Shihan Qi,Huaping Wang,Jian He,Jiandong Liu,Chunyu Cui,Mingguang Wu,Fang Li,Yuezhan Feng,Jianmin Ma
Lithium (Li) metal is widely considered as a promising anode for next-generation lithium metal batteries (LMBs) due to its high theoretical capacity and lowest electrochemical potential. However, the uncontrollable formation of Li dendrites has prevented its practical application. Herein, we propose a kind of multi-functional electrolyte additives (potassium perfluorinated sulfonates) from the multi-factor principle for electrolyte additive molecular design (EDMD) view to suppress the Li dendrite growth. The effects of these additives are revealed through experimental results, molecular dynamics simulations and first-principles calculations. Firstly, K + can form an electrostatic shield on the surface of Li anode to prevent the growth of Li dendrites . Secondly, potassium perfluorinated sulfonates can improve the activity of electrolytes as co-conductive salts, and lower the electro-potential of Li nucleation. Thirdly, perfluorinated sulfonate anions not only can change the Li + solvation sheath structure to decrease the desolvation energy barrier and increase the ion migration rate, but also can be partly decomposed to form the superior solid electrolyte interphase (SEI). Benefited from the synergistic effects , an outstanding cycle life over 250 h at 1 mA cm −2 is achieved in symmetric Li||Li cells. In particular, potassium perfluorinated sulfonate additives (e.g., potassium perfluorohexyl sulfonate, denoted as K + PFHS) can also contribute to the formation of high-quality cathode electrolyte interphase (CEI). As a result, Li||LiNi 0.6 Mn 0.2 Co 0.2 O 2 full cells exhibit significantly enhanced cycling stability. This multi-factor principle for EDMD offers a unique insight on understanding the electrochemical behavior of ion-type electrolyte additives on both the Li metal anode and high-voltage cathode.
Increasing the voltage of lithium batteries represents the most direct and effective strategy for enhancing battery capacity. However, excessively high charging voltages can result in the degradation of battery interfacial contacts and the dissolution of transition metals in the cathode, thereby limiting the cycling performance of the battery. This paper employs a fluorosulfonic acid salt electrolyte as a sacrificial agent to in situ construct a stable CEI (Cathode Electrolyte Interface) and SEI (Solid Electrolyte Interface). The resulting membrane is characterized by a uniform distribution of LiF and LiSO x , which exhibit high lithium-ion conductivity and mitigate dissolution of active materials under high voltage. This membrane effectively restricts further electrolyte consumption, allowing the remaining electrolyte to wet the interface and reduce interfacial impedance adequately. Moreover, the CEI can suppress the dissolution of transition metals from the cathode and prevent them from shuttling to the anode side. When implemented in lithium batteries, the use of the sacrificial agent enables the NCM523/Li battery (with an initial discharge capacity of 105 mAh/g) to achieve a high capacity retention of 85.7 % after 800 cycles at a 1 C rate and 30 °C.
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