KR20160029176A - Anode active material for secondary battery and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode active material comprising a core layer occluding and discharging lithium; and a porous polymer shell layer formed on the surface of the core layer, and to a secondary battery comprising the same. According to the present invention, the negative electrode active material for a secondary battery can improve safety of a secondary battery.

Description

Field of the Invention [0001] The present invention relates to an anode active material for a secondary battery, and a secondary battery including the anode active material. [0002]

The present invention relates to a negative electrode active material for a secondary battery and a secondary battery comprising the same.

Recently, miniaturization and weight reduction of electronic equipment have been realized and the use of portable electronic devices has become common, so researches on secondary batteries having high energy density have been actively conducted. The secondary battery is manufactured by using a material capable of inserting and removing lithium ions as a cathode and an anode and filling an organic electrolytic solution or a polymer electrolyte between the anode and the cathode. When lithium ions are inserted and removed from the anode and the cathode To generate electrical energy by oxidation and reduction reactions of the compound.

At present, as a cathode active material for a secondary battery, a lithium-containing metal complex oxide (e.g., LiCoO ₂ ) having a high potential (Li / Li +) relative to lithium is used and a carbon material is used as an anode active material. Thus, high capacity and high output . However, when the secondary battery is short-circuited due to internal or external conditions, electrons and lithium ions are rapidly moved from the cathode to the anode. As a result, a large amount of current is momentarily transmitted, Problems such as ignition and explosion of the battery occur.

When the temperature of the secondary battery rises due to the abnormal operation of the secondary battery or the negative electrode active material is exposed to a high temperature atmosphere, there is a risk that the secondary battery will decompose at a specific temperature or higher and generate oxygen to ignite and explode. When a side reaction occurs by contacting with the aqueous electrolyte, there is a risk of explosion due to the exothermic reaction, and this is particularly the case where gas is generated inside the secondary battery due to side reaction.

Disclosed is a lithium secondary battery comprising: a core layer capable of intercalating and deintercalating lithium; And a porous polymer shell layer formed on the surface of the core layer.

However, the technical problem to be solved by the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

The present invention provides a lithium secondary battery comprising: a core layer capable of intercalating and deintercalating lithium; And a porous polymer shell layer formed on the surface of the core layer.

The porous polymer shell layer may have a melting temperature (Tm) higher than a normal operating temperature of the secondary battery including the negative electrode active material.

The melting temperature (Tm) of the porous polymer shell layer may be 130 ° C to 150 ° C.

The porous polymer shell layer may be formed of one selected from the group consisting of polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polyethylene terephthalate Or more.

The porosity of the porous polymer shell layer may be between 5% and 70%.

The pore size of the porous polymer shell layer may be 0.1 탆 to 1 탆.

The core layer may be at least one of a carbon-based material, a silicon-based material, a tin-based material, and a silicon-carbon based material.

The core layer may be spherical with a diameter of 1 [mu] m to 20 [mu] m.

The thickness of the porous polymer shell layer may be 5% to 30% of the diameter of the core layer.

According to an embodiment of the present invention, there is provided a negative electrode for a secondary battery comprising a negative electrode current collector coated with a negative electrode mixture containing the negative electrode active material.

In another embodiment of the present invention, there is provided a secondary battery including the negative electrode.

The negative electrode active material for a secondary battery according to the present invention is excellent in the performance of the secondary battery such as the output characteristics and the internal resistance of the secondary battery due to the porosity of the polymer shell layer and can minimize the reaction with the electrolyte due to the presence of the polymer shell layer, In the overdischarge, it is possible to induce pore closure of the polymer shell layer, thereby improving the safety of the secondary battery.

1 is a schematic cross-sectional view of a negative electrode active material for a secondary battery according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In the drawings, the thicknesses are enlarged to clearly indicate layers and regions. In the drawings, for the convenience of explanation, the thicknesses of the layers and regions are exaggerated.

Hereinafter, the present invention will be described in detail.

The present invention provides a lithium secondary battery comprising: a core layer capable of intercalating and deintercalating lithium; And a porous polymer shell layer formed on the surface of the core layer.

1 is a schematic cross-sectional view of a negative electrode active material for a secondary battery according to an embodiment of the present invention.

As shown in FIG. 1, a negative electrode active material 1 for a secondary battery according to an embodiment of the present invention includes a core layer 10 capable of intercalating and deintercalating lithium; And a porous polymer shell layer (20) formed on the surface of the core layer (10).

For secondary batteries Anode active material

The negative electrode active material for a secondary battery according to the present invention comprises: a core layer capable of intercalating and deintercalating lithium; And a porous polymer shell layer formed on the surface of the core layer.

Examples of the core layer capable of intercalating and deintercalating lithium include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, soft carbon, hard carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like.

Among them, the core layer capable of intercalating and deintercalating lithium is preferably at least one of a carbon-based material, a silicon-based material, a tin-based material, and a silicon-carbon based material.

Specifically, the carbon-based material includes soft carbon having a substantially graphitized layered crystal structure (a structure in which hexagonal honeycomb planes of carbon are arranged in layers), and a structure in which these structures are amorphous portions And hard carbon, which is mixed with graphite. Also, graphite is classified into graphite when the layered crystal structure is completely formed like natural graphite. Accordingly, the carbon-based material can be classified into graphite and soft carbon as crystalline carbon and hard carbon as amorphous carbon, and all of these various carbons can be used in the present invention. Preferably, a mixture of crystalline carbon and amorphous carbon can be used. The mixture of crystalline carbon and amorphous carbon is advantageous in designing the charge / discharge power ratio required in the field of application depending on the mixing ratio thereof, and the fuel gauge, It is advantageous for measurement, and a high life characteristic (calendar life) can be achieved.

The silicon-based material or the tin-based material is meant to include silicon particles, tin particles, silicon-tin alloys, their respective alloy particles, composites, and the like. Representative examples of the alloy include a solid solution of Al, Mn, Fe, and Ti, an intermetallic compound, a process alloy, and the like in the silicon element.

The core layer is preferably spherical with a diameter of 1 to 20 mu m, but is not limited thereto. At this time, since the core layer has a diameter within the above range, it is possible to smoothly store and discharge lithium during charging and discharging.

Next, the porous polymer shell layer is formed on the surface of the core layer. The porous polymer shell layer may be partially coated on the surface of the core layer and may exist in an island shape, or may be completely coated on the surface of the core layer, However, it is more preferable that the surface of the core layer is completely coated on the surface of the core layer to be integrated as a whole in terms of securing safety of the secondary battery. This minimizes the reaction with the electrolytic solution. Therefore, when charging / discharging at a high temperature, problems of elution of metals such as Mn and Mo in the negative electrode active material due to HF produced by decomposition of the electrolytic solution can be improved.

When a metal oxide such as an antimony oxide or the like is formed as a shell layer in a negative electrode active material including a core layer and a shell layer, the thermal stability is significantly larger than that of the porous polymer shell, There is a problem that the stability at high temperature is greatly reduced. In addition, when the polymer is carbonized to form a shell layer in the negative electrode active material including the core layer and the shell layer, porosity can not be formed, so that a large amount of overcharge and overdischarge can be reduced to reduce the movement speed of lithium ions and electrons, It is possible to prevent the generation of heat by the secondary battery and improve the safety of the secondary battery. However, there is a problem that the performance of the secondary battery such as the output characteristic and the internal resistance of the secondary battery is significantly deteriorated. It is preferable to have a melting temperature (Tm) higher than the normal operating temperature of the secondary battery including the negative electrode active material, but the present invention is not limited thereto. For example, the normal operating temperature of the secondary battery including the negative electrode active material may be -40 ° C to 80 ° C.

Overcharging and overdischarging are out of the normal operating temperature range and at such temperatures the porous polymer shell layer can be melted to induce pore closure. When the pores of the porous polymer shell layer are closed, the movement speed of a large amount of lithium ions and electrons transferred from the cathode to the anode is relaxed to prevent the generation of heat due to instantaneous overcurrent generation, and the safety of the secondary battery can be improved.

That is, the porous polymer shell layer may have a melting temperature (Tm) higher than the normal operating temperature of the secondary battery including the negative electrode active material, so that the porous polymer shell layer can be melted only to overcharge and overdischarge to induce pore closure .

Specifically, the melting temperature (Tm) of the porous polymer shell layer is preferably 130 ° C to 150 ° C, but is not limited thereto. When the melting temperature (Tm) of the porous polymer shell layer is less than 130 ° C, the performance of the secondary battery is deteriorated due to the melting of the porous polymer shell layer during normal operation of the secondary battery. The melting temperature (Tm) Exceeds 150 占 폚, the safety range of the secondary battery may be exceeded.

The porous polymer shell layer is characterized in that the performance of a secondary battery such as an output characteristic and an internal resistance of the secondary battery is excellent due to porosity. In the porous polymer shell layer, the polymer is mixed with a volatile solvent such as benzene or toluene, To ensure porosity. The porosity of the porous polymer shell layer is preferably 5% to 70%, more preferably 10% to 20%, but is not limited thereto. When the porosity of the porous polymer shell layer is less than the above range, there is a problem that the porosity of the porous polymer shell layer is too small to allow lithium to move smoothly in the anode active material. When the porosity of the porous polymer shell layer exceeds the above range, There is a problem in that when the shell layer is melted, the side surface of the negative electrode active material is too much exposed to side reactions which adversely affect safety.

The pore size of the porous polymer shell layer is preferably 0.1 탆 to 1 탆, but is not limited thereto. At this time, when the pore size of the porous polymer shell layer is less than 0.1 탆, resistance to migration of lithium occurs and the performance is degraded. When the pore size of the porous polymer shell layer exceeds 1 탆, There is a problem that the polymer shell layer can not be formed on the surface of the core layer.

The thickness of the porous polymer shell layer is preferably 5% to 30%, more preferably 15% to 25%, of the diameter of the core layer, but is not limited thereto. When the thickness of the porous polymer shell layer is less than the above range, there is a problem that the polymer shell layer fails to function properly. If the thickness of the porous polymer shell layer exceeds the above range, the gap between the anode active materials Thereby increasing the internal resistance of the secondary battery.

The polymer constituting the porous polymer shell layer may be one selected from the group consisting of polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polyethylene terephthalate But it is not limited thereto. The polymer of the above kind has a melting temperature (Tm) higher than the normal operating temperature of the secondary battery, and can maintain the porosity having a constant porosity without closing the pores at the normal operating temperature of the secondary battery.

Negative electrode for secondary battery

In addition, the present invention provides a negative electrode for a secondary battery in which a negative electrode mixture containing the negative electrode active material is coated on a negative electrode collector.

Specifically, the negative electrode for a secondary battery according to the present invention is produced by mixing and stirring a solvent, a binder, a conductive material, and the like, if necessary, into the negative electrode active material, applying the negative electrode mixture to the negative electrode current collector of the metallic material Compressed and then dried.

The binder serves to adhere the negative electrode active material particles to each other and adhere the negative electrode active material to the negative electrode current collector. For example, the binder may include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride , Polymers containing carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, acrylate, Styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

As the conductive material, at least one selected from the group consisting of a carbon-based material, a metal material, a metal oxide, and an electrically conductive polymer may be used. Examples of the conductive material include carbon black, acetylene black, ketjen black, furnace black, carbon fiber, , Copper, nickel, aluminum, silver, cobalt oxide, titanium oxide, polyphenylene derivatives, polythiophene, polyacene, polyacetylene, polypyrrole and polyaniline.

The negative electrode current collector is a metal having high conductivity and capable of easily adhering to the negative electrode material mixture, and any material that is not reactive in the voltage range of the battery can be used. Specifically, copper, gold, nickel, And the like, but the present invention is not limited thereto.

Secondary battery

The present invention also provides a secondary battery comprising the negative electrode.

Specifically, the secondary battery according to the present invention may include a cathode for a secondary battery, a separator, and an electrolyte, which are coated with a cathode mixture containing a cathode active material together with the cathode, on a cathode current collector.

The positive electrode for a secondary battery according to the present invention can be produced by preparing a positive electrode mixture by mixing and stirring a solvent, a binder and a conductive material as necessary with a positive electrode active material, applying the mixture to a positive electrode current collector of a metal material, .

The positive electrode active material has been made with metal-containing oxide of lithium _{(Li), LiCo 1 - x} M x O 2 -y L y (0≤x≤0.9, 0≤y≤0.3), Li x M y Mo z O 3 - _{z L z (0.5≤x≤2.3, 0≤y≤0.3,} 0.7≤z≤1.1, 0≤z≤1.5), LiMn x - y M y O 2x - z L z (x = 1,2, 0≤ _{y≤0.5, 0≤z≤1.5), LiNi 1 -} x Mn x - y M y O 2x -z L z (0 <x <1, 0≤y≤0.3, 0≤z≤2), Li 1 - _{x- y Co x Mn y M z} O 2 - a L a (0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤a≤1), LiMn 1 - x M x PO 4 ( Mg, Nb, Zn, Cd, Ti, Co, Ni, K (where _{0 ? X?} 0.99) or LiFe _{1 - x} M _x PO ₄ At least one selected from the group consisting of Na, Ca, Si, Fe, Cu, Sn, V, B, P, Se, Bi, As, Zr, Mn, Cr, Sr, Or F. &lt; / RTI &gt;

The cathode active material is preferably composed of lithium-cobalt-manganese-nickel (Li-Co-Mn-Ni) -containing metal oxide, but is not limited thereto. At this time, the metal oxide containing lithium-cobalt-manganese-nickel (Li-Co-Mn-Ni) can be used in an economical manner because it can use elements such as manganese abundant in nature, And high stability.

In the present invention, a LiCo _{0 .2} Mn _{0 .2} Ni _{0 .6} O ₂ material metal oxide was used as a cathode active material.

The specific types of the binder and the conductive material are as described above.

The positive electrode collector may be any metal as long as the positive electrode collector has a high conductivity and can be easily bonded to the positive electrode mixture and is not reactive in the voltage range of the battery. Specifically, aluminum, nickel or the like And the like, but the present invention is not limited thereto.

The separator is sandwiched between the anode and the cathode. As the separator, a conventional porous polymer film conventionally used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / A porous polymer film made of a polyolefin-based polymer such as an ethylene / methacrylate copolymer may be used alone or in a laminated manner. Alternatively, a porous nonwoven fabric such as a high-melting glass fiber or a polyethylene terephthalate fiber Non-woven fabric may be used, but is not limited thereto. As a method of applying the separator to a battery, lamination, stacking and folding of a separator and an electrode can be performed in addition to a general method of winding.

The electrolyte solution is injected into an electrode structure composed of a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, and is made of a secondary battery. The electrolyte includes a lithium salt as an electrolyte and an organic solvent. The lithium salt is usually used in an electrolyte for a lithium secondary battery Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl Examples of the solvent include methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran One or a mixture of two or more thereof selected from the group consisting of It can be used.

The outer shape of the secondary battery is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The middle- or large-sized battery module or the battery pack may include a power tool; a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, as shown in FIG.

As described above, the negative electrode active material for a secondary battery according to the present invention has excellent performance of a secondary battery such as an output characteristic owing to the porosity of the shell layer, minimizes the reaction with the electrolyte due to the presence of the shell layer, The pore-closing of the shell layer can be induced and the safety of the secondary battery can be improved.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the following examples.

[ Example ]

Example  One

Polyethylene (PE) (SK General Chemicals, Enpass®) Material About 1 ~ 2g of porous polymer (porosity = 20%) was mixed with about 10 ~ 15g of benzene. About 4 to 7 g of hard carbon having a diameter of about 10 탆 was added to the mixed solution, and the porous polymer was coated on the hard carbon surface by a stirring process for about 2 to 3 hours on a hot plate at about 60 캜 to a thickness of about 2.5 탆 To prepare a mixed solution containing the core layer-porous polymer shell layer, and then the solvent was evaporated to prepare a negative electrode active material for a secondary battery.

The negative electrode active material thus prepared, the styrene-butadiene rubber as the binder, and carbon black as the conductive material were mixed in the weight ratio of 90: 5: 5 to prepare a negative electrode mixture, which was then coated on a copper substrate, Thereby preparing a negative electrode for a secondary battery.

LiCo _{0 .2} Mn _{0 .2} Ni _{0 .6} O ₂ material metal oxide as a cathode active material, acrylate as a binder, and carbon black as a conductive material were mixed to prepare a positive electrode mixture in a weight ratio composition of 90: 5: 5 Then, it was coated on an aluminum substrate, dried, and pressed to produce a positive electrode for a secondary battery.

The positive electrode plate and the negative electrode plate were each laminated by notching them in an appropriate size, and a cell was constituted by interposing a separator (polyethylene, thickness: 25 μm) between the positive electrode plate and the negative electrode plate and the tab portions of the positive electrode and the negative electrode were welded Respectively. A combination of a welded anode / separator / cathode was put into the pouch and three surfaces excluding the electrolyte solution surface were sealed. At this time, the part with the tab is included in the sealing part. The electrolyte was injected into the remaining part, and the remaining surface was sealed and impregnated for 12 hours or more. The electrolytic solution was prepared by mixing 1 wt% of vinylene carbonate (VC), 0.5 wt% of 1,3-propensulfone (PRS), and 1 wt% of a 1M LiPF6 solution with a mixed solvent of EC / EMC / DEC (25/45/30, And 0.5 wt% of lithium bis (oxalate) borate (LiBOB).

Pre-charging was then carried out for 36 minutes at a current of 0.25 C (2.5 A). Degasing was performed after 1 hour, aging was performed for 24 hours or more, and a flasher discharge was performed (charging condition CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharging condition CC 0.2C 2.5V CUT-OFF). Thereafter, standard charging and discharging was performed (charging condition CC-CV 0.5 C 4.2 V 0.05 C CUT-OFF, discharge condition CC 0.5 C 2.5 V CUT-OFF).

Example  2

Except that the porous polymer was coated on the surface of the lithium-metal oxide to a thickness of about 1.5 탆 by using a porous polymer (porosity = 10%), and the negative electrode active material for a secondary battery and the secondary A battery was prepared.

Comparative Example  One

A negative electrode active material for a secondary battery and a secondary battery comprising the same were prepared in the same manner as in Example 1 except that hard carbon having a diameter of about 10 mu was used alone as a negative electrode active material for a secondary battery.

Comparative Example  2

A negative electrode active material for a secondary battery and a secondary battery including the negative active material for the secondary battery were prepared in the same manner as in Example 1 except that the non-porous formed polymer (porosity = 0%) was used.

Experimental Example

(1) Evaluation of output characteristics of secondary battery

The output characteristics of the secondary batteries prepared in Examples 1 and 2 and the secondary batteries prepared in Comparative Examples 1 and 2 were measured by HPPC (Hybrid Pulse Power Characterization by Freedom Car Battery Test Manual) Respectively.

(2) Safety evaluation of secondary battery

High-temperature nail penetration tests (speed: 80 mm / sec) were performed at 4.2 V and 80 ° C. using the secondary batteries prepared in Examples 1 and 2 and the secondary batteries prepared in Comparative Examples 1 and 2, Respectively.

(3) Evaluation of internal resistance of secondary battery

The DC impedance of the secondary battery was measured by changing the current rates to 1C, 5C, 10C, 20C, and 30C using the secondary batteries manufactured in Examples 1 and 2 and the secondary batteries prepared in Comparative Examples 1 and 2, And the results are shown in Table 1 below.

Output Characteristics nail penetration Internal resistance
(DC impedance) Example 1 930 W Pass 1.85 m ohm Example 2 920 W Pass 1.88 m ohm Comparative Example 1 992 W Fail 1.74 m ohm Comparative Example 2 675 W Pass 2.2 m ohm

Referring to Table 1, it can be seen that the secondary batteries manufactured in Examples 1 and 2 have superior output characteristics and reduced internal resistance as compared with the secondary batteries manufactured in Comparative Example 2 owing to the porosity of the polymer shell layer I could. In addition, it was confirmed that the secondary batteries prepared in Examples 1 and 2 had a significantly improved high-temperature safety compared to the secondary batteries prepared in Comparative Example 1 due to the presence of the polymer shell layer.

On the other hand, the secondary battery produced in Comparative Example 1 has excellent output characteristics and low internal resistance, but it has a problem that the safety at high temperature is greatly deteriorated. In addition, it was confirmed that the secondary battery manufactured in Comparative Example 2 had a high temperature stability, but the output characteristics were low and the internal resistance was high.

Therefore, the negative electrode active material for secondary batteries manufactured in Examples 1 and 2 has excellent performance of the secondary battery such as the output characteristics and internal resistance of the secondary battery due to the porosity of the polymer shell layer and minimizes the reaction with the electrolyte due to the presence of the polymer shell layer And it is possible to induce pore closing of the polymer shell layer during overcharging and overdischarge, thereby improving the safety of the secondary battery.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (11)

A core layer capable of intercalating and deintercalating lithium; And
And a porous polymer shell layer formed on the surface of the core layer
Negative electrode active material for secondary battery.
The method according to claim 1,
Wherein the porous polymer shell layer has a melting temperature (Tm) higher than a normal operating temperature of the secondary battery including the negative electrode active material
Negative electrode active material for secondary battery.
The method according to claim 1,
The melting temperature (Tm) of the porous polymer shell layer is in the range of 130 DEG C to 150 DEG C
Negative electrode active material for secondary battery.
The method according to claim 1,
The porous polymer shell layer may be formed of one selected from the group consisting of polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polyethylene terephthalate Containing polymer
Negative electrode active material for secondary battery.
The method according to claim 1,
The porosity of the porous polymer shell layer is 5% to 70%
Negative electrode active material for secondary battery.
The method according to claim 1,
The pore size of the porous polymer shell layer is preferably 0.1 to 1 mu m
Negative electrode active material for secondary battery.
The method according to claim 1,
Wherein the core layer is made of at least one of a carbon-based material, a silicon-based material, a tin-based material, and a silicon-
Negative electrode active material for secondary battery.
The method according to claim 1,
Wherein the core layer is a spherical &lt; RTI ID = 0.0 &gt;
Negative electrode active material for secondary battery.
The method according to claim 1,
The thickness of the porous polymer shell layer is 5% to 30% of the diameter of the core layer
Negative electrode active material for secondary battery.
A negative electrode current collector comprising a negative electrode active material according to any one of claims 1 to 9,
Cathode for secondary battery.
A secondary battery comprising a negative electrode according to claim 10.

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