KR102389410B1 - Positive electrode active material powder for lithium secondary battery, preparing method of the same, positive electrode including the same - Google Patents

Abstract

The present invention relates to a positive active material powder comprising a plurality of positive active material particles of secondary particles formed by aggregation of primary particles, wherein the positive active material having a hollow inside the secondary particles with respect to the total number of positive active material particles is 40% to 80%, the positive electrode active material powder, a method for producing the positive electrode active material powder, and relates to a secondary battery positive electrode comprising the positive electrode active material powder.

Description

Positive electrode active material powder for lithium secondary battery, manufacturing method thereof, and positive electrode for lithium secondary battery comprising same

The present invention relates to a cathode active material powder for a lithium secondary battery, a method for producing the cathode active material powder, and a cathode for a lithium secondary battery comprising the cathode active material.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

A lithium transition metal composite oxide is used as a cathode active material for a lithium secondary battery, and among them, a lithium cobalt composite metal oxide such as LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO ₂ has very poor thermal properties due to the destabilization of the crystal structure due to delithiation. In addition, since the LiCoO ₂ is expensive, there is a limit to its mass use as a power source in fields such as electric vehicles.

Recently, research for using a lithium transition metal composite oxide as a power source for a large-capacity battery such as an electric vehicle is being actively conducted. For this, the realization of a high-density electrode is required.

However, when a lithium transition metal oxide is rolled to a high electrode density in order to realize a high-density electrode, cracks in the particles according to the volume change during charging and discharging are generated due to particle breakage, and thus the stability of the battery to which it is applied is reduced. There was a problem with lowering.

Therefore, there is a need to develop a positive electrode active material capable of improving the output performance of a high-density electrode while maintaining the stability of the electrode by improving the particle shape of the lithium transition metal oxide.

Republic of Korea Patent Publication No. 2016-0138048

In order to solve the above problems, a first technical object of the present invention is to provide a cathode active material powder including a cathode active material having a hollow inside the secondary particles.

A second technical object of the present invention is to provide a method for manufacturing the positive electrode active material powder.

A third technical object of the present invention is to provide a positive electrode comprising a positive electrode active material powder.

The present invention relates to a positive active material powder comprising a plurality of positive active material particles of secondary particles formed by aggregation of primary particles, wherein the positive active material having a hollow inside the secondary particles with respect to the total number of positive active material particles is 40% to It provides a positive electrode active material powder, which is 80%.

In addition, the present invention comprises the steps of preparing a transition metal-containing solution; forming positive electrode active material precursor particles by adding the transition metal-containing solution, an ammonium cation complex forming agent, and an anion-containing basic compound to a first co-precipitation reaction at pH 12 to pH 14; growing the cathode active material precursor particles by performing a second co-precipitation reaction while maintaining the pH at less than 10 for 5 to 24 hours; and 40% to 80% of the positive active material having a hollow inside the secondary particles with respect to the total number of positive active material particles in the form of secondary particles formed by aggregation of primary particles by mixing and firing the positive electrode active material precursor and lithium source %, it provides a method for producing a positive electrode active material powder comprising the step of obtaining a positive electrode active material powder.

In addition, the positive electrode current collector; A positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material powder according to the present invention; in the positive electrode comprising, the positive electrode has an electrode density of 1 g/cc to 10 g/cc, the positive electrode provides

According to the present invention, the cathode active material powder contains the cathode active material particles having a hollow part inside the secondary particles and the cathode active material particles having no hollow part inside the secondary particles in an appropriate ratio, so as to manufacture a high-density electrode. When rolling in the process, the positive active material particles that do not have a hollow inside the secondary particles increase the BET specific surface area as the particles break, and as the area reacting with the electrolyte increases, the capacity and output will be improved when applied to the battery can In addition, the particles having a hollow part inside the secondary particles are maintained without breaking the particles, and thus, even if a volume change is accompanied during charging and discharging, the occurrence of internal cracks in the particles according to the charging/discharging cycle is small, and lifespan and resistance characteristics There is an improvement effect.

1a and 1b are a cross-sectional SEM photograph at a high magnification of the cathode active material powder prepared in Example 1 and a cross-sectional SEM photograph of the cathode active material powder prepared in Example 1 at a low magnification, respectively.
2A and 2B are a cross-sectional SEM photograph at a high magnification of the cathode active material powder prepared in Example 2 and a cross-sectional SEM photograph of the cathode active material powder prepared in Example 2 at a low magnification, respectively.
3A and 3B are a cross-sectional SEM photograph at a high magnification of the cathode active material powder prepared in Comparative Example 2 and a cross-sectional SEM photograph of the cathode active material powder prepared in Comparative Example 2 at a low magnification, respectively.
4A and 4B are a cross-sectional SEM photograph at a high magnification of the cathode active material powder prepared in Comparative Example 3 and a cross-sectional SEM photograph of the cathode active material powder prepared in Comparative Example 3 at a low magnification, respectively.
5 is a cross-sectional SEM photograph of a cathode active material particle having a hollow inside the secondary particle after the charge/discharge cycle of the lithium secondary battery prepared in Example 1. FIG.
6 is a cross-sectional SEM photograph of the cathode active material particles having no hollow inside the secondary particles after the charge/discharge cycle of the lithium secondary battery prepared in Example 1. Referring to FIG.
7 is a graph showing the room temperature output characteristics of the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2;
8 is a graph showing low-temperature output characteristics of lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 1-2.
9 is a graph showing the amount of gas generated in the lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 2-3.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

cathode active material

Lithium cobalt-based oxide is widely used as a cathode active material for a conventional secondary battery, but cobalt (Co) is very expensive and has an unstable supply, so there is a limit to mass use as a power source in fields such as electric vehicles. Accordingly, a nickel-cobalt-manganese-based lithium composite metal oxide having a lower cobalt (Co) ratio and an increased nickel (Ni) or manganese (Mn) ratio is used, but as the cobalt (Co) content is reduced, the output characteristics are reduced. there was

Accordingly, the present inventors improved the shape of the nickel-cobalt-manganese-based lithium composite metal oxide, and in part, the BET specific surface area was improved due to particle breakage during rolling during the positive electrode manufacturing process, thereby greatly improving the reaction area with the electrolyte, resulting in high output characteristics and The present invention was completed by discovering that a positive active material having improved stability by preventing cracks in the active material because some particles do not break during rolling and having charge/discharge characteristics.

First, a cathode active material according to the present invention will be described.

The positive electrode active material powder according to the present invention is a positive electrode active material powder comprising a plurality of positive electrode active material particles of secondary particles formed by agglomeration of primary particles, a positive electrode having a hollow inside the secondary particles with respect to the total number of positive electrode active material particles The active material is 40% to 80%.

In the present invention, 'primary particles' means a primary structure of a single particle, and 'secondary particles' are physical between primary particles without intentional aggregation or assembly process for primary particles constituting secondary particles. Alternatively, it refers to an aggregate in which primary particles are aggregated by chemical bonding, that is, a secondary structure.

Since the positive active material is formed in the form of secondary particles in which primary particles are aggregated, the contact area between the positive active material and the electrolyte is large, and the movement distance of lithium ions in the positive active material is short, thereby exhibiting high capacity and high output characteristics. In addition, it is possible to realize a high rolling density while having a high specific surface area, thereby increasing the energy density per unit area of the electrode.

The average particle diameter (D ₅₀ ) of the cathode active material powder may be 2 μm to 13 μm, more preferably 3 μm to 11 μm. When the average particle diameter (D ₅₀ ) of the cathode active material powder satisfies the above range, it may be effective to improve capacity and output characteristics.

In the present specification, the average particle diameter (D ₅₀ ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain high reproducibility and high resolution results.

For example, in the method of measuring the average particle diameter (D ₅₀ ) of the cathode active material powder, the cathode active material powder is introduced into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000) to output an ultrasonic wave of about 28 kHz After irradiating at 60 W, the average particle diameter (D ₅₀ ) in the 50% standard of the particle size distribution volume accumulation amount in the measuring device can be calculated.

The cathode active material powder may include a plurality of lithium transition metal oxide particles represented by Formula 1 below.

[Formula 1]

Li _1+a Ni _1-xy Co _x M ¹ _y M ² _z O ₂

In Formula 1, 0≤a≤0.5, 0.2≤x+y≤0.4, x<y, 0≤z≤0.1,

M ¹ is at least one selected from the group consisting of Mn and Al, and M ² is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

Preferably, the positive electrode active material powder may be 0≤a≤0.3, 0.2≤x+y≤0.3, x<y, 0≤z≤0.05, with respect to the total moles of transition metal oxides excluding lithium, nickel is 60 It may be included in mol% to 80 mol%. When the cathode active material powder contains nickel in the above range, it may have high capacity characteristics.

M ¹ in Formula 1 may be at least one selected from the group consisting of Mn and Al. For example, when M ¹ is Mn, the structural stability of the active material may be improved, and when M ¹ is Al, the surface properties of the active material may be improved, thereby improving thermal stability.

In particular, by making the content of M ¹ higher than the content of Co in Formula 1, it is possible to provide an active material having excellent structural stability at low cost.

In addition, in the present invention, the cathode active material powder may include a cathode active material having a hollow part inside the secondary particles and a cathode active material having no hollow part inside the secondary particle.

Based on the total number of the positive active material particles, the amount of the positive active material having a hollow inside the secondary particles may be 40% to 80%, preferably 40% to 70%. As described above, when 40% to 80% of the cathode active material having a hollow part inside the secondary particles is included with respect to the total number of the cathode active material particles, the capacity and output characteristics of the battery to which it is applied may be improved. Specifically, when the positive electrode active material is rolled, the positive active material having the hollow part inside the secondary particles may be broken, and the structure having the hollow part inside may be maintained without being broken. When the cathode active material having a hollow inside the secondary particles is broken, the BET specific surface area of the cathode active material is increased because the inner surface is exposed due to the breakage of the particles of the cathode active material. As described above, when the BET specific surface area of the positive electrode active material increases, the area reacting with the electrolyte increases, thereby improving capacity and output characteristics. For example, when the shape of the positive active material having a hollow part inside the secondary particle is maintained without being broken, the hollow part inside the particle acts as a buffer layer even if a volume change of the electrode is accompanied during charging and discharging to cause cracks in the positive electrode active material. ) hardly occurs, so the stability of the positive electrode active material can be improved.

For example, when the amount of the positive active material having a hollow part inside the secondary particles is less than 40% with respect to the total number of the positive active material particles, the volume change accompanying charging and discharging is large, so that the stability and lifespan characteristics of the positive active material are improved. It may be inferior, and it may be difficult to improve the capacity and output characteristics of the positive electrode active material. In addition, when the positive active material having a hollow part inside the secondary particles is formed in an amount of more than 80% with respect to the total number of the positive active material particles, since the proportion of particles that increase the BET specific surface area of the positive active material is large, Gas generation due to side reactions may increase.

In addition, with respect to the total number of the positive active material particles, the amount of the positive active material having no hollow part inside the secondary particles may be 60% or less, preferably 20% to 60%, more preferably 30% to 50%. As described above, with respect to the total number of the positive active material particles, when the positive active material having no hollow parts inside the secondary particles is included in an amount of 60% or less, when the positive active material is rolled, the positive electrode having no hollow parts inside the secondary particles Since the active material maintains almost unbreakable particles, the stability of the positive active material may be improved.

For example, when the positive active material having no hollow part inside the secondary particles is contained in an amount of more than 60% with respect to the total number of the positive active material particles, when the positive active material is rolled, the particles of the positive active material hardly occur Even if the proportion of particles is increased and particle cracking occurs, since the positive active material does not have a hollow part inside the cathode active material, the specific surface area increase due to particle cracking is not large, so the effect of improving capacity and output characteristics may be insignificant. For example, when the amount of the positive active material having no hollow part inside the secondary particles is less than 20% with respect to the total number of the positive active material particles, the ratio of positive electrode active material particles having an increased BET specific surface area due to particle breakage is increased. , and thus the stability of the cathode active material powder may be reduced.

The internal porosity of the cathode active material powder may be measured by cross-sectional analysis of particles using a focused ion beam (FIB). Specifically, secondary particles are cut using a focused ion beam, cross-sectional images are acquired by SEM, and then divided into spatial and material parts in the cross-section by computer image processing, followed by measurement according to Equation 1 below. .

[Equation 1]

Internal porosity (%) = 100 - (surface area of lithium transition metal oxide / total surface area of secondary particles) * 100

In the cathode active material powder, the internal porosity of the cathode active material having a hollow inside the secondary particles may be 10% to 60%, preferably 20% to 50%. When the internal porosity of the positive active material having a hollow part inside the secondary particles satisfies the above range, it may have an effect on capacity and output improvement due to cracking of particles accompanying the rolling of the positive active material. For example, when the internal porosity is less than 10%, the increase in specific surface area due to particle breakage during rolling of the positive active material is not large, and thus the effect of improving capacity and output characteristics may be insignificant. In addition, when the internal porosity exceeds 60%, the increase in specific surface area due to particle breakage during rolling of the positive active material is very large, so a side reaction with the electrolyte may occur, thereby increasing resistance.

The above-described positive electrode active material powder for secondary batteries includes a positive active material having a hollow part inside the secondary particles and a positive electrode active material having no hollow part inside the secondary particle in an appropriate ratio, preferably 40:60 to 80:20, It is possible to provide a cathode active material powder having improved output characteristics and improved charge/discharge characteristics because stability is improved and insertion and/or deintercalation of lithium is excellently implemented.

Method for manufacturing a cathode active material for a secondary battery

Next, a method for manufacturing the cathode active material powder according to the present invention will be described.

Specifically, in order to prepare the cathode active material powder according to the present invention, preparing a transition metal-containing solution; forming positive electrode active material precursor particles by adding the transition metal-containing solution, an ammonium cation-containing solution, and a basic aqueous solution to a first co-precipitation reaction at pH 12 to pH 14; growing the cathode active material precursor particles by performing a second co-precipitation reaction while maintaining the pH at less than 10 for 5 to 24 hours; and 40% or more of the positive active material particles having a hollow inside the secondary particles with respect to the total number of secondary particles in the form of secondary particles formed by mixing and firing the positive electrode active material precursor and the lithium source. To obtain a cathode active material powder.

First, the transition metal-containing solution is prepared.

The transition metal-containing solution may be prepared by adding a nickel raw material, a cobalt raw material, and a manganese raw material to a solvent, specifically, water or a mixture of water or an organic solvent that can be uniformly mixed with water (alcohol, etc.) and water, or After preparing an aqueous solution containing each metal-containing raw material, it may be mixed and used.

As the raw material of nickel, cobalt, and manganese, sulfate, nitrate, acetate, halide, hydroxide, or oxyhydroxide containing each metal element may be used, and if it can be dissolved in the above solvent such as water, especially It can be used without limitation.

Specifically, as the cobalt raw material, Co(OH) ₂ , CoOOH, CoSO ₄ , Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O or Co(SO ₄ ) ₂ ㆍ7H ₂ O may be at least one selected from the group consisting of.

In addition, nickel raw materials include Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ ·2Ni(OH) ₂ ·4H ₂ O, NiC ₂ O ₂ ·2H ₂ O, Ni(NO ₃ ) ₂ ·6H ₂ O, NiSO ₄ , NiSO ₄ ·6H ₂ O, may be at least one selected from the group consisting of fatty acid nickel salt or nickel halide.

In addition, when M ¹ is manganese, as a raw material for manganese, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ ; manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, dicarboxylic acid manganese salts, manganese citrate and fatty acid manganese salts; It may be at least one selected from the group consisting of oxyhydroxide, or manganese chloride.

In addition, the transition metal-containing solution may optionally further include a metal element M ² containing raw material if necessary, wherein M ² is from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo. It may include at least one selected metal element.

Then, the transition metal-containing solution, ammonium cation-containing solution and basic aqueous solution are added to pH 12 to pH 14, preferably A first co-precipitation reaction is performed at pH 13 to pH 14 to form positive electrode active material precursor particles.

The ammonium ion-containing solution may include at least one selected from the group consisting of NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , and NH ₄ CO ₃ . there is. In this case, as the solvent, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) and water may be used.

In addition, the basic aqueous solution may include at least one selected from the group consisting of NaOH, KOH, and Ca(OH) ₂ , and the solvent is water or an organic solvent that is uniformly miscible with water (specifically, alcohol etc.) and water may be used.

Then, the second co-precipitation reaction may be performed by lowering the pH of the reaction solution than in the step of forming the cathode active material precursor particles and increasing the pH holding time compared to the forming step of the cathode active material precursor particles. Preferably, in the second co-precipitation reaction, the cathode active material precursor particles are maintained at a pH of less than 10 for 5 to 24 hours, more preferably at a pH of 9.5 or less, and most preferably at a pH of 9 to pH 9.5 for 10 to 16 hours. Grow.

Specifically, the ammonium ion-containing solution and the basic aqueous solution are added to the reaction solution in which the cathode active material particle nuclei are formed until the pH of the reaction solution becomes lower than the pH at the time of particle nucleation, preferably until the pH is less than 10, By maintaining for 5 hours to 24 hours, the cathode active material precursor particles may be grown. For example, when the pH conditions and the pH holding time are out of the scope of the present invention, the desired particle structure, specifically, the positive active material having a hollow inside the secondary particles with respect to the total number of positive active material particles is adjusted to 40% or more It can be difficult to do.

In particular, by controlling the pH holding time to 5 hours to 24 hours, it is possible to easily control the ratio of the positive electrode active material having a hollow inside the secondary particles to the total number of the positive electrode active material particles. When the pH holding time is less than 5 hours, particle growth is not sufficiently achieved, and the production rate of the positive electrode active material having a hollow part inside the secondary particles increases. Accordingly, since the ratio of active material particles whose specific surface area increases due to particle breakage during rolling of the positive active material is large, a side reaction with the electrolyte may increase, which may increase the amount of gas generated. As described above, when gas is generated due to a side reaction with the electrolyte, the battery may explode due to swelling of the battery, thereby deteriorating the stability of the battery. Alternatively, when the pH maintenance time exceeds 24 hours, the production rate of the positive electrode active material that does not have a hollow part inside the secondary particles increases. Accordingly, since the proportion of the active material in which particles are broken during rolling of the positive active material is small, and the specific surface area change is not large even if the particles are broken, the effect of improving capacity and output may be insignificant.

Finally, the cathode active material precursor and the lithium source are mixed and calcined to obtain a cathode active material powder in the form of secondary particles formed by agglomeration of primary particles.

At this time, in the secondary particles, the positive active material having a hollow inside the secondary particles is 40% or more, preferably 40% to 80%, more preferably 40% to 70% with respect to the total number of positive electrode active material particles. will be.

For example, the lithium-containing raw material is not particularly limited as long as it is a compound containing a lithium source, but preferably lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), LiNO ₃ , CH ₃ COOLi and At least one selected from the group consisting of Li ₂ (COO) ₂ may be used.

The calcination may be performed at 750° C. to 850° C. for 9 to 11 hours, more preferably at 780° C. to 830° C., for 10 hours to 11 hours. When the firing is performed at the above temperature and time range, the reaction between the lithium source and the precursor can be sufficiently achieved, and since particle growth of the positive electrode active material precursor occurs less than during high-temperature firing, the positive active material having a hollow inside and the inside It is possible to obtain a positive electrode active material powder in which all of the positive electrode active material having no hollow part is produced. On the other hand, when the sintering is performed at less than 750° C. for less than 9 hours, the reaction with the lithium source may not be sufficient. In addition, when the firing is performed at a temperature exceeding 850° C. for more than 11 hours, the cathode active material may be over-baked to cause low electrochemical properties, and it becomes difficult to produce a cathode active material having a hollow structure in the particles.

That is, according to the present invention, when preparing the cathode active material powder, the first co-precipitation reaction and the second co-precipitation reaction are performed in stages, but the primary particles are agglomerated by appropriately adjusting the pH conditions, pH holding time, calcination temperature and calcination time, etc. A cathode active material powder in the form of secondary particles can be obtained, and a cathode active material powder having 40% to 80% of the cathode active material having a hollow inside the secondary particles with respect to the total number of the cathode active material particles can be prepared.

Anode for secondary battery

Next, to provide a positive electrode for a lithium secondary battery comprising the positive electrode active material powder according to the present invention.

Specifically, the positive electrode for a secondary battery includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and containing the positive electrode active material powder according to the present invention. In this case, the positive electrode has an electrode density of 1 g/cc to 10 g/cc, preferably, an electrode density of 2 g/cc to 5 g/cc. When the positive electrode has an electrode density within the above-described range, a high-density electrode having a high energy density per unit area may be manufactured.

At this time, since the cathode active material powder is the same as described above, a detailed description will be omitted, and only the remaining components will be described in detail below.

The cathode active material powder contains a cathode active material having a hollow part inside the secondary particles and a cathode active material not having a hollow part inside the secondary particles in a ratio of 40:60 to 80:20, preferably 45:55 to 65:35, and , when having the electrode density, the internal porosity of the positive active material having a hollow inside the secondary particles may be 10 to 60%, preferably 20 to 50%. Specifically, when the positive electrode is rolled to have the electrode density, the particles having a hollow part inside the secondary particle of the positive electrode active material may be broken, and the particle may not be broken and a structure having a hollow part inside may be maintained. there is. When the particles having hollow parts inside the secondary particles of the positive electrode active material are broken, the BET specific surface area of the positive electrode active material may be higher after rolling compared to before rolling because the inner surface is exposed due to the particle cracking. When the BET specific surface area increases as the particles break, the capacity and output can be improved by increasing the area that reacts with the electrolyte. If the particle having a hollow part inside the secondary particle of the positive electrode active material is not broken and its structure is maintained, the hollow part inside the particle acts as a buffer layer even if the volume change of the electrode is accompanied during charging and discharging to prevent cracks in the positive electrode active material. Generation is suppressed, and thus the stability of the positive electrode may be improved. On the other hand, in the case of the particles having no hollow part inside the secondary particles of the positive electrode active material, cracking of the particles of the positive electrode active material hardly occurs even when the positive electrode is rolled. Accordingly, the BET specific surface area of the positive electrode active material that does not have a hollow inside the secondary particles may be the same before and after rolling. Accordingly, the stability of the electrode may be improved.

As such, when the positive active material having a hollow part inside the secondary particles and the positive active material having no hollow part inside the secondary particles are mixed in an appropriate ratio and included, a positive electrode having improved stability, capacity and output characteristics is obtained can do.

On the other hand, the positive electrode current collector may include a metal with high conductivity, and the positive electrode active material layer is easily adhered, but is not particularly limited as long as it has no reactivity in the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material powder by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

The positive active material layer may optionally include a conductive material, a binder, and a dispersing agent, if necessary, together with the positive active material powder.

In this case, the positive active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight, based on the total weight of the positive active material layer. When included in the above content range, excellent capacity characteristics may be exhibited.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

The binder serves to improve adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl meth acrylate (polymethymethaxrylate), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene Polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof and the like, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

The dispersant may include an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above-described positive electrode active material powder. Specifically, the positive electrode active material powder and the composition for forming a positive electrode active material layer prepared by selectively dissolving or dispersing a binder, a conductive material, and a dispersing agent in a solvent as needed are coated on the positive electrode current collector, followed by drying and rolling. can be manufactured.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), dimethylformamide (dimethyl formamide, DMF), acetone, or water, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is to dissolve or disperse the positive electrode active material powder, the conductive material, the binder, and the dispersant in consideration of the application thickness of the slurry and the manufacturing yield, and then have a viscosity that can exhibit excellent thickness uniformity when applied for manufacturing the positive electrode. it is enough to do

In addition, as another method, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

secondary battery

In addition, the present invention can manufacture an electrochemical device including the positive electrode. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is the same as described above, so detailed description is omitted, Hereinafter, only the remaining components will be described in detail.

In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low-crystalline carbon, and high-crystalline carbon includes natural or artificial graphite in amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite (Kish). graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The anode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the anode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the anode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro and roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the anode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the anode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

For example, the anode active material layer is prepared by applying and drying a composition for forming an anode active material layer prepared by dissolving or dispersing an anode active material, and optionally a binder and a conductive material in a solvent, on the anode current collector and drying, or the anode active material layer It can be prepared by casting the composition for forming an active material layer on a separate support, and then laminating a film obtained by peeling it off the support on an anode current collector.

The anode active material layer is, as an example, a composition for forming an anode active material layer prepared by dissolving or dispersing an anode active material, and optionally a binder and a conductive material in a solvent on an anode current collector and drying, or for forming the anode active material layer It can also be prepared by casting the composition on a separate support and then laminating the film obtained by peeling it off from the support on the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane (sulfolane) may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as an anion of the lithium salt, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be at least one selected from the group consisting of, The lithium salt is, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _{2 .} LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and lifespan characteristics, particularly in the field of electric vehicles such as hybrid electric vehicles (HEV) It can be useful for devices.

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium-to-large devices in a system for power storage.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a prismatic shape, a pouch type, or a coin type using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device, but can also be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Examples of the medium-large device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Hereinafter, examples are given in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Example One

Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in an aqueous solution in an amount such that the molar ratio of nickel:cobalt:manganese was 65:10:25 to prepare a solution containing a transition metal having a concentration of 2M.

The containers containing the transition metal-containing solution were respectively connected to a 4L batch reactor set at 60°C. In addition, 4M NaOH solution and 28% NH ₄ OH aqueous solution were prepared and connected to the batch reactor, respectively. After putting 3L of deionized water into the reactor, nitrogen gas was purged into the reactor at a rate of 0.5L/min to remove dissolved oxygen in the water, and a non-oxidizing atmosphere was created in the reactor. Thereafter, 25 mL of NaOH and 50 mL of NH ₄ OH were added, followed by stirring at a stirring speed of 1500 rpm at 60° C. to maintain pH 13.

Thereafter, the transition metal-containing solution was added at a rate of 3 mL/min, an aqueous NaOH solution of 3 mL/min, and an aqueous NH ₄ OH solution of 0.1 mL/min at a rate of 0.1 mL/min to perform a first co-precipitation reaction for 20 minutes to obtain particle nuclei of the transition metal hydroxide was formed.

Then, the transition metal-containing solution, NaOH aqueous solution, and NH ₄ OH aqueous solution were added at a rate of 3 mL/min, 2 mL/min, and 0.1 mL/min, respectively, so that the pH was 9.3 to induce particle growth of the transition metal hydroxide. Then, the reaction was maintained for 15 hours to grow the particles of the transition metal hydroxide.

The precipitated transition metal hydroxide particles were separated, washed with water, and dried in an oven at 130° C. for 10 hours to prepare a precursor for a positive electrode active material.

The cathode active material precursor prepared above and Li ₂ CO ₃ were mixed so that a molar ratio of Li:Me was 1.03:1, and calcined at 830° C. for 10 hours in an air atmosphere to obtain Li _{1 . 03} Ni _{0 . 65} Co _{0 . 10} Mn _{0 .} A positive electrode active material represented by ₂₅ O ₂ was prepared.

[Anode Manufacturing]

The positive electrode active material prepared above: carbon black conductive material: polyvinylidene fluoride binder was mixed in an N-methylpyrrolidone solvent in a weight ratio of 92.5:3.5:4 to prepare a composition for forming a positive electrode. This was applied to an aluminum current collector having a thickness of 20 μm, dried at 130° C. for 0.5 hours, and roll press was performed to prepare a positive electrode.

[Cathode Manufacturing]

A negative active material slurry was prepared by mixing natural graphite, a carbon black conductive material, and a polyvinylidene fluoride binder in a weight ratio of 85:10:5. This was coated on a copper current collector having a thickness of 12 μm, dried, and then roll press was performed to prepare a negative electrode.

[Secondary battery manufacturing]

The positive electrode and the negative electrode prepared above were laminated together with a porous polyethylene separator to prepare a polymer-type battery in a conventional manner, and then put it in a battery case and mix ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a volume ratio of 3:4:3. A lithium secondary battery was prepared by injecting an electrolyte in which 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the mixed solvent.

Example 2

A positive electrode active material and a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the pH condition during particle growth was maintained at pH 9.3 for 20 hours during the preparation of the positive electrode active material precursor. .

comparative example One

The transition metal-containing solution prepared in Example 1, NaOH aqueous solution, and NH ₄ OH aqueous solution were introduced into a batch reactor at a rate of 3 mL/min, 3 mL/min and 0.1 mL/min, respectively, and coprecipitated at pH 11 for 15 hours, A positive electrode active material and a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the positive electrode active material precursor in which particles having hollow parts were not formed was used.

comparative example 2

A positive electrode active material and a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that, during the preparation of the positive electrode active material precursor, the pH condition during particle growth was maintained at pH 9.3 for 30 hours. .

comparative example 3

A positive electrode active material and a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the pH conditions during particle growth were maintained at pH 9.3 for 4 hours during the preparation of the positive electrode active material precursor. .

Experimental example 1: Observation of cathode active material

The positive electrode active material powders prepared in Examples 1 to 2 and Comparative Examples 3 to 4 were checked for surface properties using a scanning electron microscope.

In this regard, FIGS. 1A and 1B are a cross-sectional SEM photograph at high magnification of the cathode active material powder prepared in Example 1 and a cross-sectional SEM photograph at a low magnification of the cathode active material powder prepared in Example 1, respectively, FIGS. 2A and FIG. 2b is a multi-sided SEM photograph at high magnification and a cross-sectional SEM photograph at low magnification of the cathode active material powder prepared in Example 2, respectively.

As shown in FIGS. 1A, 1B, 2A and 2B , it was confirmed that the cathode active material powders prepared in Examples 1 and 2 were in the form of secondary particles formed by agglomeration of primary particles. In addition, with respect to the total number of the positive active material particles, it was confirmed that the positive active material having a hollow inside the secondary particles was 40% or more.

Meanwhile, FIGS. 3A and 3B are multi-sided SEM photos at high magnification and cross-sectional SEM photos at low magnification of the cathode active material powder prepared in Comparative Example 2, respectively, and FIGS. 4A and 4B are the cathode active material powders prepared in Comparative Example 3, respectively. A multi-sided SEM picture at high magnification and a cross-sectional SEM picture at low magnification.

As shown in FIGS. 3A and 3B , the positive active material powder prepared in Comparative Example 2 was in the form of secondary particles formed by agglomeration of primary particles, but excessive growth of particles occurred, 2 to the total number of positive active material particles The positive active material having hollow parts inside the secondary particles was about 25%, and the internal porosity of the positive active material having hollow parts inside the secondary particles was 7%.

In addition, in the positive active material powder prepared in Comparative Example 3, as shown in FIGS. 4A and 4B, particle growth did not occur sufficiently, so that the positive active material having a hollow inside the secondary particles was 83 with respect to the total number of positive active material particles. %, and it was confirmed that the internal porosity of the positive active material having a hollow inside the secondary particles was 71%.

In addition, after preparing the cathode active material powder prepared in Example 1 to have a rolling density of 3.2 g/cc, charging and discharging for 100 cycles at 1C/1C was performed, and then cracks were checked inside the particles. As shown in FIG. 5 , in the case of the positive active material particles maintaining a shape having a hollow part inside the secondary particles after rolling, it was confirmed that cracks did not occur even after the cycle progressed. On the other hand, as shown in FIG. 6 , in the case of the positive active material particles that do not include a hollow inside the secondary particles, it was confirmed that fine cracks occurred after the cycle was performed.

Therefore, the positive electrode active material powder of the present invention can secure the stability of the positive electrode active material powder by including the positive active material particles having a hollow inside the secondary particles, 40% or more of the total positive active material particles.

Experimental example 2: Analysis of positive electrode active material

The average particle diameter, BET specific surface area, and ratio of the particles having pores to the total positive active material particles prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were measured as follows, and the results were measured in Table 1 below. shown in

(1) Average particle diameter (D ₅₀ )

After introducing into a laser diffraction particle size measuring device (eg Microtrac MT 3000) and irradiating an ultrasonic wave of about 28 kHz with an output of 60 W, the average particle diameter (D ₅₀ ) at 50% of the particle size distribution in the measuring device It was calculated and shown in Table 1 below.

(2) internal porosity

The internal porosity of the cathode active material powder may be measured by cross-sectional analysis of particles using a focused ion beam (FIB). Specifically, the secondary particles are cut using a focused ion beam, a cross-sectional image is acquired by SEM, and then divided into a spatial part and a material part in the cross-section by computer image processing. .

[Equation 1]

Internal porosity (%) = 100 - (surface area of lithium transition metal oxide / total surface area of secondary particles) * 100

(3) the inside of the secondary particles with respect to the entire positive active material particle middle school content of particles with

After the positive active material and other parts (conductive material, binder, and internal pores) were separated through cross-sectional SEM image analysis, the ratio of particles with pores to the total number of particles could be calculated, which is shown in Table 1 below.

Average particle diameter (D ₅₀ ) (㎛) Internal porosity (%) Proportion of particles with hollow inside of secondary particles (%) Example 1 3.0 35 63 Example 2 3.2 22 45 Comparative Example 1 4.3 0 0 Comparative Example 2 3.4 7 25 Comparative Example 3 3.1 71 83

Experimental example 3: of secondary battery charging and discharging efficiency

The lithium secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were evaluated for charging and discharging efficiency, and the results are shown in Table 2 below.

Specifically, the lithium secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were respectively charged at 25° C. at a constant current of 0.1 C until they reached 4.3 V, and then charged at a constant voltage of 4.3 V so that the charging current was 0.05 The first charge was carried out until C. After leaving it for 20 minutes, it was discharged to 3.0V with a constant current of 0.1C, and the charging/discharging characteristics were observed in the first cycle. Thereafter, the charging and discharging efficiency according to the C-rate was measured by changing the discharging conditions to 1C and 2C, and the results are shown in Table 2 below.

0.1C charge
(mAh/g) 0.1C discharge
(mAh/g) 0.1C efficiency
(%) 1C rate
(%) 2C rate
(%) Example 1 205.4 185.1 90.1 92.0 88.6 Example 2 205.5 183.7 89.4 91.0 87.4 Comparative Example 1 205.3 177.1 86.3 89.7 85.2 Comparative Example 2 205.3 179.4 87.4 90.1 85.9 Comparative Example 3 205.8 187.2 91.0 92.4 89.0

As shown in Table 2, the charging and discharging efficiency of the lithium secondary batteries prepared in Examples 1 and 2 including positive active material particles having hollow parts in the secondary particles and positive active material particles having no hollow parts in the secondary particles in an appropriate ratio It was confirmed that the charging and discharging efficiency of the lithium secondary batteries prepared in Comparative Examples 1 and 2 was superior.

Experimental example 4: Resistance characteristics of the secondary battery

Room temperature (25° C.) and low temperature (-20° C.) output characteristics of the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were respectively confirmed. Specifically, the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were charged at a constant current of 0.2 C at room temperature (25° C.), and then discharged at a constant current of 3.0 C for 30 seconds to a voltage for 10 seconds. The drop was measured, and the resistance at room temperature (25° C.) was measured by dividing it by the current value, and it is shown in Table 3 and FIG. 7 below.

Separately, the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were charged at a low temperature (-20° C.) with a constant current of 0.2 C, and then discharged at a constant current of 0.6 C for 1300 seconds for 1300 seconds. The voltage drop was measured, and the resistance at low temperature (-20°C) was measured by dividing it by the current value, and it is shown in Table 3 and FIG. 8 below.

The resistance at room temperature and the resistance at low temperature measured above are respectively shown in Table 3 below, and the degree of resistance reduction compared to the case including the positive active material in which pores are not formed (Comparative Example 1) was evaluated, which is also shown in Table 3 shown in

room temperature output low temperature output Ω % Ω % Example 1 1.29 86.6 38.09 70.0 Example 2 1.35 90.6 43.44 79.9 Comparative Example 1 1.49 100 54.38 100 Comparative Example 2 1.44 96.6 51.27 94.3

As shown in Table 3 and FIGS. 7 to 8, it was confirmed that the resistance characteristics of the secondary batteries prepared in Examples 1 and 2 were superior to those of the secondary batteries prepared in Comparative Examples 1 and 2 at room temperature and low temperature.

This is because the positive active material of the secondary battery contains positive active material particles having hollow parts in the secondary particles in an appropriate content, so even if a volume change is accompanied during charging and discharging, cracks are hardly generated in the particles due to the hollow parts inside the secondary particles, Accordingly, the electrode is stabilized and the resistance characteristic is improved.

Experimental example 5: gas generation

The amount of gas generated when the lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 2-3 were stored at 60° C. for 4 weeks was confirmed.

Specifically, the lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 2-3 were charged to 4.3V, and then stored at 60° C. for 4 weeks. The volume change immediately after full charge and after storage for 4 weeks of the lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 2-3 were measured, respectively, and the amount of gas increase based on the volume change before and after storage of the lithium secondary battery was calculated and shown in Table 4 and FIG. 9 below.

Gas increase (vol%) Example 1 127 Example 2 123 Comparative Example 2 119 Comparative Example 3 137

As shown in Table 4 and FIG. 9, in the secondary battery prepared in Comparative Example 3, since the proportion of positive active material particles having a hollow part in the secondary particle is large, when rolling during the manufacturing process of the secondary battery, the secondary battery is hollow in the secondary particle. It was confirmed that the negative electrode active material was broken, and the reaction area with the electrolyte was widened due to the increase in the specific surface area of the positive electrode active material, and the amount of gas increased due to the side reaction with the electrolyte was larger than in Examples 1 and 2.

On the other hand, since the secondary battery prepared in Comparative Example 2 had a small proportion of the positive active material particles having hollow parts in the secondary particles, it was confirmed that the reactivity with the electrolyte was low and the gas increase was also the lowest. However, as described above, since the proportion of the positive active material particles having hollow parts in the secondary particles is very small, there is no effect of improving output characteristics and resistance characteristics.

Experimental example 6: Lifespan characteristics of secondary batteries

Life characteristics of the secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were checked.

Specifically, for each of the secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3, charging was performed at 45°C at 0.5C to 4.3V at 0.05C cut-off. Thereafter, discharge was performed at a constant current of 0.5C until it became 3V. After repeating this cycle 300 times with the charging and discharging behavior as 1 cycle, the capacity retention ratio according to the cycles of the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 was measured, which is shown in Table 5 below. it was

Capacity retention (%) at 300th cycle Example 1 88 Example 2 85 Comparative Example 1 78 Comparative Example 2 81 Comparative Example 3 73

As shown in Table 5, since the secondary batteries prepared in Examples 1 and 2 contain the positive active material having a hollow part inside the secondary particles in an appropriate ratio, cracking of the active material particles due to volume expansion during charging and discharging occurs It was confirmed that the capacity retention rate of 85% or more was exhibited even after 300 cycles due to excellent stability.

On the other hand, in the secondary batteries prepared in Comparative Examples 1 and 2, there is no ratio of positive active material particles having hollow parts in the secondary particles, or the proportion of particles that act as a buffer during volume expansion according to the charge/discharge progress because the ratio is less than an appropriate level. It was confirmed that this was insignificant, and the life characteristics were inferior to those of Examples 1-2.

In addition, in the secondary battery prepared in Comparative Example 3, since the ratio of the positive electrode active material particles having the hollow parts in the secondary particles is higher than the appropriate level, the positive active material having the hollow parts in the secondary particles during rolling during the manufacturing process of the secondary battery It was confirmed that the reaction area with the electrolyte increased due to the increase of the specific surface area of the positive electrode active material due to cracking, and the side reaction with the electrolyte increased, resulting in deterioration of the lifespan characteristics.

Claims (10)

In the positive electrode active material powder comprising a plurality of positive active material particles of secondary particles formed by aggregation of primary particles,
With respect to the total number of positive active material particles, the amount of the positive active material having a hollow part inside the secondary particles is 40% to 70%, and the positive active material having no hollow part inside the secondary particle is 30% to 60%, the positive electrode active material powder.
The method of claim 1,
The cathode active material is a cathode active material powder comprising a lithium transition metal oxide represented by the following formula (1).
[Formula 1]
Li _1+a Ni _1-xy Co _x M ¹ _y M ² _z O ₂
In Formula 1,
0≤a≤0.5, 0.2≤x+y≤0.4, x<y, 0≤z≤0.1,
M ¹ is at least one selected from the group consisting of Mn and Al,
M ² is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.
delete The method of claim 1,
The positive electrode active material powder having an internal porosity of 10% to 60% of the positive active material having a hollow inside the secondary particles.
The method of claim 1,
The positive active material powder has an average particle diameter (D ₅₀ ) of the positive active material of 2 μm to 13 μm.
preparing a transition metal-containing solution;
forming positive electrode active material precursor particles by adding the transition metal-containing solution, an ammonium cation complex forming agent, and an anion-containing basic compound to a first co-precipitation reaction at pH 12 to pH 14;
growing the cathode active material precursor particles by performing a second co-precipitation reaction while maintaining the pH at less than 10 for 5 to 24 hours; and
By mixing and firing the positive electrode active material precursor and the lithium source, the positive active material particles having a hollow inside the secondary particles are 40% to 70% with respect to the total number of positive active material particles in the form of secondary particles formed by aggregation of primary particles %, and comprising the step of obtaining a cathode active material powder having 30% to 60% of the cathode active material particles having no hollow part inside the secondary particles, a method of producing a cathode active material powder.
7. The method of claim 6,
The first co-precipitation reaction is to be carried out at pH 13 to pH 14,
The second co-precipitation reaction is to be carried out for 10 to 16 hours at a pH of 9.5 or less, a method for producing a cathode active material powder.
7. The method of claim 6,
The method of claim 1, wherein the sintering is performed at 750° C. to 850° C. for 9 to 11 hours.
positive electrode current collector;
A positive electrode comprising a; a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material powder according to any one of claims 1, 2, 4 and 5,
The positive electrode will have an electrode density of 1 g / cc to 10 g / cc, the positive electrode.
The positive electrode according to claim 9; cathode; and a separator interposed between the positive electrode and the negative electrode. and an electrolyte; and a lithium secondary battery.

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