Sun Jie's team from Tianjin University: Micro-multifunctional additives significantly improve the ultra-high voltage performance of 4.8 V nickel-rich cathode and silicon-oxygen anode batteries

Determined to win ‖ Sun Jie's team from Tianjin University: Micro-multifunctional additives significantly improve the ultra-high voltage performance of 4.8 V nickel-rich cathode and silicon-oxygen anode batteries

 In December 2024 , Professor Sun Jie, Dr. Zhang Yiming of Tianjin University and Dr. Wang Lue of Guolian Automotive Power Battery Research Institute Co., Ltd. published an online paper in the journal Advanced Energy Materials (impact factor > 24.4) titled " Trace Multifunctional Additive Enhancing 4.8 V Ultra-High Voltage Performance of Ni-Rich Cathode and SiO _x  Anode Battery ". The study proposed a functional group integration strategy for the molecular structure design of additives, and developed a single, trace multifunctional electrolyte additive through the active synergy of multiple functional groups and electronic structures. 2- Cyano -3- fluoropyridine -5- boronic acid pinacol ester (FTDP) can simultaneously construct a strong CEI and SEI on the surface of the positive and negative electrodes , and play a multifunctional role in scavenging HF , quenching free radicals and inhibiting the dissolution of transition metal ions. With only 0.2 wt.% FTDP added , NCM811/Li batteries exhibited excellent electrochemical performance even under the harsh conditions of ultra-high voltage (4.8 V) , high temperature (60 °C) , and high rate  (10 C) . The capacity retention rate of 1.6 Ah NCM811/SiO x soft-pack batteries was as high as 84.0% after 300 cycles at _a current of 1.0 A. This work provides a practical reference for the rational screening and design of trace multifunctional electrolyte additives to promote the development of high energy density lithium-ion batteries .    

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Background

High-voltage nickel-rich cathodes ( e.g.,  LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , NCM811) combined with high-capacity silicon-based anodes are considered to be one of the ideal candidates for high-energy-density lithium-ion batteries (LIBs) . However, when operating under harsh conditions such as high nickel content, high voltage, and extreme temperature, nickel-rich cathodes will suffer from serious interfacial and structural problems, including electrolyte oxidation decomposition, cathode electrolyte interface (CEI) destruction, surface phase transition, and particle cracking, leading to a sharp decline in capacity. The harmful HF generated by the hydrolysis reaction of LiPF ₆ will further aggravate the irreversible destruction of the cathode surface interface and cause the dissolution of transition metal ions. During high-voltage charging, free radicals ( e.g., alkyl, alkoxy, and reactive oxygen radicals) released by solvent oxidation and the cathode surface lattice will trigger a chain reaction of electrolyte decomposition, leading to continuous interface deterioration and unsafe gas release. In terms of anode, the huge volume expansion of silicon-based anode (SiO _x , ~ 200% ; Si , ~ 300% ) exacerbates the continuous destruction / reconstruction of the solid electrolyte interface (SEI) , leading to electrode cracking and loss of active lithium, posing a huge challenge to battery life. To solve the above problems at the same time, the rational design of the molecular structure of electrolyte additives is crucial, aiming to build a strong double electrolyte interface layer ( CEI and SEI ) and play a multifunctional role in removing harmful components at the same time, significantly improving the electrochemical performance of high energy density LIBs .     

Graphical analysis

Figure 1. Overview of the strategy of multifunctional electrolyte additive (FTDP) to achieve high-performance LIBs 

Figure 2. Electrochemical properties and multifunctionality of  FTDP additives. a) HOMO and LUMO energy levels of each component in the electrolyte . b) Positive scan LSV (3.0-6.0 V ) at a scan rate of 1 mV s ^-1 . c) Negative scan LSV (3.0-0.01 V ) at a scan rate of 1 mV s ^-1 . d) EPR test results of DPPH solutions containing different electrolytes . e) Fading (inset) and corresponding UV absorbance spectra of DPPH solutions containing different electrolytes. f ) 19 F ^NMR spectrum of FTDP electrolyte containing 100 ppm H2O _after storage for 24 h .

Figure 3. Electrochemical performance of NCM811/Li half-cells using different electrolytes . a) Comparison of initial charge and discharge curves of NCM811/Li batteries using different electrolytes . b) Cycling performance of NCM811/Li batteries using different electrolytes at 0.5 C current (1 C = 200 mA g ^-1 ) . c) High rate performance of NCM811/Li batteries ( 3-4.3 V) using different electrolytes . d) and e ) CV curves of NCM811/Li batteries using BE and FTDP-BE electrolytes , respectively . f) Linear relationship between peak current and scan rate ^1/2 of NCM811/Li batteries under different electrolytes . g ) Cycling performance of NCM811/Li batteries using different electrolytes at 0.5 C at 60 °C . h) Cycling performance of NCM811 /Li batteries using different electrolytes at 1 C at an ultra-high cut-off voltage of 4.8 V. i ) Comparison of the electrochemical performance of this work with previously reported high-voltage NCM811/Li batteries.    

Figure 4.  FTDP -derived C EI and its protective effect on NCM811 cathode. SEM images of NCM811 cathode after 100 cycles at 0.5 C using a) BE and b ) FTDP-BE electrolytes. HRTEM images of NCM811 cathode after 100 cycles at 0.5 C using c) BE and d) FTDP-BE electrolytes . e) C 1s XPS spectra of NCM811 cathode cycled in BE . f ) C 1s ;  g) N 1s; h) B 1s XPS spectra of NCM811 cathode cycled in FTDP-BE . i) ICP-OES results of lithium anode of NCM811/Li half-cell after 100 cycles using different electrolytes state .

Figure 5. Interfacial properties and electrochemical performance of Si-based anodes. a) SEM images of SiOx anodes removed from full cells after 50 cycles at 0.2 C in BE and b) FTDP-BE. c) HRTEM images of SiOx _anodes after cycling in BE and d ) FTDP - BE . e ) F 1s XPS spectra of SiOx anodes after cycling in BE . _f ) F 1s _; g ) N 1s ; h) B 1s XPS spectra of SiOx _anodes after cycling in FTDP-BE . i) CV curves of Si-based half-cells in BE and j) FTDP-BE electrolytes. k ) High rate performance ( 2-0.01 V) of Si-based half-cells in different electrolytes . l ) Cycling performance ( 1 C=500 mA g - ¹ ) of Si-based half-cells in different electrolytes at 0.2 C.   

Figure 6. Electrochemical performance of NCM811 / SiOx full cells using different electrolytes . a ) Cycling performance _of NCM811/ SiOx full cells using different electrolytes at 0.2 C current (1 C = 200 mA g ^-1 ) . b ) Corresponding charge-discharge curves of NCM811/SiOx _full cells in _BE and c ) FTDP-BE for different number of cycles. d) High rate performance of _NCM811 /SiOx _full cells in different electrolytes (2-4.3 V) . e ) Cycling performance of NCM811/ SiOx full cells using different electrolytes at 0.2 C at an ultra-high cut-off voltage of 4.6 V. f) Cycling performance of NCM811/SiOx _soft -pack cells using FTDP-BE electrolyte at 1.0 A current.     

Summary and Outlook

As a multifunctional electrolyte additive, FTDP significantly improves the electrochemical performance of the battery with nickel-rich cathode and silicon-oxygen anode by adding a trace amount of 0.2 wt.%. FTDP can preferentially decompose on the surface of the cathode and anode to participate _in the formation of protective CEI and SEI . Specifically, the generated CEI rich in B and CN can effectively inhibit the dissolution of transition metal ions and maintain the integrity of the cathode, while the generated SEI rich in LiF and Li3N provides good mechanical properties and fast kinetics, thereby inhibiting the cracking of the anode and improving the high-rate performance. The multifunctionality of FTDP , including quenching free radicals, inhibiting the hydrolysis _of LiPF6 and the generation of HF , further improves the stability of the electrode surface interface. Therefore, the NCM811 /Li battery exhibits excellent electrochemical performance even under harsh conditions such as ultra-high voltage (4.8 V) , high temperature ( 60 °C) and high rate ( 10 C) . In particular, the capacity retention rate is as high as 80.3 % after 200 cycles at an ultra-high voltage of 4.8 V and a current of 1  C. The excellent long-cycle performance of NCM811/SiO _x soft-pack batteries also highlights the application potential of FTDP . This work provides a practical reference for the rational screening and design of single trace multifunctional electrolyte additives to promote the development of high-energy-density lithium-ion batteries .   

Original link: https://doi.org/10.1002/aenm.202403751

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