Thickness difference induced pore structure variations in cellulosic separators for lithium-ion batteries

Abstract

The pore structure of the separator is crucial to the performance of a lithium-battery as it affects the cell resistance. Herein, a straightforward approach to vary the pore structure of Cladophora cellulose (CC) separators is presented. It is demonstrated that the pore size and porosity of the CC separator can be increased merely by decreasing the thickness of the CC separator by using less CC in the manufacturing of the separator. As the pore size and porosity of the CC separator are increased, the mass transport through the separator is increased which decreases the electrolyte resistance in the pores of the separator. This enhances the battery performance, particularly at higher cycling rates, as is demonstrated for LiFePO 4 /Li half-cells. A specific capacity of around 100 mAh g -1 was hence obtained at a cycling rate of 2 C with a 10 lm thick CC separator while specific capacities of 40 and close to 0 mAh g -1 were obtained for separators with thicknesses of 20 and 40 lm, respectively. As the results also showed that a higher ionic conductivity was obtained for the 10 lm thick CC separator than for the 20 and 40 lm thick CC separators, it is clear that the different pore structure of the separators was an important factor affecting the battery performance in addition to the separator thickness. The present straightforward, yet efficient, strategy for altering the pore structure hence holds significant promise for the manufacturing of separators with improved performance, as well as for fundamental studies of the influence of the properties of the separator on the performance of lithium-ion cells.

Nanocellulose Modified Polyethylene Separators for Lithium Metal Batteries

“…This is further confirmed by the SEM images showing detailed structures of the CNFs and PE layers (Figure d,e). In accordance with our previous studies, it is seen that the CNFs layer was composed of intertwined cellulose nanofibers (≈20 nm) that created a homogenous mesoporous structure, while the PE layer featured inhomogeneous pores created by micrometer‐sized fibers with different thicknesses. From the Barrett–Joyner–Halenda (BJH) pore size distribution curves (Figure S2, left, Supporting Information), it is apparent that the laminated CNFs layers featured mesopores with an average pore size of about 20 nm and that their porosity was higher than that of the PE layer, even though they looked more compact in the low magnification SEM images.…”

“…From the Barrett–Joyner–Halenda (BJH) pore size distribution curves (Figure S2, left, Supporting Information), it is apparent that the laminated CNFs layers featured mesopores with an average pore size of about 20 nm and that their porosity was higher than that of the PE layer, even though they looked more compact in the low magnification SEM images. Therefore, the CPC separator had a higher porosity than the pristine PE separator (26% vs 20%, estimated based on our previous findings). It is also obvious that the mesopores in the CNFs layers featured a narrow distribution, which is believed to endow an even current distribution at the electrodes when using a CPC separator.…”

“…The better wettability of the CPC compared to the PE separator should therefore be advantageous during both battery assembly and battery operation. With a higher porosity mentioned above (26% vs 20%) and a better electrolyte wettability, the CPC separator therefore showed higher ionic conductivity compared with pure PE separator (Figure S2, right, Supporting Information, 0.22 vs 0.16 mS cm −1 ), measured by electrochemical impedance spectroscopy (EIS) described in our previous studies …”

Lightweight, Thin, and Flexible Silver Nanopaper Electrodes for High‐Capacity Dendrite‐Free Sodium Metal Anodes

“…At present, this thickness is ≈2 µm. However, the volume of the cell can be decreased by using thinner separators and electrodes, as discussed in our previous studies . For comparison, a thicker AgNP electrode comprising 10 mg AgNW and 30 mg nanocellulose was likewise manufactured and tested as a Na metal anode.…”

Cellulose Nanofibers Prepared via Pretreatment Based on Oxone® Oxidation

“…Cellulose nanofibers (CNF) which possess properties such as high aspect ratio (L/d), large specific surface area, biodegradability, low coefficient of thermal expansion [ 1 ], great mechanical properties [ 2 ], and high gas barrier properties [ 3 ] are nano-sized fibers less than 100 nm wide produced from cellulose [ 4 ]. Due to their unique properties, CNF has been utilized in many areas such as tissue engineering [ 5 ], hydrogel contact lenses [ 6 ], filtration [ 7 ], electronic devices [ 8 , 9 , 10 , 11 ], carbon nanofiber production [ 12 ], drug delivery [ 13 ], wound healing [ 14 ], and translucent conducting films [ 15 ].…”