Ultrahigh loading dry-process for solvent-free lithium-ion battery electrode fabrication

Abstract

The current lithium-ion battery (LIB) electrode fabrication process relies heavily on the wet coating process, which uses the environmentally harmful and toxic N-methyl-2-pyrrolidone (NMP) solvent. In addition to being unsustainable, the use of this expensive organic solvent substantially increases the cost of battery production, as it needs to be dried and recycled throughout the manufacturing process. Herein, we report an industrially viable and sustainable dry press-coating process that uses the combination of multiwalled carbon nanotubes (MWNTs) and polyvinylidene fluoride (PVDF) as a dry powder composite and etched Al foil as a current collector. Notably, the mechanical strength and performance of the fabricated LiNi_0.7Co_0.1Mn_0.2O₂ (NCM712) dry press-coated electrodes (DPCEs) far exceed those of conventional slurry-coated electrodes (SCEs) and give rise to high loading (100 mg cm^-2, 17.6 mAh cm^-2) with impressive specific energy and volumetric energy density of 360 Wh kg^-1 and 701 Wh L^-1, respectively.

Fig. 1. Fabrication of the dry press-coated electrode (DPCE).

Schematic illustration of the fabrication procedure and structural design of the DPCE.

Fig. 2. Comparison of the dry press-coating capability of the conductive scaffolds.

a–d Folding test of Super P:PVDF–1:1 dry electrode (d-SP) after cold/hot press a, b. Folding test of MWNT:PVDF–1:1 dry electrode (d-MP) after cold/hot press c, d. e Schematic illustration of the tensile strength measurement setup. f Comparison of the stress-strain curves of d-MP, PVDF, and d-SP sandwiched dry electrode; diameter of the disc is 15 mm.

Fig. 3. The electrochemical performance comparison of the SCE and DPCE.

a Rate capability. b Half-cell cycling performance at a charge/discharge current density of 1.0/1.0 C. c CV profile of both electrodes at a scan rate of 0.2 mV s⁻¹ between 2.9 and 4.3 V. d Fitted Nyquist plots. e Surface electrical resistivity of the DPCE vs. SCE. f Calculated diffusion coefficient as a function of SOC and DOD. g Full-cell cycling performance at a charge/discharge current density of 0.5/0.5 C. h Charge/discharge voltage profile comparison (full-cell).

Fig. 4. Morphologies and postmortem analysis of the cycled DPCE (versus SCE).

a Micro-CT images of the DPCE and SCE. The active material (NCM712) phase is labeled green, and the carbon phase is labeled red. b Amount of metallic Ni, Mn, and Co deposited on the Li-metal anodes (ICP–MS). c TOF–SIMS mapping images of the NiF₂⁺ byproducts formed on the surface of the cathodes. d, e XPS F 1 s spectra of the cycled DPCE d and SCE e.

Fig. 5. The high mass loading DPCEs (coin cells).

a Cross-section SEM images of the DPCE with varying mass loadings and their corresponding thicknesses. b Charge/discharge voltage profiles (in terms of areal capacities). c Cycling performance of the DPCE with different areal mass loadings at a charge/discharge current density of 1.0/1.0 C at a voltage range of 2.9–4.3 V. d Adhesion force of the high-loading DPCE (HL–DPCE) and high-loading SCE (HL–SCE), which was estimated using 180° peel-off test. The insets show the digital photos of the electrodes after the peel-off test. e Comparison of the cycling performance of the HL–DPCE and HL–SCE at a charge/discharge current density of 1.0/1.0 C at a voltage range of 2.9–4.3 V.

Fig. 6. The high mass loading DPCEs (Pouch-cells).

a Charge/discharge voltage profile of the Li-metal DPCE pouch cell (31 mg cm⁻²) at a voltage range of 2.9–4.3 V and charge/discharge current density of 0.1/0.1 C (dashed line represents the theoretical capacity of NCM712). b Cycling performance of the Li-metal DPCE pouch cell (31 mg cm⁻²) at a charge/discharge current density of 0.5/0.5 C at a voltage range of 2.9–4.3 V. c Charge/discharge voltage profiles of the Li-metal DPCE pouch cells in terms of areal mass loadings at a voltage range of 2.9–4.3 V and charge/discharge current density of 0.05/0.1 C. d Cycling performance of the Li-metal DPCE pouch cells with various areal mass loadings. e Areal capacities of cells as a function of areal mass loading (DPCEs versus previously reported solvent-free cathodes). f Specific energies (calculated based on the entire cell weight) of cells as a function of areal capacity (DPCEs versus previously reported high mass loading cathodes).