WO2019131779A1 - リチウムイオン二次電池用正極活物質及びリチウムイオン二次電池用正極活物質の製造方法、並びにリチウムイオン二次電池 - Google Patents
リチウムイオン二次電池用正極活物質及びリチウムイオン二次電池用正極活物質の製造方法、並びにリチウムイオン二次電池 Download PDFInfo
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Definitions
- the present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery.
- Lithium ion secondary batteries are widely used as small and light secondary batteries having high energy density.
- the lithium ion secondary battery is characterized in that the energy density is high and the memory effect is small as compared with other secondary batteries such as a nickel-hydrogen storage battery and a nickel-cadmium storage battery. Therefore, from small power sources such as portable electronic devices and household electrical appliances, stationary power sources such as power storage devices, uninterruptible power devices, power leveling devices, ships, railway vehicles, hybrid railway vehicles, hybrid vehicles, electric vehicles Applications are expanding to medium-sized and large-sized power supplies such as driving power supplies.
- lithium ion secondary batteries are required to have higher capacity.
- the charge and discharge capacity of the lithium ion secondary battery largely depends on the filling rate of the positive electrode active material in the positive electrode. Therefore, at the time of preparation of the positive electrode, the powder of the positive electrode active material is press-molded after its particle size is adjusted.
- the positive electrode is provided so as to form a porous body having a high filling rate, leaving a void through which secondary particles in which primary particles are aggregated permeate the electrolytic solution.
- the performance of the positive electrode is considered to be affected by the diffusion distance in the solid phase in such a state, the interface resistance between particles, and the like.
- One type of positive electrode active material for lithium ion secondary batteries is a lithium composite compound having an ⁇ -NaFeO 2 type crystal structure.
- a LiNiO 2 -based oxide having a high content of nickel exhibits a high charge / discharge capacity, and hence application to various uses is expected.
- a lithium composite compound having a high content of nickel has low structure stability and is easily degraded by charge and discharge cycles and high temperature storage.
- a large volume change occurs with charge and discharge.
- the particles of the lithium composite compound may cause breakage or deformation such as cracking due to pressure applied at the time of pressure molding and volume change associated with charge and discharge.
- secondary particles of the lithium composite compound are likely to break the aggregation structure due to such stress, and thus it is a problem to produce isolated particles that do not contribute to the conduction of ions or electrons, or to increase interface resistance.
- a technique for increasing the particle strength has been studied for a LiNiO 2 -based lithium composite compound that causes a large volume change.
- Patent Document 1 the composition formula: Li x Ni 1-(y + z) Mn y Co z O 2 + ⁇ (in the above formula, 0.9 ⁇ x ⁇ 1.2, and 0 ⁇ y + z ⁇ 0.3)
- the average particle diameter D50 is 5 to 7 ⁇ m
- the particle strength is 60 MPa or more
- a positive electrode active material for a lithium ion battery having 5% or less is described.
- Patent Document 1 describes that by controlling the temperature rising rate at the time of firing to 200 ° C./h or more, the voids (pores) in the positive electrode active material are reduced and the particle strength is improved (paragraph See 0029).
- the classification rotor and the grinding rotor are crushed at a rotational speed of 5000 rpm or more by a palperizer, the contained pores disappear and the particle strength becomes stronger (see paragraph 0030).
- Patent Document 2 describes that the charge and discharge cycle characteristics of a lithium ion secondary battery are affected by lithium carbonate and lithium hydroxide present as impurities on the particle surface of the positive electrode active material. It is known that lithium composite compounds can be in a state in which impurities such as lithium carbonate form or adhere to different phases due to raw materials used for synthesis, exposure to the atmosphere, and the like.
- a powder of a positive electrode active material having a particle strength of about 60 MPa or more is obtained (see Examples).
- the average particle diameter D50 of the positive electrode active material is controlled to 5 ⁇ m or more, and the ratio of the number of primary particles to secondary particles is also controlled to be high. Therefore, in the powder of the positive electrode active material obtained, the particles constituting the positive electrode active material are close to single particles, and the number of primary particles contained in the secondary particles is about 1.2 to 1.7.
- the powder of the positive electrode active material has a relatively large particle size and a specific surface area as small as about 0.6 m 2 / g or less.
- the positive electrode active material is synthesized by a liquid phase method using lithium carbonate as a raw material, and the precipitated lithium-containing carbonate is separated by filtration, dried and fired. (See paragraph 0028, etc.).
- the process becomes complicated and the mass production of the positive electrode active material becomes difficult, and dedicated equipment is required for the filtration processing and the reuse of the filtered lithium.
- the precursor that has been separated by filtration and dried is likely to have an irregular particle shape, and the uniformity of the particle shape tends to be low. Therefore, the coatability at the time of forming the positive electrode mixture layer is poor, which may cause a problem in handling or may easily cause breakage or deformation during firing.
- the lithium composite compound having a high content of nickel is applicable without being influenced by the design of the specific surface area, and the particles constituting the positive electrode active material are brought close to single particles as in Patent Document 1
- the breaking strength (particle breaking strength) of secondary particles decreases. It has been confirmed that there is a tendency.
- secondary particles having a low particle breaking strength are used to form the positive electrode mixture layer, there is also a problem that the adhesion between particles of the positive electrode active material and the current collector is lowered.
- the present invention provides a method for producing a positive electrode active material for a lithium ion secondary battery having high fracture strength of the secondary particles constituting the powder and having good coatability, and a method for producing a positive electrode active material for a lithium ion secondary battery, And providing a lithium ion secondary battery.
- the positive electrode active material for a lithium ion secondary battery according to the present invention comprises two primary particles of a lithium composite compound represented by the following formula (1) and two primary particles of the lithium composite compound aggregated.
- Secondary particles and the ratio (D 1 / D 2 ) of the average particle diameter (D 1 ) of the primary particles to the average particle diameter (D 2 ) of the secondary particles is 0.006 or more, and 0. It is 25 or less, the amount of lithium carbonate is 0.4 mass% or less, and the breaking strength of the secondary particles is 30 MPa or more.
- M 1 is at least one element selected from the group consisting of Mn and Al
- M 2 is selected from the group consisting of Mg, Ti, Zr, Mo and Nb
- At least one element, and a, x, y, z and ⁇ are such that ⁇ 0.1 ⁇ a ⁇ 0.2, 0.7 ⁇ x ⁇ 1.0, 0 ⁇ y ⁇ 0.3, 0 ⁇ z ⁇ 0.25, 0 ⁇ 1-x-y-z ⁇ 0.3, ⁇ 0.2 ⁇ ⁇ ⁇ 0.2.
- a mixing step is performed by mixing lithium carbonate and a compound containing a metal element other than Li in formula (1) to obtain a mixture, And calcining the mixture to obtain a lithium composite compound represented by the formula (1), wherein the calcining step comprises subjecting the mixture to a heat treatment temperature of 200 ° C. or more and 400 ° C. or less for 0.5 hours.
- the lithium composite compound whose amount of lithium carbonate is 0.4 mass% or less and the water content is 500 ppm or less is enclosed in a storage container And an enclosing step.
- a lithium ion secondary battery is provided with the positive electrode containing the said positive electrode active material for lithium ion secondary batteries.
- a method of manufacturing a positive electrode active material for a lithium ion secondary battery and a coatability favorable positive electrode active material for a lithium ion secondary battery having high fracture strength of secondary particles constituting the powder, and a positive electrode active material for a lithium ion secondary battery, And a lithium ion secondary battery can be provided.
- the positive electrode active material has a layered structure of ⁇ -NaFeO 2 type as a crystal structure, and is made of a lithium composite oxide (lithium composite compound) that is configured to include lithium and a transition metal.
- the main phase of the positive electrode active material is a lithium composite compound having a layered structure.
- the positive electrode active material can contain lithium carbonate as an unavoidable impurity depending on the production conditions. Lithium carbonate can be present in the form of a heterophase or in the form of being attached to particles of the positive electrode active material.
- the positive electrode active material according to the present embodiment is a powder composed of particles of a lithium composite compound, and is represented by primary particles of the lithium composite compound represented by the following formula (1) and the following formula (1) And secondary particles in which primary particles of the lithium composite compound are aggregated.
- M 1 is at least one element selected from the group consisting of Mn and Al
- M 2 is selected from the group consisting of Mg, Ti, Zr, Mo and Nb
- At least one element, and a, x, y, z and ⁇ are such that ⁇ 0.1 ⁇ a ⁇ 0.2, 0.7 ⁇ x ⁇ 1.0, 0 ⁇ y ⁇ 0.3, 0 ⁇ z ⁇ 0.25, 0 ⁇ 1-x-y-z ⁇ 0.3, ⁇ 0.2 ⁇ ⁇ ⁇ 0.2.
- the positive electrode active material represented by the formula (1) has a high content of nickel, and thus can exhibit high charge / discharge capacity in the range up to around 4.3 V as compared to LiCoO 2 or the like.
- the content of nickel is high, the raw material cost is low compared to LiCoO 2 or the like, and the positive electrode active material is a raw material easily obtained.
- a in the above formula is ⁇ 0.1 or more and 0.2 or less.
- A may be ⁇ 0.02 or more and 0.05 or less. If a is ⁇ 0.02 or more, a sufficient amount of lithium can be secured to contribute to charge and discharge, so that the charge and discharge capacity of the positive electrode active material can be increased. In addition, if a is 0.05 or less, charge compensation due to the transition metal valence change is sufficiently performed, so that high charge and discharge capacity and good charge and discharge cycle characteristics can be compatible.
- the coefficient x of nickel is 0.7 or more and less than 1.0.
- x is 0.7 or more, sufficiently high charge and discharge capacities can be obtained as compared with the case of using other transition metals. Therefore, if x is in the above numerical range, a positive electrode active material exhibiting high charge and discharge capacity can be manufactured inexpensively compared to LiCoO 2 or the like.
- X is preferably 0.8 or more and 0.95 or less, and more preferably 0.85 or more and 0.95 or less. As x is greater than or equal to 0.8, higher charge / discharge capacity can be obtained. In addition, as x is 0.95 or less, the smaller the value is, the smaller the lattice distortion or the change in crystal structure due to the insertion and removal of lithium ions, and the mixing of cations and the reduction of crystallinity during mixing. As a result, it is possible to suppress the deterioration of the charge and discharge capacity and the charge and discharge cycle characteristics.
- the coefficient y of cobalt is 0 or more and less than 0.3.
- the crystal structure is stabilized, and effects such as suppression of cation mixing in which nickel is mixed in the lithium site can be obtained. Therefore, the charge and discharge cycle characteristics can be improved without largely impairing the charge and discharge capacity.
- the amount of cobalt is excessive, the raw material cost becomes high, and the manufacturing cost of the positive electrode active material is increased. If y is in the above-described numerical range, high charge and discharge capacity and good charge and discharge cycle characteristics can be achieved with good productivity.
- Y may be 0.01 or more and 0.2 or less, or may be 0.03 or more and 0.2 or less. As y is greater than or equal to 0.01, the effect of elemental substitution of cobalt is sufficiently obtained, and charge / discharge cycle characteristics are further improved. Moreover, if y is 0.2 or less, the cost of the raw material becomes lower, and the productivity of the positive electrode active material becomes better.
- the coefficient 1-xyz of M1 is greater than 0 and less than 0.3.
- the layered structure can be more stably maintained even if lithium is desorbed by charging.
- these elements (M1) are in excess, the proportion of other transition metals such as nickel decreases, and the charge / discharge capacity of the positive electrode active material decreases.
- 1-xyz is within the above numerical range, the crystal structure of the positive electrode active material is stably maintained, and good charge / discharge cycle characteristics, thermal stability, etc. can be obtained together with high charge / discharge capacity. it can.
- manganese, aluminum etc. are preferable as an element represented by M1. Such an element contributes to the stabilization of the crystal structure of the positive electrode material having a high nickel content. Among them, manganese is particularly preferred. When element substitution of manganese is performed, higher charge and discharge capacity can be obtained as compared with the case of element substitution of aluminum. Further, at the time of firing of the lithium composite compound, manganese also reacts with lithium carbonate as shown in the following formula (2). By such reaction, coarsening of crystal grains is suppressed, and an oxidation reaction of nickel can be advanced at high temperature, so that a positive electrode active material exhibiting high charge and discharge capacity can be efficiently obtained.
- M ' represents metallic elements, such as Ni, Co, Mn, etc.
- the coefficient 1-xyz of M1 is preferably 0.02 or more, and more preferably 0.04 or more. As the coefficient 1-xyz of M1 is larger, the effect of elemental substitution of manganese is sufficiently obtained. That is, the oxidation reaction of nickel can be promoted at a higher temperature, and a positive electrode active material exhibiting high charge and discharge capacity can be obtained more efficiently.
- the coefficient 1-xyz of M1 is preferably 0.18 or less. If the coefficient 1-xyz of M1 is 0.18 or less, the charge and discharge capacity can be kept high even if the element is substituted.
- the coefficient z of M2 is set to 0 or more and 0.25 or less.
- element (M2) selected from the group consisting of magnesium, titanium, zirconium, molybdenum and niobium is element-substituted, various performances such as charge and discharge cycle characteristics while maintaining the activity of the positive electrode active material Can be improved.
- these elements (M2) are in excess, the proportion of other transition metals such as nickel decreases, and the charge / discharge capacity of the positive electrode active material decreases. If z is in the above numerical range, it is possible to achieve both high charge and discharge capacity and good charge and discharge cycle characteristics and the like.
- ⁇ is set to ⁇ 0.2 or more and 0.2 or less.
- the ratio of the average particle diameter (D 1 ) of the primary particles of the lithium composite compound to the average particle diameter (D 2 ) of the secondary particles in which the primary particles of the lithium composite compound are aggregated (D 2 ) D 1 / D 2) is 0.006 or more and is 0.25 or less.
- the ratio (D 1 / D 2 ) is less than 0.006, the primary particles constituting the positive electrode active material are smaller than the secondary particles, and the primary particles are not in the state of particle growth. Therefore, the bonding between the primary particles is insufficient and the strength of the secondary particles is lowered.
- the specific surface area since the specific surface area is large, it easily reacts with carbon dioxide and the like in the atmosphere, and impurities such as lithium carbonate are easily generated on the surface of the particles.
- impurities such as lithium carbonate are formed on the surface of the primary particles, the fracture strength of the secondary particles tends to be low.
- the particle breaking strength is low, fine powder is easily generated at the time of application of the positive electrode mixture, and the fine powder sucks the binder, so that the distribution of the binder becomes nonuniform and particles of positive electrode active material and current collectors There is a risk that the adhesion of the
- the particle breaking strength when the particle breaking strength is low, there is a possibility that breakage or deformation may easily occur at the time of pressure molding or at the time of volume change due to charge and discharge.
- the ratio (D 1 / D 2 ) exceeds 0.25, the primary particles constituting the positive electrode active material are large compared to the secondary particles, and the number of particles constituting the secondary particles is too small. It is a state. Therefore, the diffusion distance of the ions in the particles becomes long, and the output characteristics of the lithium ion secondary battery may be deteriorated.
- the primary particles constituting the positive electrode active material are grown to an appropriate size.
- the number of particles that make up the secondary particles is also in an appropriate state. Therefore, while the intensity
- the average particle diameter (D 1 ) of the primary particles of the lithium composite compound is preferably 0.1 ⁇ m or more and 2.0 ⁇ m or less, and more preferably 0.2 ⁇ m or more and 1.0 ⁇ m or less .
- D 1 The average particle diameter of the primary particles of the lithium composite compound is preferably 0.1 ⁇ m or more and 2.0 ⁇ m or less, and more preferably 0.2 ⁇ m or more and 1.0 ⁇ m or less .
- the particle size of primary particles of the lithium composite compound can be measured based on observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Ten particles are extracted in order of particle diameter close to the median, and a weighted average of these particle diameters is calculated to obtain an average particle diameter.
- the particle size can be determined as the average value of the major axis diameter and the minor axis diameter of the particle in the observed electron microscope image.
- the particle diameter of the secondary particles of the lithium composite compound can be determined as a 50% particle diameter in a volume-based integrated particle diameter distribution by a laser diffraction / scattering type particle size distribution measuring device.
- the secondary particles of the lithium composite compound preferably have an aspect ratio of 0.6 or more and 1.0 or less.
- the aspect ratio is in this range, the breaking strength of the secondary particles is likely to be uniformly high, and breakage and deformation are less likely to occur during pressure molding or volume change associated with charge and discharge.
- the packing property of the particles of the lithium composite compound is improved, and the molding density of the positive electrode and the packing ratio of the positive electrode active material in the positive electrode become high. Therefore, higher charge and discharge capacity and good charge and discharge cycle characteristics can be obtained.
- arbitrary secondary particles are observed with an electron microscope to extract 10 particles in order of particle diameter close to the median value, and the major axis diameter and minor axis of these particles The diameter can be measured, and the value obtained by dividing the major axis diameter by the minor axis diameter can be determined by averaging over 10 samples.
- the BET specific surface area of the positive electrode active material is 0.1 m 2 / g or more, preferably 0.2 m 2 / g or more. Further, the BET specific surface area is 1.2 m 2 / g or less, preferably 1.0 m 2 / g or less. When the BET specific surface area is in this range, the molding density of the positive electrode and the filling rate of the positive electrode active material in the positive electrode become sufficiently high. In addition, since the BET specific surface area is not excessively large, the reaction with carbon dioxide and the like in the atmosphere is suppressed, the amount of impurities such as lithium carbonate mixed in the positive electrode active material is reduced, and the breaking strength of secondary particles is reduced. It becomes difficult to decrease.
- the adhesion between the particles of the positive electrode active material and the current collector can be kept high by the secondary particles and the binder uniformly distributed. .
- breakage or deformation is less likely to occur during pressure molding or during volume change due to charge and discharge.
- the binder is not absorbed excessively in the voids of the positive electrode active material itself, and the original function of the binder is less likely to be impaired. Therefore, the coating state of the positive electrode active material is improved, the stability against external force and volume change is also enhanced, and a lithium ion secondary battery exhibiting high charge and discharge capacity and good output characteristics can be obtained.
- the filling rate of the positive electrode active material in the positive electrode can be increased.
- the reaction with carbon dioxide and the like in the atmosphere can be reduced, the amount of lithium carbonate and the like can be reduced to make destruction and deformation less likely to occur during pressure molding or volume change associated with charge and discharge. be able to.
- the open pore volume ratio of the secondary particles is preferably 12% or less, and more preferably 10% or less. By setting it in such a range, the particle strength of the secondary particles can be secured, and the coatability can be improved while maintaining the discharge capacity high. Further, the open pore volume ratio may be 0%.
- the open pore volume ratio means the ratio of the total volume of open pores having a pore diameter of 0.1 ⁇ m or more and 0.5 ⁇ m or less, based on the apparent volume of the secondary particles.
- the open pore volume ratio can be calculated from the product of the open pore volume (per unit weight) measured using the mercury intrusion method and the apparent density of secondary particles.
- the amount of lithium carbonate is 0.4% by mass or less in terms of the elution amount which elutes when immersed in pure water.
- lithium carbonate is used as a raw material of the positive electrode active material
- lithium in the lithium composite compound may rereact with carbon dioxide released during calcination.
- an alkali compound is present in the raw material or an alkali compound is generated by the reaction of lithium and water
- lithium in the lithium complex compound may react with carbon dioxide in the air.
- the activity of the positive electrode active material is reduced, or the particle breaking strength is reduced.
- the elution amount of lithium carbonate is reduced to 0.4% by mass or less, the activity of the positive electrode active material becomes good, and the breaking strength of the secondary particles constituting the positive electrode active material has a normal purity. It is higher than the active material.
- the elution amount of lithium carbonate is preferably reduced to 0.3% by mass or less, more preferably 0.2% by mass or less, and still more preferably 0.1% by mass or less.
- the amount of lithium hydroxide contained as an impurity is preferably 0.7% by mass or less in terms of elution amount which is eluted when immersed in pure water.
- Lithium in the lithium composite compound may form lithium hydroxide by reaction with water contained in the raw material or water in the air. Lithium hydroxide lowers the activity of the positive electrode active material, or generates hydrofluoric acid in the electrolyte of the lithium ion secondary battery to deteriorate the charge / discharge cycle characteristics.
- the binder or the like such as PVDF may be altered to lower the coatability and adhesion of the positive electrode active material. However, if the elution amount of lithium hydroxide is sufficiently reduced, a positive electrode active material with good activity can be obtained, and the performance of the lithium ion secondary battery is less likely to deteriorate.
- the elution amount of lithium carbonate and the elution amount of lithium hydroxide can be determined by a method of neutralization titration of a solution in which the positive electrode active material is immersed. Specifically, the positive electrode active material is immersed in pure water so as to have a solid content ratio of 0.016% by mass, immersed for 60 minutes, stirred, and then subjected to neutralization titration of a solution obtained by filtration. The amount is quantified and converted to the weight of the impurity per weight of the positive electrode active material.
- the elution amount of lithium carbonate and the elution amount of lithium hydroxide can be reduced by adjusting the heat treatment temperature, heat treatment time, atmosphere, etc.
- the fired lithium composite compound when firing the lithium composite compound, and the process of washing the fired lithium composite compound with water .
- the elution amount of lithium carbonate and the elution amount of lithium hydroxide increase due to exposure to the air and the like, in the steps after firing, the fired lithium composite compound is subjected to an atmosphere with low carbon dioxide concentration and water concentration. It can be suppressed by handling.
- the water content of the positive electrode active material according to the present embodiment is preferably 500 ppm or less, more preferably 300 ppm or less, and further preferably 250 ppm or less immediately after the baking until the time of preparation of the lithium ion battery. preferable.
- the water content is 500 ppm or less, the slurry of the positive electrode mixture is less likely to gel at the time of preparation of the positive electrode, so that the deterioration of the coating property of the positive electrode mixture can be prevented.
- the reaction between lithium and water in the lithium composite compound and the reaction between the electrolytic solution and water are less likely to occur, the performance of the lithium ion secondary battery is less likely to deteriorate.
- the moisture content of the lithium composite compound should be lowered by adjusting the heat treatment temperature, heat treatment time, atmosphere, etc. when firing the lithium composite compound, appropriate management of the storage atmosphere after firing, and drying the lithium composite compound.
- the moisture content of the lithium composite compound can be measured by the Karl Fischer method.
- the breaking strength (particle breaking strength) of the secondary particles of the lithium composite compound is 30 MPa or more, preferably 40 MPa or more, more preferably 60 MPa or more, still more preferably 80 MPa or more, It is 200 MPa or less.
- particle breaking strength breakage or deformation is less likely to occur when pressure molding or volume change associated with charge and discharge. Therefore, high charge and discharge capacity and good output characteristics can be obtained.
- particles are less likely to be broken, when a positive electrode mixture containing a lithium composite compound is coated on the positive electrode current collector to form a positive electrode mixture layer, adhesion between particles of the positive electrode active material and the current collector The properties are easily maintained, and coating defects such as peeling are less likely to occur.
- the breaking strength of the secondary particles can be made higher than that of a normal purity positive electrode active material by reducing the amount of lithium carbonate. That is, regardless of whether or not the particles constituting the secondary particles are close to single particles, it is possible to obtain the effect of improving the resistance to external force.
- the particle breaking strength can be measured, for example, using a microcompression tester capable of measuring per particle.
- the crystal structure of the positive electrode active material can be confirmed by, for example, X-ray diffraction (XRD) or the like. Further, the composition of the positive electrode active material can be confirmed by high-frequency inductively coupled plasma (ICP) emission spectroscopy, atomic absorption spectrometry (AAS), or the like.
- ICP inductively coupled plasma
- the positive electrode active material can be produced, for example, according to a general method for producing a positive electrode active material such as a solid phase method, coprecipitation method, sol-gel method, hydrothermal method and the like.
- a solid phase method such as a solid phase method, coprecipitation method, sol-gel method, hydrothermal method and the like.
- combine the said positive electrode active material by a solid-phase method is demonstrated using lithium carbonate as a raw material.
- the above positive electrode active material in which the amount of lithium carbonate is reduced and the breaking strength of the secondary particles constituting the positive electrode active material is increased is the amount of lithium carbonate remaining in the lithium composite compound at the end of the calcination, Obtained by reducing the contact with carbon dioxide in the atmosphere in the subsequent steps of handling the lithium composite compound appropriately grown by appropriately reducing the temperature by adjusting the heat treatment temperature of the firing, the heat treatment time, the atmosphere, etc. Be At this time, when the calcined lithium composite compound is washed with water, the elution amount of lithium carbonate can be reduced together with the elution amount of lithium hydroxide.
- combined by the solid-phase method is washed with water after baking, dried, and the manufacturing method which obtains the positive electrode active material of the state preserve
- the fired lithium composite compound in the process from the end of firing to the sealing in a storage container, the fired lithium composite compound is handled in an atmosphere with a low carbon dioxide concentration, and lithium carbonate is produced by contact with carbon dioxide in the atmosphere. Prevent the increase.
- FIG. 1 is a flow chart showing an example of a method of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
- the method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment includes a mixing step S10, a baking step S20, a water washing step S30, a drying step S40, and a sealing step S50. ,have. Through these steps, the lithium composite compound represented by the formula (1) is synthesized, and the quality of the positive electrode active material is obtained in the state of being enclosed in a storage container. Note that steps other than these steps may be added or subtracted. For example, in the water washing step S30 and the drying step S40, the steps may be omitted when the residual amount at the end of the firing is small.
- lithium carbonate and a compound containing a metal element other than Li in the formula (1) are mixed. That is, lithium carbonate and a nickel compound containing nickel are mixed as a raw material of a positive electrode active material. Moreover, when the lithium complex compound represented by the said Formula (1) contains the element represented by cobalt, M1, and the element represented by M2, the compound containing these elements is added and mixed. .
- At least lithium carbonate is used as a raw material containing lithium in mixing process S10.
- Lithium carbonate is inexpensive as compared with lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, lithium sulfate and the like, and can be easily obtained.
- lithium carbonate is weakly alkaline, so that there is an advantage that damage to the manufacturing apparatus is reduced.
- since lithium carbonate has a relatively high melting point, it is possible to avoid the formation of a liquid phase and coarsening of crystal grains during synthesis by the solid phase method.
- nickel compounds such as nickel hydroxide, nickel carbonate, nickel oxide, nickel sulfate and nickel acetate can be used as the raw material containing nickel.
- nickel hydroxide, nickel carbonate or nickel oxide it is particularly preferable to use nickel hydroxide, nickel carbonate or nickel oxide as the nickel compound.
- a cobalt compound containing cobalt a metal compound containing an element represented by M1, or a metal compound containing an element represented by M2, nitrate, carbonate, sulfate, acetate, oxide, A hydroxide etc. can be used. Among these, it is particularly preferable to use a carbonate, an oxide or a hydroxide.
- raw materials such as lithium carbonate are respectively weighed, ground and mixed to obtain a powdery mixture.
- a grinder which grinds a raw material general precision grinders, such as a ball mill, a jet mill, a sand mill, can be used, for example.
- the grinding of the raw material may be either dry grinding or wet grinding.
- the raw material slurry obtained by wet pulverization can be dried using, for example, various dryers such as a spray dryer, a fluidized bed dryer, and an evaporator.
- the mixing step S10 it is preferable to grind the raw material such as lithium carbonate to an average particle size of 0.5 ⁇ m or less, more preferably to an average particle size of 0.2 ⁇ m or less.
- the raw material is pulverized to such a minute particle diameter, the reactivity between lithium carbonate and the nickel compound and the like is improved, and components such as carbon dioxide are easily separated from the raw material such as lithium carbonate.
- the degree of mixing of the pulverized material is increased, and the firing is easily progressed uniformly, and the average particle diameter of the primary particles of the lithium composite compound as the positive electrode active material can be easily controlled in an appropriate range.
- the mixing step S10 it is preferable to prepare a slurry by mixing by wet grinding, and granulate the obtained slurry by spray drying.
- Raw materials such as lithium carbonate are wet-ground and mixed in a medium such as water, and the obtained slurry is granulated by spray-drying, and after firing, the average particle diameter of secondary particles is controlled, and the aspect ratio Can be stably obtained.
- a spray drier various types such as a two-fluid nozzle type, a four-fluid nozzle type, and a disc type can be used.
- the average particle diameter of secondary particles to be granulated by spray drying is preferably 5 ⁇ m or more and 25 ⁇ m or less. Granulation to such a particle diameter makes it possible to easily bring the average particle diameter of the secondary particles of the lithium composite compound obtained after firing into the target range.
- the average particle diameter of the secondary particles to be granulated may be controlled by adjusting, for example, the concentration of the slurry, the viscosity of the slurry, the spray amount of the slurry, the degree of dispersion of the suspended matter, the spray temperature, the spray pressure, the air flow rate, etc. Can.
- the precursor (mixture) obtained through the mixing step S10 is fired to obtain the lithium composite compound represented by the formula (1).
- the precursor obtained through the mixing step S10 ie, the mixture subjected to appropriate processing such as spray granulation is fired under predetermined conditions to form a lithium composite compound having a layered structure. Be done.
- the average particle diameter of the primary particles of the lithium composite compound can be mainly controlled by the heat treatment temperature and the heat treatment time in the firing step S20.
- the firing step S20 may be performed by a single step of heat treatment in which the heat treatment temperature is controlled within a certain range, or may be performed by a plurality of steps of heat treatment in which the heat treatment temperatures are controlled in different ranges.
- the firing step S20 preferably includes a first heat treatment step S21, a second heat treatment step S22, and a third heat treatment step S23.
- the particle diameter of the lithium composite compound is grown to an appropriate range by adjusting the heat treatment temperature, heat treatment time, atmosphere, etc., and carbonic acid remaining in the lithium composite compound at the end of firing. Since the amount of lithium can be greatly reduced, the strength of the primary particles themselves and the breaking strength of the secondary particles can be increased.
- the mixture obtained in the mixing step S10 is heat-treated at a heat treatment temperature of 200 ° C. or more and 400 ° C. or less for 0.5 hours or more and 5 hours or less to form the first precursor obtain.
- the first heat treatment step S21 is performed mainly for the purpose of removing water and the like that interfere with the synthesis reaction of the lithium composite compound from the mixture obtained in the mixing step S10.
- the heat treatment temperature is 200 ° C. or higher, the combustion reaction of the impurities, the thermal decomposition of the raw material, and the like sufficiently proceed, so that the formation of inactive heterophases and the like in the subsequent heat treatment is suppressed be able to. Further, if the heat treatment temperature is 400 ° C. or less, crystals of the lithium complex compound are hardly formed in this step, so that a crystalline phase with low purity is formed in the presence of a gas containing water, impurities and the like. Can be prevented.
- the heat treatment temperature in the first heat treatment step S21 is preferably 250 ° C. or more and 400 ° C. or less, and more preferably 250 ° C. or more and 380 ° C. or less. If the heat treatment temperature is in this range, water, impurities and the like can be efficiently removed, while at the same time, formation of crystals of the lithium complex compound can be reliably prevented.
- the heat treatment time in the first heat treatment step S21 is, for example, an appropriate time depending on the heat treatment temperature, the amount of water and impurities contained in the mixture, the removal target of water and impurities and the degree of crystallization, etc. It can be done.
- the first heat treatment step S ⁇ b> 21 is preferably performed under a stream of atmosphere gas or under exhaust by a pump.
- the gas containing moisture, impurities, and the like can be efficiently removed.
- the flow rate of the gas flow of the atmosphere gas and the displacement per hour by the pump be larger than the volume of the gas generated from the mixture.
- the volume of the gas generated from the mixture can be determined based on, for example, the amount of use of the raw material, the molar ratio of the component to be gasified by combustion or thermal decomposition per raw material, and the like.
- the first heat treatment step S21 may be performed under an oxidizing gas atmosphere, may be performed under a non-oxidizing gas atmosphere, or may be performed under a reduced pressure atmosphere.
- the oxidizing gas atmosphere may be either an oxygen gas atmosphere or an air atmosphere.
- the reduced pressure atmosphere for example, a reduced pressure condition of an appropriate degree of vacuum, such as an atmospheric pressure or less, may be used.
- the first precursor obtained in the first heat treatment step S21 is heat treated at a heat treatment temperature of 450 ° C. or more and 800 ° C. or less for 0.5 hours or more and 50 hours or less
- the second precursor is obtained.
- the reaction is performed between lithium carbonate and a nickel compound or the like to remove the carbonic acid component and oxidize nickel from divalent to trivalent to form crystals of a lithium composite compound. Done as.
- the second heat treatment step S22 92% by mass or more of lithium carbonate charged as a raw material is preferably reacted, and more preferably 97% by mass or more. If the reaction of lithium carbonate is insufficient and the oxidation of nickel is insufficient, bivalent nickel may be easily substituted for lithium sites, and the charge / discharge capacity of the positive electrode active material may be reduced. In addition, when a large amount of lithium carbonate remains at the end of the second heat treatment step S22, carbon dioxide is released into the atmosphere of the third heat treatment step S23 to inhibit the reaction to form crystals, or the carbonate component is lithium It may be taken into the crystal of the complex compound, and the particle breaking strength and the charge and discharge capacity may be reduced. On the other hand, when the major part of lithium carbonate is reacted in the second heat treatment step S22, the lithium composite compound exhibiting high particle breaking strength and charge / discharge capacity can be fired in the third heat treatment step S23.
- the lithium carbonate may be melted in the third heat treatment step S23 to form a liquid phase.
- the lithium composite compound is fired in the liquid phase, crystal grains may be coarsened, and the output characteristics of the lithium ion secondary battery may be deteriorated.
- the crystal grains of the lithium composite compound become coarse even if the heat treatment temperature is raised. It becomes difficult to Therefore, it is possible to promote the oxidation of nickel at high temperature while securing the output characteristics of the lithium ion secondary battery, and to fire the lithium composite compound exhibiting high particle destruction strength and charge / discharge capacity.
- the heat treatment temperature is 450 ° C. or more, the formation of a layered structure proceeds by the reaction of lithium carbonate and a nickel compound or the like, so that unreacted lithium carbonate is prevented from remaining it can. Therefore, it is difficult for lithium carbonate to form a liquid phase in the subsequent heat treatment, and coarsening of crystal grains is suppressed, and a positive electrode active material exhibiting high particle breaking strength and charge / discharge capacity can be obtained.
- the heat treatment temperature is 800 ° C. or less, grain growth does not proceed excessively, so that the charge and discharge capacity of the positive electrode active material becomes high.
- the heat treatment temperature in the second heat treatment step S22 is preferably 550 ° C. or more, more preferably 600 ° C. or more, and still more preferably 650 ° C. or more.
- the higher the heat treatment temperature the more the reaction of lithium carbonate is promoted, and the remaining of lithium carbonate is more reliably prevented.
- the coefficient 1-xyz of manganese is more than 0 and less than 0.075, 600 ° C. It is preferable to set it as the above.
- the coefficient 1-xyz of manganese is 0.075 or more, the reaction temperature is lowered, and therefore, the temperature may be 550 ° C. or more.
- the heat treatment temperature in the second heat treatment step S22 is preferably 700 ° C. or less, more preferably 680 ° C. or less. Since the grain growth is more suppressed as the heat treatment temperature is thus lower, the charge and discharge capacity of the positive electrode active material becomes higher. In addition, since lithium carbonate is difficult to melt and liquid phase is difficult to form, coarsening of crystal grains can be suppressed more reliably.
- the heat treatment time in the second heat treatment step S22 is preferably 0.5 hours or more and 50 hours or less, and more preferably 2 hours or more and 15 hours or less.
- the heat treatment time is in this range, the reaction of lithium carbonate proceeds sufficiently, so that the carbonic acid component can be reliably removed.
- the time required for the heat treatment is shortened, and the productivity of the positive electrode active material is improved.
- the second heat treatment step S22 is preferably performed in an oxidizing atmosphere.
- the oxygen concentration of the atmosphere is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 100%.
- the concentration of carbon dioxide in the atmosphere is preferably 5% or less, more preferably 1% or less, and still more preferably 0.1% or less.
- nickel can be reliably oxidized, and carbon dioxide released into the atmosphere can be reliably excluded.
- the second heat treatment step S22 may be performed multiple times as the pre-baking step.
- the second precursor obtained in the second heat treatment step S22 is heat treated at a heat treatment temperature of 755 ° C. or more and 900 ° C. or less for 0.5 hours or more and 50 hours or less A lithium complex compound is obtained.
- the third heat treatment step S23 is mainly performed to sufficiently oxidize nickel in the second precursor from divalent to trivalent and to grow crystal grains of a lithium composite compound having a layered structure to an appropriate size. It is done as a goal.
- the heat treatment temperature is 755 ° C. or more
- nickel can be sufficiently oxidized to grow primary particles to a suitable particle size, so the degree of crystallinity is high, and the open pore volume ratio
- the lithium complex compound is fired. Therefore, the amount of residual lithium carbonate at the time of firing and the amount of mixing after firing decrease, and a positive electrode active material having high particle breaking strength and high charge-discharge capacity can be obtained.
- the heat treatment temperature is 900 ° C. or less, lithium is less likely to be volatilized and decomposition of the lithium composite compound having a layered structure is suppressed, so that the purity of crystals obtained after firing is lowered and the charge / discharge capacity is lowered. You can avoid that.
- the heat treatment temperature in the third heat treatment step S23 is preferably 800 ° C. or more, more preferably 840 ° C. or more, and still more preferably 850 ° C. or more.
- the heat treatment temperature in the third heat treatment step S23 is preferably 890 ° C. or less. Since the lower the heat treatment temperature, the more difficult it is for lithium to volatilize, it is possible to more reliably prevent the decomposition of the lithium composite compound having a layered structure and obtain a lithium composite compound exhibiting high charge and discharge capacity.
- the heat treatment time in the third heat treatment step S23 is preferably 0.5 hours or more and 15 hours or less. If the heat treatment time is in this range, the crystal grains of the lithium composite compound grow efficiently to an appropriate size, sufficiently oxidize nickel, and the purity of the crystal is high, and the particle breaking strength and charge / discharge capacity are high. The lithium complex compound shown can be obtained. In addition, the time required for the heat treatment is shortened, and the productivity of the positive electrode active material is improved.
- the third heat treatment step S23 is preferably performed in an oxidizing atmosphere.
- the oxygen concentration of the atmosphere is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 100%. Further, the concentration of carbon dioxide in the atmosphere is preferably 5% or less, more preferably 1% or less, and still more preferably 0.1% or less.
- the third heat treatment step S23 is preferably performed under a stream of oxidizing gas. When heat treatment is performed under a stream of oxidizing gas, nickel can be reliably oxidized, and carbon dioxide released into the atmosphere can be reliably excluded.
- the third heat treatment step S23 is preferably performed once as the main baking step, but may be performed plural times.
- a suitable heating device such as a rotary furnace such as a rotary kiln, a roller hearth kiln, a tunnel furnace, a continuous furnace such as a pusher furnace, or a batch furnace may be used as a heat treatment means.
- the first heat treatment step S21, the second heat treatment step S22, and the third heat treatment step S23 may be performed using the same heating device or may be performed using different heating devices.
- each heat treatment step may be performed intermittently by switching the atmosphere, or may be performed continuously when performing the heat treatment while exhausting the gas in the atmosphere.
- the primary particles of the lithium composite compound represented by the formula (1) and the primary particles of the lithium composite compound represented by the formula (1) are aggregated by passing through the mixing step S10 and the firing step S20 described above Secondary particles and the ratio (D 1 / D 2 ) of the average particle size (D 1 ) of the primary particles to the average particle size (D 2 ) of the secondary particles is 0.006 or more and 0.25 or less
- the lithium complex compound is obtained.
- the lithium composite compound may be classified as necessary so that the average particle size of the secondary particles is appropriate.
- the moisture content of the lithium composite compound after firing is preferably 500 ppm or less, more preferably 300 ppm or less, and still more preferably 250 ppm or less.
- the moisture content of the lithium composite compound after firing can be measured by the Karl Fischer method.
- the lithium composite compound having a controlled particle size ratio (D 1 / D 2 ) and a relatively large specific surface area can be obtained by the usual first heat treatment step S21, second heat treatment step S22, and third heat treatment step S23.
- impurities such as lithium carbonate and lithium hydroxide may be mixed by reaction with carbon dioxide and water in the atmosphere. Therefore, when reducing the amount of impurities further, it is preferable to use for water-washing process S30.
- the lithium composite compound obtained in the baking step S20 is washed with water.
- the washing with water of the lithium composite compound can be performed by an appropriate method such as a method of immersing the lithium composite compound in water, a method of passing water through the lithium composite compound, and the like.
- the water in which the lithium composite compound is immersed may be static water or may be stirred.
- pure water such as deionized water or distilled water, ultrapure water or the like can be used.
- the solid content ratio of the lithium complex compound to water to be immersed it is preferable to set the solid content ratio of the lithium complex compound to water to be immersed to 33% by mass or more and 77% by mass or less. If the solid content ratio is 33% by mass or more, the amount of lithium eluted from the lithium complex compound into water can be reduced. Therefore, a positive electrode active material having good charge / discharge capacity, output characteristics, and the like can be obtained. Further, if the solid content ratio is 77% by mass or less, the powder can be washed with water uniformly, so that the impurities can be reliably removed.
- the lithium composite compound immersed in water can be recovered by an appropriate solid-liquid separation operation.
- a method of solid-liquid separation for example, decompression filtration, pressure filtration, filter press, roller press, centrifugation and the like can be mentioned. It is preferable to set it as 20 mass% or less, and, as for the moisture content of the lithium complex compound which carried out solid-liquid separation from water, it is more preferable to set it as 10 mass% or less.
- the moisture content of the lithium complex compound after solid-liquid separation can be measured, for example, using an infrared moisture meter.
- the lithium composite compound washed in the water washing step S30 is dried.
- water which may react with components of the electrolytic solution to deteriorate the battery or to denature the binder to cause a coating failure may be removed.
- the surface of the lithium composite compound is reformed by passing through the water washing step S30 and the drying step S40, the effect of improving the compressibility as the powder of the positive electrode active material is obtained.
- a method of drying for example, drying under reduced pressure, drying under heating, drying under heating under reduced pressure, and the like can be used.
- the atmosphere in the drying step S40 is an inert gas atmosphere that does not contain carbon dioxide or a reduced pressure atmosphere with a high degree of vacuum. Such an atmosphere prevents lithium carbonate and lithium hydroxide from being mixed in by reaction with carbon dioxide and moisture in the atmosphere.
- 300 degrees C or less is preferable, and, as for the drying temperature in drying process S40, 80 degrees C or more and 300 degrees C or less are more preferable. If the drying temperature is 300 ° C. or less, the side reaction can be suppressed and the drying can be performed, so that the performance of the positive electrode active material can be prevented from being deteriorated. Further, if the drying temperature is 80 ° C. or more, the water can be sufficiently removed in a short time.
- the moisture content of the dried lithium composite compound is preferably 500 ppm or less, more preferably 300 ppm or less, and still more preferably 250 ppm or less.
- the moisture content of the lithium complex compound after drying can be measured by the Karl Fischer method.
- the drying step S40 it is preferable to perform two or more stages of drying processing in which the drying conditions are changed.
- the drying step S40 preferably includes a first drying step S41 and a second drying step S42.
- the lithium composite compound washed with water in the water washing step S30 is dried at a drying temperature of 80 ° C. or more and 100 ° C. or less.
- most of the water present on the particle surface of the lithium composite compound is removed mainly at the drying rate during the constant rate drying period.
- the drying temperature is 80 ° C. or more, a large amount of water can be removed in a short time. Moreover, if the drying temperature is 100 ° C. or less, it is possible to suppress the deterioration of the powder surface of the lithium composite compound that is easily generated at high temperatures.
- the drying time in the first drying step S41 is preferably 10 hours or more and 20 hours or less. If the drying time is in this range, most of the water present on the particle surface of the lithium composite compound can be removed even at a relatively low drying temperature at which the deterioration of the powder surface of the lithium composite compound is suppressed. it can.
- the lithium complex compound dried in the first drying step S41 is dried at a drying temperature of 190 ° C. or more and 300 ° C. or less.
- the water existing in the vicinity of the particle surface of the lithium composite compound is reduced while suppressing the side reaction that deteriorates the performance of the positive electrode active material, and the lithium composite compound dried to an appropriate moisture content is obtain.
- the drying temperature when the drying temperature is 190 ° C. or higher, the water permeating near the particle surface layer of the lithium composite compound can be sufficiently removed. Moreover, if the drying temperature is 300 ° C. or less, it is possible to suppress the side reaction which deteriorates the performance of the positive electrode active material and to dry it.
- the drying time in the second drying step S42 is preferably 10 hours or more and 20 hours or less. When the drying time is in this range, it is possible to suppress the side reaction that deteriorates the performance of the positive electrode active material and to dry the lithium composite compound to a sufficiently low moisture content.
- the lithium composite compound dried in the drying step S40 is sealed in a storage container.
- the lithium composite compound When exposed to the atmosphere, lithium composite compounds react with the carbon dioxide and moisture in the atmosphere and deteriorate. Therefore, the lithium composite compound is subjected to post treatments such as crushing and classification as necessary, and is then stored in a storage container until manufacture of the lithium ion secondary battery.
- the lithium composite compound sealed in the storage container has at least an amount of lithium carbonate of 0.4% by mass or less and a moisture content of 500 ppm or less from the viewpoint of securing the fracture strength and the coatability of the secondary particles. Is preferred.
- a storage container As a storage container, if it has low gas permeability and can prevent contact with carbon dioxide and moisture, packaging of an appropriate shape and material, such as aluminum can, steel can, container bag, laminate film bag, etc. A container can be used.
- the atmosphere inside the storage container can be an inert gas atmosphere free of carbon dioxide and moisture, or a reduced pressure atmosphere with a high degree of vacuum.
- the amount of lithium carbonate remaining in the lithium composite compound at the end of the calcination is reduced by adjusting the heat treatment temperature, heat treatment time, atmosphere and the like, and carbon dioxide and moisture in the atmosphere are reduced in the subsequent steps. Can be suppressed from mixing with impurities such as lithium carbonate and lithium hydroxide. That is, when the amount of lithium carbonate is reduced to 0.4% by mass or less at the end of the firing step S20, pure water can be obtained by appropriately performing the washing step S30, the drying step S40, and the sealing step S50. Since the amount of lithium carbonate which is eluted by being immersed in water can be maintained at 0.4% by mass or less, a positive electrode active material having high fracture strength of secondary particles can be used for manufacturing a lithium ion secondary battery it can.
- the elution amount of lithium carbonate, the elution amount of lithium hydroxide, and the water content of the positive electrode active material are obtained by titration of the positive electrode active material immediately after production or the positive electrode active material enclosed in a storage container in an inert gas atmosphere. Etc., and can be confirmed by subjecting to neutralization titration or coulometric titration.
- the opening of the storage container and the transfer to the sample container are preferably performed in a glove box into which an inert gas such as argon gas is introduced.
- an inert gas such as argon gas
- Lithium-ion rechargeable battery Next, a lithium ion secondary battery using the above-described positive electrode active material for a lithium ion secondary battery as a positive electrode will be described.
- FIG. 2 is a partial cross-sectional view schematically showing an example of a lithium ion secondary battery.
- a bottomed cylindrical battery can 101 for containing a non-aqueous electrolytic solution, and a wound electrode group contained in the battery can 101.
- a disk-shaped battery lid 102 for sealing the opening at the top of the battery can 101.
- the battery can 101 and the battery cover 102 are formed of, for example, a metal material such as stainless steel or aluminum.
- the positive electrode 111 includes a positive electrode current collector 111a and a positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a.
- the negative electrode 112 includes a negative electrode current collector 112 a and a negative electrode mixture layer 112 b formed on the surface of the negative electrode current collector 112 a.
- the positive electrode current collector 111a is formed of, for example, a metal foil such as aluminum or aluminum alloy, an expanded metal, a punching metal, or the like.
- the metal foil can have a thickness of, for example, about 15 ⁇ m or more and about 25 ⁇ m or less.
- the positive electrode mixture layer 111 b includes the above-described positive electrode active material for a lithium ion secondary battery.
- the positive electrode mixture layer 111 b is formed of, for example, a positive electrode mixture in which a positive electrode active material, a conductive material, a binder, and the like are mixed.
- the negative electrode current collector 112a is formed of metal foil such as copper, copper alloy, nickel, nickel alloy, expanded metal, punching metal or the like.
- the metal foil can have a thickness of, for example, about 7 ⁇ m or more and about 10 ⁇ m or less.
- the negative electrode mixture layer 112 b contains a negative electrode active material for a lithium ion secondary battery.
- the negative electrode mixture layer 112 b is formed of, for example, a negative electrode mixture in which a negative electrode active material, a conductive material, a binder, and the like are mixed.
- the negative electrode active material an appropriate type used in a general lithium ion secondary battery can be used.
- the negative electrode active material include those obtained by treating a graphitizable material obtained from natural graphite, petroleum coke, pitch coke or the like at a high temperature of 2500 ° C., mesophase carbon, amorphous carbon, non-crystalline on the surface of graphite Carbon materials, carbon materials whose surface crystallinity has been reduced by mechanical treatment of natural graphite or artificial graphite surfaces, materials in which organic matter such as polymers are coated / adsorbed on carbon surfaces, carbon fibers , Lithium metal, an alloy of lithium and aluminum, tin, silicon, indium, gallium, magnesium, etc., a material in which a metal is supported on the surface of silicon particles or carbon particles, oxides such as tin, silicon, lithium, titanium etc.
- the metal to be supported include lithium, aluminum, tin, indium, gallium, magnesium, alloys thereof, and the like.
- the conductive material an appropriate type used in a general lithium ion secondary battery can be used.
- the conductive material include carbon particles such as graphite, acetylene black, furnace black, thermal black and channel black, and carbon fibers such as pitch and polyacrylonitrile (PAN). These conductive materials may be used alone or in combination of two or more.
- the amount of the conductive material can be, for example, 3% by mass or more and 10% by mass or less with respect to the entire mixture.
- the binder an appropriate type used in a general lithium ion secondary battery can be used.
- the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, polyacrylonitrile, modified polyacrylonitrile and the like. These binders may be used alone or in combination of two or more. Further, a thickening agent such as carboxymethyl cellulose may be used in combination.
- the amount of the binder can be, for example, 2% by mass or more and 10% by mass or less with respect to the entire mixture.
- the positive electrode 111 and the negative electrode 112 can be manufactured, for example, according to a general method for manufacturing an electrode for a lithium ion secondary battery. For example, a mixture preparation step of preparing an electrode mixture by mixing an active material, a conductive material, a binder and the like in a solvent, and coating the prepared electrode mixture on a substrate such as a current collector Then, it can be manufactured through a mixture coating process of drying to form an electrode mixture layer, and a forming process of pressure molding the electrode mixture layer.
- a mixing means for mixing the materials for example, an appropriate mixing apparatus such as a planetary mixer, a disperser mixer, or a rotation / revolution mixer can be used.
- an appropriate mixing apparatus such as a planetary mixer, a disperser mixer, or a rotation / revolution mixer
- the solvent depending on the type of binder, for example, N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, glycerin , Dimethyl sulfoxide, tetrahydrofuran and the like can be used.
- an appropriate coating apparatus such as a bar coater, a doctor blade or a roll transfer machine can be used.
- an appropriate drying device such as a hot air heating device or a radiation heating device can be used.
- a suitable pressing device such as a roll press can be used as a means for pressing the electrode mixture layer.
- the positive electrode mixture layer 111b can have a thickness of, for example, about 100 ⁇ m or more and about 300 ⁇ m or less. Further, the thickness of the negative electrode mixture layer 112 b can be, for example, about 20 ⁇ m or more and about 150 ⁇ m or less.
- the pressure-formed electrode mixture layer can be cut together with the positive electrode current collector, if necessary, to form a lithium ion secondary battery electrode of a desired shape.
- the wound electrode group 110 is formed by winding a strip-shaped positive electrode 111 and a negative electrode 112 with the separator 113 interposed therebetween.
- the wound electrode group 110 is wound around an axis formed of, for example, polypropylene, polyphenylene sulfide or the like, and is accommodated inside the battery can 101.
- the separator 113 may be a microporous resin such as a polyolefin resin such as polyethylene, polypropylene or polyethylene-polypropylene copolymer, polyamide resin, or aramid resin, or heat resistance such as alumina particles on the surface of such a microporous film.
- a microporous resin such as a polyolefin resin such as polyethylene, polypropylene or polyethylene-polypropylene copolymer, polyamide resin, or aramid resin, or heat resistance such as alumina particles on the surface of such a microporous film.
- a film or the like coated with a substance can be used.
- the positive electrode current collector 111 a is electrically connected to the battery cover 102 through the positive electrode lead piece 103.
- the negative electrode current collector 112 a is electrically connected to the bottom of the battery can 101 via the negative electrode lead piece 104.
- an insulating plate 105 for preventing a short circuit is disposed between the wound electrode group 110 and the battery cover 102 and between the wound electrode group 110 and the bottom of the battery can 101.
- the positive electrode lead piece 103 and the negative electrode lead piece 104 are formed of the same materials as the positive electrode current collector 111a and the negative electrode current collector 112a, respectively, and spot welding and ultrasonic waves to the positive electrode current collector 111a and the negative electrode current collector 112a, respectively. It joins by pressure welding etc.
- the non-aqueous electrolytic solution is injected into the battery can 101.
- the non-aqueous electrolyte may be injected directly from the battery lid 102 in the open state, or may be injected from the inlet provided to the battery lid 102 in the closed state. It may be.
- the battery can 102 is sealed by fixing the battery cover 102 by caulking or the like.
- a sealing material 106 made of an insulating resin material is sandwiched between the battery can 101 and the battery lid 102, and the battery can 101 and the battery lid 102 are electrically insulated from each other.
- the non-aqueous electrolytic solution is configured to include an electrolyte and a non-aqueous solvent.
- electrolyte for example, various lithium salts such as LiPF 6 , LiBF 4 , LiClO 4 and the like can be used.
- non-aqueous solvents examples include linear carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, cyclic carbonates such as ethylene carbonate, propylene carbonate and vinylene carbonate, methyl acetate, ethyl methyl carbonate and methyl propyl carbonate It is possible to use chain carboxylic acid esters, cyclic carboxylic acid esters such as ⁇ -butyrolactone and ⁇ -valerolactone, and ethers.
- the concentration of the electrolyte can be, for example, 0.6 M or more and 1.8 M or less.
- Non-aqueous electrolytes should be added with various additives for the purpose of suppressing oxidative decomposition and reductive decomposition of the electrolytic solution, preventing deposition of metal elements, improving ion conductivity, improving flame retardancy, etc.
- additives include, for example, organophosphorus compounds such as trimethyl phosphate and trimethyl phosphite, organosulfur compounds such as 1,3-propane sultone and 1,4-butane sultone, polyadipic anhydride, hexahydro Examples thereof include carboxylic anhydrides such as phthalic anhydride, and boron compounds such as trimethyl borate and lithium bis oxalate borate.
- the lithium ion secondary battery 100 having the above configuration can store the power supplied from the outside in the wound electrode group 110 with the battery lid 102 as the positive electrode external terminal and the bottom of the battery can 101 as the negative electrode external terminal. .
- the power stored in the wound electrode group 110 can be supplied to an external device or the like.
- this lithium ion secondary battery 100 is made into a cylindrical form, the shape of a lithium secondary battery is not specifically limited, For example, it is appropriate shapes, such as square shape, a button shape, a lamination sheet shape, etc. May be
- the lithium ion secondary battery 100 is, for example, a small power source such as a portable electronic device or a household electrical device, a power storage device, an uninterruptible power source, a stationary power source such as a power leveling device, a ship, a railway vehicle, a hybrid It can be used for various applications such as drive power sources for railway vehicles, hybrid vehicles, electric vehicles and the like.
- Example 1 lithium carbonate, nickel hydroxide, cobalt carbonate and manganese carbonate were prepared as starting materials. Next, each raw material is weighed so that the atomic ratio of Li: Ni: Co: Mn is 1.04: 0.80: 0.10: 0.10, ground with a grinder, and wet mixed. The slurry was prepared (mixing step S10).
- the obtained slurry was dried by a spray drier, and the dried mixture was fired to obtain a fired powder of a lithium composite compound (firing step S20).
- 300 g of the mixture obtained by drying the slurry is filled in an alumina container of 300 mm in length, 300 mm in width, and 100 mm in height, and heat treated at 350 ° C. for 1 hour in the atmosphere by a continuous transfer furnace.
- a precursor was obtained (first heat treatment step S21).
- the first precursor was heat-treated at 650 ° C. for 4 hours in an oxygen stream in a baking furnace in which the first precursor was replaced with an atmosphere having an oxygen concentration of 99% or more to obtain a second precursor (second heat treatment step S22).
- the second precursor was heat-treated at 880 ° C. for 1 hour in an oxygen stream in a baking furnace in which the second precursor was replaced with an atmosphere having an oxygen concentration of 99% or more to obtain a lithium composite compound (third heat treatment step S23).
- the fired powder of the obtained lithium composite compound was classified to an opening of 53 ⁇ m or less to obtain a positive electrode active material of a sample.
- Example 2 A positive electrode active material was obtained in the same manner as in Example 1 except that the particle diameter of the positive electrode active material was changed, and the water washing step S30 and the drying step S40 were not performed.
- Example 3 A positive electrode active material was obtained in the same manner as Example 2, except that the heat treatment temperature in the third heat treatment step S23 was 825 ° C.
- Example 4 The raw material of the positive electrode active material is weighed so that the atomic ratio of Li: Ni: Co: Mn is 1.04: 0.80: 0.15: 0.05, and the particle diameter of the positive electrode active material is changed, A positive electrode active material was obtained in the same manner as in Example 1, except that 5 mL of pure water was poured into 10 g of the positive electrode active material in the water-washing step S30.
- Example 5 The positive electrode active material was obtained in the same manner as in Example 4 except that the heat treatment time of the third heat treatment step S23 was 3 hours, the particle diameter of the positive electrode active material was changed, and the water washing step S30 and the drying step S40 were not performed. .
- Example 6 A positive electrode active material was obtained in the same manner as in Example 4 except that the particle diameter of the positive electrode active material was changed.
- Example 7 A positive electrode active material was obtained in the same manner as in Example 4 except that the particle diameter of the positive electrode active material was changed, and the water washing step S30 and the drying step S40 were not performed.
- Example 8 The particle size of the positive electrode active material is changed, and 20 mL of pure water is poured into 40 g of the positive electrode active material in the water washing step S30, and dried at 80 ° C. for 14 hours in the drying step S40 and then dried at 190 ° C. for 14 hours A positive electrode active material was obtained in the same manner as in Example 4 except for the above.
- Example 9 A positive electrode active material was obtained in the same manner as in Example 8, except that the particle diameter of the positive electrode active material was changed.
- Example 10 A positive electrode active material was obtained in the same manner as in Example 8, except that the particle diameter of the positive electrode active material was changed.
- Example 11 The particle size of the positive electrode active material is changed, and after drying at 80 ° C. for 14 hours in the drying step S40, a positive electrode active material is obtained in the same manner as in Example 8 except that drying is performed at 240 ° C. for 14 hours.
- Example 12 A positive electrode active material was obtained in the same manner as in Example 11 except that the particle diameter of the positive electrode active material was changed.
- Example 13 A positive electrode active material was obtained in the same manner as in Example 7 except that the particle diameter of the positive electrode active material was changed.
- Example 14 Further, titanium oxide is used as a raw material of the positive electrode active material, and each raw material is prepared by atomic ratio of Li: Ni: Co: Mn: Ti: 1.02: 0.90: 0.03: 0.05: 0.02
- the positive electrode active material was obtained in the same manner as in Example 2 except that the heat treatment temperature in the third heat treatment step S23 was set to 860 ° C. and the particle diameter of the positive electrode active material was changed.
- Example 15 The positive electrode active material was obtained in the same manner as in Example 14 except that the heat treatment temperature in the third heat treatment step S23 was 850 ° C., the heat treatment time in the third heat treatment step S23 was 2 hours, and the particle diameter of the positive electrode active material was changed. .
- Comparative Example 1 The positive electrode active material was obtained in the same manner as Example 2, except that the heat treatment temperature in the third heat treatment step S23 was 750 ° C. and the particle diameter of the positive electrode active material was changed.
- the positive electrode active material was obtained in the same manner as in Example 2 except that the heat treatment temperature in the third heat treatment step S23 was 725 ° C. and the particle diameter of the positive electrode active material was changed.
- the average particle diameter (D 1 ) of primary particles constituting the positive electrode active material and the aspect ratio of secondary particles were measured by electron microscope observation.
- the electron microscope using a field emission scanning electron microscope “S-4700” (manufactured by Hitachi High-Technologies Corporation), the positive electrode active material is observed at an acceleration voltage of 5.0 kV and a magnification of 3000 times, and the particle size is median.
- Ten particles were extracted in order of closeness, and the minor axis diameter and major axis diameter of these primary particles and secondary particles were measured.
- the average particle diameter of the primary particles was determined as a biaxial average diameter from the minor axis diameter and the major axis diameter.
- the aspect ratio was determined by dividing the major axis diameter of the secondary particle by the minor axis diameter.
- the average particle size and aspect ratio of the primary particles were determined by averaging the number of samples of particles as 10. Further, the average particle diameter (D 2 ) of the secondary particles was determined by measuring 50% particle diameter in the volume-based integrated particle diameter distribution of the secondary particles using a laser diffraction / scattering type particle size distribution measuring device. .
- composition of positive electrode active material was analyzed using an ICP emission spectrophotometer "OPTIMA 8300" (manufactured by Perkin Elmer).
- the sample for analysis was prepared by dissolving the positive electrode active material in aqua regia.
- specific surface area of the positive electrode active material was determined by the BET method using an automatic specific surface area measuring device “BELCAT” (manufactured by Nippon Bell Co., Ltd.).
- BELCAT automatic specific surface area measuring device
- moisture content of the positive electrode active material after firing and after drying was measured using a Karl Fischer moisture measuring device “VA-100 / CA-100” (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
- the open pore volume ratio of the secondary particles constituting the positive electrode active material was measured using a porosimeter “Autopore type 9520” (manufactured by Shimadzu Corporation), using a mercury intrusion method. 0.5 g of the positive electrode active material was accommodated in the measurement cell, and the volume distribution of open pores was measured in a range corresponding to a pore diameter of 0.1 ⁇ m or more and 0.5 ⁇ m or less. Then, the open pore volume ratio was calculated from the product of the secondary particles and the apparent density.
- the amount of lithium carbonate eluted from the positive electrode active material was measured by neutralization titration using an automatic titrator "COM-1700A" (manufactured by Hiranuma Sangyo Co., Ltd.). First, 0.5 g of a positive electrode active material was dispersed in 30 mL of pure water bubbled with argon gas. Then, the dispersion was stirred for 60 minutes, then the filtrate was recovered by suction filtration, and the filtrate was titrated with hydrochloric acid.
- the titration curve has two steps, and the first equivalent point corresponds to the total amount of hydroxide ion of lithium hydroxide and carbonate ion of lithium carbonate, and from the first equivalent point to the second equivalent point It corresponds to the amount of bicarbonate ion generated from carbonate ion. Therefore, the amount (mass%) of lithium carbonate was calculated from the titration amount from the first equivalent point to the second equivalent point.
- the particle breaking strength of the secondary particles constituting the positive electrode active material was measured using a micro compression tester “MCT-510” (manufactured by Shimadzu Corporation). A small amount of positive electrode active material was dispersed on a pressure plate, an indenter was pushed into one particle with a test force of 49 mN and a loading rate of 0.4747 mN / sec, and a load at which secondary particles were crushed was determined as a breaking strength.
- the positive electrode and the lithium ion secondary battery were manufactured using the positive electrode active material, and the coatability of the positive electrode active material and the discharge capacity of the lithium ion secondary battery were evaluated.
- a positive electrode active material, a binder, and a conductive material were mixed to prepare a positive electrode mixture slurry.
- the prepared positive electrode mixture slurry is applied to a current collector made of aluminum foil with a thickness of 20 ⁇ m, dried at 120 ° C. to form a positive electrode mixture layer, and the electrode density is 2.6 g / cm 3 .
- the resultant was compression molded by a press and punched out into a disk shape having a diameter of 15 mm to produce a positive electrode.
- the coatability of the positive electrode active material was evaluated by visually observing the adhesion state between the positive electrode mixture layer and the current collector. Specifically, the case where peeling of the positive electrode mixture layer does not occur is evaluated as "o", the peeled region spreads over the entire positive electrode mixture layer, and the case where the contact area of the electrode can not be secured is "x". It was evaluated.
- the negative electrode was produced using metallic lithium as a negative electrode active material.
- the lithium ion secondary battery was produced using the produced positive electrode and negative electrode.
- a non-aqueous electrolytic solution a solution in which LiPF 6 was dissolved to a concentration of 1.0 mol / L in a solvent in which ethylene carbonate and dimethyl carbonate were mixed so that the volume ratio was 3: 7 was used.
- charging is performed with a charging current of 0.2 CA, a constant current and a constant voltage up to a charge termination voltage (4.3 V), and discharging with a discharging current of 0.2 CA.
- the discharge capacity was measured at a constant current until the discharge termination voltage (3.3 V or 2.5 V).
- Table 1 shows chemical compositions of positive electrode active materials according to Examples and Comparative Examples, average particle size (D 1 ) of primary particles, average particle size (D 2 ) of secondary particles, and average particle size (D 1 ) of primary particles. ) And the average particle diameter (D 2 ) of secondary particles (D 1 / D 2 ), calcination temperature and calcination time (heat treatment temperature and heat treatment time of the third heat treatment step S23), presence or absence of water washing / drying (water washing Use amount of powder of positive electrode active material and pure water in step S30, drying temperature and drying time in drying step S40, "-" is not performed), moisture ratio after baking and drying, aspect ratio of secondary particles The results of specific surface area, open pore volume ratio, lithium carbonate elution amount, particle breaking strength, coatability, and discharge capacity are shown.
- FIG. 3 is a view showing the relationship between the dissolution amount of lithium carbonate and the particle breaking strength in the positive electrode active material according to the example. As shown in FIG. 3, it can be seen that as the elution amount of lithium carbonate eluted by immersing the positive electrode active material in pure water decreases, the particle breaking strength of the secondary particles constituting the positive electrode active material increases. According to FIG. 3, it can be seen that a particle breaking strength of 30 MPa or more can be obtained when the elution amount of lithium carbonate is 0.4% by mass or less.
- the ratio (D 1 / D 2 ) of the average particle diameter (D 1 ) of the primary particles to the average particle diameter (D 2 ) of the secondary particles is 0.006 or more, and 0 In the range of .25 or less, particle dissolution strength of at least 30 MPa or more is obtained by reducing the elution amount of lithium carbonate.
- the particle breaking strength is higher in Example 1 in which water washing is performed than in Example 2 closer to a single particle as compared with Example 1, and the particles constituting the positive electrode active material are brought into a state close to a single particle.
- the resistance of the secondary particles to external force can be improved by reducing the amount of lithium carbonate dissolved.
- Examples 11 and 12 have the same particle size ratio (D 1 / D 2 ), specific surface area, and open pore volume ratio as the other examples, but the elution amount of lithium carbonate is small and the particle fracture strength is high. ing.
- FIG. 4 is a view showing the relationship between the specific surface area and the particle breaking strength of the positive electrode active material according to the example.
- the specific surface area of the positive electrode active material and the particle breaking strength show a correlation similar to that of the elution amount of lithium carbonate, and the smaller the specific surface area, the higher the particle breaking strength of the secondary particles. I understand that. However, it can be seen that the dispersion among the examples 1 to 15 is relatively large, and the particle breaking strength is not determined only by the size of the specific surface area.
- the specific surface area is 1.20 m 2 / g or less, and the elution amount of lithium carbonate is 0.4 mass% or less Examples 1 to 15 and the specific surface area exceed 1.2 m 2 / g, lithium carbonate elution In comparison with Comparative Examples 1 and 2 in which the amount exceeds 0.4% by mass, Examples 1 to 15 in which specific surface area is small to some extent, lithium carbonate elution amount is also reduced, and particle breaking strength is high, The coatability of the positive electrode active material is improved. By improving the particle breaking strength, it becomes difficult to form fine powder during coating of the positive electrode mixture, and the adhesion between the particles of the positive electrode active material and the current collector is improved, and the secondary particles are less likely to be broken during pressure molding. It is surmised that these points contributed to the
- Example 3 having a large specific surface area is inferior to Examples 1 and 2 in particle breaking strength, but the discharge capacity is increased. There is.
- Example 3 when the firing temperature is low to some extent and the specific surface area and the open pore volume ratio are large, the reaction area is expanded, and therefore, a high discharge capacity can be obtained.
- the particle breaking strength and the coatability can be further improved by reducing the elution amount of lithium carbonate by water washing or the like.
- FIG. 5 is a scanning electron micrograph of a positive electrode active material according to Example 3.
- FIG. 5 the result of observing the powder of the positive electrode active material which concerns on produced Example 3 using a scanning electron microscope at an acceleration voltage of 5.0 kV and 5000 magnifications is shown.
- reference numeral 1 denotes a primary particle of the lithium composite compound
- reference numeral 2 denotes a secondary particle of the lithium composite compound.
- the positive electrode active material in which the ratio (D 1 / D 2 ) of the average particle size (D 1 ) of the primary particles to the average particle size (D 2 ) of the secondary particles is relatively small is secondary Unlike conventional positive electrode active materials in which the particles constituting the particles are close to single particles, they are composed of a large number of fine particles. The particles in such a form tend to have specific surface area and open pore volume ratio with a certain size. However, if the elution amount of lithium carbonate is reduced to improve the breaking strength of the secondary particles, it is considered that the coating properties of the positive electrode active material can be improved to improve the performance of the lithium ion secondary battery.
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Abstract
Description
Li1+aNixCoyM11-x-y-zM2zO2+α ・・・(1)
(但し、前記式(1)中、M1は、Mn及びAlからなる群より選択される少なくとも1種の元素であり、M2は、Mg、Ti、Zr、Mo及びNbからなる群より選択される少なくとも1種の元素であり、a、x、y、z及びαは、-0.1≦a≦0.2、0.7≦x<1.0、0≦y<0.3、0≦z≦0.25、0<1-x-y-z<0.3、-0.2≦α≦0.2、を満たす数である。)
本実施形態に係る正極活物質は、結晶構造としてα-NaFeO2型の層状構造を有し、リチウムと遷移金属とを含んで組成されるリチウム複合酸化物(リチウム複合化合物)からなる。正極活物質の主相は、層状構造を有するリチウム複合化合物である。但し、正極活物質は、後記するように、製造条件に依存して、炭酸リチウムを不可避的不純物として含み得る。炭酸リチウムは、異相を形成した状態や、正極活物質の粒子に付着した状態で存在し得る。
Li1+aNixCoyM11-x-y-zM2zO2+α ・・・(1)
(但し、前記式(1)中、M1は、Mn及びAlからなる群より選択される少なくとも1種の元素であり、M2は、Mg、Ti、Zr、Mo及びNbからなる群より選択される少なくとも1種の元素であり、a、x、y、z及びαは、-0.1≦a≦0.2、0.7≦x<1.0、0≦y<0.3、0≦z≦0.25、0<1-x-y-z<0.3、-0.2≦α≦0.2、を満たす数である。)
(但し、前記式(2)中、M´は、Ni、Co、Mn等の金属元素を表す。)
次に、前記のリチウムイオン二次電池用正極活物質の製造方法について説明する。前記の正極活物質は、例えば、固相法、共沈法、ゾルゲル法、水熱法等の一般的な正極活物質の製造方法に準じて製造することができる。以下においては、前記の正極活物質を炭酸リチウムを原料として用いて固相法で合成する方法を説明する。
図1に示すように、本実施形態に係るリチウムイオン二次電池用正極活物質の製造方法は、混合工程S10と、焼成工程S20と、水洗工程S30と、乾燥工程S40と、封入工程S50と、を有している。これらの工程を経ることにより、前記式(1)で表されるリチウム複合化合物が合成され、品質を保持した正極活物質が保存用容器に封入された状態で得られる。なお、これらの工程以外の工程が加わっても良いし、減じられても良い。例えば、水洗工程S30及び乾燥工程S40は、焼成の終了時における残留量が少ない場合等には、工程が省略されてもよい。
次に、前記のリチウムイオン二次電池用正極活物質を正極に用いたリチウムイオン二次電池について説明する。
図2に示すように、本実施形態に係るリチウムイオン二次電池100は、非水電解液を収容する有底円筒状の電池缶101と、電池缶101の内部に収容された捲回電極群110と、電池缶101の上部の開口を封止する円板状の電池蓋102と、を備えている。
はじめに、出発原料として、炭酸リチウム、水酸化ニッケル、炭酸コバルト及び炭酸マンガンを用意した。次に、各原料を、原子比でLi:Ni:Co:Mnが、1.04:0.80:0.10:0.10となるように秤量し、粉砕機で粉砕すると共に湿式混合してスラリーを調製した(混合工程S10)。
正極活物質の粒径を変え、水洗工程S30及び乾燥工程S40を行わなかったこと以外は、実施例1と同様にして正極活物質を得た。
第3熱処理工程S23の熱処理温度を825℃とした以外は、実施例2と同様にして正極活物質を得た。
正極活物質の原料を、原子比でLi:Ni:Co:Mnが、1.04:0.80:0.15:0.05となるように秤量し、正極活物質の粒径を変え、水洗工程S30を正極活物質10gに純水5mLを注いで行ったこと以外は、実施例1と同様にして正極活物質を得た。
第3熱処理工程S23の熱処理時間を3時間とし、正極活物質の粒径を変え、水洗工程S30及び乾燥工程S40を行わなかったこと以外は、実施例4と同様にして正極活物質を得た。
正極活物質の粒径を変えたこと以外は、実施例4と同様にして正極活物質を得た。
正極活物質の粒径を変え、水洗工程S30及び乾燥工程S40を行わなかったこと以外は、実施例4と同様にして正極活物質を得た。
正極活物質の粒径を変え、水洗工程S30を正極活物質40gに純水20mLを注いで行い、乾燥工程S40で、80℃で14時間にわたって乾燥させた後、190℃で14時間にわたって乾燥させたこと以外は、実施例4と同様にして正極活物質を得た。
正極活物質の粒径を変えたこと以外は、実施例8と同様にして正極活物質を得た。
正極活物質の粒径を変えたこと以外は、実施例8と同様にして正極活物質を得た。
正極活物質の粒径を変え、乾燥工程S40で、80℃で14時間にわたって乾燥させた後、240℃で14時間にわたって乾燥させたこと以外は、実施例8と同様にして正極活物質を得た。
正極活物質の粒径を変えたこと以外は、実施例11と同様にして正極活物質を得た。
正極活物質の粒径を変えたこと以外は、実施例7と同様にして正極活物質を得た。
正極活物質の原料としてさらに酸化チタンを用い、各原料を、原子比でLi:Ni:Co:Mn:Tiが、1.02:0.90:0.03:0.05:0.02となるように秤量し、第3熱処理工程S23の熱処理温度を860℃とし、正極活物質の粒径を変えた以外は、実施例2と同様にして正極活物質を得た。
第3熱処理工程S23の熱処理温度を850℃、第3熱処理工程S23の熱処理時間を2時間とし、正極活物質の粒径を変えた以外は、実施例14と同様にして正極活物質を得た。
第3熱処理工程S23の熱処理温度を750℃とし、正極活物質の粒径を変えた以外は、実施例2と同様にして正極活物質を得た。
第3熱処理工程S23の熱処理温度を725℃とし、正極活物質の粒径を変えた以外は、実施例2と同様にして正極活物質を得た。
正極活物質を構成する一次粒子の平均粒径(D1)と、二次粒子のアスペクト比は、電子顕微鏡観察によって測定した。電子顕微鏡としては、電界放出形走査電子顕微鏡「S-4700」(日立ハイテクノロジーズ社製)を使用し、正極活物質を加速電圧5.0kV、倍率3000倍で観察し、粒子径が中央値に近い順に10個の粒子を抽出し、これらの一次粒子及び二次粒子の短軸径と長軸径を測定した。一次粒子の平均粒径は、短軸径と長軸径から二軸平均径として求めた。また、アスペクト比は、二次粒子の長軸径を短軸径で除算して求めた。一次粒子の平均粒径及びアスペクト比は、粒子の試料数を10として平均することにより求めた。また、二次粒子の平均粒径(D2)は、レーザー回折/散乱式粒度分布測定装置を使用し、二次粒子の体積基準の積算粒子径分布における50%粒子径を測定して求めた。
正極活物質の組成を、ICP発光分光分析装置「OPTIMA8300」(パーキンエルマー社製)を使用して分析した。なお、分析用の試料は、正極活物質を王水に溶解させて調製した。また、正極活物質の比表面積を、自動比表面積測定装置「BELCAT」(日本ベル社製)を使用してBET法により求めた。また、正極活物質の焼成後と乾燥後の水分率を、カールフィッシャー水分測定装置「VA-100/CA-100」(三菱化学アナリテック社製)を用いて測定した。
正極活物質を構成する二次粒子の開気孔容積率は、ポロシメータ「オートポア 9520形」(島津製作所社製)を使用し、水銀圧入法を用いて測定した。測定用セルに正極活物質0.5gを収容し、細孔径が0.1μm以上、且つ、0.5μm以下に対応する範囲で開気孔の容積分布を測定した。そして、二次粒子のみかけの密度との積から開気孔容積率を算出した。
正極活物質から溶出する炭酸リチウムの量を自動滴定装置「COM-1700A」(平沼産業社製)を用いて中和滴定によって測定した。はじめに、アルゴンガスでバブリングした30mLの純水中に0.5gの正極活物質を分散させた。そして、分散液を60分間にわたって攪拌した後、吸引濾過により濾液を回収し、その濾液を塩酸で滴定した。滴定曲線は2段階となり、第一等量点までが水酸化リチウムの水酸化物イオンと炭酸リチウムの炭酸イオンの合計量に対応しており、第一等量点から第二等量点までが炭酸イオンから生成した炭酸水素イオンの量に対応している。そのため、第一等量点から第二等量点までの滴定量から炭酸リチウムの量(質量%)を算出した。
正極活物質を構成する二次粒子の粒子破壊強度は、微小圧縮試験機「MCT-510」(島津製作所社製)を使用して測定した。加圧板上に微少量の正極活物質を散布し、試験力49mN、負荷速度0.4747mN/秒で圧子を一粒子に押し込み、二次粒子が圧壊するときの荷重を破壊強度として求めた。
正極活物質を用いて正極及びリチウムイオン二次電池を作製し、正極活物質の塗工性とリチウムイオン二次電池の放電容量を評価した。はじめに、正極活物質と、結着剤と、導電材とを混合し、正極合剤スラリーを調製した。そして、調製した正極合剤スラリーを、厚さ20μmのアルミ箔からなる集電体に塗布し、120℃で乾燥させて正極合剤層を形成した後、電極密度が2.6g/cm3となるようにプレスで圧縮成形し、直径15mmの円盤状に打ち抜いて正極を作製した。ここで、正極活物質の塗工性を、正極合剤層と集電体との密着状態を目視して評価した。具体的には、正極合剤層の剥離が生じない場合を「○」の評価、正極合剤層の全体に剥離した領域が広がっており、電極の接触面積を確保できない場合を「×」の評価とした。
図3に示すように、正極活物質を純水中に浸漬させて溶出する炭酸リチウムの溶出量が低減するほど、正極活物質を構成する二次粒子の粒子破壊強度が高くなることが分かる。図3によれば、炭酸リチウムの溶出量が0.4質量%以下で30MPa以上の粒子破壊強度が得られることが見て取れる。
図4に示すように、正極活物質の比表面積と粒子破壊強度とは、炭酸リチウムの溶出量の場合と類似した相関を示し、比表面積が小さくなるほど、二次粒子の粒子破壊強度が高くなることが分かる。但し、実施例1~15同士のばらつきは比較的大きく、比表面積の大きさのみで、粒子破壊強度が決まるわけではないことが分かる。比表面積が1.20m2/g以下であり、炭酸リチウムの溶出量が0.4質量%以下である実施例1~15と、比表面積が1.2m2/gを超え、炭酸リチウムの溶出量が0.4質量%を超える比較例1~2とを比較すると、比表面積がある程度小さく、炭酸リチウムの溶出量も低減されており、且つ、粒子破壊強度が高い実施例1~15では、正極活物質の塗工性が改善している。粒子破壊強度の向上によって、正極合剤の塗布時に微粉を生じ難くなり、正極活物質の粒子同士や集電体との密着性が向上した点、加圧成形時に二次粒子が破壊され難くなった点等が寄与したものと推察される。
図5には、作製した実施例3に係る正極活物質の粉末を、走査型電子顕微鏡を使用して、加速電圧5.0kV、倍率5000倍で観察した結果を示す。図5において、符号1は、リチウム複合化合物の一次粒子、符号2は、リチウム複合化合物の二次粒子を示す。
101 電池缶
102 電池蓋
103 正極リード片
104 負極リード片
105 絶縁板
106 シール材
110 捲回電極群
111 正極
111a 正極集電体
111b 正極合剤層
112 負極
112a 負極集電体
112b 負極合剤層
113 セパレータ
Claims (7)
- 下記式(1)で表されるリチウム複合化合物の一次粒子と、前記リチウム複合化合物の一次粒子が凝集した二次粒子とを含み、
前記一次粒子の平均粒径(D1)と前記二次粒子の平均粒径(D2)との比(D1/D2)が0.006以上、且つ、0.25以下であり、
炭酸リチウムの量が0.4質量%以下であり、
前記二次粒子の破壊強度が30MPa以上であるリチウムイオン二次電池用正極活物質。
Li1+aNixCoyM11-x-y-zM2zO2+α ・・・(1)
(但し、前記式(1)中、M1は、Mn及びAlからなる群より選択される少なくとも1種の元素であり、M2は、Mg、Ti、Zr、Mo及びNbからなる群より選択される少なくとも1種の元素であり、a、x、y、z及びαは、-0.1≦a≦0.2、0.7≦x<1.0、0≦y<0.3、0≦z≦0.25、0<1-x-y-z<0.3、-0.2≦α≦0.2、を満たす数である。) - 炭酸リチウムの量が0.3質量%以下であり、前記二次粒子の破壊強度が40MPa以上である請求項1に記載のリチウムイオン二次電池用正極活物質。
- 比表面積が0.1m2/g以上、且つ、1.2m2/g以下である請求項1又は請求項2に記載のリチウムイオン二次電池用正極活物質。
- 前記二次粒子のアスペクト比が0.6以上、且つ、1.0以下であり、
前記二次粒子は、水銀圧入法により求められる細孔径0.1μm以上、且つ、0.5μm以下の範囲内の開気孔容積率が20%以下である請求項1から請求項3のいずれか一項に記載のリチウムイオン二次電池用正極活物質。 - リチウムイオン二次電池用正極活物質の製造方法であって、
炭酸リチウムと下記式(1)中のLi以外の金属元素をそれぞれ含む化合物とを混合して混合物を得る混合工程と、
前記混合物を焼成して下記式(1)で表されるリチウム複合化合物を得る焼成工程と、を有し、
前記焼成工程は、
前記混合物を200℃以上かつ400℃以下の熱処理温度で0.5時間以上かつ5時間以下に亘って熱処理して第1前駆体を得る第1熱処理工程と、
前記第1前駆体を450℃以上かつ800℃以下の熱処理温度で0.5時間以上かつ50時間以下に亘って酸化性雰囲気下で熱処理して第2前駆体を得る第2熱処理工程と、
前記第2前駆体を755℃以上かつ900℃以下の熱処理温度で0.5時間以上かつ50時間以下に亘って酸化性雰囲気下で熱処理して前記リチウム複合化合物を得る第3熱処理工程と、
前記焼成工程後に、炭酸リチウムの量が0.4質量%以下、且つ、水分率を500ppm以下としたリチウム複合化合物を保存用容器に封入する封入工程と、
を有するリチウムイオン二次電池用正極活物質の製造方法。
Li1+aNixCoyM11-x-y-zM2zO2+α ・・・(1)
(但し、前記式(1)中、M1は、Mn及びAlからなる群より選択される少なくとも1種の元素であり、M2は、Mg、Ti、Zr、Mo及びNbからなる群より選択される少なくとも1種の元素であり、a、x、y、z及びαは、-0.1≦a≦0.2、0.7≦x<1.0、0≦y<0.3、0≦z≦0.25、0<1-x-y-z<0.3、-0.2≦α≦0.2、を満たす数である。) - 前記焼成工程後に、前記リチウム複合化合物を水洗する水洗工程と、水洗された前記リチウム複合化合物を乾燥する乾燥工程とを、さらに有し、
前記乾燥工程後に、炭酸リチウムの量が0.4質量%以下、且つ、水分率を500ppm以下としたリチウム複合化合物を前記保存用容器に封入する請求項5に記載のリチウムイオン二次電池用正極活物質の製造方法。 - 請求項1から請求項4のいずれか一項に記載のリチウムイオン二次電池用正極活物質を含有する正極を備えるリチウムイオン二次電池。
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JP7166452B2 (ja) | 2018-11-23 | 2022-11-07 | リサーチ インスティチュート オブ インダストリアル サイエンス アンド テクノロジー | リチウム二次電池用正極活物質、その製造方法、および前記正極活物質を含むリチウム二次電池 |
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JP2021095305A (ja) * | 2019-12-17 | 2021-06-24 | 住友化学株式会社 | リチウム金属複合酸化物粉末、リチウム二次電池用正極活物質、リチウム二次電池用正極及びリチウム二次電池 |
WO2021153350A1 (ja) * | 2020-01-31 | 2021-08-05 | 三洋電機株式会社 | 非水電解質二次電池用正極活物質、及び非水電解質二次電池 |
CN115004415A (zh) * | 2020-01-31 | 2022-09-02 | 三洋电机株式会社 | 非水电解质二次电池用正极活性物质和非水电解质二次电池 |
Also Published As
Publication number | Publication date |
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US20200251733A1 (en) | 2020-08-06 |
US11677075B2 (en) | 2023-06-13 |
KR20200023468A (ko) | 2020-03-04 |
KR20210156876A (ko) | 2021-12-27 |
KR102354265B1 (ko) | 2022-01-21 |
EP3734718A1 (en) | 2020-11-04 |
CN111052463B (zh) | 2022-02-08 |
EP3734718B1 (en) | 2023-05-31 |
CN111052463A (zh) | 2020-04-21 |
EP3734718A4 (en) | 2021-09-29 |
JPWO2019131779A1 (ja) | 2019-12-26 |
JP6587044B1 (ja) | 2019-10-09 |
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