Electrolytes can be taken orally or intravenously as supplements or therapeutics. However, their therapeutic window may exceed the serum toxicity threshold, making systemic delivery a poor option. Local injection is also not adequate due to rapid diffusion of electrolytes. Here, we solved this issue with a nanocapsule technology, comprising an electrolyte nanocrystal as the drug filling and a silica sheath to regulate drug release rates. In particular, we prepared LiF@SiO₂ nanocapsules and investigated their potential as a delivery system for lithium, which was shown in recent studies to be an effective therapeutic agent for osteoarthritis (OA). We demonstrated that LiF@SiO₂ can extend lithium release time from minutes to more than 60 h. After intra- articular (i.a.) injection into a rat OA model, the nanocapsules reduced the Osteoarthritis Research Society International (OARSI) score by 71% in 8 weeks while inducing no systemic toxicity. Our study opens new doors for improved delivery of electrolyte therapeutics, which have rarely been studied in the past.