Front of the link: the impact of solid-state battery practical - a new player debut to solve the existing blind spots in electric vehicles
Solid-state battery development focus shifted to the production of batteries and the choice of suitable materials (2)
The emergence of new technologies often leads to improvements in the state-of-the-art technology, which is a frequent occurrence of liquid lithium-ion secondary batteries that were previously considered unable to further shorten the charging time and have recently gained significant improvements in power density. Others A number of features are also improving and will likely compete with all-solid-state batteries in the market in the future, but it is said to be more than mere technological competition, but it also provides clues to future all-solid-state battery performance improvements.
In the existing liquid lithium ion secondary battery, the development of related technologies for realizing ultra-fast charging has recently been very active, and EV manufacturers have not been able to use ultra-fast charging by improving the existing technology The risk of unknown new technology. The emergence of 'competitive technology' will affect the future of all solid state batteries.
The so-called number one of this 'competitive technology' should be developed by Toshiba 'next-generation SCiB' (Figure 1) SCIB lithium-ion secondary battery by using a negative electrode, the relative potential of lithium more lithium titanate (Li4Ti5O12: LTO), so that the charge-discharge cycle life and safety have been significantly improved due to the high potential, lithium will not be deposited on the negative, so there will be no shortage of Li dendrite caused by short circuit. On the 'Fit EV'.
Figure 1: Toshiba's Safe, Long-Life, and 6-Minute Battery Charging SciB, a, and b show the cell shape and characteristics of the next generation of SciB products, respectively, with a long side of less than 20 cm and a capacity of 49 Ah. Within 90% of the ultra-fast charge can be charged at 90% within 12 minutes without heating at a low temperature of -10 ° C. At the same time to confirm that the charge and discharge cycles of 5000 can maintain 90% of the capacity is expected after 25,000 cycles Capacity is still able to maintain about 80%. (Photos and pictures from Toshiba)
On the other hand, the potential difference with the positive electrode becomes small due to the high voltage of the negative electrode, resulting in low discharge voltage and low energy density whereas other electric vehicle batteries increase the energy density by using low-potential graphite or silicon as the negative electrode, SCiB makes the market downturn.
6 minutes to achieve 90% charge
Toshiba's next-generation SCiB products are significantly improved performance, achieving 2.5 times the input density of existing products, while the volumetric energy density increased to 350Wh / L, up to 2 times the existing SCiB.
A substantial increase in input density results in a discharge rate of 10 C at 25 ° C, ie 90% of the charge in 6 minutes (Figure 1 (b)). Even at -10 ° C, 90% charge. 'Just use a 350kW charger that has already been installed in Germany, and it's just 10C.'
The volumetric energy density of a new generation of products is also higher than most of the rival lithium-ion secondary batteries, Toshiba is looking forward to to restore the previous disadvantage .However, the current extent is far from the current electric vehicle mileage mileage to achieve a qualitative leap. If Toshiba could charge it for 6 minutes, the mileage of a single charge would not be that important. "If you set up an ultra-fast charging device every 200 kilometers on the highway, you can solve the problem of distance. '
7 years to complete negative production
One of the reasons why Toshiba realized this performance improvement is that TiNb2O7 (TNO) replaces LTO (Table 1), which is the negative electrode material of the original SCiB, and the biggest difference is that niobium (Nb) is added, whereby the electron acquisition / reception carrier The number of tripled, followed by material density increased by nearly 3 percent also play a role, TNO theoretical volumetric capacity density up to LTO 3 times, twice the graphite.On the other hand, TNO voltage and LTO roughly the same, so the basic LTO can extend the battery reliability and other advantages. Note 1)
Note 1) The new generation of batteries further enhances the long-term charge-discharge life of the SCiB. "Up to 90% of capacity has been confirmed after 5,000 charge and discharge cycles and the capacity is expected to remain around 80% after 25,000 cycles . "Assuming a 70-year maintenance even with one charge / discharge cycle per day, there is a good chance that the biggest issue in existing EV markets will be solved (the problem of drastic capacity reduction in the used-car market).
Table 1 The addition of Nb to a low-voltage LTO negative achieves an existing three times volumetric capacity density.
Various manufacturers and research institutes have not used TNO in the competition of new-generation battery research and development. The reason why TNO is not used is that although it is known that TNO has a high theoretical capacity density, the material has poor conductivity and high crystallinity, resulting in poor lithium ion conductivity . "Toshiba began researching the corresponding technology development of the above-mentioned topics from about 2010 and finally reached the practical level in seven years, realizing ultra-fast charging in this process as well. Note 2)
Note 2: Toshiba plans to introduce a new generation of commercial SCiBs in 2019. Although the new generation of SCiBs has many performance advantages, it is still problematic. "The current price of Nb is high, which is why competitors are less concerned with TNO However, in terms of the niobium resources themselves, they are in fact richer than lead (Pb) resources. "Mr. Gao said:" The high prices are mainly due to the current lack of demand, the amount of mining is very small, with the increase in demand With the increase in the amount of mining, the price will drop rapidly.
Electrolyte materials are used as Li ion conductivity aids
Toshiba did not disclose specific technologies for ultra-fast charging on the next-generation SCiB, but there is a clue that the technology may be developed by Ohara, which operates optical glass Ohara has long been developing solutions for all-solid-state battery electrolytes Glass materials, and ceramic glass 'LICGC' which is precipitated in the glass, etc. In oxide-based materials, LICGC has high Li ion conductivity and atmospheric stability. From the beginning of 2017, OHARA proposed to use LICGC as a liquid The additive of the positive electrode of a lithium ion secondary battery (Fig. 2) The LICGC having a high Li ion conductivity becomes a Li ion conducting aid in a positive electrode material.
Figure 2: solid electrolyte to improve the liquid battery capacity and output power Figure OHARA liquid lithium-ion battery added oxide solid state electrolyte material 'LICGC' application of the case under normal circumstances, LIB positive if increased to a certain thickness After the capacity will not increase, by adding LICGC can make the capacity continues to increase, because the cathode Li ion insertion and removal are easier. The higher the charge-discharge rate, the greater the capacity to increase. (Photos and Figure b are From OHARA company)
High permittivity increases ion conductivity
The specific effect is that by increasing the thickness of the positive electrode, the capacity can be increased to a certain extent, and in particular, the higher the charge-discharge rate, the greater the effect of increasing the capacity. The ion conductivity of this material satisfies the principle of hole diffusion in the case of large amount, However, if only a small amount of other materials added to the occasion does not apply the above principle.
One of the reasons why OHARA enhances the discharge rate by adding LICGC is the high permittivity of the material. "The polarized negatively charged particles will continue to attract lithium ions." OHARA Executive Director Special Products Division LB-BU Business Unit Manager Nakashima Toshiaki Mr. explained.
Barium titanate coating to enhance the rate
There are many more attempts to use high permittivity materials as conductive auxiliary agents for ions, such as the University of Okayama and the material manufacturer Toshima Plant, etc., using a layered ceramic capacitor material of barium titanate (BaTiO3) to coat positive electrode particles On the high charge and discharge rate significantly improved the charge capacity (Figure 3). It is said that the occasion of the button-type battery 50C rate can still run.
Figure 3 The surface of the positive electrode coated with a strong permittivity powder, charge and discharge rate into ultra-high speed.
Summary of fast chargeable positive electrode materials (a, b) jointly developed by Toshima and Okayama University The surface of LiCoO2 cathode material was covered with titanic acid by sol-gel method and organometallic compound decomposition method (MOD) Barium (BaTiO3) made button cell, found that the use of MOD method to enhance the rate of greater effect.
In addition, the research room of John Goodenough, known as the "father of lithium-ion rechargeable batteries," developed an additional result. If Ba is added to the glass electrolyte itself instead of the positive electrode to increase the permittivity, ion conduction Rate and charge-discharge characteristics of a substantial increase, but the more full charge and discharge capacity increase.
'Charge and discharge more thoroughly, the capacity increases more' This is a solid-state Li-ion capacitor it?
At the end of February 2017, we heard shocking news from overseas that the research room of John Goodenough, a professor at the University of Texas Austin in the United States, published a statement that adopting a glass solid electrolyte can achieve Li ion or Na ion conductivity More than 10-2S / cm. And, the battery can be made with the above electrolyte can be charged within a few minutes. In addition, the low temperature -20 ℃ to work properly, 1200 times the capacity without charge and discharge decay.
The above-mentioned glass electrolytes, ie, oxide-based materials, can open the door to early commercialization of Li-air batteries if the same level of ionic conductivity of the sulfide-based materials can be achieved, and the above publication and theses have caused a fever among Japanese battery researchers At the 58th Battery Symposium held in November 2017, Ms. Maria Helena Braga, author of the dissertation, was also invited to give a speech (Ms. Maria Helena Braga works as Associate Professor at Porto University, Portugal). The actual executive chairman of Kyushu University Professor Okada said, 'This presentation is a highlight of this battery seminar.'
Beyond the understanding of many researchers
However, Ms. Braga's speech is not about the high ion conductivity expected by many listeners and its effect. Since her speech, Ms. Braga mentioned that "the most important thing is not the high ion conductivity but the high permittivity," and many researchers Said "can not understand", the content of the Braga referred to the dubious.
According to Braga's thesis, the presentation at the Battery Seminar and an interview with Nikkei, Ms. Braga's summary of the technology developed is as follows: The first is a glass material consisting of A2.99Ba0.005O1 + xCl1-2x, Where A is Li or Na, Li (or Na) atoms are replaced by the addition of a small amount of Ba (barium) atoms. Since one Ba atom can replace two Li (or Na) atoms, a large number of vacancies are formed in the material . Li ions and the like are conducted through these pores and are called vacancy diffusion. In the latest data, the Li ion conductivity is 2.5 × 10 -2 S / cm and is equivalent to that of a sulfide-based material developed by Tokyo Institute of Technology Potential range up to 9V, very wide.
Battery capacity reaches 10 times the positive capacity
Braga et al. Used this electrolyte to prototype a Li-S battery and studied its charge-discharge capacity. The results show that the discharge capacity is about ten times that of the positive electrode sulfur (S), which can not be obtained by the present theory This phenomenon is explained, however, and the charge-discharge capacity does not decrease or dendrite degeneration as the number of cycles increases, and after more than 10 months and more than 15,000 cycles, the capacity continues to increase.
In fact, other institutions have also conducted studies on the phenomenon that Li-S batteries have a charge / discharge capacity exceeding the S capacity, or a more thorough charge and discharge, a larger capacity, etc. For example, the Samsung Research Institute in Japan, Tokyo Institute of Technology Of the Kanno Research Institute and other agencies have also been reported.Although not fully clarified, but there are two hypotheses: (1) the role of the electrolyte as an active material, (2) the electrode and the electrolyte at the interface what reaction.
The independent analysis by Braga et al. Concludes that the S of the prepared battery does not function as a positive electrode and Li is precipitated from the conductive auxiliary carbon material in the positive electrode. Most high-capacity batteries are That is, the reason for the increase in capacity is that the value of the permittivity ε increases as the polarization in the electrolyte slowly aligns, and the capacity of the capacitor exactly matches Q = CV = Epsilon S / d (Q: charge, C: electrostatic capacity, S: area, d: distance between electrodes) '(Ms. Braga).
From the above point of view, Ms. Braga pointed out the similarities between the prototype batteries and the existing 'EDLC' power storage devices, however, the EDLC is a cell in which both electrodes are symmetrical in carbon material and the other On the one hand, this trial battery 1 electrode is metal Li, is asymmetric type.In this sense, the new battery may be a solid material as a Li-ion capacitor (LIC) electrolyte 'all solid LIC' .
Figure B Li-S battery and electric double layer capacitor mixing
Based on Ms. Braga 's speech and interview, she described the power storage device developed by Ms. Braga and Mr. Goodenough at the University of Texas at Austin. Although the device structure is similar to the all - solid lithium - sulfur (Li - S) battery, , S also does not function as a positive electrode (does not contribute to redox). With the repetition of charge and discharge, the capacity increases. The capacity density is close to 10 times of S, which is close to the theoretical value of Li metal.
Ultra-fast charge, the discharge rate of ordinary
In contrast to the EDLC or LIC, the above battery discharges at approximately the same rate as a typical lithium-ion secondary battery (LIB) despite being very fast in charge. The discharge characteristics do not drop linearly like capacitors but are similar to LIB A certain range of platform voltage. From this point of view, it is easy to replace the LIB.
From anti-perovskite crystal was born
This time, Ms. Braga developed the glass solid electrolyte almost independently of Goodenough Labs (Figure B-2). "At the LosAlamos National Laboratory (LANL) in the U.S., she tried to form a counter-perovskite Ion-conducting pores were made in the 'Li3ClO' crystal, and after a long period of repeated testing, crystals of the hydroxide phase were finally obtained (Ms. Braga).
After that, Braga returned to Portugal. "Portugal's humidity is much higher than that of LANL, and the crystal of the hydroxide phase is very easy to get, or the humidity may be better at higher levels, with the guess that she is over 130 ° C Of the temperature, the humidity slightly higher than the environment try to re-create the result was dehydrated better than the hydroxide material.Attempt to add materials in this material to create voids, the result is to find a glass The transfer of very low temperature Tg material, which is now the glass material. '(Ms. Braga)
After that, she repeated the theoretical analysis including first-principles calculations and experimental materials including synchrotron radiation and neutron irradiation, and concluded that there is no error in values such as ion conductivity, most of the capacity comes from polarization and the like in conclusion.
Ms. Braga pointed out that the Li ion conductivity of this glass electrolyte is highly dependent on the amount of moisture and OH- contained in the material It is said that the less OH- etc., the higher the Li ion conductivity, Ms. Braga said The hydroxide phase material is impregnated into the non-woven fabric as a precursor material, immersed in anhydrous ethanol and the like, and dehydrated and dehydrated.
Can mass production be realized?
A cell company researcher at a Japanese company that has been interacting with Goodenough Labs claims to know about it, and if once it's practical, will it affect society as a whole? How is the production of glass electrolytes? "The researchers noted that ' It is important because the material is not waterproof, and assuming that the results of Team Braga's team research and the analytical results are all correct, it will take time to mass-produce it.
