Negative electrode material for lithium secondary battery and method for manufacturing the same

Abstract

The present invention discloses a negative electrode material for a lithium secondary battery and a method for manufacturing the same. For example, by using only a single negative electrode material, a lithium secondary battery can have a high energy density. In particular, the negative electrode material for the lithium secondary battery includes a Li-[Mn-Ti]-Al-O-based negative electrode active material; and carbon nanotubes (CNTs) that are attached to the surface of the negative electrode active material in an acid-treated state to form a composite.

Description

Technical Field

[0001] The present invention relates to a negative electrode material for a lithium secondary battery and a method for manufacturing the same. In particular, a lithium secondary battery with high energy density can be manufactured by using only a single negative electrode material. Background Art

[0002] Secondary batteries have been used as small, high-performance energy sources for large-capacity power storage batteries (e.g., electric vehicles or battery power storage systems) and portable electronic devices (e.g., mobile phones, camcorders, and laptop computers). Therefore, research is ongoing to reduce the size or weight of secondary batteries while achieving high capacity or low power consumption, which is particularly useful for portable electronic devices.

[0003] In particular, lithium secondary batteries, a representative type of secondary battery, have higher energy density, greater capacity per unit area, lower self-discharge rate, and longer lifespan than nickel-manganese or nickel-cadmium batteries. Furthermore, lithium secondary batteries are easy to use and have a long lifespan because they have no memory effect.

[0004] When an electrolyte is filled between the negative electrode and the positive electrode made of an active material capable of intercalating or deintercalating lithium ions, the lithium secondary battery generates electricity through oxidation and reduction reactions when lithium ions are intercalated and deintercalated into and from the negative electrode and the positive electrode.

[0005] Such lithium secondary batteries are composed of a negative electrode material, an electrolyte, a separator, a positive electrode material, and the like. In order to ensure a long battery life and reliability, it is very important to stably maintain the interfacial reaction between the components.

[0006] In order to improve the performance of the above-mentioned lithium secondary batteries, research is continuously being conducted to improve the negative electrode materials. In particular, many studies have been conducted to develop high-performance and high-safety lithium secondary batteries, but in recent years, due to the frequent explosion accidents of lithium secondary batteries, safety issues have been continuously raised.

[0007] Therefore, the present applicants have completed the present invention by realizing a high energy density lithium secondary battery by achieving a high capacity of, for example, 250 mAh / g or more in a voltage range of 2 V to 4.2 V using a lithium-rich based material.

[0008] The contents explained in the above background art are only intended to help understanding the background of the present invention, and are not intended to indicate that the present invention falls within the scope of the relevant art known to those skilled in the art. Summary of the Invention

[0009] In a preferred aspect, a negative electrode material for a lithium secondary battery and a method for manufacturing the same are provided. By simply forming a composite of acid-treated carbon nanotubes (CNTs) and a single negative electrode material, a lithium secondary battery prepared thereby can have a high energy density.

[0010] In one aspect, a negative electrode composite material for a lithium secondary battery is provided, which may include a Li-[Mn-Ti]-Al-O based negative electrode active material; and carbon nanotubes (CNTs) present on or in combination with the negative electrode active material. For example, the carbon nanotubes (CNTs) are suitably present on the surface of the negative electrode active material, for example, the carbon nanotubes (CNTs) may be fixed to the negative electrode active material by covalent or non-covalent bonds. In particular aspects, the carbon nanotubes may be suitably treated with an acid so that the acid-treated carbon nanotubes may adhere to the surface of the Li-[Mn-Ti]-Al-O based negative electrode active material.

[0011] The Li-[Mn-Ti]-Al-O based negative active material may suitably include Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2.

[0012] The negative electrode composite material may include about 1 to 5 wt % of the carbon nanotubes relative to the total weight of the negative electrode composite material.

[0013] The carbon nanotubes may have a length of about 50 μm to 100 μm and a diameter of about 20 nm to 30 nm.

[0014] On the other hand, a method for manufacturing a negative electrode composite material for a lithium secondary battery is provided, which may include preparing a Li-[Mn-Ti]-Al-O based negative electrode active material; treating carbon nanotubes (CNTs) by immersing and stirring the carbon nanotubes (CNTs) in an acidic solution; and forming a negative electrode composite material by combining the prepared Li-[Mn-Ti]-Al-O based negative electrode active material with the treated carbon nanotubes.

[0015] The Li-[Mn-Ti]-Al-O based negative electrode active material can be prepared by the following steps: synthesizing a composite by mixing Li2CO3, Mn2O3, TiO2 and Al2O3 with anhydrous ethanol and performing a first ball milling; granulating the synthesized composite by washing and then drying; heating and calcining the granulated composite in an inert atmosphere to obtain a powder.

[0016] The complex may contain Li 1.25 [Mn 0.45 Ti 0.35 ]0.975 Al 0.025 O2, and heating the composite at a temperature of about 900 to 1000°C for about 10 to 14 hours.

[0017] Carbon nanotubes (CNTs) may be treated by immersing in an acidic solution and stirring for about 10 to 14 hours.

[0018] The negative electrode composite material may suitably include about 95 to 99 wt % of a Li-[Mn-Ti]-Al-O based negative electrode active material and about 1 to 5 wt % of carbon nanotubes based on the total weight of the negative electrode composite material.

[0019] Forming the negative electrode composite material may include performing secondary ball milling on the prepared Li-[Mn-Ti]-Al-O based negative electrode active material and the treated carbon nanotubes. Preferably, the secondary ball milling may be performed for about 12 to 24 hours.

[0020] A lithium secondary battery is also provided, comprising: a negative electrode comprising the negative electrode composite material described herein; a positive electrode comprising a positive electrode active material; and an electrolyte. Specifically, the negative electrode composite material may comprise a Li-[Mn-Ti]-Al-O-based negative electrode active material and carbon nanotubes (CNTs) attached to a surface of the Li-[Mn-Ti]-Al-O-based negative electrode active material.

[0021] According to various exemplary embodiments of the present invention, a negative electrode material having high energy density (which can utilize a single negative electrode material) can be obtained simply by coating acid-treated carbon nanotubes (CNTs) on the surface of a negative electrode active material in the form of a composite.

[0022] In particular, carbon nanotubes (CNTs) can be coated on Li-[Mn-Ti]-Al-O-based negative electrode active materials (e.g., by acid-treating the carbon nanotubes), thereby overcoming the air instability, structural instability, low lifespan, and low output characteristics of the negative electrode active materials.

[0023] Therefore, it is possible to construct a pure electric vehicle model, thereby reducing the manufacturing cost of a battery-centric pure electric vehicle compared to hybrid and derivative electric vehicles in which the drive device is installed on a previously designed vehicle structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description presented in conjunction with the accompanying drawings, in which:

[0025] Figure 1 is a schematic diagram illustrating an exemplary negative electrode composite material for an exemplary lithium secondary battery and a method for manufacturing the same according to an exemplary embodiment of the present invention.

[0026] Figure 2A and Figure 2B is a graph showing charge / discharge curves and cycle results of negative electrode composite materials according to Comparative Examples and Examples, in which the composition of the negative electrode active material is changed.

[0027] Figure 3 : is a graph showing the cycle results of the negative electrode composite materials according to Comparative Examples and Examples, in which the mixing amount of carbon nanotubes was changed.

[0028] Figures 4A to 4C are photographs showing the appearance of carbon nanotubes and composites according to comparative examples and examples after molding, in which the length and diameter of the carbon nanotubes were changed.

[0029] Figure 5A and Figure 5B : is a graph showing XRD results of negative electrode composite materials according to Comparative Examples and Examples, in which the synthesis temperature and time during the synthesis process were changed.

[0030] Figure 6 is a graph showing cycle results of negative electrode composite materials according to Comparative Examples and Examples, in which the acid treatment time was changed.

[0031] Figure 7A and Figure 7B : is a graph showing charge / discharge curves of one cycle and cycle results of negative electrode composite materials according to Comparative Examples and Examples, in which ball milling time was changed.

[0032] Figures 8A to 8C It is a graph showing the measurement results of electrochemical characteristics of Examples and Comparative Examples. DETAILED DESCRIPTION

[0033] The embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and the present embodiment is only intended to complete the invention of the present invention and is provided to fully inform those skilled in the art of the scope of the present invention.

[0034] The terms used herein are only used to describe the purpose of exemplary embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are intended to also include plural forms, unless the context clearly indicates otherwise. It will also be understood that when the terms "comprise" and / or "include" are used in this specification, it is indicated that the features, values, steps, operations, elements, and / or components are present, but the presence or addition of one or more other features, values, steps, operations, elements, components and / or their groups of composition are not excluded. As used herein, the term "and / or" includes any and all combinations of one or more related enumerated items.

[0035] Unless otherwise stated or apparent from the context, the term "about" as used herein is understood to mean within the normal tolerance range in the art, for example, within 2 standard deviations of the mean. "About" can be understood to mean within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. Unless otherwise clear from the context, all numerical values ​​provided herein are modified by the term "about."

[0036] In one aspect, a negative electrode composite material for a lithium secondary battery (or "negative electrode material") is a material forming a negative electrode applied to a lithium secondary battery, which may include the negative electrode composite material. The negative electrode composite material can be manufactured by attaching acid-treated carbon nanotubes (CNTs) to a negative electrode active material. The lithium secondary battery may include: a negative electrode including a negative electrode active material; a positive electrode including a positive electrode active material; and an electrolyte.

[0037] The negative active material may include a Li-[Mn-Ti]-Al-O based material capable of reversible intercalation and deintercalation of lithium ions.

[0038] The Li-[Mn-Ti]-Al-O based material may preferably include Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 or Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2.

[0039] To ensure high reversible capacity during cycling and maintain excellent life characteristics, the atomic ratio of Mn and Ti, and the molar ratio of Li, Al, and O are expressed as Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025O2.

[0040] In addition, the carbon nanotubes (CNTs) attached to the surface of the negative electrode active material can be subjected to an acid treatment before being attached to the surface of the negative electrode material. In this case, the acid treatment of the carbon nanotubes (CNTs) can increase the crystallinity of the carbon nanotubes (CNTs), thereby facilitating the formation of the negative electrode active material and the composite.

[0041] By attaching acid-treated carbon nanotubes (CNTs) to a negative electrode active material to form a composite, low lifespan characteristics and low output characteristics can be improved while eliminating air instability and structural instability of the negative electrode active material.

[0042] The amount of the acid-treated carbon nanotubes (CNTs) relative to the total weight of the negative electrode composite material may preferably be about 1 to 5 wt %. Therefore, the negative electrode composite material can be manufactured by mixing about 95 to 99 wt % of the negative electrode active material and about 1 to 5 wt % of the carbon nanotubes (CNTs) and then ball milling.

[0043] When the amount of the mixed carbon nanotubes (CNTs) is less than about 1 wt %, desired characteristics based on the attachment of the carbon nanotubes (CNTs) may not be obtained, and when the amount of the mixed carbon nanotubes (CNTs) is greater than about 5 wt %, life characteristics may be reduced due to low efficiency of capacity after forming a composite with the negative active material.

[0044] The carbon nanotube (CNT) to be acid-treated may preferably have a length of about 50 μm to 100 μm and a diameter of about 20 nm to 30 nm.

[0045] When the carbon nanotubes (CNTs) do not meet the recommended length range and diameter range, it is difficult to realize the shape of the carbon nanotubes (CNTs) and to form a composite with a negative active material.

[0046] A method for producing the negative electrode composite material formed as described above will be described.

[0047] Figure 1 is a schematic diagram illustrating a negative electrode composite material for a lithium secondary battery and a method for manufacturing the same according to an embodiment of the present invention.

[0048] In one aspect, a method for manufacturing a negative electrode composite material for a lithium secondary battery provides the following steps: preparing a negative electrode active material; acid-treating carbon nanotubes (CNTs); and composite the prepared negative electrode active material and the acid-treated CNTs into a composite.

[0049] The negative electrode active material is prepared by using a Li-[Mn-Ti]-Al-O based material. At this time, the negative electrode active material, or in particular, the Li-[Mn-Ti]-Al-O based material may preferably include Li 1.25[Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 or Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2.

[0050] As mentioned above, in order to prepare Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 is used as the negative electrode active material. First, Li2CO3, Mn2O3, TiO2 and Al2O3 can be mixed with anhydrous ethanol and ball-milled to synthesize a composite (synthesis process). 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 as a synthetic complex.

[0051] Alternatively, the synthesized complex may be washed and then dried to be granulated (granulation process).

[0052] Then, the granulated composite may be calcined by heating at a temperature of about 900 to 1000° C. for about 10 to 14 hours in an inert atmosphere to obtain a powder (calcination process).

[0053] Within the recommended calcination temperature and time ranges for synthesizing negative electrode active materials, a single-phase material with a cubic structure and a space group of Fm-3m can be produced. On the other hand, when the calcination temperature and time are outside the recommended ranges, the negative electrode active material cannot be synthesized.

[0054] The acid treatment may include immersing the carbon nanotubes (CNTs) in an acidic solution and stirring the carbon nanotubes (CNTs). Thus, by increasing the crystallinity of the carbon nanotubes (CNTs), a composite may be easily formed or easily composited with the negative active material.

[0055] Preferably, the acid treatment may include immersing the carbon nanotubes (CNTs) in an acidic solution and stirring for about 10 to 14 hours.

[0056] For example, the acid treatment can be performed by adding about 0.5 g of MW-CNTs to 100 ml of HNO 3 (liquid or solution), followed by stirring at about 80 RPM at room temperature for about 10 to 14 hours.

[0057] When the acid treatment time of carbon nanotubes (CNTs) is shorter than about 10 hours or longer than about 14 hours, the capacity may be significantly reduced after about 20 cycles. Therefore, considering the capacity retention rate, the acid treatment time of carbon nanotubes (CNTs) may be about 10 to 14 hours.

[0058] In addition, for example, the MW-CNTs appeared to gradually disperse like a spider web during the acid treatment, and this phenomenon may be very effective in attaching carbon nanotubes (CNTs) to the surface of the negative electrode active material. However, the carbon nanotubes (CNTs) treated with acid for 16 hours had the problem that the CNTs may break quickly.

[0059] Therefore, in order to attach carbon nanotubes (CNTs) to the surface of the negative active material in an ideal form, carbon nanotubes (CNTs) having a very large surface area can be obtained by acid-treating the carbon nanotubes (CNTs) for about 10 to 14 hours.

[0060] Forming or compounding the negative electrode composite material may include coating acid-treated carbon nanotubes (CNTs) on the surface of the prepared negative electrode active material.

[0061] like Figure 1 As shown, the composite step can be achieved by filling the negative electrode active material Li in a low-energy ball milling device. 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 and carbon nanotubes (CNTs) are ball-milled and the carbon nanotubes (CNTs) are attached and coated on the surface of the negative electrode active material to form a negative electrode composite material.

[0062] About 95 to 99 weight percent of the negative electrode active material and about 1 to 5 weight percent of carbon nanotubes (CNTs) may be mixed, and then ball milled to attach the carbon nanotubes (CNTs) to the surface of the negative electrode active material to be coated. The weight percent is based on the total weight of the negative electrode composite material.

[0063] Furthermore, during compounding, ball milling is preferably performed for about 12 to 24 hours.

[0064] When the ball milling time is shorter than about 12 hours, the shape of the carbon nanotubes (CNTs) is maintained and composite with the negative electrode active material can be achieved, but the battery performance before the composite is formed is maintained. Therefore, it is impossible to composite the negative electrode active material and the carbon nanotubes (CNTs).

[0065] In addition, when the ball milling time is longer than about 24 hours, the inherent characteristics of carbon nanotubes (CNTs) may disappear, thereby insufficiently compounding the negative active material and carbon nanotubes (CNTs) and electrochemically reducing capacity and lifetime characteristics.

[0066] Example

[0067] Exemplary embodiments of the present invention will be described through comparative examples and examples.

[0068] Test Example 1

[0069] Experiments were conducted to select the atomic ratio or molar ratio of each component of the Li-[Mn-Ti]-Al-O based material used as the negative electrode active material.

[0070] At this time, in order to manufacture the negative electrode material, Li2CO3 (Li2CO3 was added in an excess of 3 wt %), Mn2O3 (synthesized by calcining MnCO3), TiO2 and Al2O3 were mixed with an anhydrous ethanol solvent in a wide-mouth bottle with a volume of 45 ml. However, the atomic ratio or molar ratio of each component of the Li-[Mn-Ti]-Al-O based material was adjusted and matched as shown in Table 1 below. At this time, ZrO2 balls of 10 mm x 5 g, 5 mm x 10 g, and 1 mm x 4 g were added. The ball milling conditions were 300 rpm / 5 h, with 17 groups set up every 15 minutes. After ball milling, it was washed with ethanol, dried and granulated. The powder was obtained by calcining at a temperature of 900 ° C for 12 hours in an Ar atmosphere. Then, the primary carbon ball milling (300 rpm / 6 h, every 15 minutes, 20 groups) [active material: acetylene black = 9 wt%: 1 wt%, ZrO2 balls: 10 mm x 3#, 5 mm x 9#, 1 mm x 2 g] was performed, followed by a secondary carbon ball milling (300 rpm / 12 h, every 15 minutes, 40 groups) [ZrO2 balls: 1 mm x 5.5 g]. During the secondary carbon ball milling, 1 wt% of acid-treated CNTs was added.

[0071] In particular, the content of each component was changed as shown in Table 1 below, and the negative electrode active material was synthesized at the same time. The electrochemical characteristics of the lithium secondary battery using the negative electrode active material were studied. The charge and discharge curves and cycle results obtained were as follows: Figure 2A and Figure 2B Shown in.

[0072] Table 1

[0073] project Types of negative electrode active materials Comparative Example 1-1 <![CDATA[Li 1.2 [Mn 0.4 You 0.4 ]O2]]> Comparative Example 1-2 <h2 style=";text-align:left;direction:ltr"><![CDATA[Li <h2 style=";text-align:left;direction:ltr"> 1.2 <h2 style=";text-align:left;direction:ltr"> [Mn<h2 style=";text-align:left;direction:ltr"> 0.4 <h2 style=";text-align:left;direction:ltr"> Ti<h2 style=";text-align:left;direction:ltr"> 0.4 <h2 style=";text-align:left;direction:ltr"> ]O2+Al 2.5%]]><h2 style=";text-align:left;direction:ltr"> Comparative Examples 1-3 <h2 style=";text-align:left;direction:ltr"><![CDATA[Li <h2 style=";text-align:left;direction:ltr"> 1.2 <h2 style=";text-align:left;direction:ltr"> [Mn<h2 style=";text-align:left;direction:ltr"> 0.4 <h2 style=";text-align:left;direction:ltr"> Ti<h2 style=";text-align:left;direction:ltr"> 0.4 <h2 style=";text-align:left;direction:ltr"> ]O2+Al 5%<h2 style=";text-align:left;direction:ltr"><!-- 5 --> ]]><h2 style=";text-align:left;direction:ltr"> Comparative Examples 1-4 <![CDATA[Li 1.25 [Mn 0.45 You 0.35 ]O2]]> Example 1 <h2 style=";text-align:left;direction:ltr"><![CDATA[Li <h2 style=";text-align:left;direction:ltr"> 1.25 <h2 style=";text-align:left;direction:ltr"> [Mn<h2 style=";text-align:left;direction:ltr"> 0.45 <h2 style=";text-align:left;direction:ltr"> Ti<h2 style=";text-align:left;direction:ltr"> 0.35 <h2 style=";text-align:left;direction:ltr"> ]O2+Al 2.5%]]><h2 style=";text-align:left;direction:ltr"> Comparative Examples 1-5 <h2 style=";text-align:left;direction:ltr"><![CDATA[Li <h2 style=";text-align:left;direction:ltr"> 1.25 <h2 style=";text-align:left;direction:ltr"> [Mn<h2 style=";text-align:left;direction:ltr"> 0.45 <h2 style=";text-align:left;direction:ltr"> Ti<h2 style=";text-align:left;direction:ltr"> 0.35 <h2 style=";text-align:left;direction:ltr"> ]O2+Al 5%]]><h2 style=";text-align:left;direction:ltr">

[0074] like Figure 2A As shown in FIG. 1 , this embodiment shows a greater reversible capacity than Comparative Examples 1-1 to 1-5. Figure 2B As shown, this embodiment has better life characteristics than Comparative Examples 1-1 to 1-5.

[0075] Therefore, it is preferable to use the Li according to the above embodiment. 1.25[Mn 0.45 Ti 0.35 ]O2+Al 2.5% as the negative electrode active material, and Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2 is used as the negative electrode active material.

[0076] Test Example 2

[0077] Experiments were conducted to select the content ranges of the negative electrode active material and carbon nanotubes (CNTs).

[0078] The content of carbon nanotubes (CNTs) was changed to 1 wt%, 5 wt% and 6 wt% relative to the total amount of the negative electrode material. At the same time, carbon nanotubes (CNTs) were coated on the negative electrode active material. The electrochemical characteristics of lithium secondary batteries using this negative electrode material were studied, and the cycling results are shown in FIG. Figure 3 .

[0079] Figure 3 : is a graph showing the cycle results of the negative electrode materials according to the comparative example and the embodiment, in which the mixing amount of the carbon nanotubes was changed.

[0080] like Figure 3 As shown in FIG. 1 , as the carbon nanotube (CNT) content increases, more carbon nanotubes (CNTs) are present in the negative electrode material. However, after forming a composite, the capacity exhibits low efficiency, which reduces the lifespan characteristics. Therefore, the carbon nanotube (CNT) content range is preferably 1 to 5 wt%.

[0081] Test Example 3

[0082] Experiments were conducted to select a range of lengths and diameters for the carbon nanotubes (CNTs) that form the negative electrode material.

[0083] As shown in Table 2 below, the length and diameter of carbon nanotubes (CNTs) were changed, and the carbon nanotubes (CNTs) were coated on the negative electrode material. The images of the carbon nanotubes (CNTs) and the negative electrode material were observed and the results are shown in Figures 4A to 4C middle.

[0084] Figures 4A to 4C are photographs showing the shapes of carbon nanotubes and composites according to comparative examples and examples after molding, in which the length and diameter of the carbon nanotubes were changed.

[0085] Table 2

[0086] project Length (μm) Diameter (nm) Example 2 50-100 20-30 Comparative Example 2-1 50-100 10-20 Comparative Example 2-2 Less than 50 More than 30

[0087] like Figure 4AAs shown, when the length of the carbon nanotube (CNT) is 50 μm to 100 μm and the diameter thereof is 20 nm to 30 nm, the shape of the carbon nanotube (CNT) is achieved and the composite is correctly formed.

[0088] On the other hand, Figure 4B and Figure 4C As shown in FIG, when the length and diameter of the carbon nanotube (CNT) exceed the given range, the shape of the carbon nanotube (CNT) cannot be properly achieved and it is difficult to form a composite. Therefore, preferably, the length of the carbon nanotube (CNT) is 50 μm to 100 μm and the diameter is 20 nm to 30 nm.

[0089] Test Example 4

[0090] Experiments were conducted to select the synthesis temperature and synthesis time during the synthesis process.

[0091] The synthesis process was carried out while changing the synthesis temperature from 700°C to 1200°C in units of 100°C. The results are shown in Figure 5A In addition, the synthesis process was carried out by changing the synthesis time from 9 hours to 17 hours, and the results are shown in FIG. Figure 5B .

[0092] Figure 5A and Figure 5B : is a graph showing XRD results of negative electrode materials according to Comparative Example and Example, in which the synthesis temperature and time during the synthesis process were changed.

[0093] like Figure 5A As shown, a single-phase material having a cubic structure and a space group of Fm-3m is present in the synthesis temperature range of 900 to 1000° C. On the other hand, no synthesis is achieved in the temperature range outside the given synthesis temperature.

[0094] Therefore, the synthesis temperature is preferably in the range of 900 to 1000°C.

[0095] In addition, if Figure 5B As shown, a single-phase material with a cubic structure and a space group of Fm-3m is present in the synthesis time interval of 10 to 14 hours. On the other hand, no synthesis is achieved in the time interval outside the given synthesis time interval.

[0096] Test Example 5

[0097] Experiments were conducted to select the acid treatment time for carbon nanotubes (CNTs).

[0098] The acid treatment was carried out by changing the acid treatment time from 0 hours to 20 hours, and the results are shown in FIG. Figure 6 .

[0099] Figure 6 is a graph showing cycle results of negative electrode materials according to Comparative Examples and Examples, in which the acid treatment time was changed.

[0100] like Figure 6 As shown, the initial discharge capacity according to the acid treatment time is about 300 mAh g -1 , there is no difference. However, the performance of the composite coated with carbon nanotubes (CNTs) treated with acid treatment times of less than 8 hours and more than 16 hours showed inefficiency, showing a large capacity reduction after about 20 cycles. Therefore, considering the capacity retention rate, the acid treatment time of carbon nanotubes (CNTs) is preferably 10 to 14 hours.

[0101] Test Example 6

[0102] Experimentation was performed to select the ball milling time for compounding.

[0103] When compounding, the ball milling time was changed to 0 hours, 11 hours, 12 hours and 25 hours. Figure 7A and Figure 7B Shown in.

[0104] Figure 7A and Figure 7B : is a graph showing charge and discharge curves of one cycle and cycle results of negative electrode materials according to Comparative Examples and Examples, in which ball milling time was changed.

[0105] like Figure 7A As shown in Figure 3, when the ball milling time is shorter than 12 hours, the battery performance is similar to that before the composite is formed. It can be inferred that this is meaningless during the composite.

[0106] like Figure 7B As shown in Figure 2, when the ball milling time is longer than 24 hours, the inherent characteristics of carbon nanotubes (CNTs) disappear (this may not be composite), and the electrochemical capacity and life characteristics are reduced. Therefore, the ball milling time for composite is preferably 12 to 24 hours.

[0107] Test Example 7

[0108] Electrochemical characteristics of the negative electrode material according to the example and the negative electrode material according to the comparative example were compared through a 12-hour acid treatment method of carbon nanotubes (CNTs).

[0109] At this time, the embodiment applies the negative electrode active material Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025The surface of O2 is attached and coated with 1 wt% of carbon nanotubes (CNT) treated with acid for 12 hours, and the comparative example uses the negative electrode active material Li[Ni 0.8 Co 0.16 Al 0.04 ]O2.

[0110] In addition, the results of the electrochemical characteristics of the examples and comparative examples are shown in Figures 8A to 8C .

[0111] like Figure 8A As shown, the Examples exhibited greater reversible capacity than the Comparative Examples.

[0112] like Figure 8B As shown, the examples showed a larger initial discharge capacity than the comparative examples.

[0113] like Figure 8C As shown, this embodiment exhibits a greater rate characteristic than the comparative example.

[0114] Although the present invention has been described with reference to the accompanying drawings and the exemplary embodiments described above, the present invention is not limited thereto but is defined by the claims described hereinafter. Therefore, those skilled in the art may make various changes and modifications to the present invention without departing from the technical spirit of the appended claims described hereinafter.

Claims

1. A negative electrode composite material for a lithium secondary battery, comprising: Li-[Mn-Ti]-Al-O based negative electrode active material; and carbon nanotubes, which are present on the Li-[Mn-Ti]-Al-O based negative electrode active material, wherein the carbon nanotubes are treated with acid to attach to the surface of the Li-[Mn-Ti]-Al-O based negative electrode active material; The carbon nanotubes have a length of 50 μm to 100 μm and a diameter of 20 nm to 30 nm. Among them, the Li-[Mn-Ti]-Al-O based negative electrode active material includes Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2, and The negative electrode composite material contains 1 to 5 wt % of carbon nanotubes relative to the total weight of the negative electrode composite material.

2. A method for producing a negative electrode composite material for a lithium secondary battery according to claim 1, comprising: Preparation of Li-[Mn-Ti]-Al-O based negative electrode active materials; treating the carbon nanotubes by immersing and stirring the carbon nanotubes in an acidic solution; forming a negative electrode composite material by combining the prepared Li-[Mn-Ti]-Al-O based negative electrode active material with the treated carbon nanotubes; The forming of the negative electrode composite material comprises performing secondary ball milling on the prepared Li-[Mn-Ti]-Al-O based negative electrode active material and the treated carbon nanotubes, wherein the secondary ball milling is performed for 12 to 24 hours, and The treating of the carbon nanotubes includes immersing the carbon nanotubes in an acidic solution and stirring the solution for 10 to 14 hours.

3. The manufacturing method according to claim 2, wherein: The Li-[Mn-Ti]-Al-O based negative electrode active material was prepared by the following steps: The composite was synthesized by mixing Li2CO3, Mn2O3, TiO2, and Al2O3 with anhydrous ethanol and performing the first ball milling; The synthesized complex is granulated by washing and then drying; The granulated composite is heated and calcined in an inert atmosphere to obtain a powder.

4. The manufacturing method according to claim 3, wherein: The complex contains Li 1.25 [Mn 0.45 Ti 0.35 ] 0.975 Al 0.025 O2, and During the firing, the composite is heated at a temperature of 900 to 1000° C. for 10 to 14 hours.

5. The manufacturing method according to claim 2, wherein: The negative electrode composite material includes 95 to 99 wt % of a Li-[Mn-Ti]-Al-O based negative electrode active material and 1 to 5 wt % of carbon nanotubes based on the total weight of the negative electrode composite material.

6. A lithium secondary battery comprising: A negative electrode comprising the negative electrode composite material according to claim 1; a positive electrode comprising a positive electrode active material; as well as electrolytes.

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