Figure 1:Theoretical and (estimated) practical energy densities of different rechargeable batteries: Pb–acid – lead acid, NiMH – nickel metal hydride, Na-ion – estimate derived from data for Li-ion assuming a slightly lower cell voltage, Li-ion – average over different types, HT-Na/S8 – high temperature sodium–sulfur battery, Li/S8 and Na/S8 – lithium–sulfur and sodium–sulfur battery assuming Li2S and Na2S as discharge products, Li/O2 and Na/O2 – lithium–oxygen battery (theoretical values include the weight of oxygen and depend on the stoichiometry of the assumed discharge product, i.e., oxide, peroxide or superoxide). Note that the values for practical energy densities can largely vary depending on the battery design (size, high power, high energy, single cell or battery) and the state of development. All values for practical energy densities refer to the cell level (except Pb–acid, 12 V). The values for the Li/S8 and Li/O2 batteries were taken from the literature (cited within the main text) and are used to estimate the energy densities for the Na/S8 and Na/O2 cells. Of the above technologies, only the lead acid, NiMH, Li-ion and high temperature Na/S8 technologies have been commercialized to date.
Lithium tetrafluoroborate (LiBF4) used as an electrolyte additive to improve the cycling performance of LiNi0.5Co0.2Mn0.3O2/graphite cell (NMC532) at higher operating voltage is investigated.
With 1.0 wt% LiBF4 addition into the electrolyte, the capacity retention of lithium ion battery after 100 cycles was greatly improved from 29.2% to 90.1% in the voltage of 3.0 V–4.5 V. To understand the mechanism of the capacity retention enhancement at high voltage operation, the properties including the cell performance, the impedance behavior as well as the characteristics of the electrode interfacial properties are examined.
It is found that LiBF4 was likely to participate in the formation of interface film on both electrodes. The improved performances of the cell are attributed to the modification of interface layer components on graphite anode and LiNi0.5Co0.2Mn0.3O2 cathode, which leading to lower the interfacial impedance.
Source: Zuo, Xiaoxi & Fan, Chengjie & Liu, Jiansheng & Xiao, Xin & Wu, Junhua & Nan, Junmin. (2013). Lithium Tetrafluoroborate as an Electrolyte Additive to Improve the High Voltage Performance of Lithium-Ion Battery. Journal of the Electrochemical Society. 160. A1199-A1204. 10.1149/2.066308jes. https://iopscience.iop.org/article/10.1149/2.066308jes
Lithium difluorophosphate (LiDFP, LFO) is greatly helpful as an electrolyte additive to enhance performances of li-ion battery’s cycle life and discharge capacity retention at high temperature, as well as reducing self-discharge. While sodium difluorophosphate has similar performance in NMC532 battery cell? Let’s take a look at a paper published on Journal of The Electrochemical Society in 2020.
Conclusion:Three new difluorophosphate salt electrolyte additives were synthesized and evaluated in NMC532/graphite pouch cells. Ammonium difluorophosphate (AFO) is readily prepared via a solid-state, benchtop reaction of ammonium fluoride and phosphorus pentoxide that requires only gentle heating to initiate. The best yield of sodium difluorophosphate (NaFO) in the present study was obtained by reacting difluorophosphoric acid and sodium carbonate in 1,2-diemethoxyethane over 3 Å molecular sieves, a very strong drying agent. Tetramethylammonium difluorophosphate (MAFO) was prepared from NaFO via cation-exchange with tetramethylammonium chloride.
NaFO is reported to be a very good electrolyte additive, with similar performance in NMC532/gr cells as the better known lithium difluorophosphate (LFO) additive, each showing ~90% discharge capacity retention after more than 1,500 cycles at 40 °C. The long-term stability during cycling between 3.0–4.3 V compares favorably with, but nonetheless is less than the 2%VC 1%DTD benchmark cells reported by Harlow et al., which have ∼94% capacity retention after 1,500 cycles. The beneficial nature of both additives is attributable to the difluorophosphate anion. In contrast, AFO and MAFO are found to be poor electrolyte additives. This is suggested to be due to the formation of lithium nitride for the former. It is unknown why tetramethylammonium cations have a negative effect on cell stability.
Synthesis and Evaluation of Difluorophosphate Salt Electrolyte Additives for Lithium-Ion Batteries, Journal of The Electrochemical Society, 2020 167 100538, David S. Hall, Toren Hynes, Connor P. Aiken and J. R. Dahn
Will LiFSI replace LiPF6 in Li-ion battery electrolytes? Using the new salt lithium bis(fluorosulfonyl)imide (LiFSI) rather than lithium hexafluorophosphate (LiPF6) as an electrolyte improves the performance of Li-ion batteries with silicon anodes, according to a paper published in the Journal of the American Chemical Society by researchers in Europe.
Lithium bis(fluorosulfonyl)imide, commonly referred to as LiFSI, has the molecular formula F2LiNO4S2 and CAS number 171611-11-3. LiFSI appears to be white powder, with a molecular weight of 187.07, and a melting point between 124-128°C (255-262.4°F).
Compared to LiPF6, LiFSI not only enhances thermal stability in li-ion battery technology, but also gives better performance in terms of electrical conductivity, cycle life, and low-temperature. However, LiFSI may have certain corrosive effects on aluminum foil. Some academic papers show that the corrosion of aluminum foil mainly comes from FSI-ions in LiFSI, but this problem can be solved by additives such as fluorine-containing passivation aluminum foil additives.
The trend is quite certain that LiFSI is becoming one of the mainstream lithium salts for next generation electrolytes. Currently, ternary lithium batteries and LFP batteries are constantly being improved and iterated generation after generation that have higher requirements for energy density, high and low-temperature performances, cycle life, and charge and discharge rate performances.
Due to high technical difficulty in mass production and high cost, LiFSI has not been directly used as a solute lithium salt, but as an additive mixed with lithium hexafluorophosphate (LiPF6) for use in the electrolytes of power li-ion batteries especially. For example, LG Chem has been using LiFSI as an additive in their electrolytes for quite some time. As technology improves, more and more LiFSI will be added to electrolytes. It is believed that the cost of LiFSI will be lowered further with the scaling up of mass production. And as time passes, LiFSI has the potential to replace LiPF6 as the main lithium salt for power li-ion battery electrolytes.
Lithium hexafluorophosphate (LiPF6) is a key raw material in today's technology, for lithium-ion battery electrolytes of lithium-ion power batteries, lithium-ion energy storage batteries and other consumer electronics' li-ion batteries. Along with the boom of EV industry, the li-ion power battery segment consumes the largest portion of LiPF6 in the market.
Since September 2020, the sales of new energy vehicles have increased substantially, which has driven the sales of lithium hexafluorophosphate to increase. It is estimated that the lithium hexafluorophosphate demand in the power battery segment will be about 66,000 tons in 2021 and about 238,000 tons in 2025, with an average annual growth rate of about 40%.
According to data from January to September 2021, China's accumulative capacity of LFP battery in EV installation is about 45.38GWh, and the accumulative capacity of ternary batteries is about 49.70GWh. It is expected that the annual total capacity of LFP battery in EV installation will exceed that of ternary in 2021, with high year-on-year growth rate expected.
As of October 18, the price of lithium hexafluorophosphate was 520,000 yuan/ton, and it has risen by nearly 500% in 2021 with its price at 107,000 yuan/ton only at the beginning of this year, setting a new record high since June 2017. Lithium hexafluorophosphate and electrolyte additives have clearly become one of the materials with the highest growth rates this year. The strong demand in the market is expected to continue, and it is currently in short supply.
Let's look at the supply-demand situations of lithium carbonate in order to evaluate its price trends.
Battery-Grade Lithium Carbonate (Li2CO3)
The main demanding areas of battery-grade lithium carbonate are currently from the preparation of NMC ternary cathode materials, lithium cobalt oxide and part of lithium iron phosphate (LFP).
In 2021, the overall growth rate of NMC532 and NMC622 has been low, comparing to Ni-rich ternary materials and LFP. In H2 of 2021, it is estimated that the demand for battery-grade lithium carbonate from production of NMC ternary cathode materials will be approximately 48,470 tons, an increase of only 2.4% from the previous H2 of 2020.
Due to the negative impact of the pandemic, the export volume of China's consumer electronics has decreased significantly, with little increase in its domestic market. The demand for battery grade lithium carbonate from lithium cobalt oxide manufacturers has declined. In H2 of 2021, it is estimated that the lithium carbonate demand from this area will be about 16,737 tons, a decrease of 9.7% from H2 of 2020.
In terms of demand from LFP materials, many mainstream power-type LFP material plants currently use battery-grade lithium carbonate as their main lithium source (accounting for about 30%) to ensure the quality of LFP power battery for EV market. Under the imbalance of supply and demand in the power LFP battery market, enterprises have begun to expand their production capacity largely. In 2021 H2, the demand for battery-grade lithium carbonate from this field is expected to be approximately 14,788 tons, an increase of 30% from H2 of 2020.
Industrial-Grade lithium Carbonate (Li2CO3)
The main demanding area of industrial-grade lithium carbonate are from production of LFP material average quality, lithium manganate, lithium hexafluorophosphate and some traditional industries.
In terms of demand from LFP material production, since H2 of 2020, sales of A00-class EV models have been growing rapidly in China market, resulting heavy demand of average quality power LFP battery. At the same time, some mid-end and high-end models, such as Tesla Model Y and Model 3, have also launched their own LFP-powered versions. Besides, the demand for LFP batteries in the energy storage and two-wheelers market is also increasing. Currently the demand of industrial-grade (including quasi-battery-grade) lithium carbonate from LFP material production accounts for about 70%, comparing to that of battery-grade lithium carbonate. In 2021 H2, the demand for industrial-grade lithium carbonate from this field is expected to be approximately 34,505 tons, an increase of 30% from 2020 H2.
As for demand from lithium manganate production, due to fewer orders of consumer electronics and two-wheelers overseas, the demand of lithium manganate cathode material is not strong. At the same time, as the price of lithium salts continues to rise, manufacturers have great pressure on cost increase and some of them reduced its output. Therefore, the demand for industrial-grade lithium carbonate continues to shrink. There was an obvious output reduction of LMO materials early this year in Spring Festival. In 2021 H2 however, the demand for industrial-grade lithium carbonate from this field is expected to be approximately 11,900 tons, a slight increase of 8% from the previous 2020 H2.
With regard to the demand from preparing lithium hexafluorophosphate, along with the hot sales in the EV market, the domestic electrolyte output has increased significantly, and the demand for lithium hexafluorophosphate (LiPF6) has increased greatly as well. In 2021 H2, it is estimated that the demand for industrial grade lithium carbonate from this area is about 11,236 tons, an increase of 40% from 2020 H2.
The remaining demand for industrial-grade lithium carbonate are from productions of metal lithium, causticizing processed lithium hydroxide and pharmaceuticals, accounted for about 26% of its overall demand, with a slight increase.
In conclusion, the overall demand for lithium carbonate continues to increase rapidly. However the overall output of lithium carbonate is shrinking in 2021 H2 due to decreased supply of spodumene, despite an increased supply from brine sources domestic and overseas. Prices for lithium carbonate are most likely to increase if the above estimates stand correct.
Poworks is a professional manufacturer and supplier of lithium compounds.