KR20010076586A - Negative active material for lithium secondary battery and method of preparing same - Google Patents

Abstract

PURPOSE: A cathode active material for lithium battery is provided to develop crystalline structure to improve capacity, efficiency and life time of the battery by comprising mesophase pitch powder and catalyst under graphitization condition. CONSTITUTION: The cathode active material comprises a core containing crystalline carbon formed from mesophase pitch; and a carbon shell formed above the core and including at least one element to modify surface structure of the core and to effect as a graphitization catalyst. The method for producing the cathode active material comprises the following steps of: oxidizing and stabilizing the mesophase pitch for 0.1-10 hours; carbonizing the stable pitch; coating the pitch with the element having 0.01-100 micrometer of particle size and the catalytic effect to graphitize and to reform the surface of the core; and graphitizing the obtained product at 2000-3100 deg.C.

Description

Negative active material for lithium secondary battery and manufacturing method thereof {NEGATIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND METHOD OF PREPARING SAME}

[Industrial use]

The present invention relates to a negative electrode active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a negative electrode active material for a lithium secondary battery having excellent capacity and efficiency, and a method for producing an active material capable of graphitizing at a low temperature.

[Prior art]

Carbon materials used as negative electrode materials for lithium secondary batteries can be largely classified into amorphous carbon and crystalline graphite depending on the crystallinity. Among them, crystalline graphite generally used can be classified into artificial graphite and natural graphite.

A typical pitch-based amorphous anode active material is obtained by finally graphitizing and pulverizing coke prepared through a series of heat treatments without an oxidation stabilization process. In this case, the amorphous negative active material obtained has high capacity and efficiency because the graphite structure can be well developed in the graphitization process. However, in the crushing process, since it is easy to be crushed in the orientation direction to have a plate-shaped granules, the tap density is low, so that compression occurs during the production of the high density electrode plate, which makes it difficult to penetrate the electrolyte solution, thereby degrading the battery life characteristics and the high rate characteristics.

In order to solve the problem of the plate-like active material, a method for producing mesophase carbon microbeads or mesocarbon fibers using mesophase pitch has been studied. In order to prepare mesophase carbon microbeads and mesophase fiber-based negative active materials, first, heat treatment (350 to 400 ° C.) of petroleum, coal, and synthetic pitches to prepare mesophase pitches, and supply oxygen to the mesophase pitches to supply oxygen. Introduce. In this way, when oxygen is introduced into the mesophase pitch, a crosslink is formed in the mesophase pitch to suppress fusion during high temperature carbonization and to prevent shape deformation. Subsequently, the mesophase pitch into which oxygen is introduced is graphitized at a high temperature of about 3000 ° C. to prepare mesophase carbon microbeads or mesophase fiber negative electrode active materials. In the graphitization process, the introduced oxygen is released to grow the graphite crystal structure.

Since the negative electrode active material manufactured by this method has a three-dimensional shape, there is an advantage that the tap density is high and the high density electrode plate condition is satisfied. However, this method does not facilitate the orientation of the graphite crystals, that is, the crystal structure development, and consequently, the capacity is lowered. In addition, the high cost of treatment by high temperature treatment, high production cost.

Therefore, in recent years, studies have been attempted to use the advantages of both the two-dimensional plate-shaped negative electrode active material manufactured using a general pitch meter and the three-dimensional negative electrode active material manufactured using a mesoface pitch meter, but have not yet obtained a satisfactory effect. I can't.

Recently, in order to use the advantages of both active materials, natural graphite or coke was coated with amorphous carbon and heat-treated at about 1000 ° C. to prepare a material having the advantages of both amorphous carbon and crystalline carbon, and used as a negative electrode material.

However, this active material has improved initial efficiency and capacity by the amorphous carbon layer, but as charge and discharge are repeated, surface layer peeling occurs or the amorphous layer is broken by physical compression in the process. In addition, there is a difficulty in manufacturing a high density electrode by using natural graphite as a base material.

The present invention is to solve the above-described problems, an object of the present invention is to provide a negative electrode active material for a lithium secondary battery that can improve the capacity and efficiency by the well-developed crystal structure.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery which has an amorphous granularity close to a spherical shape, which enables the production of high-density electrode plates, thereby improving battery capacity and efficiency.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery having excellent cycle life characteristics.

Another object of the present invention is to provide a method for producing a negative electrode active material for a lithium secondary battery having the above-described physical properties.

In order to achieve the above object, the present invention is a core containing a crystalline carbon formed from mesophase pitch; And a carbon shell formed on the core and having one or more elements or compounds of the elements capable of modifying the surface structure and having a graphitization catalyst effect.

The present invention also provides oxidation stabilization of mesophase pitch for 0.1 to 10 hours; Carbonizing the oxidatively stabilized mesoface pitch; Coating / mixing the carbonized mesophase pitch with at least one element or compound thereof that has a graphitizing catalytic effect and is capable of modifying the surface structure; Provided are a method for producing a negative electrode active material for a lithium secondary battery, including a step of graphitizing the obtained product at 2000 to 3100 ° C.

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

The negative electrode active material for a lithium secondary battery of the present invention includes a core including crystalline carbon prepared using a mesophase pitch and a carbon shell formed on the core.

The carbon shell has a graphitizing catalytic effect and is capable of surface structure modification or a compound of the elements (hereinafter "catalytic element or catalytic element M ₁ M ₂ M ₃ ..... M _n compound (n is an integer)" It is referred to as). As the catalytic element, a transition metal, an alkali metal, an alkaline earth metal, a 3A group, a 3B group, a 4A group, a 4B semimetal, a 5A group, a 5B element, a lanthanum series element, or an actinium series element may be used. Transition metals of Mn, Ni, Fe, Cr, Co, Cu, Mo, W, Te, Re, Ru, Os, Rh, Ir, Pd or Pt, alkali metals of Li, Na or K, Be, Sr, Ba, Alkaline earth metal of Ca or Mg, Group 3A semimetal of Sc, Y, La or Ac, Group 3B semimetal of B, Al or Ga, Group 4A semimetal of Ti, Zr or Hf, Group 4B of Si, Ge or Sn Semimetals, Group 5A elements of V, Nb or Ta or Group 5B elements of P, Sb or Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu The lanthanum series element of, and the actinium series element of Th, U, Nb or Pu can be used. As an example of the catalytic element M ₁ M ₂ M ₃ ..... M _n compound, a M ₁ M ₂ M ₃ ..... B compound, that is, a metal boride is preferable, TiB ₂ , ZrB _{2 , DyB 2, HfB 2, HoB} 2, LuB 2, ScB 2, Ni 2 B, TaB 2, TmB 12, VB 2, W 2 B 5, there may be mentioned the calcium boride, lithium boride or cobalt boride.

The above-described catalyst element or catalyst element M ₁ M ₂ M ₃ ..... M _n compound has a graphitizing catalytic effect and can modify the surrounding carbon structure, so that the amorphous can be changed into the crystalline structure, and the final production The surface structure of the active material may be changed into a turbostratic structure or a half onion ring structure. Therefore, the side reaction between the negative electrode active material and the electrolyte can be suppressed.

The amount of the catalytic element contained in the negative electrode active material of the present invention is 0.01 to 20% by weight of the total active material weight. When the amount of the catalytic element is less than 0.01% by weight, the effect of increasing the graphitization degree of the final active material is not only small, but the surface structure is remodeled less, and the initial charge and discharge efficiency is improved. It is not preferable because the amount of discharge may decrease due to the catalytic element of. Even when the negative electrode active material of the present invention contains a metal boride which is a catalyst element M ₁ M ₂ M ₃ ..... B compound, since the metal boride is a compound composed only of the catalytic element, the metal boride contained in the negative electrode active material It can be seen that the amount of 0.01 to 20% by weight of the total active material weight.

More preferably, B of the catalyst element contains 0.005 to 10% by weight of the total active material weight, and the remaining catalyst elements except B, that is, Mn, Ni, Fe, Cr, Co, Cu, Mo, W, Te, Re Transition metals of Ru, Os, Rh, Ir, Pd or Pt, alkali metals of Li, Na or K, alkaline earth metals of Be, Sr, Ba, Ca or Mg, group 3A semimetals of Sc, Y, La or Ac Group 3B semimetal of Al or Ga, Group 4A semimetal of Ti, Zr or Hf, Group 4B semimetal of Si, Ge or Sn, Group 5A element of V, Nb or Ta or Group 5B of P, Sb or Bi 0.005 or more of the lanthanide based elements of Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and the actinium based elements of Th, U, Nb or Pu To 10% by weight. As such, when B is included in the element used, boron may act as an acceptor in the graphitization process, and thus the electron transfer reaction may be accelerated during the initial lithium insertion reaction. In addition, as boron is added, the artificial graphite end edge portion, which is the final active material, has a half onion ring structure, so that the propylene-based electrolyte solution is strong and the irreversible capacity can be reduced.

Due to this catalytic element or catalytic element M ₁ M ₂ M ₃ ..... M _n compound, the carbon shell of the negative electrode active material of the present invention is semicrystalline having a turbostratcular structure or semi-onion ring structure having a skeletal structure Carbon shell. In this semicrystalline carbon shell, the catalyst element or the catalyst element M ₁ M ₂ M _{3 ...} M _n compound, especially metal boride nanoparticles, are uniformly distributed.

In the present invention, the crystalline carbon is prepared by using mesophase-based pitch. As described above, when crystalline carbon is used by using mesoface-based pitch, an active material having a nearly spherical amorphous grain shape, that is, a three-dimensional shape, may be prepared. Can be. Therefore, since the tap density of the active material is increased, a high density electrode plate can be manufactured, thereby improving the high rate characteristic of the battery.

The negative electrode active material of the present invention can be prepared by the following method.

100% optically anisotropic mesophase pitch. The pitch softening point is supplied with oxygen through air inflow for 0.1 to 10 hours in the temperature range of ± 50 ° C to introduce oxygen into the mesophase pitch and undergo partial or complete incompatibility. As described above, when oxygen is introduced into the pitch, a crosslinked bond with oxygen is formed in the mesophase pitch to suppress fusion at high temperature carbonization and prevent shape deformation. In other words, this step is a step of introducing thermal stability by chemical bonding. The partial dissolution process is carried out by adjusting the air introduction amount, heat treatment temperature, and time based on the time when the oxygen introduction degree becomes saturated through thermogravimetric analysis (TGA).

The mesophase pitch used in the present invention may be any that is produced by a process generally produced. The preparation of mesophase pitch with generally known 100% optical anisotropy is as follows. Petroleum or coal-based pitches are removed using organic solvents having high solubility (pyridine, quinoline, tetrahydrofuran, etc.) to remove impurities from the pitch and distillation to remove solvent to obtain optical isotropic pitch. The prepared optically isotropic pitch is heat treated at about 350 to 400 ° C. for 5 to 20 hours to prepare 100% optically anisotropic mesoface pitch.

The mesophase pitch, which has undergone partial stabilization and complete stabilization, is coated and / or mixed with the catalytic element or compound thereof. The coating and / or mixing process may be carried out using a catalyst element or a compound thereof in solution, or may be carried out using a solid phase. When used in solution phase, a suspension is prepared by adding the catalytic element or compound thereof to the solvent. As the solvent, water or an organic solvent or a mixture thereof may be used. As the organic solvent, ethanol, isopropyl alcohol, toluene, benzene, hexane, tetrahydrofuran and the like can be used.

As the catalytic element, one or more of transition metal, alkali metal, alkaline earth metal, 3A, 3B, 4A, 4B semimetal, 5A, 5B, lanthanum-based or actinium-based elements may be used. Is a transition metal of Mn, Ni, Fe, Cr, Co, Cu, Mo, W, Te, Re, Ru, Os, Rh, Ir, Pd or Pt, alkali metal of Li, Na or K, Be, Sr, Ba Alkaline earth metal of Ca or Mg, Group 3A semimetal of Sc, Y, La or Ac, Group 3B semimetal of B, Al or Ga, Group 4A semimetal of Ti, Zr or Hf, 4B of Si, Ge or Sn Group semimetals, Group 5A elements of V, Nb or Ta or Group 5B elements of P, Sb or Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or One or more of the lanthanum series elements of Lu, the actinium series elements of Th, U, Nb, or Pu may be used. As the compound of the catalytic element, any compound containing the catalytic element may be used, and examples thereof may include oxides, nitrides, carbides, sulfides, hydroxides, and hydrides, and representative examples thereof include TiO ₂ and nickel acetate. , B ₂ O ₃ can be used. Alternatively, as the compound including two or more different catalytic elements, any compound including two or more of the catalytic elements may be used, and examples thereof may include oxides, nitrides, carbides, sulfides, hydroxides, and hydrides. Representative examples include Ca (BH ₄ ), LiBH ₄ , TiB ₂ , ZrB ₂ , DyB ₂ , HfB ₂ , HoB ₂ , LuB ₂ , ScB ₂ , Ni ₂ B, TaB ₂ , TmB ₁₂ , VB ₂ , W ₂ B ₅ , Calcium boride, lithium boride or cobalt boride can be used.

Coating or mixing methods using liquid phases can mechanically mix, spray dry, spray pyrolysis, freeze dry or mimic the carbonized mesophase pitch with a catalyst element or compound solution thereof. It can be carried out by a mechanochemical method. The catalytic element or the compound thereof preferably has an average particle diameter of 0.01 to 100㎛, if less than 0.01㎛ there is a problem that can not easily adhere to the surface of the active material precursor by the flow of air during coating and mixing, and easily removed, If it exceeds, the surface area is small, there is a problem in that a large amount of catalytic element must be added to see a sufficient catalytic effect. The amount of the catalytic element or its compound added is 0.01 to 20% by weight of the carbonized mesophase pitch in terms of the weight of the pure element component.

Subsequently, a pitch coated with a catalytic element or a compound thereof or mixed with the catalytic element or a compound thereof is graphitized to a temperature of 2000 to 3100 ° C. under an inert atmosphere of argon or nitrogen to prepare a negative electrode active material for a lithium secondary battery.

In the negative electrode active material of the present invention prepared by the above method, I (110) / I (002), which is an X-ray diffraction intensity ratio between the (002) plane and the (110) plane, is 0.04 or less. In general, since the high capacity I (110) / I (002) of natural graphite is 0.04 or less, it can be considered that the negative active material of the present invention can produce a high capacity similar to natural graphite.

Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

Coal-based pitches were treated with tetrahydrofuran to prepare optically isotropic pitches. The prepared optically isotropic pitch was heat-treated at 350 ° C. for 5 hours to prepare an optically anisotropic mesoface pitch having a softening point of 280 ° C. The anisotropic mesophase pitch was pulverized, and the pulverized powder was introduced with oxygen at 300 ° C. for 1.5 hours to prepare a partially stabilized mesoface pitch having about 3 wt% oxygen introduced into the pitch powder.

5.0 weight% of B ₂ O ₃ and 5.0 weight% of TiO ₂ were added to sufficient distilled water to obtain a metal suspension, compared to 100 g of the pitch powder.

The carbon powder and the metal suspension prepared in Hosokawa's Aglomaster (fluid-bed powder mixer) were added to uniformly mix the carbon powder and the fine metal powder.

The resulting mixture was carbonized at about 1000 ° C. for 2 hours in an inert atmosphere, and then subjected to high temperature heat treatment at 2600 ° C. for 1 hour in a graphitization furnace in an argon atmosphere to prepare a negative active material for a lithium secondary battery.

Example 2

The graphitization process was carried out in the same manner as in Example 1 except that the graphitization process was performed at 2800 ° C instead of 2600 ° C.

(Example 3)

The same procedure as in Example 1 was carried out except that 5 wt% B ₂ O ₃ and 7 wt% of Ni acetate were used instead of B ₂ O ₃ and TiO ₂ .

Example 4

The graphitization process was carried out in the same manner as in Example 3 except that the graphitization process was performed at 2800 ° C instead of 2600 ° C.

(Example 5)

It was carried out in the same manner as in Example 1, except that the pitch of the mesophase pitch powder was stabilized and partially stabilized by 6% by weight.

(Example 6)

It carried out similarly to Example 5 except having performed graphitization temperature at 2800 degreeC.

(Example 7)

Except that the additive TiB ₂ 5% by weight based on 100g of the partially stabilized pitch powder was carried out in the same manner as in Example 6.

(Example 8)

The same procedure as in Example 2 was carried out except that a complete incompatibility pitch was used, which was completely immobilized (300 ° C. during air inflow, increased by 9 hours by stabilization for 6 hours).

(Comparative Example 1)

B, except that no addition of the ₂ O ₃ and TiO ₂ were conducted in the same manner as in the second embodiment.

(Comparative Example 2)

The same process as in Example 2 was carried out except that coke pulverization and classified products were used by heat treatment for at least 500 ° C. for a long time.

(Reference Example 1)

Amorphous plate-like graphite was used as the negative electrode active material.

The slurry was prepared by mixing the negative active material prepared by the method of Example 1-8, Comparative Example 1-2, and Reference Example 1, and an N-methyl pyrrolidone solvent in which a polyvinylidene fluoride binder was dissolved. At this time, the mixing ratio of the negative electrode active material and the binder was 90:10 by weight. This slurry was cast on a Cu foil current collector. The cast current collector was rolled to have a mixture density of 1.8 or more in the form of a pole plate. The rolled current collector was dried in an oven at 120 ° C. to prepare a negative electrode for a lithium secondary battery.

A coin-type lithium secondary battery was manufactured using the prepared negative electrode and lithium metal foil as a counter electrode and using 1M LiPF ₆ / ethylene carbonate / dimethyl carbonate / propylene carbonate as an electrolyte. The first cycle discharge capacity and battery efficiency of the lithium secondary battery were measured, and the 100th cycle discharge efficiency and I (110) / I (002) were measured relative to the initial capacity, and the results are shown in Table 1.

First Cycle Discharge Capacity [mAh / g] First cycle cell efficiency [%] 100th cycle discharge efficiency [%] I (110) / I (002) Example 1 335 93 84 0.021 Example 2 342 94 87 0.012 Example 3 338 93 86 0.019 Example 4 344 93 89 0.011 Example 5 335 92 85 0.020 Example 6 342 93 86 0.015 Example 7 341 92 85 0.014 Example 8 340 93 87 0.015 Comparative Example 1 295 85 72 0.049 Comparative Example 2 330 90 75 0.022 Reference Example 1 278 78 52 0.052

As shown in Table 1, Reference Example 1 is known to have a large capacity as natural graphite, but since it has a two-dimensional plate shape, it is difficult to infiltrate the electrolyte due to severe crushing between the active materials under high density plate conditions. As the propylene-based electrolyte decomposition reaction is active, the irreversible reaction increases, indicating that the discharge capacity, efficiency, and lifetime characteristics are deteriorated. Comparative Example 1 also shows that there is no structural change of the edge surface by the catalyst, so that an increase in irreversible capacity due to electrolyte decomposition reaction cannot be avoided and the efficiency is lowered. On the contrary, in Examples 1 to 8, the half onion sheath structure was formed by the catalyst during the heat treatment to suppress the irreversible decrease in capacity due to the decomposition of the electrolyte, and the degradation of the active material was relatively less even in the life characteristics. Able to know. In addition, since the material is pulverized in the mesophase state, the active material finally has a three-dimensional amorphous shape. That is, even in the case of high density battery pole plate, there is a fine path between the active materials, and the transfer rate of lithium ions at a high rate is high. It can be suppressed.

In Comparative Example 2, the material obtained by pulverizing incompatible coke through heat treatment was subjected to the same amount of catalyst and heat treatment temperature as in Example 2. Coke infusible through heat treatment also has a semi-onion ring structure at the edge surface of the graphitization reaction between carbon and catalyst, and thus can be suppressed by electrolyte decomposition reaction as in the embodiment. However, due to the flow type mesophase structure, the pulverized sheet coke has a form of needle cokes, and deterioration phenomenon as in Reference Example 1 occurs in the life characteristics.

As described above, graphitizing the three-dimensional amorphous powder obtained by pulverizing the mesophase pitch which passed through the low-cost stabilization process with the catalyst increases the capacity and efficiency, and at the same time, suppresses the deterioration of life that may occur in the high-density electrode plate. .

Claims (9)

A core comprising crystalline carbon formed from a mesophase pitch; And A carbon shell formed on the core and comprising one or more elements or compounds of the elements that have a graphitization catalytic effect and are capable of modifying the surface structure A negative electrode active material for a lithium secondary battery comprising a. According to claim 1, The graphitization catalyst effect, the element that can modify the surface structure is a transition metal, alkali metal, alkaline earth metal, Group 3A, Group 3B, Group 4A, Group 4B semimetals and Group 5A and An anode active material for a lithium secondary battery, which is at least one material selected from the group consisting of Group 5B elements, and lanthanum series elements and actinium series elements. The method of claim 2, wherein the transition metal is selected from the group consisting of Mn, Ni, Fe, Cr, Co, Cu, Mo, W, Te, Re, Ru, Os, Rh, Ir, Pd and Pt, the alkali The metal is selected from the group consisting of Li, Na and K, the alkaline earth metal is selected from the group consisting of Be, Sr, Ba, Ca and Mg, the group 3A semimetal is the group consisting of Sc, Y, La and Ac Is selected from the group consisting of B, Al and Ga, the Group 4A semimetal is selected from the group consisting of Ti, Zr and Hf, and the Group 4B semimetal is Si, Ge and Selected from the group consisting of Sn, the Group 5A element is selected from the group consisting of V, Nb and Ta, the Group 5B element is selected from the group consisting of P, Sb and Bi, and the lanthanum-based element is Ce, Pr , Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and the actinium-based element is composed of Th, U, Nb, and Pu A negative electrode active material for a lithium secondary battery that is selected from the group. The negative electrode active material of claim 1, wherein the amount of the element having the graphitization catalyst effect and the surface structure can be modified is 0.01 to 20% by weight of the total active material weight. The negative active material for a lithium secondary battery according to claim 1, wherein I (110) / I (002), which is an X-ray diffraction intensity ratio between the (002) plane and the (110) plane of the anode active material, is 0.04 or less. An anode active material for a lithium secondary battery comprising 0.01 to 20% by weight of a metal compound selected from the group consisting of metal borides, metal carbides, and metal oxides. The method of claim 6, wherein the metal compound comprises B or C or O, Mn, Ni, Fe, Cr, Co, Cu, Mo, W, Te, Re, Ru, Os, Rh, Ir, Pd and Pt Transition metal selected from the group consisting of; alkali metals selected from the group consisting of Li, Na, and K; alkaline earth metals selected from the group consisting of Be, Sr, Ba, Ca, and Mg, consisting of Sc, Y, La, and Ac Group 3A semimetal selected from the group, Group 3B semimetal selected from the group consisting of Al and Ga, Group 4A semimetal selected from the group consisting of Ti, Zr and Hf selected from the group consisting of Si, Ge and Sn Group 4B semimetals, Group 5A elements selected from the group consisting of V, Nb and Ta, Group 5B elements selected from the group consisting of P, Sb and Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb Lanthanum-based elements selected from the group consisting of Dy, Ho, Er, Tm, Yb and Lu, and at least one actinium-based element selected from the group consisting of Th, U, Nb and Pu Negative active material will. Mesophase pitch was oxidatively stabilized for 0.1 to 10 hours; Carbonizing the oxidatively stabilized mesoface pitch; Coating / mixing the carbonized mesophase pitch with at least one element or compound thereof that has a graphitizing catalytic effect and is capable of modifying the surface structure; Graphitized the obtained product at 2000 to 3100 ℃ The manufacturing method of the negative electrode active material for lithium secondary batteries containing a process. The production method according to claim 8, wherein the element or compound thereof which has the graphitization catalyst effect and which can modify the surface structure has a mean particle size of 0.01 to 100 mu m.