A General Method for High-Performance Li-Ion Battery Electrodes from Colloidal Nanoparticles without the Introduction of Binders or Conductive-Carbon Additives: The Cases of MnS, Cu_2–xS, and Ge

Abstract

In this work, we demonstrate a general lithium-ion battery electrode fabrication method for colloidal nanoparticles (NPs) using electrophoretic deposition (EPD). Our process is capable of forming robust electrodes from copper sulfide, manganese sulfide, and germanium NPs without the use of additives such as polymeric binders and conductive agents. After EPD, we show two postprocessing treatments ((NH4)2S and inert atmosphere heating) to effectively remove surfactant ligands and create a linked network of particles. The NP films fabricated by this simple process exhibit excellent electrochemical performance as lithium-ion battery electrodes. Additive-free Cu(2-x)S and MnS NP films show well-defined plateaus at ∼1.7 V, demonstrating potential for use as cathode electrodes. Because of the absence of additives in the NP film, this additive-free NP film is an ideal template for ex situ analyses of the particles to track particle morphology changes and deterioration as a result of Li ion cycling. To this end, we perform a size-dependent investigation of Cu(2-x)S NPs and demonstrate that there is no significant relationship between size and capacity when comparing small (3.8 nm), medium (22 nm), and large (75 nm) diameter Cu(2-x)S NPs up to 50 cycles; however, the 75 nm NPs show higher Coulombic efficiency. Ex situ TEM analysis suggests that Cu(2-x)S NPs eventually break into smaller particles (<10 nm), explaining a weak correlation between size and performance. We also report for the first time on additive-free Ge NP films, which show stable capacities for up to 50 cycles at 750 mAh/g.

Electrophoretic Deposition for Lithium‐Ion Battery Electrode Manufacture

“…[2,3] Examples of battery materials studied, Lithium-ion specifically, include LFP, [4] LTO, [5] LMP, [6] LCO, [7] LMO [8] and Si. [2,3] Examples of battery materials studied, Lithium-ion specifically, include LFP, [4] LTO, [5] LMP, [6] LCO, [7] LMO [8] and Si.…”

Common Battery Anode Testing Protocols Are Not Suitable for New Combined Alloying and Conversion Materials

“…The observed extra capacity above theoretical was attributed to capacitive effects (known to occur for sulfide materials and other CAMs,,), as well as the contribution from the Cu 2‐x S film formed during ligand removal. The contribution of this film has been previously demonstrated to be initially significant, but diminishes rapidly with cycling …”

Electrophoretic Deposition of Tin Sulfide Nanocubes as High‐Performance Lithium‐Ion Battery Anodes

“…In order to both improve the conductivity and reduce the inactive mass of the electrode, the films on Cu foil were subjected to a facile ligand removal treatment involving a short exposure to a solution of ammonium sulfide in methanol. This replaced the long‐chain organic ligands (hexadecylamine) with sulfide anions, thereby reducing interparticle distance and improving electrode conductivity . Additionally, this treatment brought about the formation of a thin film of Cu 2‐x S on the surface of the copper current collector …”

“…This replaced the long-chain organic ligands (hexadecylamine) with sulfide anions, thereby reducing interparticle distance and improving electrode conductivity. [24,26] Additionally, this treatment brought about the formation of a thin film of Cu 2-x S on the surface of the copper current collector. [26] The electrochemical lithiation characteristics were assessed using cyclic voltammetry from 0-3 V in a HC.…”

“…[15][16][17][18][19][20][21][22][23] Although not widely studied in nanostructured battery anode fabrication, this method is particularly advantageous in terms of enhanced film densification, conductivity and adhesion, while eliminating the need for binder and conductive additives which reduce active mass. [24][25][26][27][28] Crucially, EPD also enables uniform deposition onto 3-D current collectors, [21] which provide reduced Li + diffusion lengths, [29,30] enhanced conductivity and better expansion accommodation than their 2-D counterparts. [31,32] The utilization of tin in sulfide form brings about a combined alloying and conversion lithiation process, involving the (usually poorly reversible, [33][34][35] though not always [36] ) formation of Li 2 S during the first lithiation.…”