CN107819127A

CN107819127A - Anode material of lithium-iron disulfide battery with function of reducing open-circuit voltage and preparation method of anode material

Info

Publication number: CN107819127A
Application number: CN201711017410.7A
Authority: CN
Inventors: 谢红卫; 潘元元
Original assignee: Zhongyin Ningbo Battery Co Ltd
Current assignee: Zhongyin Ningbo Battery Co Ltd
Priority date: 2017-10-26
Filing date: 2017-10-26
Publication date: 2018-03-20

Abstract

The invention discloses a positive electrode material of a lithium-iron disulfide battery capable of reducing open-circuit voltage and a preparation method thereof, wherein a positive electrode active substance of a lithium-iron primary battery is iron disulfide, a negative electrode active substance is metallic lithium, a positive electrode is composed of an active material iron disulfide, a carbon conductive material and a binder, wherein the carbon conductive material contains or completely contains one or two materials of graphene and a carbon nano tube, and the lithium-iron battery has the characteristics that the open-circuit voltage is lower than that of a lithium-iron battery manufactured by a conventional method, and the rising amplitude of the open-circuit voltage after production is smaller than that of the lithium-iron battery manufactured by the conventional method.

Description

Anode material of lithium-iron disulfide battery with function of reducing open-circuit voltage and preparation method of anode material

Technical Field

The invention relates to the field of batteries, in particular to a positive electrode material of a lithium-iron disulfide battery capable of reducing open-circuit voltage and a preparation method thereof.

Background

The lithium-iron disulfide battery (lithium iron battery for short) is a novel 1.5V system high-energy primary battery, and has the same rated voltage as a 1.5V aqueous solution system battery (primary batteries such as the most common Zn/MnO2 battery, zn/Ag2O, zn/HgO battery and the like, secondary batteries such as a nickel-hydrogen battery, a nickel-cadmium battery and the like), and simultaneously has higher specific energy, higher capacity and longer storage time, thereby having more important application values on small-sized electric appliances such as digital products, toy cars, remote control toys, shavers, medical devices, military communication and the like, and belonging to next generation high-energy primary battery products after alkaline batteries. The specific characteristics of the battery mainly include: (1) high discharge voltage and stable discharge; (2) The discharge capacity is large and is several times of that of a common alkaline battery; (3) The power density is high, the discharge characteristic of the heavy current is excellent, under the discharge mode of the analog camera, the discharge capacity can reach 9-10 times of that of the alkaline battery; (4) lighter weight compared to a battery of the same type; (5) The working temperature range is wide, from minus 40 to 60 ℃, and the low-temperature performance is excellent; (6) The storage performance is good, the storage life is long, and the storage time at normal temperature can reach more than 10 years; (7) Because no strong base and other substances exist, the battery has good liquid leakage resistance and high use safety for electric appliances. Therefore, the lithium-iron disulfide battery is the product with the best comprehensive performance in the current 1.5V primary battery series products, and is the development direction of dry batteries.

The cathode of the lithium-iron battery is metal lithium, and the anode mainly comprises three components of iron disulfide, a conductive material and a binder. The conductive material is mainly prepared from crystalline flake graphite, acetylene black, conductive carbon black and other carbon materials singly or in combination, and the binder is usually prepared from PVDF, PTFE, SBR and other high polymer materials. The anode is produced by preparing the materials into slurry by taking NMP as a solvent, coating the slurry on an aluminum foil current collector, drying, compacting, slitting, welding lugs and the like.

The battery is formed by laminating a foil-shaped lithium metal sheet, a positive plate and a diaphragm, winding the laminated lithium metal sheet, the positive plate and the diaphragm into a battery shell, adding an organic electrolyte and packaging. Although the lithium iron battery produced by the conventional method has the performance advantages relative to the performance advantages, the lithium iron battery produced by the conventional method has incomparable superiority with other 1.5V batteries, particularly other 1.5V primary batteries, but the lithium iron battery produced by the conventional method suffers from the problem of overhigh open circuit voltage of the battery, particularly the open circuit voltage is gradually increased in the process of storage for a period of time after the battery is produced, and the maximum open circuit voltage can reach more than 1.9V and even approach 2.0V. Batteries, especially primary batteries, have strict requirements on voltage, because electrical appliances have a certain adaptive range on the power supply voltage, and cannot normally work once the adaptive range is exceeded, the power supply voltage is better than the adaptive range, generally, the batteries cannot normally work (the lowest normal working voltage for the batteries is the so-called battery discharge end voltage), and once the power supply (battery) voltage is higher than the adaptive voltage range of the electrical appliances, the circuits of the electrical appliances are very easily damaged, so that the batteries, especially the primary batteries, are regulated to have a strict range of the highest open-circuit voltage, and the upper limit of the open-circuit voltage of the batteries is strictly limited. The open circuit voltage of a 1.5V battery is usually about 1.5V, and the operating voltage during use is generally lower than 1.5V. The open circuit voltage of some 1.5V batteries is higher than 1.5V, for example, the open circuit voltage of alkaline zn-mn batteries is more than 1.6V, and the carbon voltage reaches about 1.72V, but generally not higher than 15% of the nominal voltage, otherwise there is a risk of damage to the electrical equipment. Therefore, the voltage of the lithium-iron battery produced by using the conventional method reaches and even exceeds 1.9V, exceeds the nominal voltage by more than 25%, and basically enters the range of 2.0V batteries, so that the lithium-iron battery has a considerable use risk for electric appliances, and particularly when a plurality of batteries are used in series, the risk is higher. For example, in an electrical appliance using four batteries connected in series, the rated operating voltage should be 6V, and when four lithium iron batteries with open circuit voltage of 1.9V are connected in series, the open circuit voltage will reach 7.6V, which is sufficiently higher than 1.6V, and is very close to the voltage of four batteries with 2.0V, which is very easy to damage the electrical appliance circuit.

The open circuit voltage of lithium-iron batteries produced in this way also has a problem: the open-circuit voltage of a common battery is reduced along with the increase of storage time, so that the open-circuit voltage is qualified only by factory inspection after the battery is produced, the problem that the open-circuit voltage of the battery is out of limit is not worried, and the open-circuit voltage of the lithium-iron battery slowly rises within a certain period of time (from several months to about one year) after the battery is produced, so that the open-circuit voltage of the battery after the battery is produced is difficult to be effectively controlled by a conventional factory inspection method to be not out of limit.

However, so far, no method for effectively controlling or adjusting the open-circuit voltage has been found for the lithium-iron battery, and products manufactured by various manufacturers have almost the same open-circuit voltage as a whole, so that even the national standard and the IEC standard have to be modified to adjust the upper limit of the open-circuit voltage from the initial 1.83V to 1.89V. Although the original product with the excessive open-circuit voltage can be qualified by adjusting the standard, the fact that the electrical appliance is possibly damaged by the excessive open-circuit voltage cannot be changed, and conversely, the increase of the open-circuit voltage standard integrally promotes the open-circuit voltage of the lithium iron battery in the market, so that the risk of using the lithium iron battery by a consumer is increased, and the development of the whole lithium iron battery industry can be possibly damaged.

Therefore, solving the problem of the over-high open-circuit voltage of the lithium-iron battery is a non-negligible problem of the lithium-iron battery.

Although some technical parameters of the battery, such as load voltage, internal resistance, short-circuit current, etc., have a certain relationship with the characteristics of the raw materials of the battery, the technical parameters mainly relate to the technical design of the battery and the technical parameters of the production process, etc., so the technical parameters are technical parameters, and the open-circuit voltage is different from the technical parameters, the open-circuit voltage is basically determined by the material properties of the battery, namely the electrochemical system of the battery is a systematic parameter, and the factors influencing the open-circuit voltage of the battery are mainly the characteristics of the raw materials of the battery, or the characteristics of active materials of the battery, and are also related to the concentrations of reaction products and reactants in the electrolyte of the battery. For this reason, adjusting the open circuit voltage of the battery is generally performed by changing the properties of the active material and the composition of the electrolyte. For example, in the case of an alkaline battery, the open-circuit voltage of the battery is mainly affected by several factors, i.e., the characteristics (potential) of the electrolytic manganese dioxide, the concentration of the electrolyte and the content of zinc oxide in the electrolyte, so that when the open-circuit voltage of the alkaline battery needs to be adjusted, either the electrolytic manganese dioxide with different potentials is used, or the concentration of the electrolyte or the content of zinc oxide in the electrolyte is adjusted, and when the open-circuit voltage of the battery changes, the several factors change. The production of carbon cells also risks excessive open circuit voltage, and when the open circuit voltage of the cell is too high, the open circuit voltage is reduced by increasing or adding the amount of zinc oxide or magnesium oxide in the positive electrode, which is actually the ratio of the reaction products in the electrolyte, in addition to the formulation of manganese dioxide with a lower potential. Therefore, to adjust the open circuit voltage of the battery, conventional methods are mainly performed by changing the properties of the active material or by adjusting the composition of the electrolyte and electrochemical reaction products.

The lithium-iron battery has not found a method for adjusting the open-circuit voltage by adjusting the active material or electrolyte composition, and has not solved the problem that the open-circuit voltage of the lithium-iron battery rises in a period of time.

Therefore, in the aspect of controlling the open-circuit voltage of the lithium-iron battery, a concept needs to be developed, and other methods need to be adopted, but the concept and the method are not limited to the existing concept and method.

The invention provides a lithium iron battery with lower open-circuit voltage by using a special conductive material and a preparation method of the anode in an unconventional method and by using a special conductive material and a preparation method of the anode, on one hand, the initial open-circuit voltage of the battery is reduced, and on the other hand, the rising speed of the open-circuit voltage is slowed down.

The method for preparing the positive electrode by using the special conductive material to reduce the open-circuit voltage of the lithium-iron battery is an unconventional method, because in the positive electrode of the lithium-iron battery, the conductive material is only an auxiliary material for increasing the conductivity of the electrode, because the conductivity of the positive electrode active material iron disulfide is poor, the conductivity of the whole positive electrode needs to be improved for collecting the current generated by the active material during the discharge reaction of the battery on a current collector (aluminum foil) and then supplying the current to the outside, and the method for improving the conductivity of the positive electrode is to add the conductive material into the positive electrode.

And the conductive material added to the positive electrode is subject to strict technical requirements. Besides the requirement of better conductivity, the conductive material has a very important characteristic of not reacting with active materials, electrolyte, current collectors and other materials, that is, the conductive material is a chemically inert or electrochemically inert material, and does not affect the open circuit voltage of the battery under normal conditions, so the invention has novelty that cannot be realized by the technicians in this field according to the conventional technology.

The invention can ensure normal conductivity (even better conductivity) and basic chemical and electrochemical inertness of the electrode by applying two special conductive materials which completely meet the technical requirements of the conventional conductive materials, and has the function of reducing the voltage open-circuit voltage which cannot be explained by the normal theory.

Disclosure of Invention

The invention aims to provide a lithium iron battery anode capable of controlling or reducing the open-circuit voltage of a battery and a preparation method thereof.

The technical scheme adopted by the invention to solve the technical problem is as follows: the positive electrode material of the lithium-iron disulfide battery with the reduced open circuit voltage comprises iron disulfide, a conductive material and a binder, and is characterized in that one or two of graphene and carbon nanotubes are used as the conductive material.

The further preferable scheme of the invention is as follows: the conductive material is graphene or carbon nanotubes in powder form.

The further preferable scheme of the invention is as follows: the conductive material uses graphene or carbon nanotube conductive paste, or mixed conductive paste in which graphene and carbon nanotubes are mixed.

The further preferable scheme of the invention is as follows: the preparation method of the anode material of the lithium-iron disulfide battery with reduced open-circuit voltage is characterized by comprising the following specific steps:

the method comprises the following steps: dry blending of powdered materials

Dry mixing iron disulfide, conductive material of powder and binder;

step two: wet mixing

Adding NMP into the dry-mixed powder material for wet mixing;

step three: kneading the mixture

Kneading the mixed material which is mixed evenly by the wet mixing into a mass;

step four: extruding and drying

Extruding the kneaded material out of the fine holes by using a extruder into threads, and drying;

step four: crushing and granulating

And crushing the dried filiform material into fine particles by a crusher, and screening the fine particles into proper particle size by using a vibration screen to obtain the button lithium-iron disulfide battery anode powder.

the method comprises the following steps: preparation of glue solution

Adding PVDF binder into NMP, mixing for 2-4 hours by a stirrer to prepare uniform glue solution;

step two: slurry mixing

Respectively adding iron disulfide, graphene, carbon nanotubes, carbon black and other powder materials into the glue solution, and mixing for about 8 hours;

step three: filtration

And filtering the mixed slurry by using a slurry filter to obtain the anode slurry for manufacturing the lithium-iron disulfide battery.

The further preferable scheme of the invention is as follows: the preparation method of the anode material of the lithium-iron disulfide battery with reduced open-circuit voltage is characterized by comprising the following specific steps;

the method comprises the following steps: dry mixing

Dry mixing iron disulfide, flaked graphite and powder binder in a mixer;

step two: wet mixing

Adding NMP into the dry-mixed powder and mixing for about 15-20 minutes;

step three: adding conductive slurry for mixing

Adding graphene or carbon nanotube slurry or mixed conductive slurry of the two components into the wet mixed mixture, and mixing for about 8 hours;

step four: filtration

Compared with the prior art, the invention has the advantages that: the two conductive materials are added into the positive electrode, so that the open-circuit voltage of the lithium-iron battery is lower than that of a product produced by a conventional method, and the open-circuit voltage of the lithium-iron battery has the function of delaying the increase of the open-circuit voltage, so that the open-circuit voltage of the lithium-iron battery product is lower than that of the conventional product.

Drawings

Fig. 1 is a graph showing the open-circuit voltage variation of a button lithium iron battery after graphene, carbon nanotubes and a mixture of the two materials are added.

Detailed Description

The invention is described in further detail below with reference to the following examples of the drawings.

Generally, the open-circuit voltage of a battery is related to the properties of active materials of the battery, and also related to the contents or concentrations of reactants and reaction products in the electrolyte and the positive and negative electrodes, so that when the open-circuit voltage of a carbon battery is too high and needs to be reduced, for example, the concentration of an electrolyte (which may affect the performance of the battery) is adjusted except for selecting manganese dioxide with a lower potential, or the addition amount of zinc oxide or magnesium oxide is increased in the positive electrode, and the concentration of the electrolyte of the carbon battery and the zinc oxide or magnesium oxide in the positive electrode are products of electrode reactions of the battery, and the open-circuit voltage of the battery can be adjusted by adjusting the addition amount of the substances.

The research of the invention finds that the open-circuit voltage of the lithium-iron battery presents quite unique conditions. Generally, the open-circuit voltage of a battery is the difference between the electrode potentials of a positive electrode material and a negative electrode material in the current electrolyte environment, so that the active materials in the battery can generate tiny self-discharge under the influence of factors such as impurities and the like along with the increase of the storage time of the battery after the battery is produced, the open-circuit voltage of the battery is in a tiny descending trend, the lithium iron battery is different from the lithium iron battery, the open-circuit voltage of the lithium iron battery at the beginning of production is in a constant ascending trend within a long period of storage time of the battery, and finally reaches the maximum value and then becomes stable, and the open-circuit voltage gradually descends after several years.

The phenomenon is generally considered to be caused by that the cathode material generates a trace oxidation reaction with trace moisture and other various impurity materials contained in the battery material on the surface of cathode material particles after the battery is produced, and a reaction product with a potential higher than that of iron disulfide is generated, and because the battery material cannot completely eliminate the trace impurities, the phenomenon cannot be completely avoided, and therefore, no ideal solution is provided in the whole technical field of lithium-iron batteries at present.

The invention is based on a unique experimental phenomenon discovered by accident in the research process of the lithium-iron battery: when carbon nanotubes or graphene is added as a conductive material to the positive electrode of a lithium iron battery, two phenomena occur, whether used alone or together: firstly, the initial open-circuit voltage of the battery is reduced, and the initial open-circuit voltage of the battery is obviously lower than that of the conventional lithium iron battery; and secondly, during the storage period of the battery after production, the rising amplitude of the open-circuit voltage is lower than that of the conventional lithium iron battery.

This peculiar effect of the carbon nanotube and graphene cannot be explained by the existing theory, because the carbon nanotube and graphene are both carbon materials with good conductivity but stable chemical properties, that is, they are chemically inert materials in the battery, and do not chemically or electrochemically react with and change other materials in the battery, including active materials, electrolyte components, etc., that is, they are neither active materials nor reactants or reaction products of electrode reaction in the battery, especially in the positive electrode, they are merely existing as an electron conductive material of the positive electrode, and perform electron conduction in the positive electrode, and as an electrochemical or chemically "inert" material, they do not theoretically affect the open circuit voltage of the battery, and do not affect or slow down the possibility of the reaction of the positive electrode active material iron disulfide with trace impurities in the battery, but as an objective experimental phenomenon, their effect on the open circuit voltage of the lithium iron battery exists, that is theoretically, and this phenomenon cannot be explained by the ordinary present invention, and it can be found by the conventional and professional experiments.

The graphene and the carbon nano tube have various product forms, because the two materials are ultrafine particles and have an agglomeration phenomenon, the graphene and the carbon nano tube also have a slurry form with relatively good dispersity besides conventional dry powder, and the graphene and the carbon nano tube can play roles in reducing the open-circuit voltage of the battery and slowing the increase of the open-circuit voltage when being added into the positive electrode of the lithium iron battery in any product form.

The following table shows the data of the influence of the two materials added into the positive electrode of the button lithium iron battery on the open-circuit voltage of the battery, wherein the addition amounts of the carbon nanotube and the graphene in the positive electrode are both 5%:

therefore, the invention provides a technical scheme for reducing the open circuit voltage of a lithium iron battery by using chemically and electrochemically inert materials, which comprises the following steps: graphite and carbon nano materials are used as conductive materials in the positive electrode of the lithium iron battery.

When the material is added into the positive electrode of the lithium-iron battery, one of the materials can be added independently or the two materials can be added simultaneously;

when one or two materials are added into the positive electrode of the lithium iron battery, the added materials can be powder products or slurry products. The slurry component can be single graphene or carbon nano-tubes, or mixed slurry formed by mixing graphene and carbon nano-tubes according to a certain proportion.

Example 1: one or two of graphene and carbon nano tubes are used as conductive materials in the button lithium iron battery;

1. the positive electrode formula comprises:

iron disulfide: 10kg of

Graphene or carbon nanotubes and a mixture powder of both: 0.5kg

PVDF (polyvinylidene fluoride): 0.6kg

NMP (N-methyl pyrrolidone): proper amount of

2. The preparation process of the anode powder comprises the following steps:

the method comprises the following steps: dry blending of powdered materials

Dry mixing iron disulfide, graphene or carbon nanotubes and a mixture of the graphene and the carbon nanotubes, PVDF and other powder materials.

Step two: wet mixing

NMP was added to the aforementioned dry-mixed powder material for wet mixing.

Step three: kneading the mixture

Kneading the mixed material which is mixed evenly by wet mixing into a mass, so that the inside of the material has better adhesive force.

Step four: extruding and drying

Extruding the kneaded material out of the fine hole by a extruder into filaments, and drying the filaments.

Step four: pulverizing and granulating

And crushing the dried filamentous material into fine particles by using a crusher, and screening by using a vibrating screen to obtain the anode powder with proper granularity.

3. Manufacturing a battery: and pressing the granulated positive electrode powder into a positive electrode cake, drying at the high temperature of 150 ℃, and then preparing the positive electrode cake, a negative electrode lithium sheet, a diaphragm, electrolyte and the like into the button lithium-iron disulfide battery according to the conventional battery manufacturing procedure.

Example 2: production of lithium-iron disulfide cylindrical cells using graphene powder formulations

1. Positive electrode formula (unit: kilogram)

Iron disulfide	Graphene (powder lot)	SP carbon black	PVDF	NMP
					100	1.5	1.5	2.66	35

2. Positive electrode slurry manufacturing process

The method comprises the following steps: preparation of glue solution

PVDF was added to NMP and mixed with a blenderAnd (5) preparing uniform glue solution after hours.

Step two: slurry mixing

Adding powder materials such as iron disulfide, graphene and carbon black into the glue solution, and mixing for about 8 hours;

step three: filtration

The mixed slurry is filtered by a slurry filter.

3. Battery fabrication

And carrying out battery manufacturing processes such as coating of the positive plate, rolling, slitting and the like according to a conventional process mode.

Example 3: production of lithium-iron disulfide cylindrical batteries using 5% content carbon nanotube slurry

1. Positive electrode formula (unit: kilogram)

Iron disulfide	5% carbon nanotube slurry	Flake graphite	PVDF	NMP
					100	35	1.5	2.66	35

2. Positive electrode slurry manufacturing process

The method comprises the following steps: dry blending

Iron disulfide, flaked graphite and PVDF were dry mixed together in a V-blender.

Step two: wet mixing

NMP was added to the above mixed powder and mixed for about 15 minutes.

Step three: adding carbon nano tube slurry to mix

And adding the carbon nano tube slurry into the wet mixed mixture, and mixing for about 8 hours.

Step four: filtration

The mixed slurry is filtered by a special slurry filter.

3. Battery fabrication

And (4) carrying out battery manufacturing processes such as coating, rolling and slitting on the positive plate according to a conventional process, and then carrying out battery manufacturing after the positive plate is manufactured.

Example 4: the lithium-iron cylindrical battery is produced by using 5% solid content carbon nanotube and graphene mixed conductive slurry (the mass ratio of the carbon nanotube to the graphene is 6

1. Positive electrode formula (unit: kilogram)

Iron disulfide	Mixed conductive paste	PVDF	NMP
				100	45	2.66	40

2. Positive electrode slurry manufacturing process

The method comprises the following steps: dry mixing

The iron disulfide and PVDF were dry blended together in a V-blender.

Step two: wet mixing

NMP slurry was added to the above mixed powder and mixed for about 15 minutes.

Step three: adding the mixed slurry for mixing

And adding the mixed conductive slurry into the wet mixed mixture, and mixing for about 8 hours.

Step four: filtration

And filtering the mixed slurry by using a slurry filter to obtain the anode slurry.

3. Battery fabrication

Claims

1. The positive electrode material of the lithium-iron disulfide battery with the reduced open circuit voltage comprises iron disulfide, a conductive material and a binder, and is characterized in that one or two of graphene and carbon nanotubes are used as the conductive material.

2. The positive electrode material for a lithium-iron disulfide battery with reduced open circuit voltage as claimed in claim 1, wherein the conductive material is graphene or carbon nanotubes in powder form.

3. The positive electrode material for a lithium-iron disulfide battery with reduced open-circuit voltage as claimed in claim 1, wherein the conductive material is graphene or carbon nanotube conductive paste, or mixed conductive paste of graphene and carbon nanotubes.

4. The method for preparing the positive electrode material of the lithium-iron disulfide battery with reduced open circuit voltage as claimed in claim 2, characterized by comprising the following steps:

the method comprises the following steps: dry blending of powdered materials

Dry mixing iron disulfide, conductive materials of powder and a binder;

step two: wet mixing

Adding NMP into the dry-mixed powder material for wet mixing;

step three: kneading the mixture

step four: extruding and drying

Extruding the kneaded material out of the machine into filaments in the pores, and drying;

step four: crushing and granulating

5. The method for preparing the positive electrode material of the lithium-iron disulfide battery with reduced open-circuit voltage according to claim 2, is characterized by comprising the following steps:

the method comprises the following steps: preparation of glue solution

Adding a PVDF binder into NMP, mixing for 2-4 hours by a stirrer to prepare a uniform glue solution;

step two: slurry mixing

step three: filtration

6. The method for preparing the positive electrode material of the lithium-iron disulfide battery with reduced open-circuit voltage according to claim 3, which is characterized by comprising the following specific steps;

the method comprises the following steps: dry mixing

Dry mixing iron disulfide, flaked graphite and powder binder in a mixer;

step two: wet mixing

Adding NMP into the dry-mixed powder and mixing for about 15-20 minutes;

step three: adding conductive slurry for mixing

Adding graphene or carbon nanotube slurry or mixed conductive slurry of the two components into the wet mixed mixture; mixing for about 8 hours;

step four: filtration