New Organic Complex for Lithium Layered Oxide Modification: Ultrathin Coating, High-Voltage, and Safety Performances

Abstract

Surface modification of a cathode (e.g., lithium layered oxide, NCM) has become ever more important in lithium-ion batteries, particularly for pursuing higher energy densities and safety at high voltage. This is because structural degradation of the cathode can be mitigated significantly. Herein, an organic complex is introduced for metal phosphate (e.g., AlPO 4 ) modification through a new film-forming process in nonaqueous solution. This general strategy overcomes the challenge of nonuniform coating in current precipitation methods and then opens a new avenue toward ultrathin surface modification on a molecular scale. As one example, asprepared AlPO 4 -coated NCM exhibits much improved structural and electrochemical stability; meanwhile, thermal runaway can be suppressed significantly in overcharged cells using the modified NCM, demonstrating higher and reliable safety features. The great improvements benefit from the uniform and ultrathin AlPO 4 coating, which inhibits the collapse and conversion of the layered structure to spinel, especially to the rock salt structure at high-voltage conditions, as confirmed by HRTEM and EELS.

A polymeric composite protective layer for stable Li metal anodes

“…Nano-AlPO 4 composite prepared by organic ligand coordination is reported in our previous publication [84], showing good dispersion in a solution. This inspires us to prepare well-dispersed nano-AlPO 4 composite film to protect lithium anode.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…Now that the parasitic side reactions start from the interfaces between the solid cathodes and liquid electrolytes, the most effective method is to avoid their direct contact by introducing passive physical protection layer on the cathode surface . In general, the employed coating species can be categorized into i) the chemically and electrochemically inactive coatings, including metal oxides (Al 2 O 3 , TiO 2 , MgO, SiO 2 , ZrO 2 , V 2 O 5 , Nb 2 O 5 , ZnO, MoO 3 , and Y 2 O 3 ,) and phosphates (AlPO 4 , MnPO 4 , Mn 3 (PO 4 ) 2 , La(PO 4 ) 3 , Ni 3 (PO 4 ) 2 , Co 3 (PO 4 ) 2 , ZrP 2 O 7 , and FePO 4 ) as well as some fluorides (AlF 3 and LiF); ii) the Li + conductive coatings, mainly refer to the Li‐containing compounds such as LiAlO 2 , Li 2 ZrO 3 , Li 3 VO 4 , Li 2 MnO 3 , LiMn 2 O 4 , Li 3 PO 4 (LPO), LiFePO 4 (LFP), LiMnPO 4 , Li 2 TiO 3 , LiTiO 2 , Li 2 O‐2B 2 O 3 , LiTi 2 (PO 4 ) 3 , LiZr 2 (PO 4 ) 3 , Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 , Li 0.5 La 0.5 TiO 3 , LiTaO 3 , Li 4 SiO 4 , and LiAlF 4 as well as some heterostructured electrochemical active cathodes (Li 1.2 Ni 0.2 Mn 0.6 O 2 , Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 and NCM333); and iii) the electron conducting coating, representatively, reduced graphene oxide (rGO), permeable poly (3,4‐ethylenedioxythiophene) (PEDOT),…”

“…Except the metal oxides, phosphates, especially the AlPO 4 , can equally function as a favorable protective layer. Innovatively, a precise, uniform, and ultrathin AlPO 4 coating layer is achieved on the NCM333 surface via introducing a novel organic ligand coordination complex, rendering a significant enhancement in electrochemical properties . Additionally, Chen et al first investigate the positive influence of the MnPO 4 coating on the LiNi 0.4 Co 0.2 Mn 0.4 O 2 (NCM424) cathode .…”

Performance and Stability Improvement of Layered NCM Lithium-Ion Batteries at High Voltage by a Microporous Al2O3 Sol–Gel Coating

“…13,14 This degradation becomes more serious when cycled at high voltage (4.5 V vs graphite) and high temperature, especially for the Ni-rich NCM whose phase transition occurs more easily. Thus, many efforts have been made to improve the surface structure stability of Ni-rich layered oxide cathodes via surface coating with various protection materials such as Al 2 O 3 , 15−17 TiO 2 , 18−20 ZrO 2 , 21−23 AlPO 4 , 24−26 AlF 3 , 27−29 and so forth. The general objective of these approaches is to prevent direct contact of the electrode from the electrolyte to reduce the potential parasitic side reactions at the cathode electrode/electrolyte interface.…”