2.3. The adhesion strength of acrylic acid derivative
terpolymer
Due to most of the binders being non-electrochemical active and
non-electronic conductivity, it is desirable to develop binders with
high adhesion capability to reduce the addition content (χ ) in
the electrode to reach high electrochemical performance. As regards TBs,
this is more important because the gas production of binders in thermal
decomposition at TBs operation temperature may lead to the break of the
battery bulk. LA136D is known for its excellent adhesion strength and is
used in silicon and sulfur electrode manufacturing in secondary
batteries.[29,30] In contrast to the traditional
PVDF binder, which interacts with electrode materials via weak Van der
Waals forces, LA136D interacts with electrode materials via covalent
bonds.[31] The large amounts of high polarity
groups (−C≡N, −COONH2, and −COOLi) in the side chain of
LA136D act as the adsorption points to bond the electrode materials and
current collector. In this work, we fabricated TBs thin film electrode
by using LA136D as the binder and studied the electrode adhesion
capability through an electrode peel-off test. Figure 4 (a)shows the preparation process of slurry coating and Figure 4
(b) is the prepared thin film cathode. Figure 4 (c) is the
schematics of the electrode peel-off test process. Figure 4 (d)shows the peel-off force used to peel the different electrodes. For
comparison, we also studied the electrode adhesion ability fabricated by
PVDF and SBR. The content of the different binders in the electrode is
kept to the same (1wt %), and the electrode thickness is
controlled at 100 μm and with similar tap density (~3.5
mg cm−3). From Figure 4 (d), LA136D shows the highest
peel-off force of 140 N, SBR shows a medium peel-off force of 98 N, and
PVDF shows the lowest peel-off force of 60 N. The peel-off test
indicates LA136D is capable to fabricate a mechanically robust electrode
even at a low content. Figure 4 (e) is the digital pictures of
electrodes after the peeling test. It can be seen that LA136D electrodes
have the best surface integrity. This result is consistent with the
peel-off force.
Traditional pressed-pellet technology is hard to produce electrodes with
non-circular shapes and restricts the shape-accommodation capability of
TBs.[32] Herein, it is shown that LA136D thin film
electrode can be cut into various shapes randomly, as shown inFigure 4 (f) . In addition, the LA136D electrode also shows
excellent handling properties (Figure 4(g) ). The electrode
materials do not drop even at a high crinkle angle. It is worth noting
that the content of LA136D used in the electrode is 1wt %. The
“sticky” property of LA136D can be observed visibly in Figure
4 (h) , it is consistent with the high bonding capability of LA136D that
few LA136D can bond to electrode materials efficiently through the high
polarity groups.