On November 24, 2023, Ruipu Lanjun Green Technology Day was held in Wenzhou, at which the blockbuster new 345ah energy storage battery cell empowered by Wending Technology was shockingly released: its actual capacity exceeded 350ah, and the energy of a single cell was upgraded to 112 kWh, the volumetric energy density is upgraded to 435 Wh L, and the energy efficiency reaches 962%。And it can achieve a long cycle life of 12,000 cycles @ 70% SOH and a calendar life of more than 20 years to meet the needs of large-scale energy storage systems.
Although the topping technology can improve the utilization rate of cell space by 45%, the battery capacity has also increased at the same size, but thisHow is a cycle life of up to 12,000 cycles achieved?Is it related to the structural innovation of the top technology?This article takes you through the first thing.
First, the life race of energy storage batteries
Since entering 2023, the life of energy storage batteries has become white-hot, except for Ruipu Lanjun, the life of energy storage cells of many companies has reached or even exceeded 12,000 times, as follows:
1) The LF560K battery released by EVE in 2022 has a capacity of 560AH and a cycle life of 12000+
2) SVOLT 325AH short knife laminated cell, cycle life up to 12,000 times.
3) China Innovation Aviation 305ah cells, 12000 cycles @80%SOH
4) Zhengli Xinneng 314ah large-capacity energy storage special battery, with an energy density of 180Wh kg, a cycle life of more than 12,000 times, and an energy efficiency of up to 95%.
5) Envision Power's 315ah battery cell realizes "one kilowatt-hour battery per cell", and the cycle life is as high as 12,000 times, meeting the safe and reliable operation requirements of charging and discharging once a day for 25 years.
6) Chuneng 314ah energy storage battery, with a cycle life of 12,000 times and an energy density of more than 180Wh kgAt the same time, Corne's 320ah marine battery can also achieve a life of 12,000 times and has an energy density of 185Wh kg.
7) Haichen energy storage 300ah battery cell, through the negative electrode passivation and activated lithium sustained release technology, to achieve a cycle life of 12,000 times (0.5p@70%soh)
It is worth noting that the publicity of the above companies is mainly that the life of the battery cell reaches 12,000 times, considering the consistency of the battery cell and the poor SOC estimation accuracy caused by the voltage characteristics of LFP, the life of the energy storage system is generally 80-90% of the single cell, that is, about 10,000 times. Even so, it is possible to meet the day 1 15 times charged and discharged for 20 years.
However, at this year's SNEC 16th (2023) International Solar Photovoltaic and Smart Energy (Shanghai) Conference and Exhibition, CATL released the world's first "zero auxiliary source" photovoltaic storage integration solution. EquippedThe industry's first long-life high-temperature battery cell, the cycle life of the energy storage cabinet system can reach 15,000 times, which can meet the life requirements of 20 years of charging and discharging twice a day. And with the high-temperature resistant graphite anode material and special electrolyte, this energy storageThe battery cell retains good attenuation characteristics at more than 35 °C, eliminating the need for a cooling system or an external auxiliary power supplyWhen necessary, the advanced self-heating technology achieves uniform heating, which improves the overall energy efficiency.
In addition, BYD also exhibited its latest CUBE T28 energy storage system at the SNEC conference, which adopts CTS (cell-to-system integration) technology, which "can reduce the number of components by about 36%, improve the space utilization rate by about 98%, increase the structural strength by about 30%, and can be suitable for industrial and commercial energy storage, power station-level energy storage and other application scenarios through flexible combination."
Although it did not emphasize its cycle life, at the CIBF2023 international exchange meeting, Li Shuwei, general manager of Foday Battery Commercial Vehicle Business Center, said that Foday innovatively launchedThe cycle life of the battery pack is increased to 12,000 times, and the battery pack can also meet the cycle life of 10,000 times。It can be seen that BYD also has 12,000 cycle cell technology.
However, Wu Kai, chief scientist of CATL, emphasized at the first World Energy Storage Conference held in Ningde on November 9: "Although many companies now promise that their energy storage systems can achieve 20 or 25 years, and the cycle life can reach 12,000 times, or even 15,000 times, how can customers and third parties detect these indicators?."On what basis?At the moment, there are none, they are all verbal promises".。It can be seen that achieving a life of 12,000 times is not easy to achieve. So what causes the battery to decay?
Second, the attenuation mechanism of lithium iron phosphate batteries
Whether it is a mobile phone battery, a car battery or an energy storage battery, there are different degrees of capacity attenuation during use. For lithium-ion batteries, there are many reasons for the capacity attenuation: including structural changes in the cathode and anode materials, loss of active lithium, and so on.
Although there are many factors, in recent years the academic community (including the University of Oxford in the United Kingdom, the University of Hawaii in the United States and several national laboratories in the United States, as well as major research groups in China) have basically reached a consensus to divide these reasons into:loss of active material(loss of active materials=lam),Loss of active lithium(loss of lithium inventory=lli)as well as an increase in internal resistance(impedance increase)
The first two of these are thermodynamically related irreversible losses, while the increase in internal resistance is a kinetic loss (which can be recovered at very low magnifications). Different attenuation paths will also lead to different thermal runaway behaviors of batteries after aging (refer to Academician Ouyang Minggao's article eTransportation, 2019, 2, 100034).
For energy storage batteries, almost all of them are LFP material systems, and their attenuation mechanism is different from that of high-voltage ternaries. In 2021, Dr. Liu Xiaomei of CATL cooperated with Professor He Xiangming of Tsinghua University to study in detail the attenuation mechanism of lithium iron phosphate batteries at room temperature, using 240Ah cells, 1C charge-discharge cycle, initial preload of 300kgf, and 5000 cycles when reaching 80% SOH.
Even after 5000 cycles, the gram capacity of the positive LFP and negative graphite materials is almost not attenuated, and it can be seen that there is no loss of active materials. Moreover, the RCT impedance of the cathode (cathode) LFP material is almost constant. The 50% increase in RCT of anode graphite may be mainly related to the thickening of SEI and the increase in cell expansion. VisibleThe loss of activated lithium is the main reason for the attenuation of lithium iron phosphate batteries, and the increase of battery impedance with the number of cycles is also one of the reasons for the deterioration of performance.
3. 10,000 cycleslfpDesign strategy for batteries
Since the capacity attenuation of the LFP battery is mainly the loss of active lithium, it is necessary to improve the cycle lifeThe main idea is "lithium supplementation", which makes up for the loss of active lithium through human intervention. In April this year, at the pilot meeting of the World Power Battery Conference "Yibin High-end Dialogue on the Cloud", Wu Kai, chief scientist of CATL, mentioned that the energy storage battery requires a 20-year service life with the same life as wind and solar, and the current mainstream low-cost LFP battery has a calendar life of 10 years and 5,000 cycles cannot meet the requirements.
Forlfpbattery, without increasing the cost, its life can be increased to:times or so. And if you want to be satisfiedyears exceededThe reduction of secondary life will increase the cost considerably. It can be seen that even if lithium supplementation is supplemented, there are at least two ways to increase the cost and the cost increase is very high. So what do you look like in both of these ways?
1.First of all, it should be emphasized that there are many ways to achieve lithium supplementation, which can be referred to in the following summary article. If lithium supplementation can be achieved without increasing the cost much, then the most feasible solution isCathode lithium supplementation, that is, adding lithium supplementation on the positive side。For such a lithium supplementation method, the material is required to have a suitable voltage window, low first cycle efficiency, compatibility with electrolyte, no gas production, etc.
The first material to be commercially applied was LNO(Li2NiO2), according to the research of the Korean team, in 30~4.With a voltage range of 4V, the material has a capacity of up to 340mAh g on the first charge and 3 on the first chargeThe reaction starts at 5V, from crystal to amorphous phase, and the first coulombic efficiency is only 24%, which can supplement lithium with a high capacity. And the higher the magnification, the smaller the impedance of the LNO material, considering that the addition amount of lithium supplement is generally only less than 5% of the active material, the magnification in practical application is indeed high, which shows that LNO is very suitable for this kind of application, but the early research is applied to the LCO system.
In recent years, due to the rise of energy storage batteries, there are high requirements for ultra-long life, coupled with the continuous maturity of the industrial chain, since 2021, the industry has foundin lithium iron phosphateGraphite energy storage systemlnoLithium supplements can also greatly improve the cycle life of battery cells.
For example, after 500 weeks of cycling, Yanyi added about 2% LNO lithium supplement to the LFP cathode, which was 3% higher than that of the control groupAfter 1,500 cycles, the lifting effect has exceeded 5%, *and more than 9,000 cycles can be achieved. This is very close to the life expectancy that Wu Kai mentioned to increase the life expectancy to about 8,000 timesThe method that does not increase the cost much is to rely on the cathode lithium supplement.
Of course, in addition to LNO, LFO and Li2O are also potential cathode lithium supplement additives, which are compatible with existing battery production processes and require little change, so they are cost-effective. However, the improvement of life is also relatively limited, and it is difficult to achieve more than 10,000 cycle lifeMoreover, the impedance of such materials remaining in the cathode after lithium supplementation may be too large, and there will be side reactions with the electrolyte, which will also affect the cycle life to a certain extent.
But that's itThe lithium supplement itself contains more lithium, is very alkaline, the particles are easy to bond together, and the air stability is not good, so it is still very difficult to synthesize. At present, in addition to the research one, German Nano also has a layout of LNO, but it is a pilot line of 1,000 tons. In addition, Jitri-Topsoe Company, a subsidiary of Jiangsu Industrial Technology Research Institute, is deeply engaged in the chemical field, and has also mastered the technology of mass production of LNO materials, which is currently actively promoted with the support of the Industrial Technology Research Institute, hoping to benefit battery companies in Jiangsu, Zhejiang and Shanghai, and strengthen and expand the battery industry in Jiangsu Province.
2.If you want to achieve a cycle life of more than 10,000 cycles, you need to replenish more lithium, which is what you need to rely onLithium supplementation technology for the negative electrode: including lithium powder supplementation, lithium silicide powder supplementation and lithium foil supplementation。Because lithium is unstable and reacts with oxygen, nitrogen and water vapor, lithium supplementation at the anode is still limited by several major problems in the battery manufacturing process: such as high cost, poor process compatibility, and potential safety hazards. In particular, inert lithium powder is used to supplement lithium, the full name of which is SLMP (stabilized lithium metal powder), and there is a coating layer on the surface to improve environmental stability. However, in practical application, the coating will fail after being in contact with the environment for a long time, so that the exposed lithium metal participates in the exothermic reaction, and it is easy to catch fire or even catch fire, making the road of lithium supplementation of the negative electrode thorny.
So since 2016, to:Battery companies led by CATL have switched to using lithium metal foil for anode lithium supplementationThe battery is then assembled using a micron-thick sheet of lithium metal that is compounded with the negative electrode by calendering, as shown in the figure below.
The safety of this process has been greatly improved, but it is necessary to ensure that all the metal lithium foil must be reacted for the first time, otherwise it will be equivalent to lithium separation: on the one hand, the amount of lithium foil added needs to be accurately calculated, and on the other hand, the entire surface is lithium foiled, and if the complete reaction cannot be guaranteed, the lithium foil needs to be placed intermittently.
In this regard, Professor Zhang Xiaogang of Nanjing University of Aeronautics and Astronautics conducted a systematic study and proposedLithiation margin(degree of lithium replenishment=dlrp)The concept,And it was proven at 016~0.The optimal lithiation margin range such as 23mAh cm2 can achieve both energy, life and safety performance, and the capacity retention rate of 600 cell cycles is still more than 101%, truly achieving zero attenuation. There may be a mechanism for lithium supplementation and slow releaseUsually the first 1000 weeks of LFP batteries after lithium supplementation are almost not attenuated (refer to Energy Storage Science and Technology, 2023, 12, 9, 2727-2734).
Based on the research of innovative technologies such as lithium foil pre-lithium, CATL took the lead in undertaking the key project of the National Key R&D Program "Smart Grid Technology and Equipment" in 2016 "Development and Application of 100MWh New Lithium Battery Scale Energy Storage Technology", aiming to:developmentLithium iron phosphate battery for ultra-long cycle life and high safety energy storage
The project completed the performance evaluation of the Ministry of Industry and Information Technology in 2021, and the relevant results have been successfully applied to the 30MW 108MWh energy storage power station in Jinjiang, Fujian. However, in the assessment indicators at that timeThe cost is just lessMeta/kwh, with the current oneMeta/kwhIt's nearly doubledNo wonder Wu Kai always said that "if the LFP battery is to meet the life of more than 12,000 times in 20 years, it will increase the cost considerably".
In the fifth episode of the 100th anniversary of the founding of the Communist Party of China broadcast on August 6, 2021, the fifth episode of the documentary "Chasing Dreams" for the 100th anniversary of the founding of the Communist Party of China was broadcast, the world's first 12,000 cycles of long-life battery broke through the boundaries and landed on the screen, reflecting its significance.
With the successive implementation of anode pre-lithium technology, the "zero radiation source" energy storage system demonstrated by CATL at this year's SNEC has achieved a cycle life of 15,000 times. And AMPACE, a battery company joint venture between CATL and ATL, also released a plan for household storage in the first half of the year"Kunlun battery".Through the new pre-lithiation technology and the formulation innovation of graphite and electrolyte, it can not only slow down the rate of lithium ion loss, but also supplement the lithium ion loss of the systemIt is the first to break through the cycle life of lithium iron phosphate chemical systemtimes≥80%sohtimes≥70%soh
withThe maximum life of PV has come to 25 years, and with the peak and valley frequency modulation, it needs to be charged and discharged twice a day, so that the system can cycle more than 18,000 times @70%SOH to meet the requirements。The Kunlun battery with a life of 20,000 times is expected to meet such high requirements and continue to reduce the LCOE of energy storage.
Recently, Tian Qingjun, vice president of Envision Group, publicly stated that with technological progress and cost reduction (of course, it is also related to this year's overcapacity), the current LCOE of lithium battery energy storage has been close to 02 yuan (the whole life cycle cost, the longer the life, the more advantageous), lower than pumped energy storage, has become the lowest cost energy storage technology, and may be more profitable than wind and solar in the future.
Summary:Lithium supplementation, also known as "pre-lithiation technology", was originally developed for silicon-oxygen anodes, which can improve its first coulombic efficiency, and then improve the capacity and energy density of the battery, such as NIO's 150kWh battery pack claims to use silicon-doped lithium supplementation technology.
However, the technology can also improve the cycle life of graphite LFP batteries to meet the requirements of more than 20 years of wind and solar use. At present, the cathode lithium supplementation technology, which does not increase the cost much, is in full swing, which can increase the life to about 10,000 timesThe anode lithium supplement technology, which can make the life of 20,000 times, is also ready to go.
With the lithium carbonate falling below 120,000 tons and the overcapacity, the current energy storage system has come to 638 yuan kWh, and the purchase price of battery cells has been as low as 400 yuan Wh. If it can achieve a long life and ensure the safety of the energy storage system, this industry is expected to continue to write the legend of wind energy, photovoltaic and new energy automobile industries in China.