Polyurethane Binder for Aqueous Processing of Li-Ion Battery Electrodes

Abstract

In this manuscript the investigation of the heat-curable polyurethane (PU)/carboxymethyl cellulose (CMC) mixture as binder for Li-ion battery electrodes is reported. The experimental results demonstrate the outstanding thermal and electrochemical stability of PU, as well as the good electrochemical performance of cathode (NMC) and anode (graphite) electrodes in which PU is used as binder. The most important finding is the ability of PU to prevent current collector corrosion usually occurring when an aqueous dispersion (slurry) of NMC is coated on aluminum foils. SEM investigation shows that PU encapsulates the positive active material particles preventing a pH raise in the slurry. Finally, the cycling performance of PU/CMC based anodes and cathodes are tested in half as well as full lithium-ion cell setups. The awareness of the finite nature of our earth´s natural resources as well as growing concerns for increased greenhouse gas emissions are leading to a strong demand for a more environmentally-friendly generation of energy. Considering the importance of sustainable energy solutions, strong efforts are made to develop improved systems for large and small scale energy storage.1,2 Currently, Li-ion batteries seem to be suitable energy storage devices to fulfil the requirements of small energy storage due to their high energy density and long lifetime.3 Additionally, their lightweight fulfils very well the rising demand for use in smartphones, computers and other portable devices, as well as for electromobility solutions, facilitating the development toward a modern mobile society.Lithium-ion batteries are composed of several materials including metals and metal oxides, graphite and other carbonaceous materials, organic solvents, lithium salts and polymers. These latter are present in the porous separator, laying in between the electrodes (usually a polyolefin), and as binding components in the composite electrodes. Binders are counted among the so-called inactive components since they do not directly contribute to the capacity of the cells. However, their key role in the electrode processing and their dramatic influence on the electrochemical performance of electrodes has been extensively outlined. [4][5][6] Relevant physical and chemical properties for binder materials are (i) thermal stability, chemical and electrochemical stabilities, (ii) tensile strength (strong adhesion and cohesion), (iii) flexibility, and (iv) viscosity (of the slurries). 4,[7][8][9] The main purpose of using a binder is to form stable networks of the solid electrode components, i.e., the active materials and conducting agents (cohesion). Moreover, the binder has to ensure a close contact of the composite electrode toward the current collector (adhesion).In state-of-the-art commercial Li-ion batteries polyvinylidene-difluoride (PVdF) is the binder material of choice due to its superior adhesion properties and electrochemical stability.10 Important points of criticism for this polymer, however, are the requirement of volatile and toxic so...

Evaluation of guar gum-based biopolymers as binders for lithium-ion batteries electrodes

“…Moreover, a capacity retention of 85 % and a remarkable coulombic efficiency of 99.8 % over 200 cycles were achieved. The obtained electrochemical performance is comparable with that achieved using NMC electrodes containing 5 wt.% of NaCMC (See Figure S7 in Supplementary Information), which resulted to be the best formulation for NMC cathodes in our previous works [13,14].…”

“…This specific issue has been deeply investigated by our and other research groups. Different approaches have been explored to enable aqueous processing for cathodes, such as the use of a protecting carbon layer on current collector, [11,12] the combination of NaCMC and urethanes polymers, [13] and the reduction of the slurry´s pH by addition of mild acids [14]. In particular, the last solution is simple and easy to be introduced in the already established electrode production lines.…”

New eco-friendly low-cost binders for Li-ion anodes

“…Improvements must be obtained taking into account all kinds of materials composing the whole system. The binder, present in the electrode material, is a so-called Binactive material^but it plays a key role in the formation of a stable active material network, ensuring the adhesion between the active material particles, the conductivity enhancer and the current collector [8]. In fact, if the binder does not have suitable properties, though present in the electrode for the 2-5% only, the performance and durability of the cell are compromised [7].…”

Low Molecular Weight Spandex as a Promising Polymeric Binder for LiFePO4 Electrodes

“…Aqueous binders were particularly highlighted because of their conspicuous advantages, including low cost and easy disposal of waste solvents after processing. [27][28][29] As in most LIB cathodes, polyvinylidene difluoride (PVDF) dispersed in NMP has been mainly used for LFP electrodes, to take advantages of the properties of PVDF, such as high electrochemical stability, high specific dielectric constant, and decent Li ion conductivity. [27][28][29] As in most LIB cathodes, polyvinylidene difluoride (PVDF) dispersed in NMP has been mainly used for LFP electrodes, to take advantages of the properties of PVDF, such as high electrochemical stability, high specific dielectric constant, and decent Li ion conductivity.…”