KR20240123086A - Lithium-manganese-based transition metal oxide, positive electrode additive for lithium secondary battery, lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium-manganese transition metal oxide, a cathode additive for a lithium secondary battery, and a lithium secondary battery comprising the same. According to the present invention, a lithium-manganese transition metal oxide is provided which can suppress the generation of gas during charging and discharging of a lithium secondary battery by minimizing side reactions with an electrolyte.

Description

Lithium-manganese-based transition metal oxide, positive electrode additive for lithium secondary battery, and lithium secondary battery comprising the same {LITHIUM-MANGANESE-BASED TRANSITION METAL OXIDE, POSITIVE ELECTRODE ADDITIVE FOR LITHIUM SECONDARY BATTERY, LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a lithium-manganese transition metal oxide, a cathode additive for a lithium secondary battery, and a lithium secondary battery comprising the same.

As electronic devices become more multifunctional and their power consumption increases, there are many attempts to increase the capacity of lithium secondary batteries and improve their charge/discharge efficiency.

For example, a technology has been proposed to apply a cathode active material having a nickel content of 80% or more as a cathode material to the cathode of a lithium secondary battery, and to apply a metal or metal-based cathode active material such as SiO, Si or SiC together with a carbon-based cathode active material such as natural graphite or artificial graphite to the anode.

Metal and metal oxide-based negative electrode active materials enable higher capacity expression than carbon-based negative electrode active materials. However, since the volume change of metal and metal oxide-based negative electrode active materials during charge and discharge is much larger than that of graphite, it is difficult to increase the content of metal and metal oxide in the negative electrode to more than 15%. In addition, when metal and metal oxide are added to the negative electrode, an irreversible reaction occurs during the initial charge and discharge, and the loss of lithium is greater than when carbon-based negative electrode active materials are applied. Therefore, when metal and metal oxide-based negative electrode active materials are applied, the amount of lithium lost increases as the capacity of the battery increases, and the decrease in the initial capacity due to this also increases.

Accordingly, various methods have been studied to increase the capacity of lithium secondary batteries or reduce the irreversible capacity. One of them is prelithiation, which is a concept of replenishing lithium consumed in the formation of the solid electrolyte interphase layer (SEI) layer in the initial state within the battery.

Various methods have been proposed to achieve pre-lithiation within batteries.

For example, there is a method of electrochemically lithiating the negative electrode before battery operation. However, the lithiated negative electrode is very unstable in the air, and the electrochemical lithiation method is difficult to scale up the process.

Another example is a method of coating lithium metal or lithium silicide (Li _x Si) powder on a cathode. However, since the powder has high reactivity and thus has low atmospheric stability, there is a problem in establishing suitable solvents and process conditions when coating the cathode.

One way to pre-lithiate the cathode is to coat more cathode material equal to the amount of lithium consumed from the anode. However, due to the low capacity of the cathode material itself, the amount of added cathode material increases, and the energy density and capacity per weight of the final battery decrease by the amount of the increased cathode material.

Accordingly, a material suitable for preliminary lithiation of a battery in the positive electrode must have the irreversible characteristic of releasing at least twice as much lithium as the existing positive electrode material during the first charge and not reacting with lithium during subsequent discharge. Additives that satisfy these conditions are called sacrificial positive electrode materials.

In the case of commercial batteries, after the electrolyte is injected into the case including the laminated positive electrode, separator, and negative electrode, the formation process is performed for the first time to perform the charge/discharge operation. During this process, an SEI layer formation reaction occurs on the negative electrode, and gas is generated due to the decomposition of the electrolyte. In the formation process, the sacrificial positive electrode material reacts with the electrolyte while decomposing and releasing lithium, and the gases such as N ₂ , O ₂ , and CO ₂ generated during this process are recovered through the gas pocket removal process.

As the above sacrificial anode material, over-lithiated positive electrode materials, which are lithium-rich metal oxides, are widely used. As the above over-lithiated positive electrode materials, Li ₆ CoO ₄ , Li ₅ FeO ₄ , and Li ₆ MnO ₄ , which have an anti-fluorite structure, are well known. The theoretical capacities of Li ₆ CoO ₄ are 977 mAh/g, Li ₅ FeO ₄ , and Li ₆ MnO ₄ , which are 867 mAh/g and 1001 mAh/g, respectively, which have sufficient capacities to be used as sacrificial anode materials. Among them, Li ₆ CoO ₄ has the best electrical conductivity and thus has excellent electrochemical properties to be used as a sacrificial anode material.

However, since the electrochemical structural stability of the sacrificial cathode material is insufficient due to the nature of the sacrificial cathode material, when an excessive amount of lithium is desorbed and supplied to the anode to compensate for the irreversible capacity loss during the initial charge/discharge process, the structural collapse of the sacrificial cathode material occurs. Due to this structural collapse, a large amount of O ₂ gas is generated inside the cathode and the battery, which increases the pressure inside the battery and can significantly reduce the stability of the lithium secondary battery.

Due to the problems of these conventional sacrificial cathode materials, there is a continuous demand for the development of new cathode additives that can improve the stability of the battery by suppressing gas generation during the lithium desorption process while exhibiting high irreversible capacity characteristics during the initial charging process.

The present invention provides a lithium-manganese transition metal oxide which exhibits a high initial irreversible capacity while suppressing gas generation during compensation for irreversible capacity loss, thereby improving the stability of a battery.

The present invention provides a method for producing the lithium-manganese transition metal oxide.

The present invention provides a cathode additive for a lithium secondary battery comprising the lithium-manganese transition metal oxide.

The present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode additive.

And, the present invention is to provide a lithium secondary battery including the positive electrode for the secondary battery.

According to one embodiment of the invention, a lithium (Li)-manganese (Mn) transition metal oxide containing iron (Fe) and zinc (Zn) as heterogeneous elements is provided.

According to another embodiment of the invention,

A step of providing a raw material mixture comprising a lithium precursor, a manganese precursor, an iron precursor, and a zinc precursor in a solid state; and

A step of calcining the above raw material mixture under an inert atmosphere and a temperature of 500° C. to 900° C. to obtain the lithium-manganese transition metal oxide.

A method for producing a lithium-manganese transition metal oxide, including:

According to another embodiment of the invention, a cathode additive for a lithium secondary battery comprising the lithium-manganese transition metal oxide is provided.

According to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, comprising a positive electrode active material, a binder, a conductive agent, and the lithium-manganese transition metal oxide.

According to another embodiment of the invention, a lithium secondary battery is provided, including a positive electrode; an anode; a separator; and an electrolyte for the lithium secondary battery.

Hereinafter, the lithium-manganese transition metal oxide, the method for producing the lithium-manganese transition metal oxide, the positive electrode additive for a lithium secondary battery, the positive electrode for a lithium secondary battery, and the lithium secondary battery according to embodiments of the invention will be described in more detail.

The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of the invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best way.

Unless otherwise defined herein, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of this invention is only for the purpose of effectively describing particular embodiments and is not intended to be limiting of the invention.

As used herein, the singular forms include the plural forms as well, unless the phrases clearly indicate the opposite.

The term "including" as used herein specifies a particular characteristic, region, integer, step, operation, element, and/or component, but does not exclude the presence or addition of any other particular characteristic, region, integer, step, operation, element, component, and/or group.

The present invention may have various modifications and may take various forms, and thus specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope thereof.

In this specification, when the positional relationship between two parts is described as, for example, ‘on’, ‘upper’, ‘lower’, ‘next to’, etc., one or more other parts may be located between the two parts, unless the expression ‘directly’ or ‘immediately’ is used.

In this specification, when a temporal relationship is described as, for example, “after”, “following”, “next to”, “before”, etc., it may also include cases where it is not continuous, unless the expression “immediately” or “directly” is used.

The term 'at least one' in this specification should be understood to include all possible combinations of one or more associated items.

The term “positive electrode additive” as used herein refers to a material having an irreversible characteristic of releasing at least twice as much lithium as a conventional positive electrode material during the initial charge of a battery and not reacting with lithium during subsequent discharge. The positive electrode additive may also be referred to as a sacrificial positive electrode material. Since the positive electrode additive compensates for lithium loss, the lost capacity of the battery is restored as a result, thereby increasing the capacity of the battery. In addition, by suppressing gas generation, the battery can be prevented from exploding, thereby improving the life characteristics and safety of the battery.

According to one embodiment of the invention, a lithium (Li)-manganese (Mn) transition metal oxide containing iron (Fe) and zinc (Zn) as heterogeneous elements is provided.

The lithium-manganese transition metal oxide according to the above implementation example is basically based on Li ₆ MnO ₄ compound known as a sacrificial cathode material.

However, the Li ₆ MnO ₄ compound exhibited a relatively low irreversible capacity compared to other sacrificial cathode materials, and it was confirmed that it was chemically and structurally decomposed as excess lithium was desorbed during the irreversible capacity loss compensation process, generating a large amount of gas.

The lithium-manganese transition metal oxide according to the above embodiment contains iron (Fe) and zinc (Zn) as heteroelements, which are electrochemically inactive and can form a stable single phase by alloying with manganese (Mn). Accordingly, the lithium-manganese transition metal oxide can appropriately compensate for irreversible capacity loss in a high-capacity lithium secondary battery, while suppressing the generation of gas during the irreversible capacity loss compensation process.

Since the lithium-manganese transition metal oxide above contains iron (Fe) and zinc (Zn) as heterogeneous elements, it can exhibit significantly superior effects in expression of charge capacity and reduction of gas generation compared to cases where iron, zinc or other types of elements are contained as heterogeneous elements.

According to one embodiment, the heterogeneous element may be included in an amount of 10 mol% to 90 mol% based on the total metal elements excluding lithium in the lithium-manganese transition metal oxide.

Specifically, the heterogeneous element may be included in an amount of 10 mol% or more or 15 mol% or more, and 90 mol% or less or 85 mol% or less, based on the total metal elements excluding lithium in the lithium-manganese transition metal oxide.

Preferably, the heterogeneous element may be included in an amount of 10 mol% to 90 mol%, or 15 mol% to 90 mol%, or 15 mol% to 85 mol%, based on the total metal elements excluding lithium in the lithium-manganese transition metal oxide.

As the heterogeneous element is included in the above content range, the lithium-manganese transition metal oxide can exhibit very high chemical and structural stability, and structural collapse can be suppressed and a chemically stable state can be maintained even after an excess of lithium is desorbed. Accordingly, even after compensation for irreversible capacity loss during initial charge and discharge, the generation of oxygen gas within the positive electrode and the lithium secondary battery can be suppressed, thereby greatly improving the stability of a high-capacity lithium secondary battery. Furthermore, as the heterogeneous element is included in the above content range, the lithium-manganese transition metal oxide can exhibit high irreversible capacity and high capacity characteristics during initial charge, and as a result, irreversible capacity loss can be sufficiently compensated for in a high-capacity battery.

However, if the content of the above-mentioned heterogeneous element is too low, the lithium transition metal oxide may not be sufficiently structurally stabilized, so that a large amount of oxygen gas may still be generated. On the other hand, if the content of the above-mentioned heterogeneous element is too high, the irreversible capacity and capacity characteristics of the lithium-manganese transition metal oxide may be reduced.

In one embodiment, the heterogeneous elements may include iron and zinc in a molar ratio of 1:0.1 to 1:10.

Specifically, the heterogeneous elements may include iron and zinc in a molar ratio of 1:0.1 to 1:10, or 1:0.15 to 1:10, or 1:0.15 to 1:9.5, or 1:0.2 to 1:9.5, or 1:0.2 to 1:9, or 1:0.2 to 1:9, or 1:0.2 to 1:8.5, or 1:0.2 to 1:8.

If the molar ratio of iron among the above heterogeneous elements is too low, it is difficult to expect the effect of forming a single phase and improving the electrochemical characteristics. On the contrary, if the molar ratio of iron is too high, a Li ₅ FeO ₄ crystal phase having a relatively low sintering temperature is generated, which may cause severe sintering of the particles. If the molar ratio of zinc among the above heterogeneous elements is too low, it is difficult to expect the effect of suppressing gas generation. On the contrary, if the molar ratio of zinc is too high, the electrochemical characteristics may deteriorate.

According to one embodiment, the lithium-manganese transition metal oxide may be represented by the following chemical formula 1:

[Chemical Formula 1]

Li _6-x Mn _1-xy Fe _x Zn _y O ₄

In the above chemical formula 1, 0.05 < x < 0.5 and 0.05 < y < 0.5.

In the above chemical formula 1, x may be greater than 0.05 or greater than 0.1; and less than 0.5 or less than 0.45. Preferably, x may be greater than 0.05 and less than 0.5, or greater than 0.1 and less than 0.5, or greater than 0.1 and less than 0.45.

In order to realize the effect of single-phase formation and improvement of electrochemical characteristics, it is preferable that x is greater than 0.05 or greater than 0.1. However, if x is too large, a Li ₅ FeO ₄ crystal phase having a relatively low sintering temperature is generated, which may cause severe sintering of the particles. Therefore, it is preferable that x is less than 0.5 or less than 0.45.

In the above chemical formula 1, y may be greater than 0.05 or greater than 0.1; and less than 0.5 or less than 0.45. Preferably, y may be greater than 0.05 and less than 0.5, or greater than 0.1 and less than 0.5, or greater than 0.1 and less than 0.45.

In order to enable the gas generation suppression effect to be expressed, it is preferable that y is greater than 0.05 or greater than 0.1. However, if y is too large, the electrochemical characteristics may deteriorate. Therefore, it is preferable that y is less than 0.5 or less than 0.45.

Preferably, the lithium-manganese transition metal oxide is Li _5.9 Mn _0.8 Fe _0.1 Zn _0.1 O ₄ , Li _5.9 Mn _0.75 Fe _0.1 Zn _0.15 O ₄ , Li _5.9 Mn _0.7 Fe _0.1 Zn _0.2 O ₄ , Li _5.9 Mn _0.65 Fe _0.1 Zn _0.25 O ₄ , Li _5.9 Mn _0.6 Fe _0.1 Zn _0.3 O ₄ , Li _5.9 Mn _0.55 Fe _0.1 Zn _0.35 O ₄ , Li _5.9 Mn _0.5 Fe _0.1 Zn _0.4 O ₄ , Li _5.9 Mn _0.45 Fe _0.1 Zn _0.45 O ₄ , Li _5.85 Mn _0.75 Fe _0.15 Zn _0.1 O ₄ , Li _5.85 Mn _0.7 Fe _0.15 Zn _0.15 O ₄ , Li _5.85 Mn _0.65 Fe _0.15 Zn _0.2 O ₄ , Li _5.85 Mn _0.6 Fe _0.15 Zn _0.25 O ₄ , Li _5.85 Mn _0.55 Fe _0.15 Zn _0.3 O ₄ , Li _5.85 Mn _0.5 Fe _0.15 Zn _0.35 O ₄ , Li _5.85 Mn _0.45 Fe _0.15 Zn _0.4 O ₄ , Li _5.85 Mn _0.4 Fe _0.15 Zn _0.45 O ₄ , Li _5.8 Mn _0.7 Fe _0.2 Zn _0.1 O ₄ , Li _5.8 Mn _0.65 Fe _0.2 Zn _0.15 O ₄ , Li _5.8 Mn _0.6 Fe _0.2 Zn _0.2 O ₄ , Li _5.8 Mn _0.55 Fe _0.2 Zn _0.25 O ₄ , Li _5.8 Mn _0.5 Fe _0.2 Zn _0.3 O ₄ , Li _5.8 Mn _0.45 Fe _0.2 Zn _0.35 O ₄ , Li _5.8 Mn _0.4 Fe _0.2 Zn _0.4 O ₄ , Li _5.8 Mn _0.35 Fe _0.2 Zn _0.45 O ₄ , Li _5.75 Mn _0.65 Fe _0.25 Zn _0.1 O ₄ , Li _5.75 Mn _0.6 Fe _0.25 Zn _0.15 O ₄ , Li _5.75 Mn _0.55 Fe _0.25 Zn _0.2 O ₄ , Li _5.75 Mn _0.5 Fe _0.25 Zn _0.25 O ₄ , Li _5.75 Mn _0.45 Fe _0.25 Zn _0.3 O ₄ , Li _{5. 75} Mn _0.4 Fe _0.25 Zn _0.35 O ₄ , Li _5.75 Mn _0.35 Fe _0.25 Zn _0.4 O ₄ , Li _5.75 Mn _0.3 Fe _0.25 Zn _0.45 O ₄ , Li _5.7 Mn _0.6 Fe _0.3 Zn _0.1 O ₄ , Li _5.7 Mn _0.55 Fe _0.3 Zn _0.15 O ₄ , Li _5.7 Mn _0.5 Fe _0.3 Zn _0.2 O ₄ , Li _5.7 Mn _0.45 Fe _0.3 Zn _0.25 O ₄ , Li _5.7 Mn _0.4 Fe _0.3 Zn _0.3 O ₄ , Li _5.7 Mn _0.35 Fe _0.3 Z n _0.35 O ₄ , Li _5.7 Mn _0.3 Fe _0.3 Zn _0.4 O ₄ , Li _5.7 Mn _0.25 Fe _0.3 Zn _0.45 O ₄ , Li _5.65 Mn _0.55 Fe _0.35 Zn _0.1 O ₄ , Li _5.65 Mn _0.5 Fe _0.35 Zn _0.15 O ₄ , Li _5.65 Mn _0.45 Fe _0.35 Zn _0.2 O ₄ , Li _5.65 Mn _0.4 Fe _0.35 Zn _0.25 O ₄ , Li _5.65 Mn _0.35 Fe _0.35 Zn _0.3 O ₄ , Li _5.65 Mn _0.3 Fe _0.35 Zn _0.35 O ₄ , Li _5.65 Mn _0.25 Fe _0.35 Zn _0.4 O ₄ , Li _5.65 Mn _0.2 Fe _0.35 Zn _0.45 O ₄ , Li _5.6 Mn _0.5 Fe _0.4 Zn _0.1 O ₄ , Li _5.6 Mn _0.45 Fe _0.4 Zn _0.15 O ₄ , Li _5.6 Mn _0.4 Fe _0.4 Zn _0.2 O ₄ , Li _5.6 Mn _0.35 Fe _0.4 Zn _0.25 O ₄ , Li _5.6 Mn _0.3 Fe _0.4 Zn _0.3 O ₄ , Li _5.6 Mn _0.25 Fe _0.4 Zn _0.35 O ₄ , Li _5.6 Mn _0.2 Fe Zn _{0.4 O 4} , Li _5.6 Mn _0.15 Fe _0.4 Zn _0.45 O ₄ , Li _5.55 Mn _0.45 Fe _0.45 Zn _0.1 O ₄ , Li _5.55 Mn _0.4 Fe _0.45 Zn _0.15 O ₄ , Li _5.55 Mn _0.35 Fe _0.45 Zn _0.2 O ₄ , Li _5.55 Mn _0.3 Fe _0.45 Zn _0.25 O ₄ , Li _5.55 Mn _0.25 Fe _0.45 Zn _0.3 O ₄ , Li _5.55 Mn _0.2 Fe _0.45 Zn _0.35 O ₄ , Li _5.55 Mn _0.15 Fe _0.45 Zn _0.4 O ₄ , and Li _5.55 Mn _0.1 Fe _0.45 Zn _0.45 O ₄ may be at least one compound selected from the group consisting of:

In the lithium-manganese transition metal oxide, the heterogeneous element can form an alloy with manganese (Mn) to exhibit a stable single phase. Due to the formation of this single phase, a part of the lithium-manganese transition metal oxide can be deactivated to form its structural stability, and a large amount of gas generated by decomposition of the lithium-manganese transition metal oxide can be suppressed.

The formation of a single phase in which these heterogeneous elements are alloyed can be confirmed, for example, by analyzing the lithium-manganese transition metal oxide using XRD. Specifically, when the lithium-manganese transition metal oxide is analyzed using XRD, a peak derived from manganese (Mn) may shift due to alloying, resulting in a single peak indicating a stable single phase rather than a secondary phase.

In contrast, when a secondary phase appears because another element is included in addition to the above-mentioned heterogeneous element, or when the heterogeneous element is not sufficiently included and the formation of a single phase is insufficient, an XRD analysis result different from that of the lithium-manganese transition metal oxide may be derived. For example, when the secondary phase is formed, peaks due to manganese (Mn) and another element may be confirmed to be separated from each other in XRD. In addition, when the heterogeneous element is not sufficiently included and the formation of a single phase is insufficient, the shift of the single peak may not be sufficiently observed compared to the lithium-manganese transition metal oxide. Since the lithium-manganese transition metal oxide includes the heterogeneous element in an alloyed state at a sufficient content ratio, a sufficient single peak shift can be confirmed in the XRD analysis result.

Meanwhile, the lithium-manganese transition metal oxide can have a particle size that can be uniformly mixed with the cathode active material and exhibit appropriate characteristics within the cathode.

According to one embodiment, the lithium-manganese based transition metal oxide may have a form of primary particles having a volume average particle diameter (D50) of 5 ㎛ to 20 ㎛, or 7 ㎛ to 15 ㎛, or 9 ㎛ to 13 ㎛, or secondary particles in which primary particles are aggregated. The volume average particle diameter (D50) of the lithium-manganese based transition metal oxide can be measured and calculated using a well-known laser particle size analyzer, etc.

The above-described lithium-manganese transition metal oxide can be mixed with a separate cathode active material and act as a sacrificial cathode material that compensates for the irreversible capacity of the anode during the initial charge/discharge process of a lithium secondary battery, and after this irreversible capacity compensation, the cathode active material can act.

According to another embodiment of the invention,

A step of providing a raw material mixture comprising a lithium precursor, a manganese precursor, an iron precursor, and a zinc precursor in a solid state; and

A step of calcining the above raw material mixture under an inert atmosphere and a temperature of 500° C. to 900° C. to obtain the lithium-manganese transition metal oxide.

A method for producing a lithium-manganese transition metal oxide, including:

In the first step, a raw material mixture including a lithium precursor, a manganese precursor, an iron precursor, and a zinc precursor is prepared. The raw material mixture can be prepared by solid-phase mixing the lithium precursor, the manganese precursor, the iron precursor, and the zinc precursor so as to match the stoichiometric ratio described for the lithium-manganese transition metal oxide.

As the lithium precursor, an oxide containing lithium, such as _Li2O , can be used without any special limitation.

As the manganese precursor, an oxide containing manganese, such as MnO, can be used without any special limitation.

As the above iron precursor and the above zinc precursor, one or more compounds selected from the group consisting of chlorides, nitrates, sulfur oxides, phosphates, oxides, halides, and hydrates thereof containing iron or zinc can be used.

In the second step, the lithium transition metal oxide is obtained by calcining the raw material mixture obtained in the first step under an inert atmosphere and a temperature of 500° C. or higher.

The second step can be performed under an inert atmosphere formed using an inert gas such as Ar, N ₂ , Ne, and He.

The sintering in the second step can be performed at a temperature of 500°C to 900°C or 550°C to 850°C. In order to allow crystal seeds to be generated at an appropriate rate, the sintering temperature is preferably 500°C or higher or 550°C or higher. However, if the sintering temperature is excessively high, sintering phenomenon in which grown crystal particles clump together may occur. Therefore, the sintering temperature is preferably 900°C or lower or 850°C or lower.

The above-mentioned calcination can be performed for 2 hours to 20 hours under the above-mentioned calcination temperature. The above-mentioned calcination time can be controlled in consideration of the time required for the heterogeneous element to be introduced into the lithium-manganese oxide in the form of an alloy and for the crystal to be stabilized. Specifically, the above-mentioned calcination time can be 2 hours or more, or 3 hours or more, or 4 hours or more; and 20 hours or less, or 15 hours or less, or 12 hours or less. Preferably, the above-mentioned calcination time can be 3 hours to 20 hours, or 3 hours to 15 hours, or 4 hours to 15 hours, or 4 hours to 12 hours.

According to one embodiment, in the second step, it is preferable to heat the raw material mixture at a heating rate of 1.4 °C/min to 2.0 °C/min under an inert atmosphere to reach the sintering temperature.

If the above heating rate is too slow, crystal seeds are formed slowly and the crystals continue to grow, which may cause the particles to become too large. Therefore, the heating rate is preferably 1.4 ℃/min or more. However, if the heating rate is excessively fast, crystal seeds are generated in large quantities at a very fast rate, and the growth time of the particles is relatively insufficient, which may cause the crystallinity to be relatively low and the particle size to become relatively small. Therefore, the heating rate is preferably 2.0 ℃/min or less.

Specifically, the heating rate may be 1.40° C./min or more, or 1.45° C./min or more, or 1.50° C./min or more; and 2.00° C./min or less, or 1.95° C./min or less, or 1.90° C./min or less. Preferably, the heating rate may be 1.40° C./min to 2.00° C./min, or 1.45° C./min to 2.00° C./min, or 1.45° C./min to 1.95° C./min, or 1.50° C./min to 1.95° C./min, or 1.50° C./min to 1.90° C./min.

If necessary, a step of washing and drying the lithium-manganese transition metal oxide obtained in the second step may be performed.

As a non-limiting example, the cleaning process can be performed by mixing and stirring the lithium-manganese transition metal oxide and the cleaning solution in a weight ratio of 1:2 to 1:10. Distilled water, ammonia water, or the like can be used as the cleaning solution. The drying process can be performed by heat treating at a temperature of 100° C. to 200° C. for 1 to 10 hours.

According to another embodiment of the invention, a cathode additive for a lithium secondary battery comprising the lithium-manganese transition metal oxide is provided.

The above lithium-manganese transition metal oxide exhibits high initial irreversible capacity, while suppressing gas generation during compensation of irreversible capacity loss, thereby improving the stability of the battery.

The positive electrode additive for a lithium secondary battery including the above lithium-manganese transition metal oxide has a characteristic of irreversibly releasing lithium during charging and discharging of a lithium secondary battery. Therefore, the positive electrode additive for a lithium secondary battery can be included in a positive electrode for a lithium secondary battery and play a role as a sacrificial positive electrode material for prelithiation.

According to another embodiment of the invention, a positive electrode for a lithium secondary battery comprising the lithium-manganese transition metal oxide is provided.

The above-mentioned positive electrode for a lithium secondary battery may include a positive electrode active material, a binder, a conductive material, and the lithium-manganese transition metal oxide.

Preferably, the positive electrode for the lithium secondary battery comprises a positive electrode material including a positive electrode active material, a conductive material, the lithium-manganese transition metal oxide, and a binder; and a current collector supporting the positive electrode material.

As the capacity of the battery increases, the ratio of the cathode active material in the cathode must increase, and accordingly, the amount of lithium consumed in the SEI layer also increases. Therefore, the amount of lithium consumed in the SEI layer of the cathode can be calculated, and then the amount of sacrificial cathode material to be applied to the cathode side can be reversed to determine the design capacity of the battery.

According to one embodiment, the lithium-manganese transition metal oxide may be included in an amount of more than 0 wt% and less than or equal to 15 wt% relative to the total weight of the cathode material.

In order to compensate for the irreversible lithium consumed in the formation of the SEI layer, it is preferable that the content of the lithium-manganese transition metal oxide exceeds 0 wt% based on the total weight of the cathode material.

However, when the lithium-manganese transition metal oxide is included in an excessive amount, the content of the positive electrode active material exhibiting reversible charge/discharge capacity decreases, thereby reducing the capacity of the battery, and residual lithium in the battery may plate on the negative electrode, causing a short circuit in the battery or compromising safety. Therefore, the content of the lithium-manganese transition metal oxide is preferably 15 wt% or less relative to the total weight of the positive electrode material.

Specifically, the content of the lithium-manganese transition metal oxide may be greater than 0 wt%, or greater than 0.5 wt%, or greater than 1 wt%, or greater than 2 wt%, or greater than 3 wt%; and may be less than 15 wt%, or less than 12 wt%, or less than 10 wt% relative to the total weight of the cathode material.

Preferably, the content of the lithium-manganese transition metal oxide may be 0.5 wt% to 15 wt%, or 1 wt% to 15 wt%, or 1 wt% to 12 wt%, or 2 wt% to 12 wt%, or 2 wt% to 10 wt%, or 3 wt% to 10 wt% relative to the total weight of the cathode material.

As the positive electrode active material, any material capable of reversible insertion and de-insertion of lithium ions may be used without special limitation. For example, the positive electrode active material may be a composite oxide or phosphate containing lithium and a metal such as cobalt, manganese, nickel, iron, or a combination thereof.

As a non-limiting example, the positive electrode active material may be a compound represented by any one of the following chemical formulas:

Li _a A _1-b R _b D ₂ (0.90≤a≤1.8, 0≤b≤0.5); Li _a E _1-b R _b O _2-c D _c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE _2-b R _b O _4-c D _c (0≤b≤0.5, 0≤c≤0.05); Li _a Ni _1-bc Co _b R _c D _d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d≤2); Li _a Ni _1-bc Co _b R _c O _2-d Z _d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d<2); Li _a Ni _1-bc Co _b R _c O _2-d Z ₂ (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d<2); Li _a Ni _1-bc Mn _b R _c D _d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d≤2); Li _a Ni _1-bc Mn _b R _c O _2-d Z _d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d<2); Li _a Ni _1-bc Mn _b R _c O _2-d Z ₂ (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<d<2); Li _a Ni _b E _c G _d O ₂ (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1.); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li _a NiG _b O ₂ (0.90≤a≤1.8, 0.001≤b≤0.1); Li _a CoG _b O ₂ (0.90≤a≤1.8, 0.001≤b≤0.1); Li _a MnG _b O ₂ (0.90≤a≤1.8, 0.001≤b≤0.1); Li _a Mn ₂ G _b O ₄ (0.90≤a≤1.8, 0.001≤b≤0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LITO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≤f≤2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≤f≤2); and LiFePO ₄ .

In the chemical formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, it is also possible to use a material having a coating layer on the surface of the above-mentioned positive electrode active material, or it is also possible to use a mixture of the above-mentioned positive electrode active material and a positive electrode active material having a coating layer. As the coating element included in the above-mentioned coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof can be used.

According to one embodiment, the positive electrode active material may be included in an amount of 80 wt% to 95 wt% relative to the total weight of the positive electrode material.

Specifically, the content of the positive electrode active material may be 80 wt% or more, or 82 wt% or more, or 85 wt% or more; and 95 wt% or less, or 93 wt% or less, or 90 wt% or less, relative to the total weight of the positive electrode material.

Preferably, the content of the positive electrode active material may be 82 wt% to 95 wt%, or 82 wt% to 93 wt%, or 85 wt% to 93 wt%, or 85 wt% to 90 wt% relative to the total weight of the positive electrode material.

The above-mentioned conductive material is used to provide conductivity to the electrode.

As the conductive material, any material having electronic conductivity and not causing a chemical change in the battery may be used without particular limitation. Non-limiting examples thereof include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; graphite such as natural graphite or artificial graphite; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives. The conductive material may be one or a mixture of two or more of the above-described examples.

The content of the conductive material can be adjusted within a range that does not cause a decrease in the capacity of the battery while exhibiting an appropriate level of conductivity. Preferably, the content of the conductive material can be 1 wt% to 10 wt% or 1 wt% to 5 wt% relative to the total weight of the cathode material.

The above binder is used to properly attach the positive electrode material to the current collector.

As non-limiting examples, the binder may be a polymer including polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon resin, etc. The binder may be one or a mixture of two or more of the above-described examples.

The content of the binder can be adjusted within a range that does not cause a decrease in the capacity of the lithium secondary battery while exhibiting an appropriate level of adhesiveness. Preferably, the content of the binder can be 1 wt% to 10 wt% or 1 wt% to 5 wt% relative to the total weight of the electrode material.

As the above current collector, any material known to be applicable to a positive electrode of a lithium secondary battery in the technical field to which the present invention belongs can be used without any particular limitation.

Non-limiting examples of the current collectors may include stainless steel; aluminum; nickel; titanium; calcined carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

Preferably, the current collector may have a thickness of 3 μm to 500 μm. In order to increase the adhesive strength of the positive electrode material, the current collector may have fine unevenness formed on its surface. The current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The above-described positive electrode for a lithium secondary battery can be formed by laminating a positive electrode material including the positive electrode active material, the conductive material, the lithium-manganese transition metal oxide, and a binder on the current collector.

According to another embodiment of the invention, a lithium secondary battery is provided, including a positive electrode; an anode; a separator; and an electrolyte for the lithium secondary battery.

The above lithium secondary battery has a cathode including the lithium-manganese transition metal oxide. Accordingly, the lithium secondary battery can suppress gas generation at the cathode during charging and discharging, and can exhibit improved safety and life characteristics. In addition, the lithium secondary battery can exhibit high discharge capacity, excellent output characteristics, and capacity retention rate.

The above lithium secondary battery can be used as an energy source with improved performance and safety in the field of portable electronic devices such as mobile phones, notebook computers, tablet computers, mobile batteries, and digital cameras; and in the field of transportation means such as electric vehicles, electric motorcycles, and personal mobility devices.

The above lithium secondary battery may include an electrode assembly wound with a separator interposed between the positive electrode and the negative electrode, and a case in which the electrode assembly is built. In addition, the positive electrode, the negative electrode, and the separator may be impregnated with an electrolyte.

The above lithium secondary battery can have various shapes such as square, cylindrical, and pouch shapes.

The above negative electrode may include a negative electrode material including a negative electrode active material, a conductive material, and a binder; and a current collector supporting the negative electrode material.

The above negative active material may include a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, an alloy of a lithium metal, a material capable of doping and dedoping lithium, and a transition metal oxide.

As the material capable of reversibly intercalating and deintercalating the lithium ions, carbonaceous materials may be exemplified by crystalline carbon, amorphous carbon, or a mixture thereof. Specifically, the carbonaceous material may be natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch based carbon fiber, meso-carbon microbeads, petroleum or coal tar pitch derived cokes, soft carbon, and hard carbon.

The above lithium metal alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd.

The material capable of doping and dedoping lithium may be Si, a Si-C composite, SiOx (0<x<2), a Si-Q alloy (wherein Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof; however, Si is excluded), Sn, SnO ₂ , a Sn-R alloy (wherein R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof; however, Sn is excluded). In addition, the material capable of doping and dedoping lithium may be a mixture of at least one of the above examples and SiO ₂ . The Q and R are Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, It may be Te, Po, etc.

And, the transition metal oxide may be vanadium oxide, lithium vanadium oxide, lithium titanium oxide, etc.

Preferably, the negative electrode may include at least one negative electrode active material selected from the group consisting of carbonaceous materials and silicon compounds.

Here, the carbonaceous material is at least one material selected from the group consisting of natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fibers, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon, as exemplified above. And, the silicon compound can be a compound including Si as exemplified above, that is, Si, a Si-C composite, SiOx (0<x<2), the Si-Q alloy, a mixture thereof, or a mixture of at least one of these and _SiO2 .

According to one embodiment, the negative electrode active material may be included in an amount of 85 wt% to 98 wt% relative to the total weight of the negative electrode material.

Specifically, the content of the negative electrode active material may be 85 wt% or more, or 87 wt% or more, or 90 wt% or more, and 98 wt% or less, or 97 wt% or less, or 95 wt% or less, relative to the total weight of the negative electrode material.

Preferably, the content of the negative electrode active material may be 85 wt% to 97 wt%, or 87 wt% to 97 wt%, or 87 wt% to 95 wt%, or 90 wt% to 95 wt% relative to the total weight of the negative electrode material.

The conductive material, the binder, and the current collector included in the negative electrode material are replaced with the contents described in the positive electrode for a lithium secondary battery.

The above separator separates the positive and negative electrodes and provides a passage for lithium ions to move. As the above separator, any separator known to be applicable to a separator of a lithium secondary battery in the technical field to which the present invention belongs may be used without particular limitation. It is preferable that the separator have low resistance to ion movement of the electrolyte and excellent wettability with respect to the electrolyte.

Specifically, the separator may be a porous polymer film made of a polyolefin polymer such as polyethylene, polypropylene, an ethylene-butene copolymer, an ethylene-hexene copolymer, an ethylene-methacrylate copolymer, or the like. The separator may be a multilayer film in which two or more layers of the porous polymer film are laminated. The separator may be a nonwoven fabric including glass fiber, polyethylene terephthalate fiber, or the like. In addition, the separator may be coated with a ceramic component or a polymer material to secure heat resistance or mechanical strength.

Meanwhile, as the electrolyte, any electrolyte known to be applicable to a lithium secondary battery in the technical field to which the present invention belongs may be used without any particular limitation. For example, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc.

Specifically, the electrolyte may include a non-aqueous organic solvent and a lithium salt.

Any non-aqueous organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without special restrictions.

Specifically, the non-aqueous organic solvent includes: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolane.

Among the above examples, a carbonate solvent can be preferably used as the non-aqueous organic solvent.

In particular, considering the charge/discharge performance of the battery and compatibility with the sacrificial cathode material, a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate) having high ionic conductivity and high dielectric constant and a linear carbonate (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate) having low viscosity can be preferably used as the non-aqueous organic solvent. In this case, using a mixture of the cyclic carbonate and the linear carbonate in a volume ratio of 1:1 to 1:9 can be advantageous for exhibiting the above-described performance.

In addition, as the non-aqueous organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 to 1:10; or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1 to 3:1 to 9:1 can be preferably used.

The lithium salt included in the above electrolyte is dissolved in the non-aqueous organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes.

Specifically, the lithium salt may be 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 , LiN(SO ₂ F) ₂ (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, and LiB(C ₂ O4) ₂ . Preferably, the lithium salt may be LiPF ₆ , LiFSI, and a mixture thereof.

The lithium salt may be included in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt included in the above concentration range enables the electrolyte to exhibit excellent electrolyte performance by providing appropriate conductivity and viscosity to the electrolyte.

Optionally, the electrolyte may include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

For example, the additive may be a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxy ethanol, aluminum trichloride, or the like. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

The lithium-manganese transition metal oxide according to the present invention exhibits a high initial irreversible capacity, while suppressing gas generation during compensation for irreversible capacity loss, thereby improving the stability of the battery.

These lithium transition metal oxides can compensate for the irreversible capacity loss of high-capacity lithium secondary batteries, while effectively suppressing gas generation from the battery and fire and explosion caused by such gas generation.

The following specific examples of the invention will explain the operation and effect of the invention in more detail. However, these are presented as examples to help understand the invention. The following examples are not intended to limit the scope of the invention in any way, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present invention.

Example 1

(1) Synthesis of lithium-manganese transition metal oxides

A raw material mixture was prepared by solid-phase mixing Li ₂ O, MnO, Fe ₂ O ₃ , and ZnO in a molar ratio of Li : Mn : Fe : Zn = 5.7 : 0.4 : 0.3 : 0.3.

The above raw material mixture was heated at a heating rate of 1.6 ℃/min under an Ar atmosphere and then calcined at 750 ℃ for 6 hours to obtain a lithium-manganese transition metal oxide of Li _5.7 Mn _0.4 Fe _0.3 Zn _0.3 O ₄ .

The lithium-manganese transition metal oxide was crushed using a jaw crusher and then classified using a sieve shaker.

(2) Lithium secondary battery manufacturing

A positive electrode was manufactured using the above lithium-manganese transition metal oxide as a positive electrode additive. An NCMA (Li[Ni,Co,Mn,Al] _O2 ) compound (NTA-X12M, L&F) was used as a positive electrode active material. The positive electrode active material and the positive electrode additive were mixed at a weight ratio of 98:2. A positive electrode slurry was manufactured by mixing the mixture of the positive electrode active material and the positive electrode additive, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 95:3:2 in an organic solvent (N-methylpyrrolidone). The positive electrode slurry was applied to one surface of a current collector, which is an aluminum foil having a thickness of 15 ㎛, and rolled and dried to manufacture a positive electrode.

Natural graphite as an anode active material, carbon black as a conductive material, and carboxymethyl cellulose (CMC) as a binder were mixed in an organic solvent (N-methylpyrrolidone) at a weight ratio of 95:3:2 to prepare a cathode material slurry. The cathode material slurry was applied to one surface of a current collector, which is a copper foil with a thickness of 15 ㎛, and rolled and dried to prepare a cathode.

A non-aqueous organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3. An electrolyte was prepared by dissolving lithium salts, namely, LiPF ₆ with a concentration of 0.7 M and LiFSI with a concentration of 0.5 M, in the non-aqueous organic solvent.

An electrode assembly was manufactured by interposing a porous polyethylene membrane between the positive and negative electrodes, and the electrode assembly was positioned inside a case. The electrolyte was injected inside the case to manufacture a lithium secondary battery in the form of a pouch cell.

Example 2

A lithium-manganese transition metal oxide (Li 5.7 Mn 0.6 Fe _0.3 Zn 0.1 O ₄ ) and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li _{2 O} , MnO, Fe 2 O ₃ , and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.7 : _0.6 : _0.3 : 0.1.

Example 3

A lithium-manganese transition metal oxide (Li 5.7 Mn 0.5 Fe _0.3 Zn 0.2 O ₄ ) and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li _{2 O,} MnO, Fe 2 O ₃ , and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.7 : _0.5 : _{0.3 : 0.2} .

Example 4

A lithium-manganese transition metal oxide (Li 5.7 Mn 0.3 Fe _0.3 Zn 0.4 O ₄ ) and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li _{2 O} , MnO, Fe 2 O _{3 , and ZnO} was used in a molar ratio of Li : Mn : Fe : Zn = _5.7 : _0.3 : _0.3 : 0.4.

Example 5

A lithium-manganese transition metal oxide (Li 5.9 Mn 0.6 Fe _0.1 Zn 0.3 O ₄ ) and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ , and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.9 : _0.6 : _{0.1 : 0.3} .

Example 6

A lithium-manganese transition metal oxide (Li 5.8 Mn 0.5 Fe _0.2 Zn 0.3 O ₄ ) and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ , and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.8 : _{0.5 : 0.2} : 0.3.

Example 7

A lithium-manganese transition metal oxide of Li 5.6 Mn 0.3 Fe _0.4 Zn 0.3 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li _{2 O} , MnO, Fe 2 O 3 , and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.6 : _{0.3 : 0.4} : _0.3 .

Example 8

A lithium-manganese transition metal oxide of Li 5.8 Mn 0.6 Fe 0.2 Zn _0.2 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.8 : _0.6 : _0.2 : 0.2.

Example 9

A lithium-manganese transition metal oxide of Li 5.8 Mn 0.7 Fe _0.2 Zn 0.1 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.8 : _0.7 : _0.2 : 0.1.

Example 10

A lithium-manganese transition metal oxide of Li 5.9 Mn 0.7 Fe _0.1 Zn 0.2 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.9 : _0.7 : _0.1 : 0.2.

Example 11

A lithium-manganese transition metal oxide having the structure of Li 5.9 Mn 0.8 Fe _0.1 Zn 0.1 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li _{2 O} , MnO, Fe 2 O ₃ and ZnO was used in a molar ratio of Li : Mn : Fe : Zn = _5.9 : _0.8 : _0.1 : 0.1.

Comparative Example 1

A lithium-manganese transition metal oxide of Li _5.7 Mn 0.7 Fe _0.3 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO and Fe 2 O ₃ was used so that the molar ratio of Li : Mn : Fe _{= 5.7} : _{0.7 :} 0.3.

Comparative Example 2

The raw material mixture was prepared by solid-phase mixing Li ₂ O, MnO, and Al ₂ O ₃ so that the molar ratio of Li : Mn : Al = 5.85 : 0.85 : 0.15.

The above raw material mixture was heated at a heating rate of 1.6 ℃/min under an Ar atmosphere and then calcined at 750 ℃ for 6 hours to obtain a lithium-manganese transition metal oxide of Li _5.85 Mn _0.85 Al _0.15 O ₄ .

The lithium-manganese transition metal oxide was crushed using a jaw crusher and then classified using a sieve shaker.

The obtained lithium-manganese transition metal oxide particles and carbon black (FX35) were mixed at a weight ratio of 1:0.01, and then ball-milled for 24 hours to allow the carbon black to be evenly coated on the lithium-manganese transition metal oxide particles. Thereafter, seiving was performed to obtain [lithium-manganese transition metal oxide-carbon] composite particles.

A lithium secondary battery was manufactured using the above composite particles as a cathode additive in the same manner as in Example 1.

Comparative Example 3

[Lithium-manganese transition metal oxide-carbon] composite particles and a lithium secondary battery including the same were manufactured in the same manner as in Comparative Example 2, except that Li ₂ O, MnO, and _ZnO were used as a solid-phase mixture in a molar ratio of Li:Mn _: Zn = 6 _{:0.7 :0.3} .

Comparative Example 4

A lithium-manganese transition metal oxide of Li _5.9 Mn 0.9 Fe _0.1 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO and Fe 2 O ₃ was used so that the molar ratio of Li : Mn : Fe _{= 5.9} : _{0.9 : 0.1} .

Comparative Example 5

A lithium-manganese transition metal oxide of Li _5.8 Mn 0.8 Fe _0.2 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO and Fe 2 O ₃ was used in a molar ratio of Li : Mn : Fe = 5.8 _{: 0.8 : 0.2} .

Comparative Example 6

A lithium-manganese transition metal oxide of Li _5.6 Mn 0.6 Fe _0.4 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a solid-phase mixture of Li ₂ O, MnO and Fe 2 O ₃ was used so that the molar ratio of Li : Mn : Fe _{= 5.6} : _{0.6 : 0.4} .

Comparative Example 7

A lithium-manganese transition metal oxide of Li 5.55 Mn 0.55 Fe _{0.3 Al} 0.15 O 4 and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that Li _{2 O} , MnO, Fe ₂ O ₃ and Al 2 O ₃ were solid-mixed in a molar ratio of Li : Mn : Fe : Al = _5.55 : 0.55 : _{0.3 : 0.15} as the raw material mixture. The crystal phase of the manufactured oxide was confirmed by XRD, and a phase other than the Li ₆ MnO ₄ single crystal phase was observed.

Comparative Example 8

A lithium-manganese transition metal oxide-carbon composite of Li _5.85 Mn 0.55 Zn _0.3 Al 0.15 O ₄ and a lithium secondary battery including the same were manufactured in the same manner as in Comparative Example 2, except that a solid-phase mixture of Li 2 O, MnO, ZnO and Al 2 O ₃ was used in a molar ratio of Li : Mn : Zn _{= 5.85 : 0.55} : _{0.3 : 0.15} . The crystal phase of the manufactured oxide was confirmed by XRD, and a phase other than the Li ₆ MnO ₄ single crystal phase was observed.

Comparative Example 9

Except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ and MgO was used in a molar ratio of Li : Mn : Fe : Mg = 5.7 : 0.6 : 0.3 : 0.1 as the raw material mixture, Li _5.7 Mn _0.6 Fe _0.3 Mg _0.1 O ₄ , was produced in the same manner as in Example 1. The crystal phase of the produced oxide was confirmed by XRD, and a phase other than the Li ₆ MnO ₄ single crystal phase was observed.

Comparative Example 10

Except that a solid-phase mixture of Li ₂ O, MnO, Fe ₂ O ₃ and TiO ₂ was used as the raw material mixture in a molar ratio of Li : Mn : Fe : Ti = 5.7 : 0.6 : 0.3 : 0.1, a lithium-manganese transition metal oxide of Li _5.7 Mn _0.6 Fe _0.3 Ti _0.1 O ₄ was produced in the same manner as in Example 1. The crystal phase of the produced oxide was confirmed by XRD, and a phase other than the Li ₆ MnO ₄ single crystal phase was observed.

Exam example

The cumulative gas generation amount according to high-temperature storage at 80 °C for the lithium secondary batteries obtained in the above examples and comparative examples was measured using the following method, and the results are shown in Table 1 below.

A lithium secondary battery was charged under constant current-constant voltage conditions of 45 ℃ to 4.25 V at 0.1 C, recovered, and stored in an 80 ℃ chamber. After 24 hours, 100 hours, and 300 hours, the lithium secondary battery was taken out from the chamber, and the difference between the original weight of the lithium secondary battery and its weight in water was measured using a hydrometer (MATSUHAKU, TWD-150DM), and the change in volume inside the lithium secondary battery was calculated. The change in volume was divided by the weight of the electrode active material to calculate the amount of gas evolution per weight.

Cumulative gas production (mL/g) Formation 24 hr 100 hr 300 hr Total Example 1
(Li _5.7 Mn _0.4 Fe _0.3 Zn _0.3 O ₄ ) 0.313 0.297 0.198 0.241 1.049 Example 2
(Li _5.7 Mn _0.6 Fe _0.3 Zn _0.1 O ₄ ) 0.379 0.858 0.235 0.141 1.613 Example 3
(Li _5.7 Mn _0.5 Fe _0.3 Zn _0.2 O ₄ ) 0.357 0.631 0.213 0.156 1.357 Comparative Example 1
(Li _5.7 Mn _0.7 Fe _0.3 O ₄ ) 0.381 1.488 0.385 -0.064 2.190 Comparative Example 2
(Li _5.85 Mn _0.85 Al _0.15 O ₄ ) 0.298 0.991 0.429 -0.051 1.667 Comparative Example 3
(Li ₆ Mn _0.7 Zn _0.3 O ₄ ) 0.270 0.742 0.312 0.217 1.541

Referring to Table 1 above, it can be seen that the cumulative gas generation amount during high-temperature storage at 80 °C decreases as the amount of zinc increases in Examples 1 to 3.

In the case of Comparative Example 1 without zinc, the cumulative gas generation amount after 300 hours was the largest at 2.190 mL/g. As a result, it can be seen that iron does not have a significant effect in reducing gas generation and zinc helps reduce gas generation.

In Comparative Example 2, a reduction in gas generation was observed due to the addition of aluminum alone, but the degree was less than that of zinc. In a separate experiment, aluminum was not dissolved in Li ₆ MnO ₄ at more than 20 mol%, making further application impossible.

In the case of adding zinc alone in Comparative Example 3, gas generation was reduced compared to the case of adding iron alone in Comparative Example 1, but due to insufficient conductivity, as in Comparative Example 2, it could be applied to a lithium secondary battery only when a complex was formed with carbon. In addition, Comparative Example 3 showed an insufficient gas reduction effect compared to Example 1, where iron and zinc were simultaneously employed. That is, it can be seen that the composition of Example 1, where iron and zinc were simultaneously introduced, showed the most effective gas reduction in high-temperature storage at 80 °C. In this way, it was confirmed that an additional gas generation suppression effect can be expressed when iron and zinc are applied together.

In the case of Examples 5, 6, 8, 9, 10, and 11 and Comparative Examples 4 and 5, the content of iron in the lithium-manganese transition metal oxide, which is a positive electrode additive, was low at 10 to 20 mol%, which reduced the conductivity of the particles and thus the formation capacity was not sufficiently expressed in the lithium secondary battery.

In Example 7, the amount of iron in the lithium-manganese transition metal oxide was high at 40 mol%, so some fine Li ₅ FeO ₄ phases were observed, and the degree of particle sintering was so severe that the formation capacity was not sufficiently expressed in a lithium secondary battery.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of the present invention and the equivalent scope of the patent claims to be described below by a person skilled in the art to which the present invention pertains.

Claims (11)

A lithium (Li)-manganese (Mn) transition metal oxide containing iron (Fe) and zinc (Zn) as heteroelements.
In the first paragraph,
A transition metal oxide, wherein the above heterogeneous element is contained in an amount of 10 mol% to 90 mol% based on the total metal elements excluding lithium in the lithium-manganese transition metal oxide.
In the first paragraph,
The above heterogeneous elements are lithium-manganese transition metal oxides containing iron and zinc in a molar ratio of 1:0.1 to 1:10.
In the first paragraph,
The above lithium-manganese transition metal oxide is a lithium-manganese transition metal oxide represented by the following chemical formula 1:
[Chemical Formula 1]
Li _6-x Mn _1-xy Fe _x Zn _y O ₄
In the above chemical formula 1, 0.05 < x < 0.5 and 0.05 < y < 0.5.
In the first paragraph,
The above lithium-manganese transition metal oxides are Li _5.9 Mn _0.8 Fe _0.1 Zn _0.1 O ₄ , Li _5.9 Mn _0.75 Fe _0.1 Zn _0.15 O ₄ , Li _5.9 Mn _0.7 Fe _0.1 Zn _0.2 O ₄ , Li _5.9 Mn _0.65 Fe _0.1 Zn _0.25 O ₄ , Li _5.9 Mn _0.6 Fe _0.1 Zn _0.3 O ₄ , Li _5.9 Mn _0.55 Fe _0.1 Zn _0.35 O ₄ , Li _5.9 Mn _0.5 Fe _0.1 Zn _0.4 O ₄ , Li _5.9 Mn _0.45 Fe _0.1 Zn _0.45 O ₄ , Li _5.85 Mn _0.75 Fe _0.15 Zn _0.1 O ₄ , Li _5.85 Mn _0.7 Fe _0.15 Zn _0.15 O ₄ , Li _5.85 Mn _0.65 Fe _0.15 Zn _0.2 O ₄ , Li _5.85 Mn _0.6 Fe _0.15 Zn _0.25 O ₄ , Li _5.85 Mn _{0. 55} Fe _0.15 Zn _0.3 O ₄ , Li _5.85 Mn _0.5 Fe _0.15 Zn _0.35 O ₄ , Li _5.85 Mn _0.45 Fe _0.15 Zn _0.4 O ₄ , Li _5.85 Mn _0.4 Fe _0.15 Zn _0.45 O ₄ , Li _5.8 Mn _0.7 Fe _0.2 Zn _0.1 O ₄ , Li _5.8 Mn _0.65 Fe _0.2 Zn _0.15 O ₄ , Li _5.8 Mn _0.6 Fe _0.2 Zn _0.2 O ₄ , Li _5.8 Mn _0.55 Fe _0.2 Zn _0.25 O ₄ , Li _5.8 Mn _0.5 Fe _0.2 Zn _0.3 O ₄ , Li _5.8 Mn _0.45 Fe _0.2 Zn _0.35 O ₄ , Li _5.8 Mn _0.4 Fe _0.2 Zn _0.4 O ₄ , Li _5.8 Mn _0.35 Fe _0.2 Zn _0.45 O ₄ , Li _5.75 Mn _0.65 Fe _0.25 Zn _0.1 O ₄ , Li _5.75 Mn _0.6 Fe _0.25 Zn _0.15 O ₄ , Li _5.75 Mn _0.55 Fe _0.25 Zn _0.2 O ₄ , Li _5.75 Mn _0.5 Fe _0.25 Zn _0.25 O ₄ , Li _5.75 Mn _0.45 Fe _0.25 Zn _0.3 O ₄ , Li _{5. 75} Mn _0.4 Fe _0.25 Zn _0.35 O ₄ , Li _5.75 Mn _0.35 Fe _0.25 Zn _0.4 O ₄ , Li _5.75 Mn _0.3 Fe _0.25 Zn _0.45 O ₄ , Li _5.7 Mn _0.6 Fe _0.3 Zn _0.1 O ₄ , Li _5.7 Mn _0.55 Fe _0.3 Zn _0.15 O ₄ , Li _5.7 Mn _0.5 Fe _0.3 Zn _0.2 O ₄ , Li _5.7 Mn _0.45 Fe _0.3 Zn _0.25 O ₄ , Li _5.7 Mn _0.4 Fe _0.3 Zn _0.3 O ₄ , Li _5.7 Mn _0.35 Fe _0.3 Z n _0.35 O ₄ , Li _5.7 Mn _0.3 Fe _0.3 Zn _0.4 O ₄ , Li _5.7 Mn _0.25 Fe _0.3 Zn _0.45 O ₄ , Li _5.65 Mn _0.55 Fe _0.35 Zn _0.1 O ₄ , Li _5.65 Mn _0.5 Fe _0.35 Zn _0.15 O ₄ , Li _5.65 Mn _0.45 Fe _0.35 Zn _0.2 O ₄ , Li _5.65 Mn _0.4 Fe _0.35 Zn _0.25 O ₄ , Li _5.65 Mn _0.35 Fe _0.35 Zn _0.3 O ₄ , Li _5.65 Mn _0.3 Fe _0.35 Zn _0.35 O ₄ , Li _5.65 Mn _0.25 Fe _0.35 Zn _0.4 O ₄ , Li _5.65 Mn _0.2 Fe _0.35 Zn _0.45 O ₄ , Li _5.6 Mn _0.5 Fe _0.4 Zn _0.1 O ₄ , Li _5.6 Mn _0.45 Fe _0.4 Zn _0.15 O ₄ , Li _5.6 Mn _0.4 Fe _0.4 Zn _0.2 O ₄ , Li _5.6 Mn _0.35 Fe _0.4 Zn _0.25 O ₄ , Li _5.6 Mn _0.3 Fe _0.4 Zn _0.3 O ₄ , Li _5.6 Mn _0.25 Fe _0.4 Zn _0.35 O ₄ , Li _5.6 Mn _0.2 Fe Zn _{0.4 O 4} , Li _5.6 Mn _0.15 Fe _0.4 Zn _0.45 O ₄ , Li _5.55 Mn _0.45 Fe _0.45 Zn _0.1 O ₄ , Li _5.55 Mn _0.4 Fe _0.45 Zn _0.15 O ₄ , Li _5.55 Mn _0.35 Fe _0.45 Zn A _lithium- manganese _transition metal _oxide , wherein the lithium-manganese transition metal oxide is at least one compound selected from the group consisting of Li- _0.2 O ₄ , Li- _5.55 Mn _{-0.3 Fe - 0.45} Zn- _0.25 O ₄ , Li _-5.55 Mn _{- 0.25} Fe _{- 0.45} Zn _{- 0.3} O 4 , Li-5.55 Mn- _0.2 Fe-0.45 Zn-0.35 O 4 , Li-5.55 Mn _-0.15 Fe- _0.45 Zn-0.4 O ₄ , and Li _-5.55 Mn- _0.1 Fe- _0.45 Zn-0.45 O ₄ .
A step of providing a raw material mixture comprising a lithium precursor, a manganese precursor, an iron precursor, and a zinc precursor in a solid state; and
A step of calcining the above raw material mixture under an inert atmosphere and a temperature of 500° C. to 900° C. to obtain a lithium-manganese transition metal oxide according to claim 1.
A method for producing a lithium-manganese transition metal oxide, comprising:
In paragraph 6,
The second step is a method for producing a lithium-manganese transition metal oxide, wherein the raw material mixture is heated at a heating rate of 1.4°C/min to 2.0°C/min under an inert atmosphere and calcined at a temperature of 500°C to 900°C for 2 to 20 hours.
A cathode additive for a lithium secondary battery comprising a lithium-manganese transition metal oxide according to claim 1.
A cathode for a lithium secondary battery, comprising a cathode active material, a binder, a conductive agent, and a lithium-manganese transition metal oxide according to claim 1.
A lithium secondary battery comprising a cathode; an anode; a separator; and an electrolyte according to claim 9.
In Article 10,
A lithium secondary battery, wherein the negative electrode comprises at least one negative electrode active material selected from the group consisting of carbonaceous materials and silicon compounds.