2.75-4.55 V in a pouch cell. The electrochemical passivation coating layer has already been noticed to effectively inhibit the side reactions at the electrode/electrolyte interface and enhance the cycling stability of electrodes, while it also leads to the hindered Li + diffusion and resulted poor rate capability.…”

A hydrophobic layer of amino acid enabling dendrite-free Zn anodes for aqueous zinc-ion batteries

“…Rechargeable lithium-ion batteries (LIBs) are well established commercially in portable devices, automobiles, and emergency equipment. [1][2][3][4] However, the commercialization of LIBs for largescale energy storage is limited by the poor natural abundance and high price of lithium metal. Besides, the organic electrolyte used in LIBs is toxic and ammable, causing safety problems.…”

A Molten‐Salt Method to Synthesize Ultrahigh‐Nickel Single‐Crystalline LiNi0.92Co0.06Mn0.02O2 with Superior Electrochemical Performance as Cathode Material for Lithium‐Ion Batteries

“…Compared to polycrystalline particles, the SC materials with better crystallinity and enhanced mechanical integrity are capable of withholding the generation of microcracks and eliminating interfacial parasitic reactions between active materials and electrolytes. [16][17][18] Li et al compared the electrochemical performance of SC and polycrystalline LiNi 0.80 Co 0.15 Al 0.05 O 2 cathodes, and the former exhibits enhanced structural stability and higher capacity retention even at elevated temperature. [19] Moreover, several literatures demonstrate that the SC Ni-rich layered cathodes with good mechanical integrity can tightly contact with solid electrolyte, and have greater potential for application in all-solid-state batteries.…”