I wrote this code : 

global class mailSendBatchJob implements Database.Batchable<sObject> {
public List<String> usr{get;set;} //
public List<sObject> usr_email{get;set;}
public Map<string,string> Map_usr{get;set;}

global mailSendBatchJob(){
}

global Database.QueryLocator start(Database.BatchableContext BC){
return Database.getQueryLocator([select id,E_mail__c from invoice_statement__c where Status__c = 'Otwarta']);
}

global void execute(Database.BatchableContext BC,List<sObject> scope){
usr=new List<String>();
usr_email=new List<sObject>();
usr.clear();
usr_email.clear();
usr_email=[select id,E_mail__c from invoice_statement__c where Status__c = 'Otwarta'];
Map_usr=new Map<string,string>();
Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
String[] toAddresses = new String[] {};
for(sobject s : scope){
toAddresses.add(string.valueof(usr_email));
}

mail.setToAddresses(toAddresses);
mail.setSubject('Twoja faktura jest otwarta');
mail.setPlainTextBody('Twoja faktura jest otwarta');
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
}

global void finish(Database.BatchableContext BC){

}
}

when i launch this batch apex give me error like this : 

Apex script unhandled exception by user/organization: 005i0000000Hm7C/00Di0000000HTKm

Failed to process batch for class 'mailSendBatchJob' for job id '707i00000008eVb'

caused by: System.EmailException: SendEmail failed. First exception on row 0; first error: LIMIT_EXCEEDED, Too many to addresses.: []

Class.mailSendBatchJob.execute: line 29, column 1

somebody show me what i'm doing wrong