Li-rich　Mn-based　cathode　materials　(LRMs)　have　garnered　considerable　interest　for　their　high　specific　capacity.　Nevertheless,　the　elevated　operating　voltage　window　presents　a　great　hurdle　to　the　high-voltage　tolerance　of　the　conventional　electrolytes,　and　the　induced　issues　such　as　rapid　capacity　and　structure　degradation　also　further　impede　their　industrial　application.　In　this　regard,　an　efficient　method　to　alleviate　this　problem　is　proposed　via　a　cyano　functional　additive.　By　introducing　the　trimethylsilyl　cyanide　(TMS)　additive　into　a　carbonate　electrolyte　to　construct　a　complex　with　TM-CN　bonds　on　the　cathode　surface　and　form　a　low-impedance　and　durable　cathode/electrolyte　interphase　(CEI),　both　electrolyte　decomposition　and　cathode　degradation　are　suppressed　effectively.　Moreover,　harmful　substances　are　also　removed　through　the　reaction　between　TMS　and　HF　to　purify　the　electrolyte.　Therefore,　the　electrochemical　performance　of　the　LRM　cathode　is　enhanced　with　a　discharge　capacity　of　224　mA　h　g-1　after　200　cycles　at　1C.　A　high　discharge　capacity　of　227　mA　h　g-1　is　also　achieved　after　50　cycles　at　0.5C　under　a　high　mass　loading　of　13　mg　cm-2.　This　work　presents　a　new　path　to　develop　high-voltage　electrolytes　for　LRM　cathodes.