Semi‐Flooded Sulfur Cathode with Ultralean Absorbed Electrolyte in Li–S Battery

Abstract

times higher than state-of-art lithiumion batteries (LIB). [1] However, highly porous S 8 cathode [2] and superabundant electrolyte (e.g., E/S ratio >10 µL mg −1 for coin cells and >3 µL mg −1 for pouch cells) [3] are often cited in the literature to reach satisfactory sulfur utilization and cycling numbers. In contrast, E/S in LIB is only ≈0.3 µL mg −1 . [3e] A high E/S drastically reduces the Li-S full-cell gravimetric energy density. [1c,4] For example, when E/S > 10 µL mg −1 , the energy density of full-cell cannot be more than 200 Wh kg −1 even with S 8 loading of 6 mg cm −2 , 75 wt% S 8 in the cathode and 80% sulfur utilization (1337 mAh g −1 ), as shown in Figure S1a in the Supporting Information. [5] Fundamentally, ether-based liquid electrolyte phase serves two purposes in such S 8 cathode, as illustrated in Figure 1: a) it serves as the "waterways" for the long-range transport of Li + and b) it dissolves lithium polysulfide (LiPS) and boosts the redox kinetics in contact with conductive carbon black, [3b,6] as local sulfur mobility (LSM) [7] is often required to mediate the redox reaction. However, global sulfur mobility (GSM) is undesirable because it leads to sulfur crossover to the anode or layering of electronically insulating phases within the cathode. [7,8] To fulfill the above-mentioned two electrolyte functions in S 8 cathode, one must carefully and rationally engineer the electrolyte/electrode pore space distributions within the cathode. Inspired by the plant leaf illustrated in Figure 1, to support function (a), end-to-end canal "waterways" are essential for the long-range mass transport of Li + over a length scale of 10 1 µm; On the other hand, to support function (b), multiconnected capillary network at a length scale of 10 1 -10 2 nm are also needed because the conductive carbon nanoparticles are dispersed at such length scale, and LSM is needed at such 10 1 -10 2 nm length scale for the solubilized LiPS to waft to the nearest conductive carbon particle to sustain redox reactions: such local consumptions also help shut down GSM and eliminate insulator-dense-layering (without porosity or carbon black) tendencies within the cathode. [7,8] Here we want to emphasize that the electrode pores are completely different from sulfur-host pores, which were generally elaborately constructed to induce sulfur impregnation. The sulfur-host porosity needs to be big in order to load in more sulfur. [9] They also need to be highly tortuous and less connected in order to suppress GSM. [10] However, these rules are Lean electrolyte (small E/S ratio) is urgently needed to achieve high practical energy densities in Li-S batteries, but there is a distinction between the cathode's absorbed electrolyte (AE) which is cathode-intrinsic and total added electrolyte (E) which depends on cell geometry. While total pore volume in sulfur cathodes affects AE/S and performance, it is shown here that pore morphology, size, connectivity, and fill factor all matter. Compared to conventional thermally dried sulfur cathod...

Anthraquinone Covalent Organic Framework Hollow Tubes as Binder Microadditives in Li−S Batteries

“…[25b] Moreover,c ontact angle tests have been conducted to evaluate the electrolyte wettability of electrodes with different samples.I ntroduced POAC-4 can result in decreased contact angle (13.18 8)o fP OAC-4 based electrode when compared with that of PVDF based electrode (20.98 8), which might be attributed to the presence of abundant polar groups in POAC-4 that are beneficial for the improvement of wettability (Figure S20). [27] To verify the electrocatalytic activity of POAC-4 based electrode within ap otential window from À0.8 to 0.8 V, symmetric cells are assembled using POAC-4 or bare PVDF based electrodes as both anode and cathode and carried out in cyclic voltammogram (CV) profiles at ascan rate of 50 mV s À1 (Figure S21). As ar esult, the symmetric cells with POAC-4 based electrode exhibit higher current with obvious redox peaks compared to bare PVDF based electrode,implying that POAC-4 possesses better electrochemical kinetics for the rapid redox conversion reactions of LiPSs on the electrolyte/ electrode surface (Figure S21).…”

Rationally Design a Sulfur Cathode with Solid‐Phase Conversion Mechanism for High Cycle‐Stable Li–S Batteries

“…[ 10–12 ] Moreover, to ensure fast redox kinetics, an electrolyte/sulfur ratio (E/S) of higher than 15 µL mg −1 is widely adopted for the “dissolution‐precipitation” cathode mode, which sacrifices the total energy density. [ 13–16 ]…”

Anthraquinone Covalent Organic Framework Hollow Tubes as Binder Microadditives in Li−S Batteries

“…Moreover, contact angle tests have been conducted to evaluate the electrolyte wettability of electrodes with different samples. Introduced POAC‐4 can result in decreased contact angle (13.1°) of POAC‐4 based electrode when compared with that of PVDF based electrode (20.9°), which might be attributed to the presence of abundant polar groups in POAC‐4 that are beneficial for the improvement of wettability (Figure S20) [27] …”