Dry Goods | Introduction and Synthesis of Lithium Ion Batteries Negative Material Introduction and Synthesis of Lithium Ion Batteries Negative Material At present, the negative materials used in lithium-ion batteries are generally carbon materials, such as graphite, soft carbon （such as coke）, hard carbon, etc。The negative electrode materials being explored are nitrides, PAS ，Tin oxides, tin oxides and tin alloys, as well as nano-negative electrode materials.As the negative electrode material of lithium-ion battery, it is required to have the following properties: （ 1 ）The intercalation oxidation-reduction potential of lithium ions in the negative electrode matrix is as low as possible, close to the potential of metallic lithium, so that the output voltage of the battery is high； （ 2 ）A large amount of lithium in the matrix can be reversibly inserted and removed to obtain a high capacity density, that is, a reversible x value as large as possible； （ 3 ）During insertion / extraction, the insertion and extraction of lithium should be reversible and the structure of the main body should not change or change very little, as far as possible； （ 4 ）The oxidation-reduction potential with x changes should be as little as possible, so that the voltage of the battery does not change significantly, and the charging and discharging can be kept stable； （ 5 ）The inserted compound should have good electrical conductivity and ionic conductivity, which can reduce polarization and carry out large current charging and discharging. （ 6 ）The main material has a good surface structure and can form a good SEI film with liquid electrolyte； （ 7 ）The inserted compound has good chemical stability in the whole voltage range, and does not react with the electrolyte SEI film after forming； （ 8 ）The lithium ion has a larger diffusion coefficient in the main body material, which is convenient for fast charging and discharging； （ 9 ）From a practical point of view, the main material should be cheap and non-polluting to the environment. I. Carbon negative material Carbon negative electrode lithium-ion batteries show good performance in safety and cycle life, and carbon materials are cheap and non-toxic, and carbon negative electrode lithium-ion batteries are widely used in commercial lithium-ion batteries。In recent years, with the continuous deepening of research work on carbon materials, it has been found that surface modification and structural adjustment of graphite and various carbon materials are achieved.Or the graphite is partially disordered, or nano-scale pores, holes and channels are formed in various carbon materials. The lithium can be inserted and deintercalated not only according to the stoichiometric LiC6, but also in a non-stoichiometric manner. The specific capacity is greatly increased from the theoretical value of LiC6 372mAh/g to 700mAh/g ~ 1000mAh/g.，As a result, the specific energy of lithium-ion batteries is greatly increased. At present, the main negative electrode materials for lithium-ion batteries are graphite, petroleum coke, carbon fiber, pyrolytic carbon, mesophase pitch-based carbon microspheres （ MCMB ），Carbon black, glass carbon, etc., of which graphite and petroleum coke have the most application value. The lithium-inserting properties of graphite carbon materials are: （ 1 ) The plug-in lithium potential is low and flat, which can provide a high and smooth working voltage for lithium-ion batteries. Most of the plug-in lithium capacity is distributed in 0.00~0.20V between (vs. Li + /Li) ； （ 2 ）The lithium insertion capacity is high, LiC 6 has a theoretical capacity of 372mAh.g -1 ; （ 3 ）The compatibility with organic solvents is poor, and solvent co-insertion is easy to occur, which reduces the lithium insertion performance. The characteristics of plug and delithium in petroleum coke carbon materials are: （ 1 ）There is no obvious potential plateau during the initial lithiation process； （ 2 ）Intercalated compound Li x C 6 of the composition , x = 0.5 or so , the lithium intercalation capacity is related to the heat treatment temperature and surface state ； （ 3 ）Compatible with solvents, good circulation performance. According to the degree of graphiticization, the general carbon negative material is divided into graphite, soft carbon and hard carbon. 1 、Graphite The graphite material has good conductivity , high crystallinity and good lamellar structure , suitable for lithium insertion - desorption , forming lithium - graphite intercalation compounds , the charge and discharge capacity can reach 300mAh.g -1 or more , charging and discharging efficiency is 90% or more , irreversible capacity is less than 50mAh.g -1 。The insertion and extraction reaction of lithium in graphite at 0 ~ 0.25V has a good charging and discharging platform, which can be matched with lithium source cathode materials such as lithium cobaltate, lithium manganate and lithium nickelate. The battery has a high average output voltage, and is the most widely used anode material for lithium-ion batteries. Graphite consists of two categories: artificial graphite and natural graphite. （ 1 ）Artificial graphite Artificial graphite is made by graphitizable carbon （such as pitch coke） in N2 atmosphere at 1900 ~ 2800 ° C by high temperature graphitization。Common artificial graphite is mesocarbon microballoons （ MCMB ） and graphite fibers . MCMB is a highly ordered lamellar structure made from coal tar （asphalt） or petroleum residue oil。At 700 ℃ below pyrolysis and carbonization, the capacity of lithium insertion can reach 600mAh.g -1 Above, but the irreversible capacity is relatively high。At 1000 ℃ or above, the heat treatment, MCMB graphitization degree increased, the reversible capacity increased。Graphitization temperature is usually controlled at 2800 ℃ Above, the reversible capacity can reach 300mAh.g -1 ，The irreversible capacity is less than 10% . The gas-phase deposited graphite fiber is a tubular hollow structure , which has 320mAh.g-1 discharge specific capacity and 93 % first charge and discharge efficiency . It can discharge large current , has long cycle life , but the preparation process is complex and the cost is high . （ 2 ）Natural graphite Natural graphite is a good negative electrode material, its theoretical capacity is 372Amh / g, forming LiC6 structure, reversible capacity, charge and discharge efficiency and working voltage are high。The graphite material has obvious charging and discharging platforms, and the discharge platform has a very low voltage for lithium, and the battery output voltage is high. There are two kinds of natural graphite: formed graphite and phosphate graphite. The impurities of amorphous graphite are low.The reversible specific capacity is only 260mAh.g -1 , The irreversible specific capacity is greater than 100mAh.g-1 or so。The reversible specific capacity of graphite flakes is only 300 ~ 350mAh.g-1, The irreversible specific capacity is less than 50mAh.g-1 or more。Natural graphite has a high capacity due to its complete structure and many lithium-embedded locations, and is very ideal for lithium ion battery negative electrode material. Its main disadvantage is that it is sensitive to electrolytes and has poor charge and discharge performance with high current.During the discharge process, a solid electrolyte interface （ SEI, Solid Electrolyte Interface ） is formed on the cathode surface due to chemical reactions of electrolytes or organic solvents。The membrane , In addition , the process of insertion and removal of lithium ions causes the volume expansion and contraction of graphite sheets , which is also easy to cause graphite pulverization , so the irreversible capacity of natural graphite is relatively high , and the cycle life needs to be further improved . （ 3 ）Modified graphite By modifying graphite , such as graphite surface oxidation , coating polymer pyrolysis carbon , forming a core - shell structure of composite graphite , can improve the charging and discharging performance of graphite . Through the oxidation of graphite surface , it can reduce the Li / LiC6 irreversible capacity , improve the cycle life of the battery , the reversible capacity can reach 446mAh.g-1 （ Li1.2C6 ） , the oxidant of graphite material can choose HNO 3 ,O 3 ,H 2 O 2 ,NO + ,NO 2+ etc。Graphite fluorination can be obtained by reacting graphite with fluorine vapor at high temperature 。 （CF）n and （ C 2 F )n ，Can also be Lewis acid （such as HF ）Existence, in 100 ℃ for fluorination to obtain C x F n 。The capacity of carbon materials can be improved by oxidation or fluorination. （ 4 ） Graphitized Carbon Fiber Gas phase growth carbon fiber VGCF is a negative electrode material prepared from hydrocarbons , which was treated at 2800 ° C for VGCF High capacity and stable structure . The mesophase pitch carbon fibers （ MCF ） 3000 ℃ treated MCF , which has a radially crystalline structure with lamellar texture , belongs to disordered graphite structure like pyrolytic graphite . It has high specific capacity and coulomb efficiency . The structure of carbon fibers is different, and the lithium embedding properties are also different, among which carbon fibers with a forward structure have the best charge and discharge performance, and carbon fibers in a coherent structure are prone to co-embedding with solvent molecules. Therefore, the performance of graphitized bitumen-based carbon fibers is superior to that of natural scale graphite. Graphite reaches the maximum lithium insertion limit （i.e. LiC6 ）The volume only increases by 10% or so。So graphite is repeatedly embedded - The electrode size can be kept stable during the process of removing lithium, and the carbon electrode has good cycling performance。Graphite also has some shortcomings, such as it is highly selective for electrolytes, and can only have good electrode properties in certain electrolytes;Poor overcharge and overdischarge performance, Li + diffusion coefficient in graphite is small, which is not conducive to fast charging and discharging。It is necessary to modify graphite, and meso-carbon microballoons （ MCMB ） have been synthesized。Amorphous carbon （thermal carbon of organic matter）, coated graphite and so on, their charging and discharging performance is significantly improved compared with graphite. 2 、Soft carbon Soft carbon is easy to graphitize carbon, which means 2500 ℃ above the high temperature can graphitize amorphous carbon。Soft carbon has low degree of crystallinity, small crystal size, large crystal plane spacing and good compatibility with electrolytes.Common soft carbon is petroleum coke, needle coke, carbon fiber, carbon microspheres and so on. 3 、Hard carbon Hard carbon is difficult to graphitize carbon, is the pyrolysis carbon of polymer。Such carbon in 2500 ℃ or more difficult to graphitization, common hard carbon resin carbon （phenolic resin, epoxy resin, polyfurfuryl alcohol PFA-C etc.）, organic polymer pyrolysis carbon （ PVA 、 PVC 、 PVDF 、 PAN Etc . , carbon black （ acetylene black . Hard carbon has a large lithium capacity （ 500 ~ 1000mAh.g-1 ） , but they also have obvious disadvantages , such as low charge and discharge efficiency , no obvious charge and discharge platform and impurity atoms H And caused a great potential lag , etc . II. Non-carbon negative electrode materials 1 、The nitride Lithium transition metal nitrides have good ion conductivity, electronic conductivity and chemical stability, and are used as negative electrodes of lithium-ion batteries, with discharge voltage usually above 1.0V 。The discharge capacity, cycle performance and smoothness of the charge-discharge curve of the electrode vary greatly depending on the type of material.Like Li 3 FeN 2 Used as LIB negative electrode , the discharge capacity is 150mAh / g ，The discharge potential is at 1.3V （vs Li / Li +） near, the charge and discharge curve is very flat, no discharge lag, but the capacity has a significant attenuation。 Li 3-x Co x N has 900mAh / g high discharge capacity, discharge potential at 1.0V or so, but the charge and discharge curve is not stable, there is a significant potential lag and capacity decay。At present, it is necessary to further study such materials to achieve practical application. The nitride system belongs to anorthite （ CaF2 ） or to Li3N compounds with good ion conductivity . The electrode potential is close to that of metallic lithium and can be used as an anode for lithium ion batteries Anti-fluorite structure Li-M-N （M for transition metal ） compounds such as Li 7 MnN 4 and Li 3 FeN 2 can be synthesized by ceramic method。Transition metal oxides and lithium nitrides （ M x N x +Li 3 N ）At 1% H 2 + 99 % N 2 reacts directly in the atmosphere , and can also be reacted with Li 3 N reacts with metal powder。 Li 7 MnN 4 And Li 3 FeN 2 both have good reversibility and high specific capacities （respectively 210 and 150mAh.g-1 ）。 Li 7 MnN 4 In the process of charging and discharging, the valence of transition metal changes to maintain electrical neutrality, the specific capacity of the material is relatively low, about 200mAh / g ，However, the cycle performance is good, the charging and discharging voltage is flat, and there is no irreversible capacity. In particular, when this material is used as the negative electrode of lithium-ion batteries, it can be matched with positive electrodes that cannot provide lithium sources. Li 3-x Co x N 属于 Li3N structural lithium transition metal nitride （with the general formula Li 3-x M x N , M for Co , Ni 、 Cu ），The material has a high specific capacity, up to 900mAh / g ，There is no irreversible capacity, the average charging and discharging voltage is 0.6V or so , and can also be matched with positive materials that can not provide lithium sources to form a battery . At present , the mechanism of lithiation and delithiation of this material and its charging and discharging performance need further study . 2 、Tin-based cathode materials （ 1 ） Tin oxide Tin oxides, including tin oxide, tin oxide and their mixtures, have a certain reversible lithium capacity, lithium capacity is higher than graphite materials, up to 500mAh / g or more, but the first irreversible capacity is also large。 SnO / SnO2 as an anode has a high specific capacity and a relatively low discharge potential （ At 0.4 ~ 0.6V vs Li / Li + near ） advantages。However, for the first time, its irreversible capacity loss is large, capacity decay is fast, and the discharge potential curve is not stable. SnO/SnO2 Due to different preparation methods, the electrochemical properties are quite different。For example, the SnO2 reversible capacity is 500mAh / g or more, and the cycle life is ideal, 100 There is no attenuation after the second cycle。And SnO as well as sol - gel method by simple heating prepared SnO2 The cycle performance is not ideal . To SnO （SnO2） introduce some non-metallic, metal oxides, such as B , Al 、 Ge 、 Ti 、 Mn , Fe and heat treatment can be obtained amorphous composite oxides called amorphous tin-based composite oxides （ Amorphous Tin-based Composite Oxide referred to as ATCO ）, its reversible capacity can reach 600mAh / g or more, and the volume specific capacity is greater than 2200mAh / cm3 ，is currently the negative electrode of carbon materials （ 500~1200mAh/cm3 ）More than twice that, showing application prospects.The current problem of the material is that the irreversible capacity is relatively high for the first time, and the charge and discharge cycle performance needs to be further improved. （ 2 ） Tin compound oxides A method for preparing tin-based composite oxides for negative electrodes of lithium-ion batteries is to mix SnO , B2O3 , P2O5 in a certain stoichiometric ratio , sinter at 1000 DEG C with oxygen , rapidly condense to form amorphous compounds , and the composition of the compounds can be expressed as SnBxPyOz （x = 0.4 ~ 0.6, y = 0.6 ~ 0.4, z = （2 + 3x - 5y） / 2）, where tin is Sn2 + 。Compared with tin oxides （SnO / SnO2） the cycling life of tin-based composite oxides has been greatly improved, but it is still difficult to reach the industrialization standard. （3） Tin alloy Certain metals such as Sn , Si , Al When other metals are embedded in lithium, high lithium content lithium - metal alloys are formed。For example , Sn has a theoretical capacity of 990mAh/cm3 , close to the theoretical volumetric capacity of graphite 10 times。In order to reduce the irreversible capacity of the electrode and maintain the stability of the negative electrode structure, tin alloy can be used as the negative electrode of lithium ion electrode, its composition is: 25% Sn 2 Fe + 75% SnFe 3 C 。 Sn 2 Fe Active particles can form alloys with metallic lithium, SnFe 3 C non-active particles can maintain the basic skeleton of the electrode during the electrode cycling process。The volume-to-capacity ratio of this tin alloy is twice that of graphite.With 25% Sn2Fe + 75% SnFe3C Constructed electrodes can obtain 1600mAh.g-1 reversible capacity and exhibit good cycling performance . The main problems of alloy negative electrode materials are, for the first time, low efficiency and circular stability, and the volume effect of the negative electrodes during repeated charge and discharge must be solved to cause electrode structure damage. The passive cycle performance of simple metal materials is poor and the safety is not good. The use of alloy negative electrodes combined with other flexible materials is expected to solve these problems. 3 、Lithium titanium composite oxide The lithium titanium composite oxides used as negative electrodes of lithium ion batteries are mainly Li4Ti5O12 , whose preparation methods include high temperature solid phase synthesis , sol-gel - gel method and so on . （ 1 ）High temperature solid phase synthesis method By a certain measure TiO2,LiCO3 Mix and grind in the air atmosphere. 1000℃ heat preservation 26h The product was cooled to room temperature Li4Ti5O12 . Will be TiO2, LiOH.H 2 O was mixed and ground , and was kept at 700 ° C for 24 hours before being cooled to room temperature . 4 、Carbon nanotube Nanocarbon tube is a new carbon crystalline material discovered in recent years. It is a hollow tube with a diameter of several nanometers to tens of nanometers and a length of several tens of nanometres to tens of micrometers. Its properties are as follows: The electrical properties of nanocarbon tubes Specific surface area / m2 Initial charge capacity （ mAh.g-1 ） Initial discharge capacity （ mAh.g-1 ） Irreversible capacity （ mAh.g-1 ） Initial charge efficiency （ % ） 170.4 1049 223.1 825.9 21.2 Nanotubes are prepared by DC arc and catalytic pyrolysis. Catalytic thermal method is to 20 % H2 + 80 % CH4 mixed gas in Ni + Al2O3 on the catalyst particles at 500 ℃ Pyrolysis, after grinding the pyrolysis sample, add hot nitric acid （ 80 ℃ ）Soaking 48 hours to remove the catalyst in the carbon tube, repeatedly washing and filtering with water until the washing solution PH = 6 , the filtered sample was dried at 160 ° C for drying . The DC arc method is to use high-purity graphite rod as electrode, under argon gas protection, in a closed arc furnace, through the arc, the product is a C60 series of products of carbon nanotubes。Carbon nanotubes can be separated by chemical oxidation. The main purpose of nanoscale negative electrode materials is to take advantage of their nanoscale characteristics , reduce the effect of volume expansion and contraction on the structure during charging and discharging , and thus improve the cycling performance。Practical applications show that: The effective utilization of nanoscale characteristics can improve the cycling performance of these negative electrode materials , however, there is still a long way to go before practical application。The key reason is that the nanoparticles are gradually combined with the circulation , thus losing the unique properties of the nanoparticles , Causes the structure to be destroyed , reversible capacity to decay。Moreover, the high cost of nanomaterials has also become a major obstacle to their application. All in all, in the negative electrode materials of lithium-ion batteries, graphite-like carbon negative electrode materials have been the main type of negative electrode materials due to their wide sources and cheap price。Except for graphitized mesophase carbon microspheres （ MCMB ），In addition to the small market share of low-end artificial graphite, modified natural graphite is gaining more and more market share. Non-carbon negative electrode materials have high volumetric energy density and are increasingly of interest to researchers, but they also have shortcomings such as poor cycling stability, large irreversible capacity, and high material preparation costs, so far they have not been industrialized.The development trend of negative electrode materials is to improve the capacity and cycle stability as the goal, through various methods to combine carbon materials with various high-capacity non-carbon negative electrode materials to develop new applicable high-capacity, non-carbon composite negative electrode materials. ——End—— Canrd Brief Introduce：Canrd use high battery R&D technology(core members are from CATL) and strong Chinese supply chain to help many foreign companies with fast R&D. We provide lab materials, electrodes, custom dry cells, material evaluation, perfomance and test, coin/pouch/cylindrical cell equipment line, and other R&D services. 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Introduction and Synthesis of Lithium Ion Batteries Negative Material At present, the negative materials used in lithium-ion batteries are generally carbon materials, such as graphite, soft carbon （such as coke）, hard carbon, etc。The negative electrode materials being explored are nitrides, PAS ，Tin oxides, tin oxides and tin alloys, as well as nano-negative electrode materials.As the negative electrode material of lithium-ion battery, it is required to have the following properties: （ 1 ）The intercalation oxidation-reduction potential of lithium ions in the negative electrode matrix is as low as possible, close to the potential of metallic lithium, so that the output voltage of the battery is high； （ 2 ）A large amount of lithium in the matrix can be reversibly inserted and removed to obtain a high capacity density, that is, a reversible x value as large as possible； （ 3 ）During insertion / extraction, the insertion and extraction of lithium should be reversible and the structure...