Construction And Electrochemical Performance Of Elastomer Interfacial Layer On Electrode Materials Surface

The global demand for rechargeable lithium battery is growing tremendously due to rapid development for electric vehicles and portable electronics.Designing lithium battery with high energy density and high safety has become a research hotspot.High gravimetric energy density batteries can be achieved by adapting high-nickel ternary cathode and Li metal anode,which is a ideal battery system.However,anisotropic changes in lattice parameters of Ni-rich layered cathode and dendrite growth of Li metal anode will lead to large interfacial mechanical stress and electrode volume change upon the charge/discharge cycles,which will affect the cycle life and safety of the battery.Therefore,it is crucial to improve battery performance by enhancing electrode interfacial stability.The paper will concentrate on the interfacial stability of high-nickel ternary cathode and Li metal anode,mainly divided into the following two parts:（1）The polyrotaxane-co-poly（acrylic acid）protective layer on high-nickel ternary cathode to improve interfacial stabilityLayered Ni-rich cathode Li Ni_0.6Co_0.2Mn_0.2O₂（NCM622）has been considered as the ideal cathode material to increase the energy density of battery due to its high specific capacity.However,the anisotropic change of the lattice dimensions of polycrystalline Ni-rich cathode will lead to the formation of intergranular cracks,and the dissolution of transition metal ions due to the immersion of electrolyte,resulting in poor cycle stability.In this work,we demonstrate a highly elastic polyrotaxane-co-poly（acrylic acid）（PR-co-PAA）polymer as a protective coating for Li Ni_0.6Co_0.2Mn_0.2O₂（NCM622）cathode to improving cathode’s structural stability.The sliding motion ofα-cyclodextrin（α-CD）molecules passing through the main chain endows the PR-co-PAA with high toughness.The movement ofα-CD can alleviate the mechanical stress caused by the anisotropic volume deformation inside the NCM particles and repair the microcracks induced by mechanical stress to maintain the stability of the electrode volume.In addition,PR-co-PAA interfacial layer as a physicochemical barrier can inhibit the side effect caused by electrolyte erosion.Meanwhile,the PAA chains with abundant carboxyl groups reduce transition metal ion dissolution via chelation,and improve the structural stability of NCM cathode.Benefiting from the synergetic effects of the protective coating,a modified NCM622 cathode with improved structural stability and cycling performance is achieved under high-C-rate（1 C）and extended cutoff voltage（4.7 V）.（2）Polyurethane artificial interphase layer for stable lithium metal anodeLithium metal is a promising anode material,but the formation of Li dendrites and fragile solid electrolyte interface（SEI）can lead to the unstable Li metal/electrolyte interface,which hinders the practical application of Li metal in secondary batteries.In this work,polyurethane（SPU-UPy）with excellent strength and self-healing ability is introduced as an artificial protective layer to stabilize Li/electrolyte interface.Polyurethane is composed of soft phase polyether and hard phase isocyanate.The soft phase of polyether can conduct lithium ion through the movement of the molecular chain,which can ensure the uniform Li ion flux and deposition at the interface.The hard phase featuring dynamic disulfide metathesis and strong supramolecular quadruple hydrogen bonding can contribute to the high elasticity and self-healing ability,which can adapt to dynamic volume variations,quickly repair the surface rupture caused by dendrite growth,and stabilize the Li/electrolyte interface.The deposition/precipitation efficiency of the SPU-UPy modified Li anode is maintained at 96.3%at 0.5 m A cm^-2 in 1 M Li PF₆（EC/DEC）carbonate electrolyte.When paired with NCM622,SPU-UPy@Li|NCM exhibits capacity retention of 88.7%after 100cycles at 0.5 C.