Highly Adhesive and Soluble Copolyimide Binder: Improving the Long-Term Cycle Life of Silicon Anodes in Lithium-Ion Batteries

Abstract

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g(-1)), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g(-1) and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g(-1) after 300 cycles at 1.2 A g(-1) and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm(-2), which is a commercially acceptable level, the Si anode could deliver 647 mAh g(-1) until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g(-1).

Mussel‐Inspired Polydopamine‐Functionalized Super‐P as a Conductive Additive for High‐Performance Silicon Anodes

“…[ 31,52,53 ] Because, thus far, there is no specifi c analysis tool to measure the adhesion strength of the electrodes in an accurate manner, we believe that it is meaningful to evaluate the physical features of Si electrodes using SAICAS. SAICAS is a unique tool that is capable of measuring the adhesion strength of the electrodes at a specifi c fi lm depth by using a V-shaped microblade to cut the fi lm.…”

“…However, these traditional LIBs, containing two intercalation electrodes (e.g., C 6 LiMO 2 , where "M" is a transition metal such as Ni, Mn, or Co), [ 6 ] are now reaching the limits of their theoretical energies. By using polymeric binders other than conventional poly(vinylidene fl uoride) binders, which are widely used for both cathodes and anodes in commercial LIBs, [ 24 ] polymers that contain carboxylic groups (such as poly(acrylic acid) (PAA), [ 4,25,26 ] carboxymethyl cellulose, [ 24,27,28 ] and alginate [ 29 ] ), polymers with high mechanical strength (such as polyamide-imide [ 30 ] and polyimide [ 31 ] ), and polymers forming crosslinking networks [32][33][34] have been shown to yield superior cycle performance of Si-based anodes. [7][8][9] The theoretical specifi c capacity of a conventional graphite anode is 372 mAh g -1 (LiC 6 ).…”

Understanding the Effect of Polydopamine Interlayer on the Long‐Term Cycling Performance of Silicon Anodes: A Multiphysics‐Based Model Study

“…[1][2][3][4] As one of the most promising anode material candidates to be used in LIBs, silicon has a relatively higher theoretical specific capacity (3579 mAh g À1 ) as well as other advantages such as environmental friendly and terrestrial abundance. [11][12][13][14] However, the mechanisms underlying the enhancement in the electro-chemical performance by these binding materials are complicated and not well understood. To address these issues, the use of binding materials with stronger adhesion forces such as alginate, copolyimide, poly(acrylic acid) (PAA), carboxymethyl cellulose and polymers that form crosslinked networks have been widely investigated.…”

Elucidating the Polymeric Binder Distribution within Lithium‐Ion Battery Electrodes Using SAICAS

“…To address these issues, many researchers have attempted to increase the binder content or enhance the adhesion strength of the binders; however, as mentioned above, the binder content should be minimized for a design with higher energy density. Therefore, without developing groundbreaking binder materials, a good solution is to control the conventional binder material dispersion within the electrodes by optimizing the drying conditions during the electrode fabrication process or by modifying the rheological properties of electrode slurries .…”