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Lithium–sulfur (Li–S) batteries have attracted great attention in environmentally and friendly energy storage systems due to their excellent theoretical specific capacities and high energy densities. In addition, the element sulfur has a wide range of raw materials and low production costs and is considered to be a material with the most development potential. However, the poor electrical conductivity of sulfur, the volume expansion of sulfur during polarization, and the shuttle effect of lithium polysulfides (LiPSs) severely hinder the commercialization of Li–S batteries. Since carbon materials containing light nonpolar or weakly polar substances are used as sulfur hosts, there will be some difficulties in cycling stability, and the volumetric energy densities of Li–S batteries will be destroyed. In order to solve the existing problems, some polar substances are introduced into the cathode material to improve the cycle stability and effectively suppress the shuttle effect. This review presents polar materials commonly used in Li–S batteries, including single metals, metal nitrides, metal oxides, metal sulfides, and conducting polymers. Finally, this review not only summarizes the research directions and challenges of polar material applications but also looks forward to the development prospects of batteries, provides a pathway for the practical application of noncarbon sulfur host materials in Li–S batteries, and inspires more researchers to work on cathode materials.

Background Current data indicate that supplements such as folic acid and vitamin B may be beneficial in halting and even reversing atrophic gastritis, intestinal metaplasia and intraepithelial neoplasia, generally referred to as gastric precancerous conditions(GPC). However, there is no Meta-analysis article to evaluate the prevention and treatment of folic acid in the gastric precancerous conditions. We therefore conducted a meta-analysis to confirm the efficacy of folic acid in treating GPC. Methods Using a systematic review method, consider randomized controlled trials (RCT), including clinical trial reports, unpublished clinical trial data, and conference papers. The search time was been set from the database’s establishment to June 2, 2021. The language was not limited, using PubMed, SinoMed, Lancet, Web of Science, CNKI, Cochrane, Ovid, Science Direct, Embase, and EBSCO databases. Data were extracted using a pre-designed extraction tool and analysis was undertaken using RevMan5.2.Besides,we use Origin software to construct the Time-dose interval analysis. Results Of the 225 records identified, 13 studies involving 1252 patients (including 11 clinical controlled trials, 1 conference paper report and 1 unpublished research report) met the inclusion conditions. Folic acid dose maintained at 20–30 mg / d for 3–6 months may be beneficial to pathological changes of GPC. Moreover, in the 3 month treatment of 5 trials, the effect was more obvious when the folic acid dose was maintained at 30 mg / d. In the 7 trials, the symptom ineffective rate of GPC treated with folic acid was 32% (RR:0.32, 95% confidence interval CI:0.21–0.48), which was combined using a fixed analysis model; The effect of folic acid on gastric mucosal atrophy in 5 trials (RR: 1.61, 95%CI 1.07–2.41). The changes of folic acid on intestinal metaplasia in the 2 experiments (RR: 1.77, 95% CI: 1.32–2.37).The 2 results are combined using a fixed analytical model. However, the subgroup analysis of 9 trials revealed no significant effectiveness of symptom. Conclusions Our research showed that folic acid supplementation brings benefits in preventing and even reversing the progression of GPC in the stomach, and provided evidence for its potential clinical use in management of GPC. Registration: The logn number of our Meta-anlysis on PROSPERO is CRD420223062.