CN111952584B

CN111952584B - Lithium battery

Info

Publication number: CN111952584B
Application number: CN202010678752.9A
Authority: CN
Inventors: 刘秦
Original assignee: Shenzhen Jeramic Materials Technology Co ltd
Current assignee: Shenzhen Jeramic Materials Technology Co ltd
Priority date: 2020-07-13
Filing date: 2020-07-13
Publication date: 2022-07-08
Anticipated expiration: 2040-07-13
Also published as: CN111952584A

Abstract

The invention discloses a lithium battery, which comprises a positive electrode, a lithium metal or lithium alloy negative electrode, anhydrous electrolyte and a diaphragm; a conducting layer is arranged between the diaphragm and the negative electrode, and the conducting layer contains a material with conducting property; the positive electrode includes a fluorinated carbon material and at least one of an irreversible gamma-type lithium manganese oxide and a doped lithium manganese oxide. The invention aims to provide a lithium-manganese battery which can work in an environment higher than 100 ℃ and can still maintain high-current discharge capacity at a low temperature of-40 ℃, the positive electrode material of the lithium battery adopts the combination of gamma-type lithium-manganese oxide and carbon fluoride, has a life-span early warning characteristic, has inhibited activity of reacting with electrolyte at a high temperature, and solves the problem of interface resistance deterioration of the surface of the lithium-manganese battery at a high temperature by a conducting layer arranged between a diaphragm and a lithium metal negative electrode.

Description

Lithium battery

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a lithium battery.

Background

In recent years, electronic devices using lithium batteries as power sources are more and more widely used, and particularly, lithium manganese batteries using manganese oxide as a positive electrode, lithium metal or lithium alloy as a negative electrode, and anhydrous electrolytes as electrolytes are widely used in consumer electronics and industrial electronic products, which is the most common lithium battery. Lithium manganese batteries are classified into primary lithium manganese batteries that are discharged only once and secondary lithium manganese batteries that can be charged and discharged many times.

Generally, the operating temperature range of lithium manganese batteries manufactured by the prior art is-20 to +80 ℃. The structure of the lithium ion battery comprises a manganese dioxide anode, a lithium metal or lithium alloy metal cathode and a diaphragm arranged between the manganese dioxide anode and the lithium metal or lithium alloy metal cathode, and also comprises electrolyte, and the substances and elements coexist in a sealed containing cavity with an electric output. When the battery works at a higher temperature near 100 ℃, internal polarization is intensified to cause internal resistance to rise, so that the capacity of the battery is attenuated and large current can not be discharged; on the surface of the lithium metal cathode, the reaction between the electrolyte and the active lithium metal is accelerated, the thickness of a passivation film formed by a reaction product is increased, and the polarization is increased; at the positive electrode, the reaction product of manganese dioxide and electrolyte increases and will coat the surface of the manganese dioxide particles, increasing polarization. Therefore, the lithium manganese battery manufactured by the prior art can not meet the application with wider temperature requirement, for example, the lithium battery used as the power supply of the automobile tire pressure monitoring system needs to work at 100 ℃ or higher in a certain time, and must also work by discharging at the low temperature of-40 ℃.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a lithium battery.

In order to achieve the purpose, the invention adopts the technical scheme that: a lithium battery comprising a positive electrode, a lithium metal or lithium alloy metal negative electrode, an anhydrous electrolyte, and a separator; a conducting layer is arranged between the diaphragm and the negative electrode, and the conducting layer contains a material with conducting property; the positive electrode comprises a carbon fluoride material and at least one of lithium manganese oxide and doped lithium manganese oxide; the stoichiometric formula of the lithium manganese oxide is Li_xMnO_2-δWherein x is more than 0 and less than 0.5, and delta is more than or equal to 0.01 and less than or equal to 0.09; the carbon fluoride material has the stoichiometric formula of (CF)_y)_nWherein y is more than or equal to 0.1 and less than or equal to 2, and n is more than or equal to 1; the main crystal form of the lithium manganese oxide or the doped lithium manganese oxide is a gamma crystal form.

In the prior art, the lithium manganese primary battery generally adopts gamma crystal form Electrolytic Manganese Dioxide (EMD), is converted into gamma/beta mixed crystal form manganese oxide after heat treatment at 350-430 ℃ and water removal, and the initial potential relative to lithium and lithium alloy in anhydrous electrolyte is far higher than 3.4V. The electrolytic manganese dioxide after heat treatment is a mixed domain structure material taking a beta crystal form as a main material (60-90% by weight) and a gamma crystal form as a secondary material, wherein a (1x1) tunnel of the beta crystal form has low capacity contribution, and the capacity contribution mainly comes from a (1x2) tunnel of the gamma crystal form. At low temperature, the difficulty of lithium ion diffusion and migration into a gamma crystal form (1x2) tunnel is increased, so that the high-current discharge characteristic of the lithium-manganese battery at low temperature is poor.

The lithium manganese oxide adopted by the anode material of the invention is formed by leading lithium ions to enter MnO₂The (1x2) lattice tunnel of (1x2) to stabilize the material structure, mainly comprises a gamma-type (pyrolusite/ramsdellite intergrowth) crystal lattice tunnel with (1x2), and a beta-type (pyrolusite) structure and possibly a spinel-like structure with a secondary (1x1) lattice tunnel; in the present invention, the main crystal form of lithium manganese oxideThe gamma form represents that the gamma crystal form accounts for more than or equal to 50 percent in the crystal form structure, so that the lithium manganese oxide still keeps higher gram capacity at certain lithium content percentage, and is different from reversible small-capacity lithium manganese oxide used as a secondary battery, such as lithium manganate (LiMn)₂O₄) Spinel crystal form and LiMO of₂(M ═ Co, Ni, Mn, and the like) layer-structured lithium manganese oxide. Compared with the prior art in which the electrolytic manganese dioxide is subjected to heat treatment, the electrolytic manganese dioxide has lower activity of reacting with electrolyte at high temperature, and has lower initial open-circuit voltage, higher working voltage at the initial discharge stage, higher discharge platform voltage, higher discharge capacity at low temperature and better pulse discharge capacity. The lithium battery positive electrode of the present invention comprises a carbon fluoride material in a smaller percentage than that of a lithium manganese oxide material, and its main use as one of the positive electrode compositions in the present invention is to provide a low voltage warning to the battery near the end of discharge, to improve the safety of the lithium manganese battery in supporting the operation of electronic devices at high temperatures, and to balance the capacity of the lithium battery, to improve the self-discharge rate, and to improve the high temperature storage characteristics.

In the invention, the lithium manganese oxide and the carbon fluoride material can be uniformly mixed with particles of the two, and the bonding function of other organic and/or inorganic dopants is utilized to realize better combination of the two, for example, polytetrafluoroethylene emulsion is added to realize uniform mixing of the two, and low-melting-point molten salt is added to promote stronger combination of the two at a certain temperature; it is also possible that the carbon fluoride material coats at least a portion of or all of the particles of the lithium manganese oxide, preferably that the carbon fluoride coats all of the particles of the lithium manganese oxide on a micron and/or submicron scale.

The lithium manganese oxide and the carbon fluoride material may be formed into a mixture in which the particles are bonded with weak bonding force in a general sense, such as a mixture bonded with van der waals force, or may be formed into a polycrystalline multiphase material in which at least a portion of the particles are bonded with stronger bonding force, such as by a mechanical alloying process and manner to achieve bonding of the particles, wherein at least a portion of the fluorocarbon groups and/or F ions enter the lithium manganese oxide lattice to achieve strong bonding.

Another important feature of the present invention is that the lithium battery is provided with a separate conductive layer between the separator and the negative electrode, which serves to suppress and prevent the formation and accumulation of excessive deposits on the surface of the lithium metal when the battery is operated at high temperature, and to solve the problems of increased polarization and deteriorated resistance at high temperature on the surface of the negative electrode of lithium metal, as a useful improvement and difference to the existing lithium manganese battery manufacturing technology. When the conducting layer is at high temperature, even if side reaction products are deposited in pores of the conducting layer, the higher conductivity of the surface of the negative electrode can be kept, and the increase of the contact resistance of the surface of the negative electrode at high temperature is avoided.

The conductive layer is attached to or closely attached to at least a part of the surface of the side of the negative electrode opposite to the positive electrode;

the conductive material is a carbon material such as natural graphite, artificial graphite, hard carbon, soft carbon, carbon black, carbon fiber, and carbon nanotube, and usable carbon blacks include, but are not limited to, acetylene black, ketjen black, furnace black, and the like. These carbon materials may be used alone or in combination of two or more. Particularly preferably, a carbon black material having a crystal grain of 5nm to 10 μm is used. The material is attached or closely attached to at least one part of the surface of the negative electrode opposite to the positive electrode, the surface area of at least one part of the negative electrode is 10-100% of the surface area of the negative electrode opposite to the positive electrode, preferably, at least one part of the surface of the negative electrode is 80-100% of the surface area of the negative electrode opposite to the positive electrode, and the larger the surface of the negative electrode is covered by the conductive material, the more beneficial the resistance of the surface/interface of the negative electrode is reduced, and the large-current discharge characteristic of the battery is improved, especially the large-current discharge characteristic at low temperature after high-temperature storage. In order to achieve the above object, it is preferable that the conductive material is attached to or mixed with a substrate, and then the conductive material is attached to a surface of the negative electrode, and one side of the conductive material is attached to a surface of the negative electrode facing the positive electrode, and the substrate is a bulk material or a thin film material for molding the conductive layer, for example, a moldable binder mixture.

The conductive material is selected from titanium nitride, titanium carbide, titanium carbonitride and siliconAt least one of titanium compounds; preferably, the titanium nitride and/or titanium carbide is 200-mesh or higher micro-powder or nano-powder, and has a typical NaCl type structure. Titanium nitride TiN is a non-stoichiometric compound having a stable composition range of TiN_0.37～TiN_1.16。

The titanium silicide includes one of titanium disilicide and pentatitanium trisilicide, preferably titanium disilicide of 200 mesh or more, more preferably 400 mesh or more.

The carbon material, titanium nitride, titanium carbide, titanium carbonitride and titanium silicide have high electrical conductivity and chemical stability at high temperature, and particularly, the titanium nitride and the titanium silicide have electrical conductivity close to that of metal. In the present invention, as demonstrated by the experimental results in the examples, the conductive layer containing these high conductivity materials functions to inhibit or even avoid the accumulation of non-conductive products formed by the intensified electrolyte reactions on the surface of the lithium metal negative electrode at high temperatures, thereby increasing the interfacial resistance, and these intensified reactions are avoided if the prior art lithium manganese battery has no or weak temperatures at or below the conventional upper operating temperature limit of 80 ℃. It is further noted that the conductive layer arrangement goals and efficiencies of the present invention are independent of lithium metal surface dendrite suppression measures.

The carbon material, titanium nitride, titanium carbide, titanium carbonitride and titanium silicide in powder form are combined with a binder to form an independent battery component, and the battery component is arranged between a diaphragm and a negative electrode, and the conductive component containing the conductive substance arranged between the diaphragm and the negative electrode can inhibit the increase of interface resistance caused by accumulation of nonconductive products formed by electrolyte reaction intensified on the surface of the negative electrode at the temperature higher than 80 ℃. Such a member constituted by a binder alone does not have such an effect as to be interposed between the separator and the negative electrode. More preferably, the conductive material is titanium nitride and/or titanium disilicide, which have better chemical stability at high temperatures in the battery.

Preferably, the separator is a fibrous cloth, more preferably, the separator is a non-woven fabric, more preferably, the non-woven fabric is Polyethylene (PE) non-woven fabric, polypropylene (pp) non-woven fabric(PP) non-woven fabric, nylon (PTFE) non-woven fabric, Polyester (PET) non-woven fabric, polyphenylene sulfide (PPS) non-woven fabric, aramid non-woven fabric, glass fiber non-woven fabric, and modified non-woven fabric thereof. The mass density of the non-woven fabric per unit area is 5-60 g/m²The thickness is 0.05-0.5 mm. Preferably, the non-woven fabric is polyphenylene sulfide (PPS) non-woven fabric or aramid non-woven fabric.

Preferably, 0.03. ltoreq. x.ltoreq.0.4. The larger x, the higher the discharge plateau voltage and the initial stage discharge voltage, while the gram capacity is slightly decreased. When x is less than 0.03, the difficulty of uniformly dispersing and mixing the materials during preparation is high, and the stoichiometric ratio of the burnt materials is difficult to accurately control; when x is more than 0.4, the gram capacity of the material is close to 100mAh/g, and the practicability is poor. Therefore, x preferably adopts the above range.

More preferably, 0.03. ltoreq. x.ltoreq.0.29. The lithium battery of the present invention is particularly suitable for manufacturing an irreversible lithium battery, which can be manufactured when the lithium content is within this range.

Preferably, 0.8. ltoreq. y.ltoreq.1.1. The graphite fluoride has (CF) n and (C)₂F) n two, the chemical analysis shows that the fluorine-carbon ratio is 0.1-2.0, which results in that (CF) n and (C) in the product are different due to different reaction conditions₂F) The ratio of n being different and the edges of the carbon layer being loaded with a certain amount of ═ C and-CF₃Thereby, the effect is achieved. Therefore, the (CF) of the present invention_y) The material science meaning of n is this meaning.

In the carbon fluoride material, y can be more widely located 0.1-2.0, and the lower the y value, the lower the discharge voltage platform, the advantage is that active material electric conductivity is good, and the larger the y value, the higher the discharge voltage platform, the shortcoming is that electric conductivity is poor, and the cost is also higher. When y is more than or equal to 0.8 and less than or equal to 1.1, the discharge performance is better and the cost is acceptable. More preferably, 0.9. ltoreq. y.ltoreq.1.1.

Preferably, the weight ratio of at least one of the lithium manganese oxide and the doped lithium manganese oxide to the carbon fluoride material is: at least one of lithium manganese oxide and doped lithium manganese oxide: the carbon fluoride material is 80:20 to 99.5: 0.5. The invention aims to manufacture a high-temperature lithium-manganese battery with cost performance, the coordination effect of the high-temperature lithium-manganese battery and a lithium manganese oxide under a specific proportion is mainly used for warning the service life of the lithium-manganese battery to be terminated by taking the low voltage of the carbon fluoride as the warning in the final discharge stage of the battery by utilizing the difference of electrochemical potentials of the carbon fluoride and the lithium manganese oxide, so that the safety of power supply to electronic equipment is improved, and the consumption of the carbon fluoride is small. In addition, the auxiliary function of the carbon fluoride is to improve the high-temperature storage performance of the battery.

More preferably, the weight ratio of at least one of the lithium manganese oxide and the doped lithium manganese oxide to the carbon fluoride material is: at least one of lithium manganese oxide and doped lithium manganese oxide: the carbon fluoride material is 90:10 to 99.5: 0.5. Since increasing the amount of the carbon fluoride material increases the gram capacity of the positive electrode but decreases the capacity per unit volume, and the cost increases, it is preferable to adopt the above-mentioned composition in consideration of the cost, the gram capacity of the battery, and the battery operating voltage plateau. Most preferably, the weight ratio of at least one of the lithium manganese oxide and doped lithium manganese oxide to carbon fluoride is: at least one of lithium manganese oxide and doped lithium manganese oxide: the carbon fluoride material is 95:5 to 99: 1.

Preferably, the carbon fluoride material is at least one of graphite fluoride, fluorinated coke, fluorinated carbon black, fluorinated bamboo carbon, fluorinated ketjen carbon, fluorinated graphene and fluorinated multi-walled carbon nanotubes. The carbon fluoride material has better performance when being at least one of fluorinated bamboo charcoal and fluorinated ketjen black, and is more economical and applicable when being graphite fluoride.

Preferably, the positive electrode material further includes a conductive agent, and the conductive agent is at least one of natural graphite, artificial graphite, carbon black, carbon nanotubes, and carbon fibers. Carbon black includes, but is not limited to, acetylene black and ketjen black. The amount of the conductive agent is 2-30% of the mass of the anode material.

Preferably, the positive electrode material further includes a binder. Alternative binder types include olefin-based resins such as polyethylene and polypropylene; fluorinated resins such as Polytetrafluoroethylene (PTFE), polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber, fluoro rubber and polymethacrylic acid, polydioxyethylthiophene/polystyrene sulfonate copolymer (PEDOT/PSS), carboxymethylcellulose (CMC), and the like. The binder is at least one of them. The dosage of the binder is 2-15% of the mass of the positive active material.

Preferably, the doped lithium manganese oxide has the stoichiometric formula Me-Li_xMnO_2-δMe is a doped element or group, Me is Al, Mg, Fe, La, Zr, Cr, Cd, Ti, Bi, Ni, Co, F, B, P, S and PO₄ ^3-At least one of (1).

Preferably, the non-aqueous electrolyte solution comprises a non-aqueous solvent, an electrolyte and an electrolyte additive; the electrolyte additive comprises a first additive and a second additive, wherein the first additive is a lithium salt containing B and F as anions, and the second additive is a lithium fluorophosphate salt containing P and F as anions; the weight percentage of the first additive in the electrolyte is 1-5%; the weight percentage of the second additive in the electrolyte is 0.1-0.5%.

The lithium salt containing B and F as the anion forms a continuous solid electrolyte interface film (SEI) on the surface of the positive and negative electrodes, which is an electron insulator but Li⁺The excellent conductor of (2) is insoluble in organic solvent, and solvent molecules can not pass through SEI film, so that damage to electrode material caused by co-intercalation of solvent molecules can be effectively prevented, decomposition of electrolyte caused by contact of electrolyte and positive and negative electrode active materials can be inhibited, and storage stability of the battery at high temperature is improved. The higher the concentration is, the better the effect of inhibiting the decomposition and gas production of the electrolyte at high temperature is, but the too high concentration will cause the increase of the internal resistance of the battery and the deterioration of the pulse discharge performance.

The product of the lithium fluorophosphate salt containing P and F in the electrolyte has a protection effect on the positive and negative electrodes, particularly the lithium metal negative electrode, and stable solid electrolyte films are generated on the surfaces of the positive electrode and the negative electrode, so that the reaction between the positive electrode and the negative electrode and the electrolyte at high temperature is isolated, the generation of gas in the battery is inhibited, and the high-temperature performance can be improved.

During high-temperature storage, the reaction product of the electrolyte additive on the surface of the negative electrode improves the resistance at the interface, and is not beneficial to high-current discharge at low temperature, and the conducting layer can maintain high-current discharge at low temperature.

Preferably, the first additive is LiBF₄、Li₂B₁₂F₁₂And LiBF₂C₂O₄At least one of (a) and (b); and/or the second additive is Li₂PO₃F、LiPO₂F₂、LiPF₄(C₂O₄)、LiPF₂(C₂F₅)₂And LiPF₃(C₂F₅)₃At least one of them.

Preferably, the weight percentage of the first additive in the electrolyte is 2-4%.

Preferably, the mass of the first additive is 1-100% of the mass of the electrolyte.

Preferably, the mass of the second additive is 0.2-3% of the mass of the electrolyte.

Preferably, the anhydrous solvent is at least one of cyclic carbonate, chain ether, cyclic ether and cyclic carboxylate; the anhydrous solvent includes cyclic carbonates such as Propylene Carbonate (PC), Ethylene Carbonate (EC) and Butylene Carbonate (BC), and also includes chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and also includes chain ethers such as 1, 2-Dimethoxyethane (DME), 1,2 Diethoxyethane (DEE), ethoxymethoxyethyl ester (EME), and also includes cyclic ethers such as Tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1, 3-Dioxolane (DOL), 4-methyl-1, 3-dioxolane, and also includes cyclic carboxylates such as γ -lactone. These solvents may be used alone, or in combination of two or more.

Preferably, the anhydrous solvent employs a cyclic carbonate with a high boiling point and a chain ether with a low viscosity at a low temperature, such as Propylene Carbonate (PC) and Dimethoxyethane (DME), and further preferably, the volume ratio of PC and DME is: PC: DME 5: 95-100: 0, even more preferably, the volume ratio of PC to DME is: PC: DME 10: 90-80: 20. thus, the solvent has electrochemical stability in a wide high-low temperature range, and the electrolyte has high solubility.

Preferably, the electrolyte comprises a first electrolyte, which is LiClO₄Said LiClO₄The weight percentage content in the electrolyte is more than or equal to 90 percent.

Preferably, the electrolyte further comprises a second electrolyte, and the second electrolyte is LiPF₆、LIR¹SO₃₍R¹Is C1-C4 fluorinated alkyl), LiN (SO)₂R²)(SO₂R³) (wherein R is²And R³Each independently a C1-C4 fluorinated alkyl group). Preferably, the second electrolyte is present in the electrolyte in an amount of < 10% by weight. Preferably, the concentration of the electrolyte in the electrolyte is 0.2-2 mol./L; preferably 0.3 to 1.5 mol./L; more preferably 0.4 to 1.2 mol./L.

Preferably, the negative electrode comprises metallic lithium and/or a lithium alloy, the lithium alloy being an alloy of lithium and a metal M, the M being at least one of Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn and B. More preferably, the weight percentage content of M in the alloy is less than or equal to 25 percent. For example, in a coin cell, the lithium or lithium alloy is pressed into a sheet form, and may be adhered directly to the planar surface of the negative electrode casing, or a current collector may be introduced between the two, for example, a sheet or mesh type current collector made of copper, nickel or stainless steel.

The invention has the beneficial effects that: the invention provides a lithium battery, the positive electrode material of the lithium battery adopts the main crystal form of lithium manganese oxide as a gamma crystal form, and has the advantages of low initial open circuit voltage, high working voltage in the initial discharge stage, higher discharge platform voltage, higher discharge capacity at low temperature and better pulse discharge capacity, and the addition of carbon fluoride material enables the lithium battery to have the advantages of large gram capacity, low self-discharge rate and excellent high-temperature storage property.

Drawings

FIG. 1 is a schematic diagram of a lithium battery according to the present invention; wherein, 1, the negative electrode shell; 2. a positive electrode case; 3. a lithium-containing negative electrode; 4. a positive plate; 5. a diaphragm; 6. an insulating seal ring; 7. a conductive layer;

FIG. 2 is a schematic diagram of a prior art lithium battery; wherein, 1, the negative electrode shell; 2. a positive electrode case; 3. a lithium-containing negative electrode; 4. a positive plate; 5. a diaphragm; 6. an insulating seal ring;

FIG. 3 is an XRD pattern of samples g, d and EMD;

FIG. 4 is a discharge test chart of battery I;

FIG. 5 is a graph of the relationship between the storage time at high temperature of 110 ℃ and the instantaneous closed-circuit voltage of pulse discharge at low temperature of-40 ℃ for batteries I-III;

FIG. 6 is a graph of the high temperature 110 ℃ storage time versus the pulse discharge transient closed circuit voltage at low temperature-40 ℃ for cells I, IV-VII;

FIG. 7 is a graph of the relationship between the storage time at high temperature of 110 ℃ and the instantaneous closed-circuit voltage of pulse discharge at low temperature of-40 ℃ for cells III, VIII-X;

FIG. 8 is a graph of the high temperature 110 ℃ storage time of batteries IV, XI-VIII versus the pulse discharge instantaneous closed circuit voltage at low temperature-40 ℃.

Detailed Description

One embodiment of the lithium battery of the present invention has a schematic structural diagram as shown in fig. 1, and includes a negative electrode case 1, a positive electrode case 2, a lithium-containing negative electrode 3, a positive electrode sheet 4, a diaphragm 5, an insulating seal ring 6, and a conductive layer 7 disposed between the lithium metal negative electrode and the diaphragm; the conductive layer 7 comprises a material with conductive properties. Fig. 2 is a schematic structural diagram of a lithium battery in the prior art, which includes a negative electrode case 1, a positive electrode case 2, a lithium-containing negative electrode 3, a positive electrode sheet 4, a diaphragm 5, and an insulating sealing ring 6.

The lithium manganese oxide of the present invention is a mixed domain material having a gamma phase as a main phase and containing a small amount of beta phase and/or spinel-like phase, although the stoichiometric formula can be expressed as Li_xMnO_2-δBut such molecules are not present in the material. In the examples, although only two lithium manganese oxides of the type described are mentioned for the preparationThe method of the compound, but other methods for preparing the material do not form the restriction of the invention, one method is a wet process route, and the idea is to add lithium hydroxide into the suspension aqueous solution of EMD, replace hydrogen ions in EMD crystal lattices with lithium ions, and then obtain lithium manganese hydroxide through filtration, drying and heat treatment. The other is a dry process route, namely EMD and lithium salt or lithium hydroxide are fully mixed and then are subjected to heat treatment to realize lithium ion replacement of hydrogen ions in crystal lattices. After heat treatment, the gamma phase is stabilized, and lithium ions are easy to diffuse and migrate into a (1x2) tunnel in a crystal lattice when the battery is discharged, so that the discharge capacity at low temperature and the pulse characteristic are improved.

To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples.

Example 1

Preparation of lithium manganese oxide:

(0) purification of EMD

Adding 8kg of electrolytic manganese dioxide into 20L of deionized water, continuously stirring, slowly adding an HCl solution with the concentration of 1M until the pH value is 1, continuously stirring at room temperature for 24 hours, standing, pumping and filtering after supernatant liquid is removed, adding deionized water, and pumping and filtering for four times until the pH value of filtrate is 6 to obtain filter cakes, and dividing into four parts uniformly.

(1) The preparation method of the wet lithium manganese oxide comprises the following steps:

respectively putting four parts of the EMD filter cake into four parts of 2L deionized water, and rapidly stirring to prepare a suspension for at least 20 minutes; analytically pure LiOH powder (LiOH. H can also be used) is added in portions and in small portions₂O) until the pH of the suspension increases to 7.5, and stirring is continued for at least 30 minutes; one part of the suspension is placed aside and stirred continuously, and the other three parts of the suspension are added with LiOH step by step until the pH value is increased to 9.0, and stirring is continued for at least 30 minutes; one part of the suspension was left to stand and stirred continuously, and the pH values of the other two parts of the suspension were adjusted to 11.0 and 12.5 (close to LiOH saturated solution) by adding LiOH; all four suspensions were continuously stirred for 15 hours, during which the pH was monitored every 1-2 hours, and if the pH dropped, LiOH, which was added in the appropriate amount, was addedA total of 100g of lioh was added to saturation in one portion at medium pH 12.5; respectively obtaining four kinds of turbid liquids with pH values of 7.5, 9, 11 and 12.5, and standing until a supernatant and a precipitation interface clearly appear; after the supernatant fluid is pumped out, four parts of mud are filtered by suction; after blowing drying for 4 hours at 100 ℃, vacuum drying for 8 hours at 150 ℃; after being crushed, the mixture is placed in a muffle furnace and is kept at 380 ℃ for 8 hours under the air atmosphere, and the obtained lithium manganese oxide samples are marked as a, b, c and d.

(2) The preparation method of the dry lithium manganese oxide comprises the following steps:

three 2kg portions of EMD, 154.2g, 159.8g, 181.8g and 214.9g of analytically pure anhydrous LiOH, are ball-milled for 24 hours and then placed in a muffle furnace to be subjected to two-stage heat treatment at 300 ℃/2 hours and 380 ℃/8 hours to obtain lithium manganese oxide samples e, f, g and h.

The samples were subjected to X-ray diffraction (XRD) testing, wherein the XRD testing results for g, d and EMD are shown in FIG. 3, and it can be seen from FIG. 3 that reference is made to gamma MnO₂The spectral peaks, g and d samples have the spectral peak characteristics of gamma phase dominance and slightly have impurity phases.

XRD measurements of the other samples (a, b, c, e, f and h) showed that the samples were all predominantly gamma phase with a slight impurity phase.

Example 2

Button cell fabrication

(1) Positive electrode active material: samples a, b, c, d, e, f, g, h of example 1.

(2) Positive plate

The mass ratio of the positive electrode mixture is shown in table 1.

TABLE 1

The positive electrode mixture was thoroughly mixed and pressed into a disk having a diameter of 15.5mm and a thickness of 1.5mm, followed by vacuum drying at 200 ℃ for 12 hours. The carbon-coated nickel foil (average thickness of the conductive carbon layer: 4 μm) having a thickness of 12 μm was cut into a circular piece having a diameter of 16.5, and laid on the inner flat surface of the positive electrode can as a positive electrode current collector.

(3) Negative electrode

And pressing a LiAl (Al content of 0.8 wt.%) alloy sheet on the flat surface of the negative electrode shell.

(4) Conductive layer

Carbon paper (TGP-H-060) having a thickness of 0.19mm and made of PAN-based carbon fiber was cut into a circular piece having a diameter of 16 mm.

(5) Electrolyte solution

The electrolyte solvent is PC/DME ═ 1:1(v./v.), LiClO₄A concentration of 0.8M (mol./L), LiBF₄The addition concentration is 1% of the electrolyte mass.

(6) Button cell

The CR2032 positive and negative electrode cups and the covers are made of 304 stainless steel, polyphenylene sulfide is used as a sealing ring between the positive and negative electrode shells, and the button cell is manufactured according to the sequence of laying and pressing a lithium sheet, a conducting layer, polyphenylene sulfide non-woven fabrics, injecting liquid, laying the positive electrode sheet, injecting liquid and covering and sealing the cups.

Comparative example 1

The coin cell of this comparative example differs from that of example 2 only in the positive active material of (1), which is the prior art primary cell positive manganese dioxide, and the treatment method is: 2kg of EMD was placed in a muffle furnace and incubated at 380 ℃ for 8 hours and recorded as sample O.

Testing and evaluation:

and calculating the content of metal ions in the positive electrode materials a, b, c, d, e, f, g, h and O samples by using an inductively coupled plasma emission spectrum test. Calculation of the stoichiometric formula Li by potentiometric titration_xMnO_2-δThe (2-. delta.) values in (1) are shown in Table 2. Discharging the CR2032 coin cell by using a high-precision coin cell testing system, and calculating the gram capacity of the active substances according to the content of the active substances of the positive electrode, which is shown in Table 3.

TABLE 2

Li_xMnO_2-δWherein x is more than or equal to 0.030 and less than or equal to 0.4, and delta is more than or equal to 0.01 and less than or equal to 0.09

TABLE 3

As can be seen from table 3, as the Li/Mn molar ratio increases, the gram capacity of the lithium manganese oxide decreases, but the operating voltage plateau of the battery increases and the open circuit voltage decreases. The higher the operating voltage plateau, indicating that the power density will be greater, the open circuit voltage of the fresh cells is reduced, in particular below 3.4V, or below 3.4V after a few hours of standing, and the pre-discharge production step can be omitted.

Example 3

The coin cell of this embodiment is different from that of embodiment 2 only in the difference of the positive active material in (1), and in this embodiment, the positive active material is a mixture of lithium manganese oxide and graphite fluoride.

Active material Li Mn O samples C and (CF)_1.08) And n is mixed according to the mass ratio of 95:5 and is subjected to ball milling for 4 hours to obtain a positive active material sample C. The cell made from material sample C in this example was designated as cell I and the discharge test results are shown in fig. 4.

Fig. 4 shows that the lithium manganese oxide material and graphite fluoride have a good synergistic effect with a low voltage warning level at the end of battery discharge.

Example 4

The button cell of the present embodiment is different from the button cell of embodiment 3 only in the difference of the electrolyte, in the present embodiment, LiBF is not added to the electrolyte₄And is denoted as battery II.

Example 5

The button cell of the present embodiment is different from the button cell of embodiment 3 only in the difference of the electrolyte, in the present embodiment, LiBF is not added to the electrolyte₄And no conductive layer, denoted as cell III.

Example 6

The button cell of this embodiment is different from embodiment 3 only in the difference of the electrolyte, in this embodiment, electricityAdding LiBF into the solution₄Is 2% of the electrolyte. Denoted as battery IV.

Example 7

The button cell in this embodiment is different from the button cell in embodiment 3 only in the difference of the electrolyte, in this embodiment, LiBF is added to the electrolyte₄The mass of (b) is 3% of the electrolyte. Denoted as battery V.

Example 8

The button cell of this embodiment is different from that of embodiment 3 only in the difference of the electrolyte, in this embodiment, LiBF is added to the electrolyte₄The mass of (b) is 4% of the electrolyte. Denoted as battery VI.

Example 9

The button cell of this embodiment is different from that of embodiment 3 only in the difference of the electrolyte, in this embodiment, LiBF is added to the electrolyte₄The amount of (B) is 5% by mass of the electrolyte. Denoted as cell VII.

Low-temperature pulse testing and evaluation after high-temperature storage of the batteries I to VII:

placing the button cell in an oven, keeping the temperature at 110 ℃ for 90 days, taking out a sample every ten days, transferring the sample into a constant-temperature freezer at-40 ℃, standing for 4 hours to enable the temperature of the cell to reach-40 ℃, connecting the positive electrode and the negative electrode with a high-precision cell tester through silver-plated leads, and enabling the cell to carry out 10mA (the current density is 5.3 mA/cm)²) The 200ms pulse was discharged and the end of pulse instantaneous voltage (closed circuit voltage, CCV) was recorded.

As shown in FIG. 5, the electrolyte in example 3 contains an electrolyte additive LiBF₄And the low-temperature pulse characteristics of the batteries in which the conductive carbon fiber layer was provided between the nonwoven fabric separator and the negative electrode were significantly superior to those of the batteries of examples 4 and 5.

Example 4 electrolyte solution without electrolyte additive LiBF₄And the battery with the conductive carbon fiber layer arranged between the non-woven fabric diaphragm and the negative electrode has better low-temperature pulse discharge performance than that of the battery with the electrolyte in example 5, which does not contain electrolyte additive LiBF₄And the battery without the conductive carbon fiber layer between the non-woven fabric diaphragm and the negative electrode shows that the negative electrode of the non-woven fabric diaphragm has smaller surface electricityAnd (4) blocking.

As shown in FIG. 6, the electrolyte additive LiBF in examples 6 to 8₄The low-temperature pulse characteristic of the battery with the content of 2-4% is better.

Example 10

The button cell in this example is different from that in example 3 only in the electrolyte, and in this example, 2% by mass of LiBF was added to the electrolyte₄And no conductive carbon fiber layer is arranged between the non-woven fabric diaphragm and the negative electrode, and the battery is marked as a battery VIII.

Example 11

The button cell in this example is different from that in example 3 only in the electrolyte, and in this example, 3% by mass of LiBF was added to the electrolyte₄And no conductive carbon fiber layer was provided between the nonwoven fabric separator and the negative electrode, and this was designated as battery IX.

Example 12

The button cell in this example is different from that in example 3 only in the electrolyte, and in this example, LiBF was added to the electrolyte in an amount of 4% by mass₄And no conductive carbon fiber layer was provided between the nonwoven fabric separator and the negative electrode, and this was designated as cell X.

And (3) carrying out low-temperature pulse test and evaluation after high-temperature storage on the batteries III, VIII-X:

placing the button cell in an oven, keeping the temperature at 110 ℃ for 90 days, taking out a sample every ten days, transferring the sample into a constant-temperature freezer at-40 ℃, standing for 4 hours to enable the temperature of the cell to reach-40 ℃, connecting the positive electrode and the negative electrode with a high-precision cell tester through silver-plated leads, and enabling the cell to carry out 10mA (the current density is 5.3 mA/cm)²) The 200ms pulse was discharged and the end of pulse transient voltage (closed circuit voltage, CCV) was recorded.

FIG. 7 shows that LiBF was added to the electrolyte when no conductive carbon fiber layer was provided between the nonwoven fabric separator and the negative electrode₄The low-temperature pulse performance of the battery after high-temperature storage is deteriorated and along with LiBF₄The increase in the amount added worsens the low-temperature performance. This may be due to the severe accumulation of side reaction products of the electrolyte additive on the surface of the negative electrode under high temperature storage conditions, which results in negative electrode interfacial electricityThe resistance increases. The above results indicate that the addition of an electrolyte additive for improving high-temperature characteristics to the electrolyte solution or the application of a carbon layer to the surface of the negative electrode does not completely improve low-temperature pulse characteristics, and both of them are necessary to obtain excellent low-temperature pulse characteristics.

Example 13

The button cell of this embodiment is different from that of embodiment 6 only in the difference of the electrolyte, and in this embodiment, LiPO is further added to the electrolyte₂F₂The mass was 0.1% of the electrolyte. Denoted as battery XI.

Example 14

The button cell of this embodiment is different from that of embodiment 6 only in the difference of the electrolyte, and in this embodiment, LiPO is further added to the electrolyte₂F₂The mass was 0.3% of the electrolyte. Denoted as cell XII.

Example 15

The button cell of this embodiment is different from that of embodiment 6 only in the difference of the electrolyte, and in this embodiment, LiPO is further added to the electrolyte₂F₂The mass was 0.5% of the electrolyte. And is taken as a battery XIII.

Low temperature pulse testing and evaluation after high temperature storage of batteries IV, XI to XIII:

FIG. 8 shows that example 6 contains only LiBF₄An electrolyte additive, LiPO added with 0.1-0.5% of a second additive₂F₂Electrolyte additive for remarkably improving low-temperature pulse characteristics of the battery, and LiPO₂F₂Is added in a small amount, the low-temperature pulse characteristic can be effectively improved in cooperation with the first additive.

Example 16

To explore the effect of the conductive layer on the performance of the cell, the following test and control groups were set up:

test group 1

Referred to as cell a1, the only difference from cell I of example 3 was that the conductive layer was a carbon cloth having a thickness of 0.3mm (W1S 1009).

Test group 2

Cell a2, which is different from cell I of example 3 only in the conductive layer having a thickness of 0.15mm, was prepared by the following method:

in a dry environment, firstly preparing a binder, namely polyacrylonitrile, according to the following components and proportions: lithium trifluoromethanesulfonate: ethylene carbonate: propylene carbonate: uniformly mixing a binder and conductive carbon black according to a ratio of 90:10(w./w.), heating to 125 ℃, extruding, pressing by a pair of rollers, and cooling to obtain the film.

Test group 3

The difference between cell a3 and test group 2, which is a conductive layer having a thickness of 50 μm, is that:

the binder was mixed with test group 2, and the binder and activated carbon were mixed at a ratio of 94:6(w./w.), printed and pressed on a base surface having a teflon coating after heating, and peeled off after cooling to obtain a conductive film.

Test group 4

The difference from test group 3, which was designated as cell a4, was only the conductive layer thickness, which was 20 μm, and the preparation method was as follows:

the binder was mixed with test group 3, the binder and activated carbon were mixed at a ratio of 50:50(w./w.), printed and pressed on a base surface having a teflon coating after heating, and peeled off after cooling to obtain a conductive film.

Test group 5

The difference from test group 3, which was designated as cell a5, was only the conductive layer, which was 15 μm in this test group, and the preparation method was as follows:

the binder and test group 3 were mixed at a ratio of 60:40(w./w.) and a 400 mesh titanium carbide, and the mixture was heated, printed and pressed on a base surface having a teflon coating, and peeled off after cooling to obtain a conductive film.

Test group 6

The difference from test group 3, which was designated as cell a6, was only the conductive layer, which was 10 μm in this test group, and the preparation method was as follows:

the adhesive was mixed with test group 3, and the mixture was pressed on a teflon-coated hard base surface precoated with polydimethylsiloxane, and peeled off after cooling to obtain a conductive film, wherein the adhesive and 400 mesh titanium disilicide were mixed at a ratio of 75:25 (w./w.).

Test group 7

The difference from the battery I of example 3, which is denoted as battery a7, is only the difference in the material of the conductive layer, and the manufacturing method is as follows:

mixing titanium nitride, polytetrafluoroethylene and carboxymethyl cellulose according to a ratio of 95:4:1(w./w.), mixing with a plurality of mixed solvents of deionized water, ethanol and octanol to prepare a mixture, rolling the mixture into a thin material with the thickness of 0.19mm, and carrying out vacuum drying for 8 hours at 280 ℃ after preparing a round piece.

Control group 1

The difference from test group 2, which was designated as cell c1, was only the conductive layer, and the conductive layer of this control group was embossed into a film having a thickness of 0.15mm without conductive carbon black.

Test group 8

The difference between cell a8 and test group 2 is the type of conductive material in the conductive layer, and the conductive material in this test group is titanium carbide.

Test group 9

The difference between cell a9 and test group 2 is the type of conductive material in the conductive layer, and the conductive material in this test group is titanium nitride.

Test group 10

The difference between cell a10 and test group 2 is the type of conductive material in the conductive layer, and the conductive material in this test group is titanium carbonitride.

Test group 11

The difference between cell a11 and test group 2 is the type of conductive material in the conductive layer, and the conductive material in this test group is titanium disilicide.

And (3) carrying out low-temperature pulse test and evaluation on the batteries a 1-a 11 and the battery c1 after high-temperature storage:

placing the button cell in an oven, keeping the temperature at 110 ℃ for 30 days, taking out a sample, transferring the sample into a constant-temperature freezer at-40 ℃, standing for 4 hours to ensure that the temperature of the cell reaches-40 ℃, connecting the positive electrode and the negative electrode with a high-precision cell tester through silver-plated leads, and enabling the cell to carry out the process of 10mA (the current density is 5.3 mA/cm)²) The 200ms pulse was discharged and the end of pulse instantaneous voltage (closed circuit voltage, CCV) was recorded.

The test results are shown in tables 4 and 5.

TABLE 4

Group of	Battery with a battery cell	CCV
			Example 3	Battery I	2.50V
Example 4	Battery II	0.94V
			Example 5	Battery III	0.48V
Test group 1	Battery a1	2.15V
			Test group 2	Battery a2	2.42V
Test group 3	Battery a3	2.38V
			Test group 4	Battery a4	2.52V
Test group 5	Battery a5	2.57V
			Test group 6	Battery a6	2.60V
Test group 7	Battery a7	2.44V
			Control group 1	Battery c1	1.80V

TABLE 5

Table 4 shows that the conductive layer suppresses the accumulation of reaction products on the surface of the lithium metal negative electrode through high-temperature storage, thereby being capable of maintaining a superior pulse discharge performance at a low temperature. The conductive material in the conductive layer plays a role in reducing the surface resistance of the negative electrode, and the same effect cannot be achieved by singly adopting the conductive adhesive. Table 5 shows that titanium nitride and titanium disilicide have a higher CCV than carbon material at the same thickness.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A lithium battery comprising a positive electrode, a lithium metal or lithium alloy metal negative electrode, an anhydrous electrolyte, and a separator; a conducting layer is arranged between the diaphragm and the negative electrode, and the conducting layer contains a material with conducting property; the conductive material is titanium nitride and/or titanium disilicide; the positive electrode comprises a carbon fluoride material and at least one of lithium manganese oxide and doped lithium manganese oxide; the stoichiometric formula of the lithium manganese oxide is Li_xMnO_2-δWherein x is more than 0 and less than 0.5, and delta is more than or equal to 0.01 and less than or equal to 0.09; the carbon fluoride material has the stoichiometric formula of (CF)_y)_nWherein y is more than or equal to 0.8 and less than or equal to 1.1, and n is more than or equal to 1; the main crystal form of the lithium manganese oxide or the doped lithium manganese oxide is a gamma crystal form; the weight ratio of at least one of the lithium manganese oxide and the doped lithium manganese oxide to the carbon fluoride material is as follows: at least one of lithium manganese oxide and doped lithium manganese oxide: the carbon fluoride material is =90: 10-99.5: 0.5;

the non-aqueous electrolyte comprises a non-aqueous solvent, an electrolyte and an electrolyte additive; the electrolyte additive comprises a first additive and a second additive, wherein the first additive is a lithium salt containing B and F as anions, and the second additive is a lithium fluorophosphate salt containing P and F as anions; the weight percentage of the first additive in the electrolyte is 2-4%; the weight percentage of the second additive in the electrolyte is 0.1-0.5%.

2. A lithium battery as claimed in claim 1, characterized in that the electrically conductive layer is attached to or in close proximity to at least a part of the surface of the negative electrode on the side opposite to the positive electrode.

3. The lithium battery as claimed in claim 1, wherein the separator is one of polyethylene non-woven fabric, polypropylene non-woven fabric, nylon non-woven fabric, polyester non-woven fabric, polyphenylene sulfide non-woven fabric, aramid non-woven fabric, and glass fiber non-woven fabric, and modifications thereof.

4. The lithium battery according to claim 1, wherein at least one of the following (a) - (c):

（a）0.03≤x≤0.4；

(b) the doped lithium manganese oxide has the stoichiometric formula Me-Li_xMnO_2-δMe is a doped element or group, Me is Al, Mg, Fe, La, Zr, Cr, Cd, Ti, Bi, Ni, Co, F, B, P, S and PO₄ ^3-At least one of (a);

(c) the carbon fluoride material is at least one of graphite fluoride, fluorinated coke, fluorinated carbon black, fluorinated bamboo carbon, fluorinated ketjen carbon, fluorinated graphene and fluorinated multi-walled carbon nanotubes.

5. The lithium battery of claim 1, wherein 0.03. ltoreq. x.ltoreq.0.29.

6. The lithium battery of claim 1, wherein the weight ratio of the carbon fluoride to at least one of the lithium manganese oxide and the doped lithium manganese oxide is: at least one of lithium manganese oxide and doped lithium manganese oxide: the carbon fluoride material is 95: 5-99: 1.

7. The lithium battery of claim 1 wherein the first additive is LiBF₄、Li₂B₁₂F₁₂And LiBF₂C₂O₄At least one of (a) and (b);

and/or the second additive is Li₂PO₃F、LiPO₂F₂、LiPF₄(C₂O₄)、LiPF₂(C₂F₅)₂And LiPF₃(C₂F₅)₃At least one of them.

8. The lithium battery according to claim 1, wherein at least one of the following (d) - (f):

(d) the anhydrous solvent is at least one of cyclic carbonate, chain ether, cyclic ether and cyclic carboxylate;

(e) the electrolyte comprises a first electrolyte which is LiClO₄Said LiClO₄The weight percentage content in the electrolyte is more than or equal to 90 percent;

(f) the lithium alloy metal is an alloy of lithium and metal M, and the M is at least one of Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Sn.