Li2FeSiO4 Preparation and electrochemical properties

Li2FeSiO4 Preparation and electrochemical properties

Peter Larsson, who by DFT (density functional theory) calculated, Li2FeSiO4 the average voltage of 2.77V (relative to Li / Li +),Hp Pavilion ZT1000 battery the energy density of 1200Wh / l, than the energy of 440Wh/Kg [6]. Armand [9] and others made use of the patent are silicate as cathode material for lithium-ion battery idea, they FeO and Li2SiO3 as raw materials, after milling sintered 4 hours at 800 ℃ are Li2FeSiO4 material. Anton Nyten [5] using FeC2O4H2O and Li2SiO3 as raw materials in the milling process of adding 10% of the carbon gel, in CO/CO2 atmosphere (to prevent oxidation of Fe2 +) 750 ℃ heating 24h, obtained orthogonal structure Li2FeSiO4 material to 1M LiN-(SO2CF3) 2 (LiTFSI) / EC-DEC (2:1, volume ratio) as electrolyte, electrochemical window is 2.0-3.7V, at 60 ℃ to C/16 charge and discharge, first charge capacity is 165mAh / g (theoretical capacity of 99%), after several charge and discharge cycle capacity stable at 140mAh / g (theoretical capacity of 84%). Cyclic voltammetry results show that after the first cycle charge voltage platform reduced from 3.10 to 2.80V, show that the charge-discharge process experienced a structural change to form a more stable structure, may be due to a number of positions in Li-ion and 4b 2b position of the exchange of Fe ions caused. They then use 10wt% of the organic polymer precursor of carbon to enhance conductivity of cathode material. CO/CO2 atmosphere in (to prevent oxidation of Fe2 +) 700 ℃ heating 20h, synthesized Li2FeSiO4 material. With 1M LiTFSI / EC-PC (1:1) as electrolyte, electrochemical window is 2.0-3.7V, at 60 ℃ to C/25 charge and discharge, the first capacity 120mAh / g, after multiple cycle capacity of 120 loss of less than 3% with good reversibility [10]. And use of PES, XPS study Li2FeSiO4 first cathode material surface properties. Not exposed to the air circulation Li2FeSiO4 laptop battery pole piece pole than in the inert atmosphere there is more surface Li2CO3. 60 ℃ when the Li2FeSiO4 electrode LiTFSI / EC-PC electrolyte after the electrochemical cycling stability of electrode materials is only part of the solvent and the active material of the reaction products, these products are mainly LiTFSI, and a small amount of acid containing lithium salt, did not produce carbonate and LiF. However, in order to LiTFSI / EC-DEC (2:1) and LiPF6/EC-DEC (2:1) as the electrolyte for the electrochemical cycling, the electrode surface found in Li2FeSiO4 Li2CO3 existence. But also in the base electrolyte Li2FeSiO4 LiPF6 electrode surface there LixPFy, LixPOyFz and LiF, and because of the HF and the role of hydrolysis, Li2FeSiO4 corrosion occurred, unstable cycling performance [11].

Nyte'n [12] also used the in situ X-ray diffraction and Mossbauer spectroscopy study of the lithium insertion mechanism of de-Li2FeSiO4. Found, Li2FeSiO4 electrode charge and discharge cycle, lithium ions in Li2FeSiO4 and LiFeSiO4 transfer between the two materials are the same structure, both the cell volume was less than 1%. Mossbauer spectroscopy and XRD results show that in the full charge and full discharge state, Li2FeSiO4 and LiFeSiO4 the residual of 5% and 10%, which is also consistent with results of electrochemical tests. Li2FeSiO4 first produced during charge and discharge the reorganization of the structure, part of the occupied 4 b bits of lithium ion and occupy the 2 a bit of iron ions were exchanged, 4 b position of Li: Fe from 96:4 to 40: 60, led to the first discharge voltage plateau during discharge from 3.10 V down to 2.80 V (Figure 2). Ion rearrangement may be more stable structure, follow-up the electrochemical cycle, Hp F3172A battery 4 b position Li: Fe in the transition between 60:40 and 40:60.

Figure 2 Li2FeSiO4 typical charge and discharge curve
Fig. 2 Charge and discharge curves of Li2FeSiO4

Dominko [13] and others through the modification of the sol-gel precursor obtained in the Ar atmosphere of 700 ℃ heat treatment after synthesis of the orthorhombic structure Li2FeSiO4. To 1M LiPF6/EC-DMC (1:1) as electrolyte, at room temperature with a small current of C/30 discharge capacity achieved under the first type 0.5 Li per chemical reversible embedding. And Nyten reported similar after the first cycle charge voltage plateau from 3.2 down to 3.1V, but a larger electrode polarization, the reversible capacity lower. Electrochemical properties caused by different reasons One is that material has very low conductivity, the greatest impact by the test temperature; In addition, the electrolyte used in different, Nyten use of LiTFSI LiPF6 higher than the ion conductivity. Dominko [14] further studied the synthesis conditions on Li2FeSiO4 performance, were synthesized using three different methods (hydrothermal, sol-gel method and modified sol-gel method) was successfully prepared Li2FeSiO4 samples. Samples obtained in the morphology, particle size and in situ carbon coating has a different situation. With the synthesis of the increase in carbon content, higher content of impurities in the product. Hydrothermal process without any carbon involved, get the most pure phase; sol-gel products obtained with 5.5wt% of carbon, such Li2FeSiO4 / C composite materials containing up to impurities (Fe2O3, SiO2, and Li2SiO3), by Mossbauer spectrometer analysis, only 68.8% of the iron is Fe2 + form. However, due to the product obtained by hydrothermal layers of carbon and particle size distribution is not very wide, capacity is very low by the sol-gel method under the optimum conditions obtained with the smallest particles (50 nm or so) of the carbon coated sample shows The best electrochemical performance, with 0.8M LiBOB / EC-DEC (1:1) as electrolyte, Hp F2299A batteryelectrochemical window is 2.0-3.8V, 60 ℃ for the product to C/20 charge and discharge capacity of 100mAh the first time / g, has a very good cycle performance; in C / 2 to C/20 discharge capacity under 75%, indicating a good rate capability. Low capacity is due to the higher synthesis of the carbon content of the product resulted in high levels of impurities, phase impurities. If you do not consider the impurities, then the active material in the reversible capacity close to theoretical capacity of the material.
Xiamen University, Yong discussion group were prepared by sol - gel method and hydrothermal assisted sol - gel materials were prepared Li2FeSiO4 [15]. To 1M LiPF6/EC-DEC (3:7) as electrolyte, at 30 ℃, 1.5-4.8V voltage range for charge and discharge. Obtained Li2FeSiO4 in 1/16C discharge conditions, the initial discharge capacity of 160mAh / g, while in the 2C discharge conditions, the initial discharge capacity up to 125mAh / g, and has excellent cycle stability.

K. Zaghib [16], Compaq Presario NX9000 battery who used FeC2O4H2O and Li2SiO3 as raw materials under the conditions of 800 ℃ in vacuum for 12 hours synthesized Li2FeSiO4. XRD and SEM analysis showed that the active material is about 80 nm in size. With LiTFSI-PEO electrolyte at 80 ℃ for the slow scan 20 mV / h for Li / / Li2FeSiO4 cell cyclic voltammetry test, cyclic voltammetry experiments show that the structural stability of the first cycle, oxidation and reduction peaks were compared to Li 2.80V and 2.74V. Compaq Presario NX9010 battery